Finding That Greenhouse Gas Emissions From Aircraft Cause or Contribute to Air Pollution That May Reasonably Be Anticipated To Endanger Public Health and Welfare, 54421-54475 [2016-18399]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 81, Number 157 (Monday, August 15, 2016)]
[Rules and Regulations]
[Pages 54421-54475]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2016-18399]



[[Page 54421]]

Vol. 81

Monday,

No. 157

August 15, 2016

Part V





 Environmental Protection Agency





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40 CFR Parts 87 and 1068





Finding That Greenhouse Gas Emissions From Aircraft Cause or Contribute 
to Air Pollution That May Reasonably Be Anticipated To Endanger Public 
Health and Welfare; Final Rule

Federal Register / Vol. 81 , No. 157 / Monday, August 15, 2016 / 
Rules and Regulations

[[Page 54422]]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 87 and 1068

[EPA-HQ-OAR-2014-0828; FRL-9950-15-OAR]
RIN 2060-AS31


Finding That Greenhouse Gas Emissions From Aircraft Cause or 
Contribute to Air Pollution That May Reasonably Be Anticipated To 
Endanger Public Health and Welfare

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: In this action, the Administrator finds that elevated 
concentrations of greenhouse gases in the atmosphere endanger the 
public health and welfare of current and future generations within the 
meaning of section 231(a)(2)(A) of the Clean Air Act (CAA, or Act). She 
makes this finding specifically with respect to the same six well-mixed 
greenhouse gases--carbon dioxide (CO2), methane, nitrous 
oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride--
that together were defined as the air pollution in the 2009 
Endangerment Finding under section 202(a) of the CAA and that together 
constitute the primary cause of the climate change problem. The 
Administrator also finds that emissions of those six well-mixed 
greenhouse gases from certain classes of engines used in certain 
aircraft are contributing to the air pollution--the aggregate group of 
the same six greenhouse gases--that endangers public health and welfare 
under CAA section 231(a)(2)(A).

DATES: These findings are effective on September 14, 2016.

ADDRESSES: The EPA has established a docket for this rulemaking under 
Docket ID No. EPA-HQ-OAR-2014-0828. All documents in the docket are 
listed in the www.regulations.gov Web site. Although listed in the 
index, some information is not publicly available, e.g., confidential 
business information (CBI) or other information whose disclosure is 
restricted by statute. Certain other material, such as copyrighted 
material, is not placed on the Internet and will be publicly available 
only in hard copy in the EPA's docket. Publicly available docket 
materials are available either electronically in www.regulations.gov or 
in hard copy at the Air and Radiation Docket and Information Center, 
EPA/DC, EPA WJC West, Room 3334, 1301 Constitution Ave. NW., 
Washington, DC. The Public Reading Room is open from 8:30 a.m. to 4:30 
p.m., Monday through Friday, excluding legal holidays. The telephone 
number for the Public Reading Room is (202) 566-1744, and the telephone 
number for the Air Docket is (202) 566-1742.

FOR FURTHER INFORMATION CONTACT: Lesley Jantarasami, Office of 
Atmospheric Programs, Climate Change Division, Environmental Protection 
Agency, 1200 Pennsylvania Ave. NW., Mail Code 6207-A, Washington, DC 
20460; Telephone number: (202) 343-9990; Email address: 
ghgendangerment@epa.gov. For additional information regarding these 
final findings, please go to the Web site https://www3.epa.gov/otaq/climate/regs-aviation.htm.

SUPPLEMENTARY INFORMATION:

Judicial Review

    Under CAA section 307(b)(1), judicial review of this final action 
is available only by filing a petition for review in the U.S. Court of 
Appeals for the District of Columbia Circuit by October 14, 2016. This 
final action is a nationally applicable action because it triggers the 
EPA's statutory duty to promulgate aircraft engine emission standards 
under CAA section 231, which are nationally applicable regulations and 
for which judicial review will be available only in the U.S. Court of 
Appeals for the District of Columbia Circuit. In the alternative, even 
if this action were considered to be only locally or regionally 
applicable, the Administrator determines that it has nationwide scope 
and effect within the meaning of CAA section 307(b)(1) both because of 
the obligation to establish standards under CAA section 231 that it 
triggers and because it concerns risks from GHG pollution and 
contributions to such pollution that occur across the nation. Under CAA 
section 307(d)(7)(B), only an objection to this final action that was 
raised with reasonable specificity during the period for public comment 
can be raised during judicial review. This section also provides a 
mechanism for us to convene a proceeding for reconsideration, ``[i]f 
the person raising an objection can demonstrate to [EPA] that it was 
impracticable to raise such objection within [the period for public 
comment] or if the grounds for such objection arose after the period 
for public comment (but within the time specified for judicial review) 
and if such objection is of central relevance to the outcome of this 
rule.'' Any person seeking to make such a demonstration to us should 
submit a Petition for Reconsideration to the Office of the 
Administrator, Environmental Protection Agency, Room 3000, William 
Jefferson Clinton Building, 1200 Pennsylvania Ave. NW., Washington, DC 
20460, with a copy to the person listed in the preceding FOR FURTHER 
INFORMATION CONTACT section, and the Associate General Counsel for the 
Air and Radiation Law Office, Office of General Counsel (Mail Code 
2344-A) Environmental Protection Agency, 1200 Pennsylvania Ave. NW., 
Washington, DC 20460.

Table of Contents

I. General Information
    A. Does this action apply to me?
II. Introduction: Overview and Context for This Final Action
    A. Summary
    B. Background Information Helpful To Understanding This Final 
Action
    C. The EPA's Responsibilities Under the Clean Air Act
    D. U.S. Aircraft Regulations and the International Community
III. Legal Framework for This Action
    A. Section 231(a)(2)(A)--Endangerment and Cause or Contribute
    B. Air Pollutant, Public Health and Welfare
IV. The Administrator's Finding Under CAA Section 231 That 
Greenhouse Gases Endanger Public Health and Welfare
    A. The Science Upon Which the Agency Relied
    B. The Air Pollution Consists of Six Key Well-Mixed Greenhouse 
Gases
    C. The Air Pollution Is Reasonably Anticipated To Endanger Both 
Public Health and Welfare
    D. Summary of the Administrator's Endangerment Finding Under CAA 
Section 231
V. The Administrator's Cause or Contribute Finding for Greenhouse 
Gases Emitted by Certain Classes of Engines Used by Covered Aircraft 
Under CAA Section 231
    A. The Air Pollutant
    B. The Administrator's Finding Under CAA Section 231(a)(2)(A) 
That Greenhouse Gas Emissions From Certain Classes of Aircraft 
Engines Used in Certain Aircraft Cause or Contribute to Air 
Pollution That May Be Reasonably Anticipated To Endanger Public 
Health and Welfare
    C. Response to Key Comments on the Administrator's Cause or 
Contribute Finding
VI. Statutory Authority and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review and 
Executive Order 13563: Improving Regulation and Regulatory Review
    B. Paperwork Reduction Act (PRA)
    C. Regulatory Flexibility Act (RFA)
    D. Unfunded Mandates Reform Act (UMRA)
    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination With 
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children From 
Environmental Health Risks and Safety Risks

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    H. Executive Order 13211: Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution or Use
    I. National Technology Transfer and Advancement Act (NTTAA)
    J. Executive Order 12898: Federal Actions To Address 
Environmental Justice in Minority Populations and Low-Income 
Populations
    K. Congressional Review Act (CRA)
    L. Determination Under Section 307(d)
VII. Statutory Provisions and Legal Authority

I. General Information

A. Does this action apply to me?

    These final findings trigger new duties that apply to the EPA but 
do not themselves apply new requirements to other entities outside the 
federal government. Specifically, in issuing these final findings that 
emissions of the six well-mixed GHGs from certain classes of engines 
used in certain aircraft cause or contribute to air pollution which may 
reasonably be anticipated to endanger public health or welfare, the EPA 
becomes subject to a duty under CAA section 231 to propose and 
promulgate aircraft engine emission standards applicable to emissions 
of that air pollutant from those classes of engines. We are 
anticipating indicating an expected timeline for proposed GHG emission 
standards for the classes of aircraft engines included in the 
contribution finding in EPA's Unified Agenda of Federal Regulatory and 
Deregulatory Actions. Only those future standards will apply to and 
have an effect on other entities outside the federal government. 
Entities potentially interested in this final action include those that 
manufacture and sell aircraft engines and aircraft in the United 
States. Categories that may be regulated in a future regulatory action 
include:
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    \1\ Manufacturers of new aircraft engines refers to 
manufacturers of new type engines and in-production engines, and 
manufacturers of new aircraft refers to manufacturers of new type 
aircraft and in-production aircraft.

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                                                                               Examples of Potentially Affected
                  Category                   NAICS \a\ Code   SIC \b\ Code               Entities \1\
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Industry...................................         3364412            3724  Manufacturers of new aircraft
                                                                              engines.
Industry...................................          336411            3721  Manufacturers of new aircraft.
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\a\ North American Industry Classification System (NAICS).
\b\ Standard Industrial Classification (SIC) code.

    This table is not intended to be exhaustive, but rather provides a 
guide for readers regarding entities likely to be interested in this 
final action. This table lists the types of entities that the EPA is 
now aware could potentially have an interest in this final action. By 
issuing these final findings under CAA section 231(a)(2)(A) regarding 
emissions of greenhouse gases from aircraft engines, the EPA is now 
required to undertake a separate notice and comment rulemaking to 
propose and issue emission standards applicable to greenhouse gas 
emissions from the classes of aircraft engines subject to the findings, 
and the Federal Aviation Administration (FAA) is to prescribe 
regulations to ensure compliance with EPA's future emissions standards 
pursuant to CAA section 232. Other types of entities not listed in the 
table could also be interested and potentially affected by subsequent 
actions at some future time. If you have any questions regarding the 
scope of this final action, consult the person listed in the preceding 
FOR FURTHER INFORMATION CONTACT section.

II. Introduction: Overview and Context for This Final Action

A. Summary

    Pursuant to CAA section 231(a)(2)(A), the Administrator finds that 
emissions of the six well-mixed \2\ greenhouse gases (GHGs) from 
certain classes of aircraft engines used in certain types of aircraft 
(referred to interchangeably as ``covered aircraft'' or ``US covered 
aircraft'' throughout this document) contribute to air pollution that 
may reasonably be anticipated to endanger the public health and welfare 
of current and future generations. This final action follows the 
Administrator's proposed findings,\3\ and responds to public comments 
submitted to the EPA following that proposal. It is based on careful 
consideration of the scientific evidence, as well as a thorough review 
of the public comments. In light of the large number of comments 
received and overlap between many comments, EPA has not responded to 
each comment individually. Instead, EPA has summarized and provided 
responses to each significant argument, assertion and question 
contained within the totality of these comments. Covered aircraft are 
those aircraft to which the International Civil Aviation Organization 
(ICAO) has agreed the recently recommended international CO2 
standard will apply \4\: Subsonic jet aircraft with a maximum takeoff 
mass (MTOM) greater than 5,700 kilograms and subsonic propeller-driven 
(e.g., turboprop) aircraft with a MTOM greater than 8,618 kilograms. 
Examples of covered aircraft include smaller jet aircraft such as the 
Cessna Citation CJ3+ and the Embraer E170, up to and including the 
largest commercial jet aircraft--the Airbus A380 and the Boeing 747. 
Other examples of covered aircraft include larger turboprop aircraft, 
such as the ATR 72 and the Bombardier Q400.
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    \2\ The term ``well-mixed GHGs''--used both in the definition of 
``air pollution'' in the endangerment finding and in the definition 
of ``air pollutant'' in the cause or contribute finding--is based on 
the fact that these gases are sufficiently long lived in the 
atmosphere such that, once emitted, concentrations of each gas 
become well mixed throughout the entire global atmosphere. These 
shared attributes are one of five primary reasons that the EPA 
considers the six gases as an aggregate group rather than as 
individual gases. See section IV.B for more information on the 
definition of ``air pollution'' and section V.A for more information 
on the definition of the ``air pollutant.''
    \3\ U.S. EPA, 2015: Proposed Finding That Greenhouse Gas 
Emissions From Aircraft Cause or Contribute To Air Pollution That 
May Reasonably Be Anticipated To Endanger Public Health and Welfare 
and Advance Notice of Proposed Rulemaking; Proposed Rule, 80 Federal 
Register (FR) 37758 (July 1, 2015).
    \4\ ICAO, 2013: CAEP/9 Agreed Certification Requirement for the 
Aeroplane CO2 Emissions Standards, Circular (Cir) 337, 40 pp, AN/
192, Available at: https://www.icao.int/publications/catalogue/cat_2016_en.pdf (last accessed May 9, 2016). The ICAO Circular 337 
is found on page 87 of the catalog and is copyright protected; Order 
No. CIR337.
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    In this final action, the EPA is informed by and places 
considerable weight on the extensive scientific and technical evidence 
in the record supporting the 2009 Endangerment and Cause or Contribute 
Findings under CAA section 202(a) (hereafter, collectively referred to 
as the 2009 Endangerment Finding).\5\ This includes the major, peer-
reviewed scientific assessments that were used to address the question 
of whether elevated concentrations of GHGs in the

[[Page 54424]]

atmosphere endanger public health and welfare under CAA section 202(a), 
as well as the analytical framework and conclusions upon which the EPA 
relied in making that finding. The Administrator's view is that the 
body of scientific evidence amassed in the record for the 2009 
Endangerment Finding also compellingly supports an endangerment finding 
under CAA section 231(a)(2)(A). Furthermore, this finding under section 
231(a)(2)(A) reflects the EPA's careful consideration not only of the 
scientific and technical record for the 2009 Endangerment Finding, but 
also of science assessments released since 2009, which, as illustrated 
below, strengthen and further support the judgment that GHGs in the 
atmosphere may reasonably be anticipated to endanger the public health 
and welfare of current and future generations. No information or 
assessments published since late 2009 suggest that it would be 
reasonable for the EPA to now reach a different or contrary conclusion 
for purposes of CAA section 231(a)(2)(A) than the Agency reached for 
purposes of section 202(a).
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    \5\ U.S. EPA, 2009: Endangerment and Cause or Contribute 
Findings for Greenhouse Gases Under Section 202(a) of the Clean Air 
Act; Final Rule, 74 FR 66496 (December 15, 2009).
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    The Administrator defines the ``air pollution'' referred to in 
section 231(a)(2)(A) of the CAA to be the combined mix of 
CO2, methane, nitrous oxide, hydrofluorocarbons, 
perfluorocarbons, and sulfur hexafluoride (henceforth the six ``well-
mixed GHGs''). This is the same definition that was used for the 
finding for purposes of section 202(a). It is the Administrator's 
judgment that the total body of scientific evidence compellingly 
supports a positive endangerment finding that elevated concentrations 
of the six well-mixed GHGs constitute air pollution that endangers both 
the public health and welfare of current and future generations within 
the meaning of CAA section 231(a)(2)(A). The Administrator is not at 
this time making a finding regarding whether other substances emitted 
from aircraft engines cause or contribute to air pollution which may 
reasonably be anticipated to endanger public health or welfare.
    Under CAA section 231(a)(2)(A), the Administrator must also 
determine whether emissions of any air pollutant from a class or 
classes of aircraft engines cause or contribute to the air pollution 
that may reasonably be anticipated to endanger public health or 
welfare. Following the rationale outlined in the 2009 Endangerment 
Finding, the Administrator in this action is using the same definition 
of the air pollutant as was used for purposes of section 202(a) for 
purposes of making the cause or contribute determination under section 
231(a)(2)(A)--that is, the aggregate group of the same six well-mixed 
GHGs. With respect to this pollutant, based on the data summarized in 
section V.B, the Administrator finds that emissions of the six well-
mixed GHGs from aircraft engines used in covered aircraft contribute to 
the air pollution that endangers public health and welfare under 
section 231(a)(2)(A). The Administrator is not at this time making a 
cause or contribute finding regarding GHG emissions, or emissions of 
other substances, from engines used in non-covered aircraft.
    The Administrator's final findings come in response to a citizen 
petition submitted by Friends of the Earth, Oceana, the Center for 
Biological Diversity, and Earthjustice (Petitioners) requesting that 
the EPA issue an endangerment finding and standards under CAA section 
231(a)(2)(A) for the GHG emissions from aircraft. Further, the EPA 
anticipates that the 39th ICAO Assembly will approve a final 
CO2 emissions standard in October 2016, and that 
subsequently, ICAO will formally adopt the final CO2 
emissions standard in March 2017. These final endangerment and cause or 
contribute findings for aircraft engine GHG emissions are also part of 
preparing for a subsequent domestic rulemaking process under CAA 
section 231. If an international standard is approved and finalized by 
ICAO, member states that wish to use aircraft in international 
transportation will then be required under the Chicago Convention \6\ 
to adopt standards that are of at least equivalent stringency to those 
set by ICAO. Section II.D provides additional discussion of the 
international aircraft standard-setting process. This document does not 
take action or respond to comments on the 2015 U.S. EPA Aircraft 
Greenhouse Gas Emissions Advance Notice of Proposed Rulemaking 
(henceforth the ``2015 ANPR''),\7\ which discussed such standards. 
Technical issues and comments for the 2015 ANPR would be addressed in a 
future notice of proposed rulemaking related to such standards.
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    \6\ ICAO, 2006: Convention on International Civil Aviation, 
Ninth Edition, Document 7300/9, 114 pp. Available at: https://www.icao.int/publications/Documents/7300_9ed.pdf (last accessed May 
9, 2016).
    \7\ 80 FR 37758 (July 1, 2015).
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B. Background Information Helpful to Understanding This Final Action

1. Greenhouse Gases and Their Effects
    GHGs in the atmosphere have the effect of trapping some of the 
Earth's heat that would otherwise escape to space. GHGs are both 
naturally occurring and anthropogenic. The primary GHGs directly 
emitted by human activities include CO2, methane, nitrous 
oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride. 
Of these six gases, two (CO2 and nitrous oxide) are emitted 
by aircraft engines.
    These six gases, once emitted, remain in the atmosphere for decades 
to centuries. Thus, they become well mixed globally in the atmosphere, 
and their concentrations accumulate when emissions exceed the rate at 
which natural processes remove them from the atmosphere. Observations 
of the Earth's globally averaged combined land and ocean surface 
temperature over the period 1880 to 2012 show a warming of 0.85 degrees 
Celsius or 1.53 degrees Fahrenheit.\8\ The Intergovernmental Panel on 
Climate Change's (IPCC) 2013-2014 Fifth Assessment Report concluded 
that heating effect caused by the human-induced buildup of these and 
other GHGs in the atmosphere, plus other human activities (e.g., land 
use change and aerosol emissions), is extremely likely (>95 percent 
likelihood) to be the cause of most of the observed global warming 
since the mid-20th century.\9\ Further information about climate change 
and its impact on health, society, and the environment is included in 
the record for the 2009 Endangerment Finding. The relevant scientific 
information from that record has also been included in the docket for 
this determination under CAA section 231(a)(2)(A) (EPA-HQ-OAR-2014-
0828). Section IV of this preamble discusses this information, as well 
as information from the most recent scientific assessments, in the 
context of the Administrator's endangerment finding under CAA section 
231.
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    \8\ IPCC, 2013: Summary for Policymakers. In: Climate Change 
2013: The Physical Science Basis. Contribution of Working Group I to 
the Fifth Assessment Report of the Intergovernmental Panel on 
Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, 
S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley 
(eds.)]. Cambridge University Press, 29 pp.
    \9\ Ibid.
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    The U.S. transportation sector constitutes a meaningful part of 
total U.S. and global anthropogenic GHG emissions. In 2014, aircraft 
remained the single largest GHG-emitting transportation source not yet 
subject to any GHG standards. Aircraft clearly contribute to U.S. 
transportation emissions, accounting for 12 percent of all U.S. 
transportation GHG emissions and representing more than 3 percent of 
total U.S. GHG emissions in 2014.\10\

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Globally, U.S. aircraft GHG emissions represent 29 percent of all 
global aircraft GHG emissions and 0.5 percent of total global GHG 
emissions. Section V of this preamble provides detailed information on 
aircraft GHG emissions in the context of the Administrator's cause or 
contribute finding under CAA section 231(a)(2)(A).
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    \10\ U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions 
and Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and 
Radiation, EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed 
June 14, 2016).
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2. Statutory Basis for This Final Action
    Section 231(a)(2)(A) of the CAA states that ``The Administrator 
shall, from time to time, issue proposed emission standards applicable 
to the emission of any air pollutant from any class or classes of 
aircraft engines which in [her] judgment causes, or contributes to, air 
pollution which may reasonably be anticipated to endanger public health 
or welfare.''
    Before the Administrator may propose and issue final standards 
addressing emissions of an air pollutant under section 231, the 
Administrator must satisfy a two-step test. First, the Administrator 
must decide whether, in her judgment, the air pollution under 
consideration may reasonably be anticipated to endanger public health 
or welfare. Second, the Administrator must decide whether, in her 
judgment, emissions of an air pollutant from certain classes of 
aircraft engines cause or contribute to this air pollution.\11\ If the 
Administrator answers both questions in the affirmative, she must 
propose and issue final standards under section 231. See Massachusetts 
v. EPA, 549 U.S. 497, 533 (2007) (interpreting analogous provision in 
CAA section 202). Section III of this document summarizes the legal 
framework for this final action under CAA section 231. Typically, past 
endangerment and cause or contribute findings have been proposed and 
promulgated concurrently with proposed and promulgated standards under 
various sections of the CAA, including section 231. In those actions, 
public comment was taken on the proposed findings as part of the notice 
and comment process for the proposed emission standards. See, e.g., 
Rulemaking for non-road compression-ignition engines under section 
213(a)(4) of the CAA, Proposed Rule at 58 FR 28809, 28813-14 (May 17, 
1993), Final Rule at 59 FR 31306, 31318 (June 17, 1994); Rulemaking for 
highway heavy-duty diesel engines and diesel sulfur fuel under sections 
202(a) and 211(c) of the CAA, Proposed Rule at 65 FR 35430 (June 2, 
2000), and Final Rule at 66 FR 5002 (January 18, 2001). However, there 
is no requirement that the Administrator propose or finalize the 
endangerment and cause or contribute findings concurrently with the 
related standards. See 74 FR 66502 (December 15, 2009). As explained in 
the 2009 Endangerment Finding, nothing in section 202(a) requires the 
EPA to propose or issue endangerment and cause or contribute findings 
in the same rulemaking, and Congress left the EPA discretion to choose 
an approach that satisfied the requirements of section 202(a). See id. 
The same analysis applies to section 231, which is analogous to section 
202(a). The EPA is choosing to finalize these findings at this time for 
a number of reasons, including its previous commitment to issue such 
findings in response to a 2007 citizens' petition.\12\
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    \11\ To clarify the distinction between air pollution and air 
pollutant, in the context of GHGs, the air pollution is the 
atmospheric concentrations and can be thought of as the total, 
cumulative stock of GHGs in the atmosphere. The air pollutant, on 
the other hand, is the emissions of GHGs and can be thought of as 
the flow that changes the size of the total stock.
    \12\ Center for Biological Diversity, Center for Food Safety, 
Friends of the Earth, International Center for Technology 
Assessment, and Oceana, 2007: Petition for Rulemaking Under the 
Clean Air Act to Reduce the Emissions of Air Pollutants from 
Aircraft the Contribute to Global Climate Change, December 31, 2007. 
Available at https://www3.epa.gov/otaq/aviation.htm (last accessed 
April 8, 2016). EPA, 2012: Response to the Petition for Rulemaking 
Under the Clean Air Act to Reduce the Emission of Air Pollutants 
from Aircraft that Contribute to Global Climate Change, June 14, 
2012. Available at https://www3.epa.gov/otaq/aviation.htm (last 
accessed April 8, 2016).
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    The Administrator has applied the rulemaking provisions of CAA 
section 307(d) to this action, pursuant to CAA section 307(d)(1)(V), 
which provides that the provisions of 307(d) apply to ``such other 
actions as the Administrator may determine.'' \13\ CAA section 307(d) 
provides specific procedural requirements for the EPA to follow in 
taking certain rulemaking actions under the CAA, that apply in lieu of 
the otherwise applicable provisions of the Administrative Procedure 
Act, 5 U.S.C. 553-557, and 706. See, CAA section 307(d)(1). Any 
standard-setting rulemaking under section 231 will also be subject to 
the notice and comment rulemaking procedures under 307(d), as provided 
in CAA section 307(d)(1)(F) (applying the provisions of 307(d) to the 
promulgation or revision of any aircraft emission standard under 
section 231). Thus, these findings were subject to the same rulemaking 
procedures and requirements, as applicable, as would have applied if 
they had been part of a standard-setting rulemaking.
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    \13\ As the Administrator is applying the provisions of section 
307(d) to this rulemaking under section 307(d)(1)(V), we need not 
determine whether those provisions would apply to this action under 
section 307(d)(1)(F).
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C. The EPA's Responsibilities Under the Clean Air Act

    The CAA provides broad authority to combat air pollution to protect 
public health and welfare and the environment. Cars, trucks, 
construction equipment, airplanes, and ships, as well as a broad range 
of electricity generation, industrial, commercial and other facilities, 
are subject to various CAA programs. Many of these programs are 
targeted at ensuring protection of public health and welfare with a 
margin of safety, others are directed at encouraging improved 
industrial emissions performance and use of lesser polluting 
technologies and processes, and some address the prevention of adverse 
environmental effects. Implementation of the Act over the past four 
decades has resulted in significant reductions in air pollution that 
have benefited human health and the environment. The EPA's duties 
regarding aircraft air pollution emissions under CAA section 231 
reflect a combination of the CAA's goals to protect public health and 
welfare and encourage improved emissions performance. This is shown by 
section 231(a)(2)(A)'s directive that EPA first identify whether 
emissions of aircraft engine air pollutants cause or contribute to air 
pollution that may reasonably be anticipated to endanger public health 
or welfare (which is broadly defined in section 302(h) of the CAA).\14\ 
This is also shown by section 231(b)'s subsequent requirement that 
EPA's standards, which may require improved emissions performance over 
the status quo, provide sufficient time for the development and 
application of requisite technology to meet emission standards, after 
consideration of costs.
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    \14\ Previously the EPA has made the prerequisite endangerment 
and cause or contribute findings under CAA section 231(A) that 
formed the basis to begin addressing the issue of various aircraft 
pollutants including NOX aircraft pollution. U.S. EPA, 
``Control of Air Pollution from Aircraft and Aircraft Engines, 
Emission Standards and Test Procedures for Aircraft.'' Final Rule, 
38 FR 19088 (July 17, 1973). See also section IV.B.7.d of this 
preamble for a discussion of previous NOX section 231(A) 
findings.
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1. The EPA's Regulation of Greenhouse Gases
    In Massachusetts v. EPA, 549 U.S. 497 (2007), the Supreme Court 
found that GHGs are air pollutants that can be regulated under the CAA. 
The Court held that the Administrator must determine whether emissions 
of GHGs from new motor vehicles cause or contribute to air pollution 
which may

[[Page 54426]]

reasonably be anticipated to endanger public health and/or welfare, or 
whether the science is too uncertain to make a reasoned decision. In 
making these decisions, the Administrator was bound by the provisions 
of section 202(a) of the CAA. The Supreme Court decision resulted from 
a petition for rulemaking under section 202(a) filed by more than a 
dozen environmental, renewable energy, and other organizations.
    Following the Supreme Court decision, the EPA proposed (74 FR 
18886, April 24, 2009) and then finalized (74 FR 66496, December 15, 
2009) the 2009 Endangerment Finding, which can be summarized as 
follows:
     Endangerment Finding: The Administrator found that the 
then-current and projected concentrations of the combined mix in the 
atmosphere of the six well-mixed GHGs--CO2, methane, nitrous 
oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride--
endanger the public health and welfare of current and future 
generations.
     Cause or Contribute Finding: The Administrator found that 
the combined emissions of the six well-mixed GHGs from new motor 
vehicles and new motor vehicle engines contribute to the GHG pollution 
which threatens public health and welfare.
    The Administrator made both of these findings with respect to the 
six well-mixed GHGs, recognizing that CAA section 202(a) sources emit 
only four of the six substances. The findings did not themselves impose 
any requirements on industry or other entities. However, these findings 
compelled the EPA to promulgate GHG emission standards for new motor 
vehicles under section 202(a). Subsequently, in May 2010 the EPA, in 
collaboration with the National Highway Traffic Safety Administration 
(NHTSA), finalized Phase 1 GHG emission standards for light-duty 
vehicles (2012-2016 model years).\15\ This was followed in August 2011 
by adoption of the first-ever GHG emission standards for heavy-duty 
engines and vehicles (2014-2018 model years).\16\ On August 29, 2012, 
the EPA finalized the second phase of the GHG emission standards for 
light-duty vehicles (2017-2025 model years), further reducing GHG 
emissions from light-duty vehicles.\17\ In 2014, the President directed 
the EPA and the Department of Transportation to set standards in 2016 
that further increase fuel efficiency and reduce GHG emissions from 
medium- and heavy-duty vehicles.\18\
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    \15\ U.S. EPA, 2010: Light-Duty Vehicle Greenhouse Gas Emission 
Standards and Corporate Average Fuel Economy Standards; Final Rule, 
75 FR 25324 (May 7, 2010).
    \16\ U.S. EPA, 2011: Greenhouse Gas Emissions Standards and Fuel 
Efficiency Standards for Medium- and Heavy-Duty Engines and 
Vehicles; Final Rule, 76 FR 57106 (September 15, 2011).
    \17\ U.S. EPA, 2012: 2017 and Later Model Year Light-Duty 
Vehicle Greenhouse Gas Emissions and Corporate Average Fuel Economy 
Standards; Final Rule, 77 FR 62623 (October 15, 2012).
    \18\ Executive Office of the President, 2014: Remarks by the 
President on Fuel Efficiency Standards of Medium and Heavy-Duty 
Vehicles, Office of the Press Secretary, February 18. Available at: 
https://www.whitehouse.gov/the-press-office/2014/02/18/remarks-president-fuel-efficiency-standards-medium-and-heavy-duty-vehicl 
(last accessed April 27, 2016).
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    The GHG rules for cars and trucks have been supported by a broad 
range of stakeholders, including states, major automobile and truck 
manufacturers, and environmental and labor organizations. Together 
these new standards for cars and trucks are resulting in significant 
reductions in GHG emissions, and over the lifetime of these vehicles 
GHG emissions will have been reduced more than 6.25 billion metric 
tons.19 20
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    \19\ U.S. EPA, 2012: EPA and NHTSA Set Standards to Reduce 
Greenhouse Gases and Improve Fuel Economy for Model Years 2017-2025 
Cars and Light Trucks. Document No. EPA-420-F-12-051, 10 pp. 
Available at https://www.epa.gov/otaq/climate/documents/420f12051.pdf 
(last accessed April 27, 2016). See also Table 7.4-2 in U.S. EPA, 
2012: Regulatory Impact Analysis: Final Rulemaking for 2017-2025 
Light-Duty Vehicle Greenhouse Gas Emissions Standards and 
Corporation Average Fuel Economy Standards, EPA-420-R-12-016, 555 
pp. Available at: https://www3.epa.gov/otaq/climate/documents/420r12016.pdf (last accessed April 27, 2016).
    \20\ U.S. EPA, 2011: Greenhouse Gas Emissions Standards and Fuel 
Efficiency Standards for Medium-and Heavy-Duty Engines and Vehicles; 
Final Rule, 76 FR 57106 (September 15, 2011).
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    On June 25, 2013, President Obama announced a Climate Action Plan 
that set forth a series of executive actions to further reduce GHGs, 
prepare the U.S. for the impacts of climate change, and lead 
international efforts to address global climate change.\21\ As part of 
the Climate Action Plan, the President issued a Presidential Memorandum 
directing the EPA to work expeditiously to complete carbon pollution 
standards for the power sector.\22\ In August 2015, after notice and 
comment rulemaking, the EPA finalized two carbon pollution rulemakings: 
One for new, modified, and reconstructed electric utility generating 
units \23\ and another for existing power plants.\24\
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    \21\ Executive Office of the President, 2013: The President's 
Climate Action Plan, June 25, 21 pp. Available at: https://www.whitehouse.gov/sites/default/files/image/president27sclimateactionplan.pdf (last accessed April 8, 2016).
    \22\ Executive Office of the President, 2013: Presidential 
Memorandum--Power Sector Carbon Pollution Standards, Office of the 
Press Secretary, June 25. Available at: https://www.whitehouse.gov/the-press-office/2013/06/25/presidential-memorandum-power-sector-carbon-pollution-standards (last accessed April 8, 2016).
    \23\ U.S. EPA, 2015: Standards of Performance for Greenhouse Gas 
Emissions From New, Modified, and Reconstructed Stationary Sources: 
Electric Utility Generating Units; Final Rule, 80 FR 64510 (October 
23, 2015).
    \24\ U.S. EPA, 2014: Carbon Pollution Emission Guidelines for 
Existing Stationary Sources: Electric Utility Generating Units; 
Final Rule, 80 FR 64661 (October 23, 2015). On February 9, 2016 the 
Supreme Court stayed this rule pending judicial review. The Court's 
stay order does not articulate a basis for the stay and does not 
address the merits of the rule.
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    In the Climate Action Plan, the President also indicated that the 
United States was working internationally to make progress in a variety 
of areas and specifically noted the progress being made by ICAO to 
develop global CO2 emission standards for aircraft.\25\ The 
final endangerment and cause or contribute findings for aircraft GHG 
emissions under section 231(a)(2)(A) of the CAA are a preliminary but 
necessary first step to begin to address GHG emissions from the 
aviation sector, the highest-emitting category of transportation 
sources that the EPA has not yet addressed. As presented in more detail 
in Section V of this document, total U.S. aircraft GHG emissions in 
2014 represented 12 percent of GHG emissions from the U.S. 
transportation sector,\26\ and in 2010, the latest year with complete 
global emissions data, U.S. aircraft GHG emissions represented 29 
percent of global aircraft GHG emissions.27 28 U.S. aircraft 
GHG emissions are projected to increase by 43 percent over the next two 
decades.\29\

[[Page 54427]]

See section V of this preamble for more information about the data 
sources that comprise the aircraft GHG emissions inventory.
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    \25\ Executive Office of the President, 2013: The President's 
Climate Action Plan, June 25, 21 pp. Available at https://www.whitehouse.gov/sites/default/files/image/president27sclimateactionplan.pdf (last accessed April 8, 2016).
    \26\ U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions 
and Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and 
Radiation, EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed 
June 14, 2016).
    \27\ Ibid.
    \28\ IPCC, 2014: Climate Change 2014: Mitigation of Climate 
Change. Contribution of Working Group III to the Fifth Assessment 
Report of the Intergovernmental Panel on Climate Change [Edenhofer, 
O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, 
A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J. 
Savolainen, S. Schl[ouml]mer, C. von Stechow, T. Zwickel and J.C. 
Minx (eds.)]. Cambridge University Press, pp. 599-670.
    \29\ As discussed in section V.B.4.c, fuel burn growth rates for 
air carriers and general aviation aircraft operating on jet fuel are 
projected to grow by 43 percent from 2010 to 2036, and this provides 
a scaling factor for growth in GHG emissions which would increase at 
a similar rate as the fuel burn by 2030, 2036, and 2040. FAA, 2016: 
FAA Aerospace Forecast Fiscal Years 2016-2036, 94 pp. Available at 
https://www.faa.gov/data_research/aviation/aerospace_forecasts/media/FY2016-36_FAA_Aerospace_Forecast.pdf (last accessed April 8, 
2016).
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2. Background on the Aircraft Petition, the 2008 Advance Notice of 
Proposed Rulemaking, and the D.C. District Court Decision
    Section 231(a)(2)(A) of the CAA directs the Administrator of the 
EPA to, from time to time, propose aircraft engine emissions standards 
applicable to the emission of any air pollutant from any classes of 
aircraft engines which in her judgment causes or contributes to air 
pollution which may reasonably be anticipated to endanger public health 
or welfare.
    On December 5, 2007, Friends of the Earth, Oceana, the Center for 
Biological Diversity, Earthjustice, and others (Petitioners) sent a 
letter to the EPA petitioning the Agency to undertake rulemaking 
regarding GHG emissions from aircraft.\30\ Specifically, Petitioners 
requested that the EPA make a finding that GHG emissions from aircraft 
engines ``may reasonably be anticipated to endanger public health and 
welfare'' and that the EPA promulgate standards for GHG emissions from 
aircraft.
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    \30\ Center for Biological Diversity, Center for Food Safety, 
Friends of the Earth, International Center for Technology 
Assessment, and Oceana, 2007: Petition for Rulemaking Under the 
Clean Air Act to Reduce the Emissions of Air Pollutants from 
Aircraft the Contribute to Global Climate Change, December 5, 26 pp. 
Available at https://www.epa.gov/otaq/aviation.htm (last accessed 
April 8, 2016) and Docket EPA-HQ-OAR-2014-0828.
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    Following the Supreme Court's decision in Massachusetts v. EPA in 
2007, the EPA issued an advance notice of proposed rulemaking (ANPR) in 
2008 presenting information relevant to potentially regulating GHGs 
under the Act and soliciting public comment on how to respond to the 
Court's ruling and the potential ramifications of the Agency's decision 
to regulate GHGs under the CAA. This ANPR described and solicited 
comment on numerous petitions the Agency had received to regulate GHG 
emissions from both stationary and mobile sources, including aircraft. 
73 FR 44354, 44468-73 (July 30, 2008). With regard to aircraft, the 
Agency sought comment on the impact of aircraft operations on GHG 
emissions and the potential for reductions in GHG emissions from these 
operations.
    On July 31, 2008, Earthjustice, on behalf of Petitioners, notified 
the EPA of its intent to file suit under CAA section 304(a) against the 
EPA for the Agency's alleged unreasonable delay in responding to its 
aircraft petition and in making an endangerment finding under section 
231. On June 11, 2010, Petitioners filed a complaint against the EPA in 
the U.S. District Court for the District of Columbia claiming that, 
among other things, the EPA had unreasonably delayed because it had 
failed to answer the 2007 Petition and to determine whether GHG 
emissions from aircraft cause or contribute to air pollution which may 
reasonably be anticipated to endanger public health and/or welfare.
    The District Court found that while CAA section 231 generally 
confers broad discretion to the EPA in determining what standards to 
promulgate, section 231(a)(2)(A) imposed a nondiscretionary duty on the 
EPA to make a finding with respect to endangerment from aircraft GHG 
emissions. Center for Biological Diversity, et al. v. EPA, 794 F. Supp. 
2d 151 (D.D.C. 2011). This ruling was issued in response to the EPA's 
motion to dismiss the case on jurisdictional grounds and did not 
address the merits of the Plaintiffs' claims regarding the Agency's 
alleged unreasonable delay. Therefore, it did not include an order for 
the EPA to make such a finding by a certain date. In a subsequent 
ruling on the merits, the Court found that the Plaintiffs had not shown 
that the EPA had unreasonably delayed in making an endangerment 
determination regarding GHG emissions from aircraft. Center for 
Biological Diversity, et al. v. EPA, No. 1:10-985 (D.D.C. March, 20, 
2012). Thus, the Court did not find the EPA to be liable based on the 
Plaintiffs' claims and did not place the Agency under a remedial order 
to make an endangerment finding or to issue standards. The Plaintiffs 
did not appeal this ruling to the U.S. Court of Appeals for the 
District of Columbia Circuit (also called the ``D.C. Circuit'' in this 
document).
    The EPA issued a Response to the Aircraft Petition \31\ on June 27, 
2012, stating our intention to move forward with a proposed 
endangerment finding for aircraft GHG emissions under section 231, 
while explaining that it would take the Agency significant time to 
complete this action. The EPA explained that the Agency would not begin 
this effort until after the U.S. Court of Appeals completed its then-
pending review of the previous section 202 Endangerment Finding, since 
the then-awaited ruling might provide important guidance for the EPA in 
conducting future GHG endangerment findings. The EPA further explained 
that after receiving the Court of Appeal's ruling, it would take at 
least 22 months from that point for the Agency to conduct an additional 
finding regarding aircraft GHG emissions.
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    \31\ U.S. EPA, 2012: Memorandum in Response to Petition 
Regarding Greenhouse Gas Emissions from Aircraft, June 14, 11 pp. 
Available at https://www.epa.gov/otaq/aviation.htm (last accessed 
April 8, 2016) and Docket EPA-HQ-OAR-2014-0828.
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    Meanwhile, the Court of Appeals upheld the EPA's section 202 
findings in a decision of a three-judge panel on June 26, 2012, and 
denied petitions for rehearing of that decision on December 20, 2012. 
Coalition for Responsible Regulation, Inc., v. EPA, 684 F.3d 102 (D.C. 
Cir. 2012), reh'g denied 2012 U.S. App. LEXIS 26315, 25997 (D.C. Cir 
2012).\32\ Given these rulings, we are proceeding with these findings 
regarding aircraft engine GHG emissions as a further step toward 
responding to the 2007 Petition for Rulemaking.
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    \32\ Petitions for certiorari were filed in the Supreme Court, 
and the Supreme Court granted six of those petitions but ``agreed to 
decide only one question: `Whether EPA permissibly determined that 
its regulation of greenhouse gas emissions from new motor vehicles 
triggered permitting requirements under the Clean Air Act for 
stationary sources that emit greenhouse gases.' '' Utility Air Reg. 
Group v. EPA, 134 S. Ct. 2427, 2438 (2014); see also Virginia v. 
EPA, 134 S. Ct. 418 (2013), Pac. Legal Found. v. EPA, 134 S. Ct. 418 
(2013), and CRR, 134 S. Ct. 468 (2013) (all denying cert.). Thus, 
the Supreme Court did not disturb the D.C. Circuit's holding that 
affirmed the 2009 Endangerment Finding.
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D. U.S. Aircraft Regulations and the International Community

    The EPA and the FAA traditionally work within the standard-setting 
process of ICAO's Committee on Aviation Environmental Protection (CAEP 
or the Committee) to establish international emission standards and 
related requirements, which individual nations later adopt into 
domestic law in fulfillment of their obligations under the Convention 
on International Civil Aviation (Chicago Convention). Historically, 
under this approach, international emission standards have first been 
adopted by ICAO, and subsequently the EPA has initiated rulemakings 
under CAA section 231 to establish domestic standards that are at least 
as stringent as ICAO's standards. This approach has been affirmed as a 
reasonable way to implement the Agency's duties under CAA section 231 
by the U.S. Court of Appeals for the D.C. Circuit. Nat'l Ass'n of Clean 
Air Agencies (NACAA) v. EPA, 489 F.3d 1221, 1230-32 (D.C. Cir. 2007). 
After EPA promulgates aircraft engine emissions standards, CAA section 
232 requires the FAA to issue regulations to ensure compliance with 
these standards when issuing certificates under its authority under 
Title 49 of the United

[[Page 54428]]

States Code. These final endangerment and cause or contribute findings 
for aircraft GHG emissions are in preparation for this domestic 
emissions standards rulemaking process.
1. International Regulations and U.S. Obligations
    The EPA has worked with the FAA since 1973, and later with ICAO, to 
develop domestic and international standards and other recommended 
practices pertaining to aircraft engine emissions. ICAO is a United 
Nations (UN) specialized agency, established in 1944 by the Chicago 
Convention, ``in order that international civil aviation may be 
developed in a safe and orderly manner and that international air 
transport services may be established on the basis of equality of 
opportunity and operated soundly and economically.'' \33\ ICAO sets 
international standards and regulations for aviation safety, security, 
efficiency, capacity, and environmental protection and serves as the 
forum for cooperation in all fields of international civil aviation. 
ICAO works with the Chicago Convention's member states and global 
aviation organizations to develop international Standards and 
Recommended Practices (SARPs), which member states reference when 
developing their legally enforceable national civil aviation 
regulations. The United States is currently one of 191 participating 
ICAO member states.34 35
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    \33\ ICAO, 2006: Convention on International Civil Aviation, 
Ninth Edition, Document 7300/9, 114 pp. Available at: https://www.icao.int/publications/Documents/7300_9ed.pdf (last accessed 
April 20, 2016).
    \34\ Members of ICAO's Assembly are generally termed member 
states or contracting states. These terms are used interchangeably 
throughout this preamble.
    \35\ There are currently 191 contracting states according to 
ICAO's Web site: www.icao.int (last accessed April 8, 2016).
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    In the interest of global harmonization and international air 
commerce, the Chicago Convention urges its member states to collaborate 
in securing the highest practicable degree of uniformity in 
regulations, standards, procedures and organization. The Chicago 
Convention also recognizes that member states may adopt standards that 
are more stringent than those agreed upon by ICAO. Any member state 
which finds it impracticable to comply in all respects with any 
international standard or procedure, or that deems it necessary to 
adopt regulations or practices differing in any particular respect from 
those established by an international standard, is required to give 
immediate notification to ICAO of the differences between its own 
practice and that established by the international standard.\36\
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    \36\ ICAO, 2006: Doc 7300-Convention on International Civil 
Aviation, Ninth Edition, Document 7300/9, 114 pp. Available at 
https://www.icao.int/publications/Documents/7300_9ed.pdf (last 
accessed April 8, 2016).
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    ICAO's work on the environment focuses primarily on those problems 
that benefit most from a common and coordinated approach on a worldwide 
basis, namely aircraft noise and engine emissions. SARPs for the 
certification of aircraft noise and aircraft engine emissions are 
covered by Annex 16 of the Chicago Convention. To continue to address 
aviation environmental issues, in 2004, ICAO established three 
environmental goals: (1) Limit or reduce the number of people affected 
by significant aircraft noise; (2) limit or reduce the impact of 
aviation emissions on local air quality; and (3) limit or reduce the 
impact of aviation GHG emissions on the global climate.
    The Chicago Convention has a number of other features that govern 
international commerce. First, member states that wish to use aircraft 
in international transportation must adopt emissions standards and 
other recommended practices that are at least as stringent as ICAO's 
standards. Member states may ban the use of any aircraft within their 
airspace that does not meet ICAO standards.\37\ Second, the Chicago 
Convention indicates that member states are required to recognize the 
airworthiness certificates of any state whose standards are at least as 
stringent as ICAO's standards.\38\ Third, to ensure that international 
commerce is not unreasonably constrained, a member state which elects 
to adopt more stringent domestic emission standards is obligated to 
notify ICAO of the differences between its standards and ICAO 
standards.\39\
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    \37\ ICAO, 2006: Convention on International Civil Aviation, 
Article 87, Ninth Edition, Document 7300/9, 114 pp. Available at 
https://www.icao.int/publications/Documents/7300_9ed.pdf (last 
accessed April 8, 2016).
    \38\ ICAO, 2006: Convention on International Civil Aviation, 
Article 33, Ninth Edition, Document 7300/9, 114 pp. Available at 
https://www.icao.int/publications/Documents/7300_9ed.pdf (last 
accessed April 8, 2016).
    \39\ ICAO, 2006: Convention on International Civil Aviation, 
Article 38, Ninth Edition, Document 7300/9, 114 pp. Available at 
https://www.icao.int/publications/Documents/7300_9ed.pdf (last 
accessed April 8, 2016).
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    ICAO's CAEP, which consists of members and observers from states, 
intergovernmental and non-governmental organizations representing 
aviation industry and environmental interests, undertakes ICAO's 
technical work in the environmental field. The Committee is responsible 
for evaluating, researching, and recommending measures to the ICAO 
Council that address the environmental impacts of international civil 
aviation. CAEP's terms of reference indicate that ``CAEP's assessments 
and proposals are pursued taking into account: Technical feasibility; 
environmental benefit; economic reasonableness; interdependencies of 
measures (for example, among others, measures taken to minimize noise 
and emissions); developments in other fields; and international and 
national programs.'' \40\ The ICAO Council reviews and adopts the 
recommendations made by CAEP. It then reports to the ICAO Assembly, the 
highest body of the Organization, where the main policies on aviation 
environmental protection are adopted and translated into Assembly 
Resolutions. If ICAO adopts a CAEP proposal for a new environmental 
standard, it then becomes part of ICAO standards and recommended 
practices (Annex 16 to the Chicago Convention).41 42
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    \40\ ICAO: CAEP Terms of Reference. Available at https://www.icao.int/environmental-protection/Pages/Caep.aspx#ToR (last 
accessed April 27, 2016).
    \41\ ICAO, 2008: Aircraft Engine Emissions, International 
Standards and Recommended Practices, Environmental Protection, Annex 
16, Volume II, Third Edition, July, 110 pp. Available at https://www.icao.int/publications/catalogue/cat_2016_en.pdf (last accessed 
April 8, 2016). The ICAO Annex 16 Volume II is found on page 19 of 
the ICAO Products & Services 2016 catalog and is copyright 
protected; Order No. AN16-2.
    \42\ CAEP develops new emission standards based on an assessment 
of the technical feasibility, cost, and environmental benefit of 
potential requirements.
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    At CAEP meetings, the United States is represented by the FAA and 
plays an active role.\43\ The EPA has historically been a principal 
participant in various ICAO/CAEP working groups and other international 
venues, assisting and advising FAA on aviation emissions, technology, 
and environmental policy matters. In turn, the FAA assists and advises 
the EPA on aviation environmental issues, technology and certification 
matters.
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    \43\ Pursuant to the President's memorandum of August 11, 1960 
(and related Executive Order No. 10883 from 1960), the Interagency 
Group on International Aviation (IGIA) was established to facilitate 
coordinated recommendations to the Secretary of State on issues 
pertaining to international aviation. The DOT/FAA is the chair of 
IGIA, and as such, the FAA represents the U.S. on environmental 
matters at CAEP.
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    The first international standards and recommended practices for 
aircraft engine emissions were recommended by CAEP's predecessor, the 
Committee on Aircraft Engine Emissions (CAEE), and

[[Page 54429]]

adopted by ICAO in 1981.\44\ These standards limited aircraft engine 
emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of 
nitrogen (NOX). The 1981 standards applied to newly 
manufactured engines, which are those engines built after the effective 
date of the regulations--also referred to as in-production engines. In 
1993, ICAO adopted a CAEP/2 proposal to tighten the original 
NOX standard by 20 percent and amend the test 
procedures.\45\ These 1993 standards applied both to newly certified 
turbofan engines, which are those engine models that received their 
initial type certificate after the effective date of the regulations--
also referred to as newly certified engines or new engine designs--and 
to in-production engines, but with different effective dates for newly 
certified engines and in-production engines. In 1995, CAEP/3 
recommended a further tightening of the NOX standards by 16 
percent and additional test procedure amendments, but in 1997 the ICAO 
Council rejected this stringency proposal and approved only the test 
procedure amendments. At the CAEP/4 meeting in 1998, the Committee 
adopted a similar 16 percent NOX reduction proposal, which 
ICAO approved in 1998. The CAEP/4 standards applied only to new engine 
designs certified (or newly certified engines) after December 31, 2003 
(i.e., unlike the CAEP/2 standards, the CAEP/4 requirements did not 
apply to in-production engines). In 2004, CAEP/6 recommended a 12 
percent NOX reduction, which ICAO approved in 
2005.46 47 The CAEP/6 standards applied to new engine 
designs certified after December 31, 2007. In 2010, CAEP/8 recommended 
a further tightening of the NOX standards by 15 percent for 
new engine designs certified after December 31, 2013.48 49 
The Committee also recommended that the CAEP/6 standards be applied to 
in-production engines (eliminating the production of CAEP/4 compliant 
engines with the exception of spare engines), and ICAO approved these 
recommendations in 2011.\50\
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    \44\ ICAO, 2008: Aircraft Engine Emissions: Foreword, 
International Standards and Recommended Practices, Environmental 
Protection, Annex 16, Volume II, Third Edition, July, 110 pp. 
Available at https://www.icao.int/publications/catalogue/cat_2016_en.pdf (last accessed April 8, 2016). The ICAO Annex 16 
Volume II is found on page 19 of the ICAO Products & Services 2016 
catalog and is copyright protected; Order No. AN16-2.
    \45\ CAEP conducts its work over a period of years. Each work 
cycle is numbered sequentially and that identifier is used to 
differentiate the results from one CAEP to another by convention. 
The first technical meeting on aircraft emission standards was 
CAEP's successor, i.e., CAEE. The first meeting of CAEP, therefore, 
is referred to as CAEP/2.
    \46\ CAEP/5 did not address new aircraft engine emission 
standards.
    \47\ ICAO, 2008: Aircraft Engine Emissions, Annex 16, Volume II, 
Third Edition, July 2008, Amendment 5 effective on July 11, 2005, 
110 pp. Available at https://www.icao.int/publications/catalogue/cat_2016_en.pdf (last accessed April 8, 2016). The ICAO Annex 16 
Volume II is found on page 19 of the ICAO Products & Services 2016 
catalog and is copyright protected; Order No. AN16-2.
    \48\ CAEP/7 did not address new aircraft engine emission 
standards.
    \49\ ICAO, 2010: Committee on Aviation Environmental Protection 
(CAEP), Report of the Eighth Meeting, Montreal, February 1-12, 2010, 
CAEP/8-WP/80 Available in Docket EPA-HQ-OAR-2010-0687.
    \50\ ICAO, 2014: Aircraft Engine Emissions, Annex 16, Volume II, 
Third Edition, July 2008, Amendment 8, 108 pp. CAEP/8 corresponds to 
Amendment 7 effective on July 18, 2011. Available at https://www.icao.int/publications/catalogue/cat_2016_en.pdf (last accessed 
April 8, 2016). The ICAO Annex 16 Volume II is found on page 19 of 
the ICAO Products & Services 2016 catalog and is copyright 
protected; Order No. AN16-2/E/11.
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2. The International Civil Aviation Organization's Reasons for 
Addressing Aircraft GHG Emissions
    In October 2010, the 37th Assembly (Resolution A37-19) of ICAO 
requested the development of an ICAO CO2 emissions 
standard.\51\ The Resolution provided a framework towards the 
achievement of an environmentally sustainable future for international 
aviation. With this Resolution, the ICAO Assembly agreed to a global 
aspirational goal for international aviation of improving annual fuel 
efficiency by two percent up to the year 2050, and stabilizing 
CO2 emissions at 2020 levels.\52\ Reducing climate impacts 
of international aviation is a critical element of ICAO's strategic 
objective of achieving environmental protection and sustainable 
development of air transport. ICAO is currently pursuing a 
comprehensive set of measures to reduce aviation's climate impact, 
including lower-carbon alternative fuels, CO2 emissions 
technology-based standards, operational improvements, and market based 
measures. The development and adoption of a CO2 emissions 
standard is an important part of ICAO's comprehensive set of measures.
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    \51\ A consolidated statement of continuing policies and 
practices related to environmental protection (known as Assembly 
Resolutions) is revised and updated by the Council every three years 
for adoption by the ICAO Assembly. ICAO, 2010: Resolutions Adopted 
by the Assembly, 37th Session, Montreal, September 29-October 8, 
2010, Provisional Edition, November 2010.
    \52\ The global aspirational goal for international aviation of 
improving annual fuel efficiency by 2 percent is for the annual 
international civil aviation in-service fleet. Fuel efficiency is 
measured on the basis of the volume of fuel used per revenue tonne 
kilometer performed. ICAO CAEP, 2009: Aspirational Goals and 
Implementation Options, Working Paper HLM-ENV/09-WP/5, 5 pp. 
Available at https://www.icao.int/Meetings/AMC/MA/High%20Level%202009/hlmenv_wp005_en.pdf (last accessed April 8, 
2015).
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3. EPA's Regulation of Aircraft Emissions and the Relationship of the 
Final Endangerment and Cause or Contribute Findings to International 
Aircraft Standards
    As required by the CAA, the EPA has been engaged in reducing 
harmful air pollution from aircraft engines for over 40 years, 
regulating gaseous exhaust emissions, smoke, and fuel venting from 
aircraft engines.\53\ We have periodically revised these regulations. 
In a 1997 rulemaking, for example, we made our emission standards and 
test procedures more consistent with those of ICAO's CAEP for turbofan 
engines used in commercial aviation with rated thrusts greater than 
26.7 kilonewtons.\54\ These ICAO requirements are generally referred to 
as CAEP/2 standards.\55\ The 1997 rulemaking included new 
NOX emission standards for newly manufactured commercial 
turbofan engines (as described earlier, those engines built after the 
effective date of the regulations that were already certified to pre-
existing standards--also referred to as in-production engines) \56\ and 
for newly certified commercial turbofan engines (as described earlier, 
those engine models that received their initial type certificate after 
the effective date of the regulations--also referred to as new engine 
designs).\57\ It also included a CO emission standard for in-production 
commercial turbofan engines.\58\ In 2005, we promulgated more stringent 
NOX emission standards for newly certified commercial 
turbofan
---------------------------------------------------------------------------

    \53\ U.S. EPA, 1973: Emission Standards and Test Procedures for 
Aircraft; Final Rule, 38 FR 19088 (July 17, 1973).
    \54\ U.S. EPA, 1997: Control of Air Pollution from Aircraft and 
Aircraft Engines; Emission Standards and Test rocedures; Final Rule, 
62 FR 25355 (May 8, 1997).
    \55\ The full CAEP membership meets every three years and each 
session is denoted by a numerical identifier. For example, the 
second meeting of CAEP is referred to as CAEP/2, and CAEP/2 occurred 
in 1994.
    \56\ This does not mean that in 1997 we promulgated requirements 
for the re-certification or retrofit of existing in-use engines.
    \57\ In the existing EPA regulations, 40 CFR part 87, newly 
certified aircraft engines are described as engines of a type or 
model of which the date of manufacture of the first individual 
production model was after the implementation date. Newly 
manufactured aircraft engines are characterized as engines of a type 
or model for which the date of manufacturer of the individual engine 
was after the implementation date.
    \58\ U.S. EPA, 1997: Control of Air Pollution from Aircraft and 
Aircraft Engines; Emission Standards and Test Procedures; Final 
Rule, 62 FR 25355 (May 8, 1997).

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[[Page 54430]]

engines.\59\ That final rule brought the U.S. standards closer to 
alignment with ICAO CAEP/4 requirements that became effective in 2004. 
In 2012, we issued more stringent two-tiered NOX emission 
standards for newly certified and in-production commercial and non-
commercial turbofan aircraft engines, and these NOX 
standards align with ICAO's CAEP/6 and CAEP/8 requirements that became 
effective in 2013 and 2014, respectively.60 61 The EPA's 
actions to regulate certain pollutants emitted from aircraft engines 
come directly from the authority in section 231 of the CAA, and we have 
aligned the U.S. emissions requirements with those promulgated by ICAO. 
All of these previous emission standards have generally been considered 
anti-backsliding standards (most aircraft engines meet the standards), 
which are technology-following.
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    \59\ U.S. EPA, 2005: Control of Air Pollution from Aircraft and 
Aircraft Engines; Emission Standards and Test Procedures; Final 
Rule, 70 FR 69664 (November 17, 2005).
    \60\ U.S. EPA, 2012: Control of Air Pollution from Aircraft and 
Aircraft Engines; Emission Standards and Test Procedures; Final 
Rule, 77 FR 36342 (June 18, 2012).
    \61\ While ICAO's standards were not limited to ``commercial'' 
aircraft engines, our 1997 standards were explicitly limited to 
commercial engines, as our finding that NOX and carbon 
monoxide emissions from aircraft engines cause or contribute to air 
pollution which may reasonably be anticipated to endanger public 
health or welfare was so limited. See 62 FR 25358 (May 8, 1997). In 
the 2012 rulemaking, we expanded the scope of that finding and of 
our standards pursuant to CAA section 231(a)(2)(A) to include such 
emissions from both commercial and non-commercial aircraft engines 
based on the physical and operational similarities between 
commercial and noncommercial civilian aircraft and to bring our 
standards into full alignment with ICAO's.
---------------------------------------------------------------------------

    In addressing CO2 emissions, ICAO has moved to 
regulating a whole aircraft. ICAO explained its decision to regulate 
pollutant emissions from the whole aircraft in a 2013 ICAO 
circular.\62\ Several factors are considered when addressing whole-
aircraft CO2 emissions, as CO2 emissions are 
influenced by aerodynamics, weight, and engine technology. Since the 
aircraft-specific characteristics of aerodynamics and weight affect 
fuel consumption, they ultimately affect CO2 engine exhaust 
emissions. Rather than viewing CO2 as a measurable emission 
from the engine alone, ICAO addresses CO2 emissions as an 
aircraft-specific characteristic based on fuel consumption.
---------------------------------------------------------------------------

    \62\ ICAO, 2013: CAEP/9 Agreed Certification Requirement for the 
Aeroplane CO2 Emissions Standard, Circular (Cir) 337, 40 pp, AN/192. 
Available at https://www.icao.int/publications/catalogue/cat_2016_en.pdf (last accessed April 8, 2016). The ICAO Circular 337 
is found on page 87 of the ICAO Products & Services 2016 catalog and 
is copyright protected; Order No. CIR337.
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    The EPA has worked diligently over the past six years within the 
ICAO/CAEP process on a range of technical issues regarding aircraft 
CO2 emission standards. The 2015 ANPR discussed the issues 
arising from those international proceedings and requested public 
comment on a variety of issues to assist the Agency in developing its 
position with regard to these issues, to help ensure transparency and 
obtain views on aircraft engine GHG emission standards that it might 
potentially adopt under the CAA.
    As described in the 2015 ANPR, in 2013 CAEP agreed on a metric \63\ 
to compare CO2 emissions from aircraft. The CO2 
metric value is a comparative metric meant to differentiate between 
generations of aircraft and to equitably capture improvements in 
aerospace technology that contribute to a reduction in the airplane 
CO2 emissions. The CO2 metric is not intended for 
use as a direct measure of CO2 emissions rates or 
operational fuel burn, rather it is a comparative measure of technology 
on different aircraft.
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    \63\ The CO2 metric is the average of three cruise 
test points normalized by a dimensionless parameter representing 
aircraft fuselage size. The units of the metric value are kilograms 
of fuel burned per kilometer flown. However, because the metric is a 
normalized value it cannot be used to estimate operational fuel burn 
or emission rates of aircraft. The metric value is described in 
detail in both ICAO Circular 337 and in section D of the 2015 ANPR. 
ICAO, 2013: CAEP/9 Agreed Certification Requirement for the 
Aeroplane CO2 Emissions Standard, Circular (Cir) 337, 40 pp., AN/
192, Available at https://www.icao.int/publications/catalogue/cat_2016_en.pdf (last accessed April 27, 2016). The ICAO Circular 
337 is found on page 87 of the catalog and is copyright protected; 
Order No. CIR337.
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    Using this metric, CAEP considered and analyzed 10 different 
stringency levels for both in-production and new type standards, 
comparing aircraft with a similar level of technology on the same 
stringency level. These levels were generically referred to numerically 
from ``1'' as the least stringent to ``10'' as the most stringent, 
which correspond to the upper and lower lines of constant technology, 
respectively, from the 2015 ANPR. The 2015 ANPR described the range of 
stringency levels under consideration at CAEP as falling into three 
categories as follows: (1) CO2 stringency levels that could 
impact \64\ only the oldest, least efficient aircraft in-production 
around the world, (2) middle range CO2 stringency levels 
that could impact many aircraft currently in-production and comprising 
much of the current operational fleet, and (3) CO2 
stringency levels that could impact aircraft that have either just 
entered production or are in final design phase but will be in-
production by the time the international CO2 standards 
becomes effective.\65\
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    \64\ As described in the 2015 ANPR, the aircraft shown in 
[Figure II.1 and II.2] are in-production and current in-development. 
These aircraft could be impacted by an in-production standard in 
that, if they were above the standard, they would need to either 
implement a technology response or go out of production. For a new 
type only standard there will be no regulatory requirement for these 
aircraft to respond.
    \65\ 80 FR at 37797.
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    At its meeting in February of 2016, CAEP agreed on an initial set 
of international standards to regulate CO2 emissions from 
aircraft.\66\ It was agreed that these international standards should 
apply to both new type and in-production aircraft. The applicability 
date for the in-production standard was agreed to be later than for the 
new type standard. CAEP explained that this will allow manufacturers 
and certification authorities additional preparation time to 
accommodate the standards. The new type and in-production stringency 
levels for smaller and larger aircraft were agreed to be set at 
different levels to reflect the range of technology being used and the 
availability of new fuel burn reduction technologies that vary across 
aircraft of differing size and weight. Table II.1 provides a brief 
overview of the applicability dates and stringency levels of the 
standards agreed to at ICAO/CAEP. As described earlier, CAEP considered 
and analyzed 10 different stringency levels for both in-production and 
new type standards (from 1 as the least stringent to 10 as the most 
stringent).
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    \66\ Further, the EPA anticipates that the 39th ICAO Assembly 
will approve these CO2 emissions standards in October 
2016, and that subsequently, ICAO will formally adopt these 
CO2 emissions standards in March 2017.

[[Page 54431]]



           Table II.1--Stringency Levels and Applicability Dates for ICAO/CAEP CO2 Emission Standards
----------------------------------------------------------------------------------------------------------------
                                                                                                   In-production
                                                                                                     aircraft
                                           Aircraft MTOM thresholds     New type aircraft \67\        maximum
                                                     (kg)                maximum permitted CO2     permitted CO2
                                                                             metric value          metric value
 
----------------------------------------------------------------------------------------------------------------
Stringency Level........................  >5,700 to <60,000.........  \A\ 5.....................           \B\ 3
                                          Horizontal Transition \68\  \C\.......................             \D\
                                          60,000 to ~70,000.........
                                          > ~70,000.................  \E\ 8.5...................           \F\ 7
Applicability Date......................  Application for a new type  2020......................            2023
                                           certificate or a change    (2023 for planes with less
                                           to an existing type         than 19 seats).
                                           certificate.
                                          Production Cut Off........  n/a.......................            2028
----------------------------------------------------------------------------------------------------------------
\A\ Equation of ICAO Stringency Option #5: MV = 10-2.73780+(0.681310*\l\\o\\g\ 10(\M\\T\\O\\M\))+(-
  0.0277861*(\l\\o\\g\ 10(\M\\T\\O\\M\))2)
\B\ Equation of ICAO Stringency Option #3: MV = 10-2.57535+(0.609766*\l\\o\\g\ 10(\M\\T\\O\\M\))+(-
  0.0191302*(\l\\o\\g\ 10(\M\\T\\O\\M\))2)
\C\ Equation of New Type transition--60,000 to 70,395 kg: MV = 0.764
\D\ Equation of In-production transition--60,000 to 70,107 kg: MV = 0.797
\E\ Equation of ICAO Stringency Option #8.5: MV = 10-2.57535+(0.609766*\l\\o\\g\ 10(\M\\T\\O\\M\))+(-
  0.0191302*(\l\\o\\g\ 10(\M\\T\\O\\M\))2)
\F\ Equation of ICAO Stringency Option #7: MV = 10-1.39353+(-0.020517*\l\\o\\g\
  10(\M\\T\\O\\M\))+(0.0593831*(\l\\o\\g\ 10(\M\\T\\O\\M\))2)

    Figures II.1 and II.2 show a graphical depiction of both the new 
type and in-production standards compared against the lines of constant 
technology described in the 2015 ANPR and CO2 metric value 
levels of current (as of February 2016) in-production and in-
development \69\ aircraft. The aircraft data shown were generated by 
the EPA using a commercially available aircraft modeling tool called 
PIANO.\70\ It should be noted that a number of the aircraft currently 
shown as in-production are expected to go out of production and be 
replaced by known in-development aircraft prior to both the new type 
and the in-production CO2 standards going into effect 
internationally.
---------------------------------------------------------------------------

    \67\ ``In Development'' aircraft shown in Figures II.1 and II.2 
are the aircraft that were in development by manufacturers at the 
time the 2015 ANPR was published.
    \68\ Stringency lines above and below 60,000 kilograms (MTOM) 
are connected by a horizontal transition starting at 60,000 
kilograms (MTOM) and continuing right (increasing mass) until it 
intersects with the next level.
    \69\ Aircraft that are currently in-development but will be in 
production by the applicability dates. These could be new types or 
significant partial redesigned aircraft.
    \70\ PIANO (Project Interactive Analysis and Optimization), 
Aircraft Design and Analysis Software by Dr. Dimitri Simos, Lissys 
Limited, UK, 1990-present; Available at www.piano.aero (last 
accessed April 8, 2016). This is a commercially available aircraft 
design and performance software suite used across the industry and 
academia. This model contains non-manufacturer provided estimates of 
performance of various aircraft.
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BILLING CODE 6560-50-P

[[Page 54432]]

[GRAPHIC] [TIFF OMITTED] TR15AU16.000


[[Page 54433]]


[GRAPHIC] [TIFF OMITTED] TR15AU16.001

BILLING CODE 6560-50-C
    In this final action, the EPA is promulgating findings under 
section 231(a)(2) that emissions of the six well-mixed GHGs from 
certain classes of engines used in covered aircraft cause or contribute 
to endangering air pollution. The EPA is not yet issuing proposed or 
final emission standards, nor is the EPA taking final action that 
prejudges what future standards will be. Instead, the EPA's final 
endangerment and cause or contribute findings for aircraft GHG 
emissions are in preparation for a subsequent, expected domestic

[[Page 54434]]

rulemaking process to adopt future GHG emissions standards. If the ICAO 
Assembly, in October 2016, approves the final CO2 standards 
and subsequently ICAO formally adopts the final CO2 
standards in March 2017, the EPA's standards will need to be at least 
as stringent as the ICAO CO2 aircraft standards for the 
United States to meet its treaty obligations under the Chicago 
Convention. As a result of these positive findings, the EPA is 
obligated under section 231 of the CAA to set emission standards 
applicable to GHG emissions from the classes of aircraft engines 
included in the contribution finding, no matter the outcome of ICAO's 
future actions in October 2016 and March 2017.

III. Legal Framework for This Action

    The EPA has previously made an endangerment finding for GHGs under 
Title II of the CAA, in the 2009 Endangerment Finding for section 
202(a) source categories. In the 2009 Endangerment Finding, the EPA 
explained its legal framework for making an endangerment finding under 
section 202(a) of the CAA (74 FR 18886, 18890-94 (April 24, 2009), and 
74 FR 66496, 66505-10 (December 15, 2009)). The text in section 202(a) 
that was the basis for the 2009 Endangerment Finding addresses ``the 
emission of any air pollutant from any class or classes of new motor 
vehicles or new motor vehicle engines, which in [the Administrator's] 
judgment cause, or contribute to, air pollution which may reasonably be 
anticipated to endanger public health or welfare.'' Similarly, section 
231(a)(2)(A) concerns ``the emission of any air pollutant from any 
class or classes of aircraft engines which in [the Administrator's] 
judgment causes, or contributes to, air pollution which may reasonably 
be anticipated to endanger public health or welfare.'' Thus, the text 
of the CAA section concerning aircraft emissions in section 
231(a)(2)(A) mirrors the text of CAA section 202(a) that was the basis 
for the 2009 Endangerment Finding.
    The EPA's approach in the 2009 Endangerment Finding (described 
below in sections III.A and III.B) was affirmed by the U.S. Court of 
Appeals for the D.C. Circuit in Coalition for Responsible Regulation, 
Inc. v. EPA, 684 F.3d 102 (D.C. Cir. 2012), reh'g denied 2012 U.S. App. 
LEXIS 26313, 26315, 25997 (D.C. Cir. 2012) (CRR). In particular, the 
D.C. Circuit ruled that the 2009 Endangerment Finding (including the 
Agency's denial of petitions for reconsideration of that Finding) was 
not arbitrary or capricious, was consistent with the U.S. Supreme 
Court's decision in Massachusetts v. EPA and the text and structure of 
the CAA, and was adequately supported by the administrative record. 
CRR, 684 F.3d at 116-128. The D.C. Circuit found that the EPA had based 
its decision on ``substantial scientific evidence'' and noted that the 
EPA's reliance on major scientific assessments was consistent with the 
methods that decision-makers often use to make a science-based 
judgment. Id. at 120-121. Petitions for certiorari were filed in the 
Supreme Court, and the Supreme Court granted six of those petitions but 
``agreed to decide only one question: `Whether EPA permissibly 
determined that its regulation of greenhouse gas emissions from new 
motor vehicles triggered permitting requirements under the Clean Air 
Act for stationary sources that emit greenhouse gases.' '' Utility Air 
Reg. Group v. EPA, 134 S. Ct. 2427, 2438 (2014); see also Virginia v. 
EPA, 134 S. Ct. 418 (2013), Pac. Legal Found. v. EPA, 134 S. Ct. 418 
(2013), and CRR, 134 S. Ct. 468 (2013) (all denying cert.). Thus, the 
Supreme Court did not disturb the D.C. Circuit's holding that affirmed 
the 2009 Endangerment Finding. Accordingly, the Agency finds that it is 
reasonable to use that same approach under section 231(a)(2)(A)'s 
similar endangerment text, and as explained in the following 
discussion, is acting consistently with that judicially sanctioned 
framework for purposes of this final section 231 finding.
    Two provisions of the CAA govern this final action. Section 
231(a)(2)(A) sets forth a two-part predicate for regulatory action 
under that provision: Endangerment and cause or contribute. Section 302 
of the Act contains definitions of the terms ``air pollutant'' and 
``welfare'' used in section 231(a)(2)(A). These statutory provisions 
are discussed below.

A. Section 231(a)(2)(A)--Endangerment and Cause or Contribute

    As noted above, section 231(a)(2)(A) of the CAA (like section 
202(a)) calls for the Administrator to exercise her judgment and make 
two separate determinations: first, whether the relevant kind of air 
pollution--here, the six well-mixed GHGs--may reasonably be anticipated 
to endanger public health or welfare, and second, whether emissions of 
any air pollutant from classes of the sources in question (aircraft 
engines under section 231 and new motor vehicles or engines under 
section 202) cause or contribute to this air pollution.\71\
---------------------------------------------------------------------------

    \71\ See CRR, 684 F.3d at 117 (explaining two-part analysis 
under section 202(a)).
---------------------------------------------------------------------------

    The Administrator interprets the two-part test required under 
section 231(a)(2)(A) as being the same as that explained in the 2009 
Endangerment Finding. See 74 FR 66505-06. As in the section 202(a) 
context, this analysis entails a scientific judgment by the 
Administrator about the potential risks posed by GHG emissions to 
public health and welfare. See CRR, 684 F.3d at 117-118.\72\
---------------------------------------------------------------------------

    \72\ When agencies such as the EPA make determinations based on 
review of scientific data within their technical expertise, those 
decisions are given an ``extreme degree of deference'' by the 
courts. As the D.C. Circuit noted in reviewing the 2009 Endangerment 
Finding, ``although we perform a searching and careful inquiry into 
the facts underlying the agency's decisions, we will presume the 
validity of the agency action as long as a rational basis for it is 
presented.'' CRR, 684 F.3d at 120 (internal citations and marks 
omitted).
---------------------------------------------------------------------------

    In making this scientific judgment, the Administrator is guided by 
five principles. First, the Administrator is required to protect public 
health and welfare. She is not asked to wait until harm has occurred 
but instead must be ready to take regulatory action to prevent harm 
before it occurs.\73\ The Administrator is thus to consider both 
current and future risks.
---------------------------------------------------------------------------

    \73\ See id. at 121-122.
---------------------------------------------------------------------------

    Second, the Administrator is to exercise judgment by weighing 
risks, assessing potential harms, and making reasonable projections of 
future trends and possibilities. It follows that when exercising her 
judgment the Administrator balances the likelihood and severity of 
effects. This balance involves a sliding scale: on one end the severity 
of the effects may be significant, but the likelihood low, while on the 
other end the severity may be less significant, but the likelihood 
high.\74\ At different points along this scale, the Administrator is 
permitted to find endangerment. Accordingly, the Administrator need not 
set a precise or minimum threshold of risk or harm as part of making an 
endangerment finding, but rather may base her determination on `` `a 
lesser risk of greater harm . . . or a greater risk of lesser harm' or 
any combination in between.'' CRR, 684 F.3d at 123 (quoting Ethyl Corp. 
v. EPA, 541 F.2d, 1, 18 (D.C. Cir. 1976)).
---------------------------------------------------------------------------

    \74\ See id. at 122-123 (noting that the Sec.  202(a)(1) inquiry 
``necessarily entails a case-by-case, sliding scale approach'' 
because endangerment is `` `composed of reciprocal elements of risk 
and harm, or probability and severity' '' (quoting Ethyl Corp. v. 
EPA, 541 F.2d, 1, 18 (D.C. Cir. 1976)).
---------------------------------------------------------------------------

    Third, because scientific knowledge is constantly evolving, the 
Administrator may be called upon to make decisions while recognizing 
the uncertainties and limitations of the data or information available, 
as risks to public health or

[[Page 54435]]

welfare may involve the frontiers of scientific or medical 
knowledge.\75\ At the same time, the Administrator must exercise 
reasoned decision making, and avoid speculative inquiries.
---------------------------------------------------------------------------

    \75\ See id. at 121-122.
---------------------------------------------------------------------------

    Fourth, the Administrator is to consider the cumulative impact of 
sources of a pollutant in assessing the risks from air pollution, and 
is not to look only at the risks attributable to a single source or 
class of sources. We additionally note that in making an endangerment 
finding, the Administrator is not limited to considering only those 
impacts that can be traced to the amount of air pollution directly 
attributable to the subject source classes. Such an approach would 
collapse the two prongs of the test by requiring that any climate 
change impacts upon which an endangerment determination is made result 
solely from the GHG emissions of aircraft. See 74 FR at 66542 
(explaining the same point in the context of analogous language in 
section 202(a)). Similarly, the Administrator is not, in making the 
endangerment and cause or contribute findings, to consider the effect 
of emissions reductions from the resulting standards.\76\ The threshold 
endangerment and cause or contribute criteria are separate and distinct 
from the standard setting criteria that apply if the threshold findings 
are met, and they serve a different purpose. Indeed, the more serious 
the endangerment to public health and welfare, the more important it 
may be that action be taken to address the actual or potential harm 
even if no one action alone can solve the problem, and a series of 
actions is called for.
---------------------------------------------------------------------------

    \76\ As the D.C. Circuit explained in reviewing the 2009 
Endangerment Finding under analogous language in section 202(a): 
``At bottom, Sec.  202(a)(1) requires EPA to answer only two 
questions: whether particular `air pollution'--here, greenhouse 
gases--`may reasonably be anticipated to endanger public health or 
welfare,' and whether motor-vehicle emissions `cause, or contribute 
to' that endangerment.'' CRR, 648 F.3d at 117.
---------------------------------------------------------------------------

    Fifth, the Administrator is to consider the risks to all parts of 
our population, including those who are at greater risk for reasons 
such as increased susceptibility to adverse health and welfare effects. 
If vulnerable subpopulations are especially at risk, the Administrator 
is entitled to take that point into account in deciding the question of 
endangerment. Here too, both likelihood and severity of adverse effects 
are relevant. As explained previously in the 2009 Endangerment Finding 
and as reiterated below for this section 231 finding, vulnerable 
subpopulations face serious health and welfare risks as a result of 
climate change.
    As the Supreme Court recognized in Massachusetts v. EPA, 549 U.S. 
at 534, the EPA may make an endangerment finding despite the existence 
of ``some residual uncertainty'' in the scientific record. See also 
CRR, 684 F. 2d at 122. Thus, this framework recognizes that regulatory 
agencies such as the EPA must be able to deal with the reality that 
``[m]an's ability to alter his environment has developed far more 
rapidly than his ability to foresee with certainty the effects of his 
alterations.'' Ethyl Corp v. EPA, 541 F.2d 1, 6 (D.C. Cir.), cert. 
denied 426 U.S. 941 (1976). Both ``the Clean Air Act `and common sense 
. . . demand regulatory action to prevent harm, even if the regulator 
is less than certain that harm is otherwise inevitable.' '' 
Massachusetts v. EPA, 549 U.S. at 506, n.7 (citing Ethyl Corp.); see 
also CRR, 684 F.3d at 121-122.
    In the 2009 Endangerment Finding, the Administrator recognized that 
the scientific context for an action addressing climate change was 
unique at that time because there was a very large and comprehensive 
base of scientific information that had been developed over many years 
through a global consensus process involving numerous scientists from 
many countries and representing many disciplines. 74 FR at 66506. That 
informational base has since grown. The Administrator also previously 
recognized that there are varying degrees of uncertainty across many of 
these scientific issues, which remains true. It is in this context that 
she is exercising her judgment and applying the statutory framework in 
this final section 231 finding. Further discussion of the language in 
section 231(a)(2)(A), and parallel language in 202(a), is provided 
below to explain more fully the basis for this interpretation, which 
the D.C. Circuit upheld in the 202(a) context.
1. The Statutory Language
    The interpretation described above flows from the statutory 
language itself. The phrase ``may reasonably be anticipated'' and the 
term ``endanger'' in section 231(a)(2)(A) (as in section 202(a)) 
authorize, if not require, the Administrator to act to prevent harm and 
to act in conditions of uncertainty. They do not limit her to merely 
reacting to harm or to acting only when certainty has been achieved; 
indeed, the references to anticipation and to endangerment imply that 
to fail to look to the future or to less than certain risks would be to 
abjure the Administrator's statutory responsibilities. As the D.C. 
Circuit explained, the language ``may reasonably be anticipated to 
endanger public health or welfare'' in CAA section 202(a) requires a 
``precautionary, forward-looking scientific judgment about the risks of 
a particular air pollutant, consistent with the CAA's precautionary and 
preventive orientation.'' CRR, 684 F.3d at 122 (internal citations 
omitted). The court determined that ``[r]equiring that EPA find 
`certain' endangerment of public health or welfare before regulating 
GHGs would effectively prevent EPA from doing the job that Congress 
gave it in [section] 202(a)--utilizing emission standards to prevent 
reasonably anticipated endangerment from maturing into concrete harm.'' 
Id. The same language appears in section 231(a)(2)(A), and the same 
interpretation applies in that context.
    Moreover, by instructing the Administrator to consider whether 
emissions of an air pollutant cause or contribute to air pollution in 
the second part of the two-part test, the Act makes clear that she need 
not find that emissions from any one sector or class of sources are the 
sole or even the major part of an air pollution problem. The use of the 
term ``contribute'' clearly indicates that such emissions need not be 
the sole or major cause of the pollution. In addition, the absence of 
the term ``significantly'' or any other word that modifies 
``contribute'' shows that the EPA need not find that contributing 
emissions cross a minimum percentage- or mass-based threshold to be 
cognizable. The phrase ``in [her] judgment'' authorizes the 
Administrator to weigh risks and to consider projections of future 
possibilities, while also recognizing uncertainties and extrapolating 
from existing data. Finally, when exercising her judgment in making 
both the endangerment and cause or contribute findings, the 
Administrator balances the likelihood and severity of effects. Notably, 
the phrase ``in [her] judgment'' modifies both ``may reasonably be 
anticipated'' and ``cause or contribute.''
2. How the Origin of the Current Statutory Language Informs the EPA's 
Interpretation of Section 231(a)(2)(A)
    In the proposed and final 2009 Endangerment Finding, the EPA 
explained that when Congress revised the section 202(a) language that 
governed that finding, along with other provisions, as part of the 1977 
amendments to the CAA, it was responding to decisions issued by the 
D.C. Circuit in Ethyl Corp. v. EPA regarding the pre-1977 version of 
section 211(c) of the Act. 74 FR at

[[Page 54436]]

18891; see also 74 FR at 66506. The legislative history of those 
amendments, particularly the report by the House Committee on 
Interstate and Foreign Commerce, demonstrates that the EPA's 
interpretation of the section 231(a)(2)(A) language as set forth here 
in support of the Agency's section 231 finding is fully consistent with 
Congress' intention in crafting these provisions. See H.R. Rep. 95-294 
(1977), as reprinted in 4 A Legislative History of the Clean Air Act 
Amendments of 1977 (1978) at 2465 (hereinafter LH). The committee 
explained that its action addressed not only section 211(c)(1)(A) but 
rather the entirety of the proposed legislative amendments, and stated 
that the committee's bill would thus apply the interpretation of 
section 211(c)(1)(A) in the en banc decision in Ethyl Corp. to all 
other sections of the Act relating to public health protection. 4 LH at 
2516. It also noted that it had used the same basic formulation in 
section 202 and section 231, as well as in other sections. Id. at 2517. 
As both CAA sections 231 and 202 were included in the 1977 amendments, 
the Agency's discussion for the 2009 Endangerment Finding regarding the 
history of section 202 and how it supports the EPA's approach is also 
relevant for section 231. EPA's interpretation of section 231 is the 
same as its interpretation of the parallel language in section 202(a), 
which is explained in the 2009 Endangerment Finding. See 74 FR at 
18891; see also 74 FR at 66506.
    The legislative history clearly indicates that the House Committee 
believed the Ethyl Corp. decisions posed several ``crucial policy 
questions'' regarding the protection of public health and welfare. H.R. 
Rep. 95-294 at 48, 4 LH at 2515.\77\ The following paragraphs summarize 
the en banc decision in Ethyl Corp. v. EPA and describe how the House 
Committee revised the endangerment language in the 1977 amendments to 
the CAA to serve several purposes consistent with that decision. In 
particular, the language: (1) Emphasizes the preventive or 
precautionary nature of the CAA;\78\ (2) authorizes the Administrator 
to reasonably project into the future and weigh risks; (3) assures the 
consideration of the cumulative impact of all sources; (4) instructs 
that the health of susceptible individuals, as well as healthy adults, 
should be part of the analysis; and (5) indicates an awareness of the 
uncertainties and limitations in information available to the 
Administrator. H.R. rep. 95-294 at 49-50, 4 LH 2516-17.\79\
---------------------------------------------------------------------------

    \77\ The Supreme Court recognized that the current language in 
section 202(a)(1), which uses the same formulation as that in 
section 231(a)(2)(A), is ``more protective'' than the 1970 version 
that was similar to the section 211 language before the D.C. Circuit 
in Ethyl Corp. Massachusetts v. EPA, 549 U.S. at 506, fn 7.
    \78\ See H.R. Rep. 95-294 at 49, 4 LH at 2516 (``To emphasize 
the preventive or precautionary nature of the Act, i.e. to assure 
that regulatory action can effectively prevent harm before it 
occurs'').
    \79\ Congress also standardized this language across the various 
sections of the CAA which address emissions from both stationary and 
mobile sources. H.R. Rep. 95-294 at 50, 4 LH at 2517; section 401 of 
the CAA Amendments of 1977.
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    In revising the statutory language, Congress relied heavily on the 
en banc decision in Ethyl Corp. v. EPA, which reversed a three-judge 
panel opinion regarding an EPA rule restricting the content of lead in 
leaded gasoline.\80\ After reviewing the relevant facts and law, the 
full court evaluated the statutory language at issue to see what level 
of ``certainty [was] required by the Clean Air Act before EPA may 
act.'' 541 F.2d at 7.
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    \80\ At the time of the 1973 rules requiring the reduction of 
lead in leaded gasoline, section 211(c)(1)(A) of the CAA stated that 
the Administrator may promulgate regulations that: ``control or 
prohibit the manufacture, introduction into commerce, offering for 
sale, or sale of any fuel or fuel additive for use in a motor 
vehicle or motor vehicle engine (A) if any emissions product of such 
fuel or fuel additive will endanger the public health or welfare . . 
.'' CAA section 211(c)(1)(A) (1970).
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    The petitioners argued that the statutory language ``will 
endanger'' required proof of actual harm, and that the actual harm had 
to come from emissions from the fuels in and of themselves. Id. at 12, 
29. The en banc court rejected this approach, finding that the term 
``endanger'' allowed the Administrator to act when harm is threatened, 
and did not require proof of actual harm. Id. at 13. ``A statute 
allowing for regulation in the face of danger is, necessarily, a 
precautionary statute.'' Id. Optimally, the court found, regulatory 
action would not only precede, but prevent, a perceived threat. Id.
    The court also rejected petitioners' argument that any threatened 
harm must be ``probable'' before regulation was authorized. 
Specifically, the court recognized that danger ``is set not by a fixed 
probability of harm, but rather is composed of reciprocal elements of 
risk and harm, or probability and severity.'' Id. at 18. Next, the 
court held that the EPA's evaluation of risk is necessarily an exercise 
of judgment, and that the statute did not require a factual finding. 
Id. at 24. Thus, ultimately, the Administrator must ``act, in part on 
`factual issues,' but largely `on choices of policy, on an assessment 
of risks, [and] on predictions dealing with matters on the frontiers of 
scientific knowledge . . .'' Id. at 29 (citations omitted). Finally, 
the en banc court agreed with the EPA that even without the language in 
section 202(a) (which is also in section 231(a)(2)(A)) regarding 
``cause or contribute to,'' it was appropriate for the EPA to consider 
the cumulative impact of lead from numerous sources, not just the fuels 
being regulated under section 211(c). Id. at 29-31.
    The dissent in the original Ethyl Corp. decision and the en banc 
opinion were of ``critical importance'' to the House Committee which 
proposed the revisions to the endangerment language in the 1977 
amendments to the CAA. H.R. Rep. 95-294 at 48, 4 LH at 2515. The 
Committee addressed those questions with the language that now appears 
in section 231(a)(2)(A) and several other CAA provisions--``emission of 
any air pollutant . . . which in [the Administrator's] judgment causes, 
or contributes to, air pollution which may reasonably be anticipated to 
endanger public health or welfare.''
    As noted above in section III.A.1, the phrase ``in [her] judgment'' 
calls for the Administrator to make a comparative assessment of risks 
and projections of future possibilities, consider uncertainties, and 
extrapolate from limited data. Thus, the Administrator must balance the 
likelihood of effects with the severity of the effects in reaching her 
judgment. The Committee emphasized that the Administrator's exercise of 
``judgment'' \81\ may include making projections, assessments and 
estimates that are reasonable, as opposed to a speculative or `` 
`crystal ball' inquiry.'' Moreover, procedural safeguards apply to the 
exercise of judgment, and final decisions are subject to judicial 
review. Also, the phrase ``in [her] judgment'' modifies both the 
phrases ``cause and contribute'' and ``may reasonably be anticipated,'' 
as discussed above. H.R. Rep. 95-294 at 50-51, 4 LH at 2517-18.
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    \81\ Throughout this document under CAA section 231, as 
throughout the previous notices concerning the 2009 Endangerment 
Finding under section 202, the judgments on endangerment and cause 
or contribute are described as a finding or findings. This is for 
ease of reference only, and is not intended to imply that the 
Administrator's judgment is solely a fact finding exercise; rather, 
the Administrator's exercise of judgment is to consider and weigh 
multiple factors when applying the scientific information to the 
statutory criteria.
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    As the Committee further explained, the phrase ``may reasonably be 
anticipated'' points the Administrator in the direction of assessing 
current and future risks rather than waiting for proof of actual harm. 
This phrase is also intended to instruct the Administrator to consider 
the limitations and

[[Page 54437]]

difficulties inherent in information on public health and welfare. H.R. 
Rep. 95-294 at 51, 4 LH at 2518.\82\
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    \82\ Thus, the statutory language does not require that the EPA 
prove the effects of climate change ``beyond a reasonable doubt.'' 
Indeed, such an approach is inconsistent with the concepts of 
reasonable anticipation and endangerment embedded in the statute. 
See also CRR, 684 F.3d at 121-122.
---------------------------------------------------------------------------

    Finally, the phrase ``cause or contribute'' ensures that all 
sources of the contaminant which contribute to air pollution are 
considered in the endangerment analysis (e.g., not a single source or 
category of sources). It is also intended to require the Administrator 
to consider all sources of exposure to a pollutant (for example, food, 
water, and air) when determining risk. Id.
3. Additional Considerations for the Cause or Contribute Analysis
    By instructing the Administrator to consider whether emissions of 
an air pollutant cause or contribute to air pollution, the statute is 
clear that she need not find that emissions from any one sector or 
class of sources are the sole or even the major part of an air 
pollution problem. The use of the term ``contribute'' clearly indicates 
a lower threshold than the sole or major cause.
    Moreover, like the section 202(a) language that governed the 2009 
Endangerment Finding, the statutory language in section 231(a)(2)(A) 
does not contain a modifier on its use of the term ``contribute.'' This 
contrasts with other CAA provisions that expressly require 
``significant'' contribution. Compare, e.g., CAA sections 
110(a)(2)(D)(i)(I); 111(b); 213(a)(2), (4). In the absence of specific 
language regarding the degree of contribution, the Administrator is to 
exercise her judgment in determining contribution. Congress clearly 
authorized regulatory controls to address air pollution even if the air 
pollution problem results from a wide variety of sources. While the 
endangerment test looks at the entire air pollution problem and the 
risks it poses, the cause or contribute test is designed to authorize 
the EPA to identify and then address what may well be many different 
sectors, classes, or groups of sources that are each part of the 
problem.
    As explained for the 2009 Endangerment Finding, the D.C. Circuit 
has discussed the concept of contribution in the CAA, and its case law 
supports the EPA's interpretation that the level of contribution in 
this context need not be significant. 74 FR at 66542. In Catawba County 
v. EPA, 571 F.3d 20 (D.C. Cir. 2009), the court upheld EPA's 
PM2.5 attainment and nonattainment designation decisions, 
analyzing CAA section 107(d), which requires EPA to designate an area 
as nonattainment if it ``contributes to ambient air quality in a nearby 
area'' that does not meet the national ambient air quality standards. 
Id. at 35. The court noted that it had previously held that the term 
``contributes'' is ambiguous in the context of CAA language. See EDF v. 
EPA, 82 F.3d 451, 459 (D.C. Cir. 1996). ``[A]mbiguities in statutes 
within an agency's jurisdiction to administer are delegations of 
authority to the agency to fill the statutory gap in reasonable 
fashion.'' 571 F.3d at 35 (citing Nat'l Cable & Telecomms. Ass'c v. 
Brand X Internet Servs, 545 U.S. 967, 980 (2005)). The court then 
proceeded to consider and reject petitioners' argument that the verb 
``contributes'' in CAA section 107(d) necessarily connotes a 
significant causal relationship. Specifically, the D.C. Circuit again 
noted that the term is ambiguous, leaving it to EPA to interpret in a 
reasonable manner. In the context of this discussion, the court noted 
that ``a contribution may simply exacerbate a problem rather than cause 
it . . .'' 571 F.3d at 39.
    This is consistent with the D.C. Circuit's discussion of the 
concept of contribution in the context of CAA section 213 and rules for 
nonroad vehicles in Bluewater Network v. EPA, 370 F.3d 1 (D.C. Cir. 
2004). In that case, industry argued that section 213(a)(3) requires a 
finding of a significant contribution from classes of new nonroad 
engines or vehicles to ozone or carbon monoxide concentrations before 
the EPA can regulate those engines or vehicles, while the EPA's view 
was that the CAA requires a finding only of contribution. Id. at 13. 
Section 213(a)(3)'s regulatory authority for specific classes of 
nonroad engines or vehicles, like that of section 231(a)(2)(A) for 
classes of aircraft engines, is triggered by a finding that certain 
sources ``cause, or contribute to,'' air pollution, whereas an adjacent 
provision, section 213(a)(2), is triggered by a finding of a 
``significant'' contribution from all new and existing nonroad engines 
and vehicles. The court looked at the ``ordinary meaning of 
`contribute' '' when upholding the EPA's reading of section 213(a)(3). 
After referencing dictionary definitions of ``contribute,'' the court 
also noted that ``[s]tanding alone, the term has no inherent 
connotation as to the magnitude or importance of the relevant `share' 
in the effect; certainly it does not incorporate any `significance' 
requirement.'' 370 F.3d at 13.\83\ The court found that the bare 
``contribute'' language in section 213(a)(3) invests the Administrator 
with discretion to exercise judgment regarding what constitutes a 
sufficient contribution for the purpose of making a cause or contribute 
finding. Id. at 14.\84\
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    \83\ Specifically, the decision noted that `` `contribute' means 
simply `to have a share in any act or effect,' Webster's Third New 
International Dictionary 496 (1993), or `to have a part or share in 
producing,' 3 Oxford English Dictionary 849 (2d ed. 1989).'' Id. at 
13.
    \84\ The court explained, ``[t]he repeated use of the term 
`significant' to modify the contribution required for all nonroad 
vehicles, coupled with the omission of this modifier from the 
`cause, or contribute to' finding required for individual categories 
of new nonroad vehicles, indicates that Congress did not intend to 
require a finding of `significant contribution' for individual 
vehicle categories.'' Id. at 13.
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    Like the statutory language considered in Catawba County and 
Bluewater Network, as well as the section 202(a) language that governed 
the Agency's previous findings for GHGs emitted by other types of 
mobile sources, section 231(a)(2)(A) refers to contribution and does 
not specify that the contribution must be significant before an 
affirmative finding can be made. To be sure, any finding of a 
``contribution'' requires some measureable amount of pollutant 
emissions to be resulting from the analyzed source category; a truly 
trivial or de minimis ``contribution'' might not count as such 
(although such a small level is not presented by the facts of today's 
findings). The Administrator therefore has ample discretion in 
exercising her reasonable judgment and determining whether, under the 
circumstances presented, the cause or contribute criterion has been 
met.\85\ As noted above, in addressing provisions in section 202(a), 
the D.C. Circuit has explained that the Act at the endangerment finding 
step did not require the EPA to identify a precise numerical value or 
``a minimum threshold of risk or harm before determining whether an air 
pollutant endangers.'' CRR, 684 F.3d at 122-123. Accordingly, EPA ``may 
base an endangerment finding on `a lesser risk of greater harm . . . or 
a greater risk of lesser harm' or any combination in between.'' Id. 
(quoting Ethyl Corp., 541 F.2d at 18). Recognizing the substantial 
record of empirical data and scientific evidence that the EPA relied 
upon in the 2009 Endangerment Finding, the court determined that its 
``failure to

[[Page 54438]]

distill this ocean of evidence into a specific number at which 
greenhouse gases cause `dangerous' climate change is a function of the 
precautionary thrust of the CAA and the multivariate and sometimes 
uncertain nature of climate science, not a sign of arbitrary or 
capricious decision-making.'' Id. at 123. As the language in section 
231(a)(2)(A) is analogous to that in section 202(a), it is clearly 
reasonable to apply this interpretation to the endangerment 
determination under section 231(a)(2)(A). Moreover, the logic 
underlying this interpretation supports the general principle that 
under CAA section 231 the EPA is not required to identify a specific 
minimum threshold of contribution from potentially subject source 
categories in determining whether their emissions ``cause or 
contribute'' to the endangering air pollution. The reasonableness of 
this principle is further supported by the fact that section 231 does 
not impose on the EPA a requirement to find that such contribution is 
``significant,'' let alone the sole or major cause of the endangering 
air pollution. This context further supports the EPA's interpretation 
that section 231(a)(2)(A) does not require some level of contribution 
that rises to a pre-determined numerical level or percentage- or mass-
based portion of the overall endangering air pollution.
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    \85\ Section V discusses the evidence in this case that supports 
the finding of contribution. The EPA need not determine at this time 
the circumstances in which emissions would be trivial or de minimis 
and would not warrant a finding of contribution.
---------------------------------------------------------------------------

    In addition, when exercising her judgment in making a cause or 
contribute determination, the Administrator not only considers the 
cumulative impact, but also looks at the totality of the circumstances 
and weight of evidence (e.g., the air pollutant, the air pollution, the 
nature of the endangerment, the type or classes of sources at issue, 
the number of sources in the source sector or class, and the number and 
type of other source sectors or categories that may emit the air 
pollutant) when determining whether the emissions ``justify 
regulation'' under the CAA. See Catawba County, 571 F.3d at 39 
(discussing EPA's interpretation of the term ``contribute'' under CAA 
section 107(d) and finding it reasonable for the agency to apply a 
totality of the circumstances approach); see also 74 FR at 66542. 
Further discussion of this issue can be found in sections IV and V of 
this preamble.
4. Summary of Responses to Key Legal Comments on the Interpretation of 
the CAA Section 231(a) Endangerment and Cause or Contribute Test
    Here we summarize key public comments regarding the legal 
interpretation of CAA section 231(a)(2)(A) that supports this finding 
and the Agency's response. The Response to Comments document contains 
the Agency's full response to comments on this topic.
    Some commenters strongly supported the proposed findings. These 
comments stated, for example, that the proposed findings were clearly 
authorized under CAA section 231(a)(2)(A) and further noted that the 
U.S. Supreme Court had upheld EPA's authority under section 202(a) of 
the CAA to make an endangerment finding with regard to GHG emissions 
from motor vehicles and that the findings required under section 
202(a)(1) are the same as the findings required under section 
231(a)(2)(A). Another commenter, however, questioned the EPA's 
authority to make endangerment and cause or contribute findings for 
GHGs, stating that the EPA had not sufficiently explained its authority 
to address pollutants other than NAAQS under CAA section 231. This 
commenter made the following points in support of this view. First, the 
comment pointed to the use of the term ``air quality control regions'' 
in CAA sections 231(a)(1)(A) and 231(a)(3) as suggesting that Congress 
intended to authorize EPA to issue standards only for pollutants for 
which a NAAQS has been established. Second, the comment stated that the 
EPA should address this issue in light of a recent Supreme Court case, 
Utility Air Regulatory Grp. v. EPA, 134 S.Ct. 2427 (2014).
    After consideration of these comments, we disagree with the 
argument that Congress intended to only authorize the EPA to address 
NAAQS pollutants under section 231(a)(2)(A). That provision of the Act 
requires the EPA to issue standards ``applicable to the emission of any 
air pollutant from any class or classes of aircraft engines which in 
[her] judgment causes, or contributes to, air pollution which may 
reasonably be anticipated to endanger public health or welfare.'' CAA 
section 231(a)(2)(A) (emphasis added). Looking to that plain language, 
there is nothing that limits the scope of the air pollutants that can 
be found to contribute to possible endangerment, and therefore which 
the EPA may be required to regulate, under that section to NAAQS 
pollutants. To the contrary, the language is clear that the EPA would 
be required to regulate aircraft engine emissions of ``any air 
pollutant'' as long the pre-requisite endangerment and cause or 
contribute findings are made. ``Air pollutant'' is not defined in 
section 231; instead, the definition under CAA section 302(g) applies, 
which states in relevant part that `` `air pollutant' means any air 
pollutant agent or combination of such agents, including any physical, 
chemical . . . substance or matter which is emitted into or otherwise 
enters ambient air.'' CAA section 302(g) (emphasis added). Interpreting 
this provision in Massachusetts v. EPA, the U.S. Supreme Court observed 
that ``[o]n its face, the definition embraces all airborne compounds of 
whatever stripe, and underscores that intent through the repeated use 
of the word `any.' '' 549 U.S. 497, 529 (2007). It further stated that 
``[b]ecause greenhouse gases fit well within'' this ``capacious 
definition of `air pollutant' '' the EPA has the statutory authority to 
regulate the emission of such gases from new motor vehicles under CAA 
section 202(a)(2). Id. at 532. As noted above, sections 231(a)(2)(A) 
and 202(a)(1) have parallel structures, use substantially the same 
language, and use the same definition of air pollutant. As that 
definition is ``unambiguous'' in its inclusion of GHGs, Massachusetts, 
549 U.S. at 529, the Act clearly authorizes the EPA to make these 
findings for GHGs under CAA section 231(a)(2)(A). Moreover, one U.S. 
District Court has also ruled that the EPA has a duty to determine 
whether aircraft engine emissions of GHGs cause or contribute to 
endangerment, and that ruling was not appealed to the D.C. Circuit. 
Center for Biological Diversity, et al. v. EPA, 794 F. Supp. 2d 151 
(D.D.C. 2011). Consequently, the statutory language imposing the EPA's 
duties under section 231(a)(2)(A), and relevant case law in the GHG 
context, do not support the commenter's limited reading of the EPA's 
authority under that language.
    The commenter points to the use of the term ``air quality control 
regions'' in nearby paragraphs of CAA sections 231(a)(1)(A) and (a)(3) 
to support its suggestion that Congress intended to limit the EPA's 
analysis and regulatory authority to NAAQS pollutants in section 
231(a)(2)(A). That argument is flawed for several reasons. The 
commenter points to section 231(a)(1), which relates to a study the EPA 
was to conduct of emissions of air pollutants from aircraft, and to 
section 231(a)(3), which requires the EPA to hold public hearings with 
respect to proposed standards under section 231(a)(2) in ``air quality 
control regions . . . most seriously affected by aircraft emissions'' 
to the extent practicable. These obligations are imposed in addition to 
those imposed by section 231(a)(2)(A), and their separate establishment 
does not by that fact narrow the EPA's scope of authority regarding its 
obligations imposed under section 231(a)(2)(A). They are additive, not 
subtractive, duties. Moreover, one of those added

[[Page 54439]]

duties, to investigate the extent to which aircraft emissions affect 
air quality in air quality control regions under section 231(a)(1)(A), 
was a one-time duty that corresponded to NAAQS that have long-since 
been revised, whereas the EPA's duty to propose and promulgate aircraft 
emission standards is a continuing one to be conducted ``from time to 
time'' under section 231(a)(2)(A). The commenter provides no reasoning 
to explain why these provisions imposing additional duties should be 
read to limit the scope of section 231(a)(2) beyond their proximity. 
Sections 231(a)(1) and (a)(3) do not speak to what pollutants may be 
addressed under section 231(a)(2). Further, there is no incompatibility 
between the use of the term ``air quality control regions'' in those 
provisions to identify geographic areas where certain activities are to 
occur and making the endangerment and cause or contribute findings for 
GHGs that are finalized in this action. In fact, the EPA long ago 
discharged its one-time duty under CAA section 231(a)(1)(A) \86\ and, 
after proposing new aircraft engine emission standards, could also meet 
its obligations to hold public hearings in the air quality control 
regions most seriously affected by aircraft emissions, to the extent 
practicable, all while meeting its obligations under section 
231(a)(2)(A). Accordingly, the EPA does not interpret sections 
231(a)(1) and (a)(3) to limit the scope of the duties and authority 
established by section 231(a)(2) to NAAQS pollutants. Further, the EPA 
has previously implemented section 231(a)(2) to reach air pollutants 
for which no NAAQS exists and has applied that provision to establish 
standards for non-NAAQS pollutants, such as smoke. See, e.g., 40 CFR 
87.21(a)-(c), (e), 87.23(a)-(c), and 87.31(a)-(c) emission standards 
for smoke. The EPA's regulation of non-NAAQS smoke emissions from 
aircraft engines has never been judicially challenged. Finally, even if 
the Act were ambiguous, which it is not, the EPA's interpretation of 
section 231(a)(2) to include authority to address GHGs, is reasonable 
for the reasons described above.
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    \86\ USEPA, 1973: Aircraft Emissions: Impact On Air Quality And 
Feasibility Of Control. U.S. Environmental Protection Agency, 102 
pp. Available at https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=2000T6Z0.txt (last accessed April 26, 2016).
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    The U.S. Supreme Court's opinion in UARG cited by the commenter 
does not change this analysis. The commenter misinterprets the UARG 
decision to mean that for purposes of determining applicability of the 
CAA's Prevention of Significant Deterioration (PSD) preconstruction 
permitting program, ``air pollutant'' meant only pollutants for which 
NAAQS had been established. The UARG decision, however, does not limit 
PSD applicability to only NAAQS pollutants. In fact, the Court 
recognized that such theories had been advanced during the course of 
that litigation but expressly declined to consider them in its 
decision. See 134 S.Ct. 2427, 2442 n.6 (2014). Rather, in UARG, the 
Court's holding pertained only to GHGs. More specifically, the Court 
held that the EPA may not treat GHGs as an air pollutant for the 
specific purpose of determining whether a source is a major source (or 
a modification thereof) and thus required to obtain a PSD permit or an 
operating permit under title V of the CAA. Id. at 2449.
    Further, the regulatory context that was addressed in UARG is 
distinguishable from that of this action. In UARG, the Court explained 
that Massachusetts does not prevent an Agency from using statutory 
context to infer that in some provisions ``air pollutant'' refers only 
to those airborne substances that ``may sensibly be encompassed within 
the particular regulatory program.'' 134 S.Ct. at 2441. However, the 
commenter offers no reason why GHG emissions from U.S. covered aircraft 
could not ``sensibly be encompassed'' under CAA section 231; nor is the 
EPA aware of any such reasons. In fact, UARG itself recognizes a 
distinction between the statutory scheme of the CAA permitting programs 
at issue in that case and the mobile source programs under Title II of 
the Act which were at issue in Massachusetts. Namely, the UARG opinion 
notes that part of the Court's reasoning in Massachusetts was based on 
its understanding that ``nothing in the Act suggested that regulating 
greenhouse gases under [Title II] would conflict with the statutory 
design. Title II would not compel EPA to regulate in any way that would 
be `extreme,' `counterintuitive,' or contrary to `common sense.' . . . 
At most, it would require EPA to take the modest step of adding 
greenhouse-gas standards to the roster of new-motor-vehicle emission 
regulations.'' 134 S.Ct. at 2441 (quoting Massachusetts, 549 U.S. at 
531). Like Massachusetts, the statutory provisions for this action are 
found in Title II, and closely parallel the structure and language of 
the statutory program at issue in Massachusetts.\87\ Compare CAA 
section 231(a)(2)(A) with 202(a)(1). Nor will reading the Title II 
provision section 231(a)(2)(A) to extend to GHGs result in a regulatory 
outcome that would be extreme, counterintuitive or contrary to common 
sense. Instead, as the D.C. Circuit has previously ruled, the EPA's 
discretion when establishing reasonable standards under section 231 is 
exceptionally broad. See NACAA, 489 F.3d at 1230-32. In short, the UARG 
opinion in no way precludes the EPA's interpretation that ``air 
pollutant'' as used in CAA section 231(a)(2)(A) includes GHGs, but 
rather supports that interpretation.
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    \87\ Although this comment asserts that section 202(a) does not 
include mention of ``air quality control region'' as other 
provisions of section 231(a) do, that distinction is immaterial. As 
described above, the use of that term in other paragraphs imposing 
additional duties beyond those established by section 231(a)(2)(A) 
does not affect what pollutants may be addressed under section 
231(a)(2)(A).
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    To the extent that the commenter is suggesting that the EPA should 
exercise its discretion to interpret CAA section 231(a)(2)(A) to 
exclude GHGs, the EPA declines to do so. The commenter has provided no 
persuasive reason for such an exclusion. Moreover, to make the 
threshold findings in this action, the EPA must, fundamentally, answer 
only two questions: Whether the particular ``air pollution''--here, the 
six well-mixed GHGs--``may reasonably be anticipated to endanger public 
health or welfare,'' and whether emissions of those six well-mixed GHGs 
from U.S. covered aircraft engines ``cause, or contribute to'' that 
endangerment. See CRR, 648 F.3d at 117 (interpreting analogous 
provisions in CAA section 202(a)). Because the EPA answers both of 
these questions in the affirmative for emissions of the six well-mixed 
GHGs from U.S. covered aircraft engines--based on extensive scientific 
evidence and emissions information, as explained in detail in sections 
IV and V below--it is appropriate and reasonable to make both 
endangerment and cause or contribute findings under section 
231(a)(2)(A) in this action.
    In sum, after considering all of the relevant information, 
including that in public comments, the EPA interprets section 
231(a)(2)(A) to include authority to address GHGs from U.S. covered 
aircraft engines. This interpretation is consistent with both its own 
and with judicial interpretations that the EPA's authority under the 
analogous section 202(a) unambiguously extends to GHGs.

B. Air Pollutant, Public Health and Welfare

    The CAA defines both ``air pollutant'' and ``welfare.'' Air 
pollutant is defined as: ``any air pollution agent or combination of 
such agents, including any physical, chemical, biological,

[[Page 54440]]

radioactive (including source material, special nuclear material, and 
byproduct material) substance or matter which is emitted into or 
otherwise enters the ambient air. Such term includes any precursors to 
the formation of any air pollutant, to the extent the Administrator has 
identified such precursor or precursors for the particular purpose for 
which the term `air pollutant' is used.'' CAA section 302(g). GHGs fit 
well within this capacious definition. See Massachusetts v. EPA, 549 
U.S. at 532. They are ``without a doubt'' physical chemical substances 
emitted into the ambient air. Id. at 529. Section V below contains 
further discussion of the term ``air pollutant'' for purposes of this 
section 231(a)(2)(A) contribution finding, which uses the same 
definition of air pollutant as the one the EPA adopted for purposes of 
the 2009 Endangerment Finding.
    Regarding ``welfare,'' the CAA states that ``[a]ll language 
referring to effects on welfare includes, but is not limited to, 
effects on soils, water, crops, vegetation, manmade materials, animals, 
wildlife, weather, visibility, and climate, damage to and deterioration 
of property, and hazards to transportation, as well as effects on 
economic values and on personal comfort and well-being, whether caused 
by transformation, conversion, or combination with other air 
pollutants.'' CAA section 302(h). This definition is quite broad. 
Importantly, it is not an exclusive list due to the use of the term 
``includes, but is not limited to . . .'' Effects other than those 
listed here may also be considered effects on welfare.
    Moreover, the terms contained within the definition are themselves 
expansive. For example, deterioration to property could include damage 
caused by extreme weather events. Effects on vegetation could include 
impacts from changes in temperature and precipitation as well as from 
the spreading of invasive species or insects. Prior welfare effects 
evaluated by the EPA in other contexts include impacts on vegetation, 
as well as reduced visibility, changes in nutrient balance and acidity 
of the environment, soiling of buildings and statues, and erosion of 
building materials. See, e.g., Final Secondary National Ambient Air 
Quality Standards for Oxides of Nitrogen and Sulfur, 77 FR 20218 (April 
3, 2012); Control of Emissions from Nonroad Large Spark Ignition 
Engines and Recreational Engines (Marine and Land-Based), 67 FR 68242 
(November 8, 2002); Final Heavy-Duty Engine and Vehicle Standards and 
Highway Diesel Sulfur Control Requirements, 66 FR 5002 (January 18, 
2001).
    Although the CAA defines ``effects on welfare'' as discussed above, 
there is no definition of ``public health'' in the Clean Air Act. The 
Supreme Court has discussed the concept of ``public health'' in the 
context of whether costs can be considered when setting NAAQS. Whitman 
v. American Trucking Ass'n, 531 U.S. 457 (2001). In Whitman, the Court 
imbued the term with its most natural meaning: ``the health of the 
public.'' Id. at 466. When considering public health, the EPA has 
looked at morbidity, such as impairment of lung function, aggravation 
of respiratory and cardiovascular disease, and other acute and chronic 
health effects, as well as mortality. See, e.g., Final National Ambient 
Air Quality Standard for Ozone, 73 FR 16436 (March 27, 2008).

IV. The Administrator's Finding Under CAA Section 231 That Greenhouse 
Gases Endanger Public Health and Welfare

    The Administrator finds, for purposes of CAA section 231(a)(2)(A), 
that elevated concentrations of the six well-mixed GHGs constitute air 
pollution that may reasonably be anticipated to endanger both the 
public health and welfare of current and future generations. The 
Administrator is making this finding specifically with regard to the 
same definition of the ``air pollution'' under CAA section 231(a)(2) as 
that used under CAA section 202(a)(1), namely the combined mix of 
CO2, methane, nitrous oxide, hydrofluorocarbons, 
perfluorocarbons, and sulfur hexafluoride, which together are the root 
cause and best understood drivers of human-induced climate change and 
the resulting impacts on public health and welfare. The EPA received 
public comments on this definition of air pollution from the proposed 
findings, and summarizes responses to some of those key comments below; 
fuller responses to public comments can be found in EPA's Response to 
Comments document included in the docket. The Administrator addresses 
other climate-forcing agents both in the 2009 Endangerment Finding \88\ 
and in this action; however, these substances are not included in the 
air pollution definition used in this action for the reasons discussed 
below in section IV.B.7.
---------------------------------------------------------------------------

    \88\ 74 FR at 66519-21.
---------------------------------------------------------------------------

    Section IV.A below discusses the EPA's approach to evaluating the 
scientific evidence before it. Section IV.B discusses the scope and 
nature of the relevant air pollution for the endangerment finding under 
CAA section 231(a)(2)(A), including a discussion of other substances 
with climate effects that were addressed but not included in the 
definition of air pollution. Section IV.C summarizes the scientific 
evidence that the air pollution is reasonably anticipated to endanger 
both public health and welfare. Section IV.D summarizes the 
Administrator's conclusion for purposes of section 231(a)(2)(A), in 
light of the evidence, analysis, and conclusions that led to the 2009 
Endangerment Finding as well as more recent evidence and consideration 
of public comments, that emissions of the six well-mixed GHGs in the 
atmosphere may reasonably be anticipated to endanger public health and 
welfare.

A. The Science Upon Which the Agency Relied

    This finding under section 231(a)(2)(A) reflects the EPA's careful 
consideration not only of the scientific and technical record for the 
2009 Endangerment Finding, but also of science assessments released 
since 2009, which, as illustrated below, strengthen and further support 
the judgment that the six well-mixed GHGs in the atmosphere may 
reasonably be anticipated to endanger public health and welfare. The 
Administrator's view is that the body of scientific evidence amassed in 
the record for the 2009 Endangerment Finding compellingly supports an 
endangerment finding for the six well-mixed GHGs under CAA section 
231(a)(2)(A). While the EPA is providing a summary of newer scientific 
assessments below, the EPA is also relying on the same scientific and 
technical evidence discussed in the notices for the 2009 Endangerment 
Finding in these final findings for purposes of CAA section 
231(a)(2)(A).\89\
---------------------------------------------------------------------------

    \89\ See sections III of the 2009 Proposed Endangerment Finding 
and sections III and IV of the 2009 Endangerment Finding. 74 FR at 
18894-18904 and 74 FR at 66510-36.
---------------------------------------------------------------------------

    The EPA is following the same approach toward technical and 
scientific information in this finding under section 231(a)(2)(A) as it 
used in the 2009 Endangerment Finding. More specifically, in the 2009 
Endangerment Finding the EPA's approach to providing the technical and 
scientific information to inform the Administrator's judgment regarding 
the question of whether GHGs endanger public health and welfare was to 
consider the recent, major assessments by the U.S. Global Change 
Research Program (USGCRP), the IPCC, and the National Research Council 
of the

[[Page 54441]]

National Academies of Sciences, Engineering, and Medicine (referred to 
interchangeably as NRC or NAS) as the primary scientific and technical 
basis informing the endangerment finding. These assessments draw 
synthesis conclusions across thousands of individual peer-reviewed 
studies that appear in scientific journals, and the reports themselves 
undergo additional peer review. The EPA has considered the processes 
and procedures employed by the USGCRP, IPCC, and the NRC in terms of 
factors such as their objectivity, integrity, utility, and 
transparency, including how they have employed rigorous peer review 
processes. The EPA considers these assessments to represent the best 
available science that maintains the highest level of adherence to 
Agency guidelines for information quality.\90\ These assessments have 
been adequately peer reviewed in a manner commensurate with the EPA's 
Peer Review Policy \91\ and guidance in the EPA's Peer Review 
Handbook.\92\
---------------------------------------------------------------------------

    \90\ Applicable guidance includes U.S. EPA 2012: Addendum to A 
Summary of General Assessment Factors for Evaluating the Quality of 
Scientific and Technical Information, 9 pp. Available at https://www.epa.gov/risk/guidance-evaluating-and-documenting-quality-existing-scientific-and-technical-information (last accessed July 
11, 2016) and U.S. EPA, 2002: Guidelines for Ensuring and Maximizing 
the Quality, Objectivity, Utility, and Integrity of Information 
Disseminated by the EPA, 61 pp. Available at https://www.epa.gov/quality/guidelines-ensuring-and-maximizing-quality-objectivity-utility-and-integrity-information (last accessed July 11, 2016).
    \91\ U.S. EPA, 2006: Memorandum on Peer Review and Peer 
Involvement at the U.S. EPA, 4 pp. Available at https://www.epa.gov/osa/memorandum-peer-review-and-peer-involvement-epa (last accessed 
April 12, 2016).
    \92\ U.S. EPA, 2015: EPA Peer Review Handbook, Fourth Edition, 
248 pp. Available at https://www.epa.gov/osa/peer-review-handbook-4th-edition-2015-0 (last accessed April 12, 2016). Also, the EPA 
Science Advisory Board reviewed this approach to the underlying 
technical and scientific information supporting this action, and 
concluded that the approach had precedent and the action will be 
based on well-reviewed information. A copy of this letter and all 
other relevant EPA peer review documentation is located in the 
docket for today's final action (EPA-HQ-OAR-2014-0828).
---------------------------------------------------------------------------

    The EPA is giving careful consideration to all of the scientific 
and technical information in the record. However, the Administrator 
considers the major scientific assessments as the primary scientific 
and technical basis of her endangerment decision. This provides 
assurance that the Administrator is basing her judgment on the best 
available, well-vetted science that reflects the consensus of the 
climate science research community. These assessments addressed the 
scientific issues that the EPA was required to examine, were 
comprehensive in their coverage of the GHG and climate change issues, 
and underwent rigorous and exacting peer review by the expert 
community, as well as rigorous levels of U.S. government review, in 
which the EPA took part. The major findings of the USGCRP, IPCC, and 
NRC assessments support the Administrator's determination that elevated 
concentrations of GHGs in the atmosphere may reasonably be anticipated 
to endanger the public health and welfare of current and future 
generations. The EPA presented this scientific support at length in the 
comprehensive record for the 2009 Endangerment Finding.
    The EPA reviewed ten administrative petitions for reconsideration 
of the 2009 Endangerment Finding in 2010.\93\ In the Reconsideration 
Denial, the Administrator denied those petitions on the basis of the 
Petitioners' failure to provide substantial support for their argument 
that the EPA should revise the 2009 Endangerment Finding and their 
objections' lack of ``central relevance'' to the Finding.\94\ The EPA 
prepared an accompanying three-volume Response to Petitions document to 
provide additional information, often more technical in nature, in 
response to the arguments, claims, and assertions by the Petitioners to 
reconsider the Endangerment Finding.\95\
---------------------------------------------------------------------------

    \93\ Administrative petitions are available from www3.epa.gov/climatechange/endangerment/petitions.html (last accessed June 21, 
2016), and in the docket for the 2009 Endangerment Finding: EPA-HQ-
OAR-2009-0171.
    \94\ U.S. EPA, 2010: Denial of the Petitions to Reconsider the 
Endangerment and Cause or Contribute Findings for Greenhouse Gases 
Under section 202(a) of the Clean Air Act, 75 FR 49557 (August 13, 
2010) (``Reconsideration Denial''). In that notice, the EPA 
thoroughly considered the scientific and technical information 
relevant to the petitions. In addition to the other information 
discussed in the present notice, the EPA is also relying on the 
scientific and technical evidence discussed in that prior notice for 
purposes of its proposed determination under CAA section 231. See 
section III of the Reconsideration Denial.
    \95\ The Response to Petitions document is available from 
www3.epa.gov/climatechange/endangerment/petitions.html (last 
accessed June 21, 2016), and in the docket for the 2009 Endangerment 
Finding: EPA-HQ-OAR-2009-0171.
---------------------------------------------------------------------------

    The 2009 Endangerment Finding and the 2010 Reconsideration Denial 
were challenged in a lawsuit before the D.C. Circuit.\96\ On June 26, 
2012, the D.C. Circuit upheld the Endangerment Finding and the 
Reconsideration Denial, ruling that the Finding (including the 
Reconsideration Denial) was not arbitrary or capricious, was consistent 
with the U.S. Supreme Court's decision in Massachusetts v. EPA (which 
affirmed the EPA's authority to regulate GHGs) \97\ and the text and 
structure of the CAA, and was adequately supported by the 
administrative record.\98\ The D.C. Circuit also agreed with the EPA 
that the Petitioners had ``not provided substantial support for their 
argument that the Endangerment Finding should be revised.'' \99\ It 
found that the EPA had based its decision on ``substantial scientific 
evidence,'' observing that ``EPA's scientific evidence of record 
included support for the proposition that greenhouse gases trap heat on 
earth that would otherwise dissipate into space; that this `greenhouse 
effect' warms the climate; that human activity is contributing to 
increased atmospheric levels of greenhouse gases; and that the climate 
system is warming,'' as well as providing extensive scientific evidence 
for EPA's determination that anthropogenically induced climate change 
threatens both public health and welfare.\100\ The D.C. Circuit further 
noted that the EPA's reliance on assessments was consistent with the 
methods decision-makers often use to make a science-based 
judgment.\101\ Moreover, it supported the EPA's reliance on the major 
scientific assessment reports conducted by USGCRP, IPCC, and NRC and 
found:
---------------------------------------------------------------------------

    \96\ Coalition for Responsible Regulation, Inc. v. Environmental 
Protection Agency, 684 F.3d 102 (D.C. Cir. 2012), reh'g en banc 
denied, 2012 U.S. App. LEXIS 25997, 26313, 26315 (D.C. Cir. 2012) 
(CRR).
    \97\ 549 U.S. 497 (2007).
    \98\ CRR, 684 F.3d at 117-27.
    \99\ Id. at 125.
    \100\ Id. at 120-121.
    \101\ Id. at 121.

    The EPA evaluated the processes used to develop the various 
assessment reports, reviewed their contents, and considered the 
depth of the scientific consensus the reports represented. Based on 
these evaluations, the EPA determined the assessments represented 
the best source material to use in deciding whether GHG emissions 
may be reasonably anticipated to endanger public health or welfare . 
. . It makes no difference that much of the scientific evidence in 
large part consisted of ``syntheses'' of individual studies and 
research. Even individual studies and research papers often 
synthesize past work in an area and then build upon it. This is how 
science works. The EPA is not required to re-prove the existence of 
the atom every time it approaches a scientific question.\102\
---------------------------------------------------------------------------

    \102\ Id. at 120.

    In addition, the EPA's consideration of the major assessments to 
inform the Administrator's judgment allowed for full and explicit 
recognition of scientific uncertainty regarding the endangerment posed 
by the atmospheric buildup of GHGs. The Administrator considered the 
fact that ``some aspects of climate change science and the projected 
impacts are more certain than others.'' \103\ The D.C. Circuit

[[Page 54442]]

subsequently noted that ``the existence of some uncertainty does not, 
without more, warrant invalidation of an endangerment finding.'' \104\
---------------------------------------------------------------------------

    \103\ 74 FR at 66524.
    \104\ CRR, 684 F.3d at 121.
---------------------------------------------------------------------------

    As noted above, the Supreme Court granted some of the petitions for 
certiorari that were filed, while denying others, but agreed to decide 
only the question: ``Whether EPA permissibly determined that its 
regulation of greenhouse gas emissions from new motor vehicles 
triggered permitting requirements under the Clean Air Act for 
stationary sources that emit greenhouse gases.'' \105\ Thus, the 
Supreme Court did not disturb the D.C. Circuit's holding that affirmed 
the 2009 Endangerment Finding.
---------------------------------------------------------------------------

    \105\ Utility Air Reg. Group v. EPA, 134 S. Ct. 2427, 2438 
(2014) (internal marks and citations omitted). See also Virginia v. 
EPA, 134 S. Ct. 418 (2013), Pac. Legal Found. v. EPA, 134 S. Ct. 418 
(2013), and CRR, 134 S. Ct. 468 (2013) (all denying cert.).
---------------------------------------------------------------------------

    Since the closure of the administrative record concerning the 2009 
Endangerment Finding (including the denial of petitions for 
reconsideration), a number of new major, peer-reviewed scientific 
assessments have been released. The EPA carefully reviewed the updated 
scientific conclusions in these assessments, largely to evaluate 
whether they would lead the EPA in this CAA section 231(a)(2)(A) 
finding to use a different interpretation of, or place more or less 
weight on, the major findings reflected in the previous assessment 
reports that underpinned the Administrator's judgment that the six 
well-mixed GHGs endanger public health and welfare. The EPA reviewed 
the following new major peer-reviewed scientific assessments:

 IPCC's 2013-2014 Fifth Assessment Report (AR5) \106\
---------------------------------------------------------------------------

    \106\ IPCC, 2013: Climate Change 2013: The Physical Science 
Basis. Contribution of Working Group I to the Fifth Assessment 
Report of the Intergovernmental Panel on Climate Change [Stocker, 
T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. 
Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)].Cambridge University 
Press, 1535 pp, doi:10.1017/CBO9781107415324; IPCC, 2014: Climate 
Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global 
and Sectoral Aspects. Contribution of Working Group II to the Fifth 
Assessment Report of the Intergovernmental Panel on Climate Change 
[Field, C.B., V.R. Barros, D.J. Dokken, K.J. Mach, M.D. Mastrandrea, 
T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. 
Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and 
L.L. White (eds.)]. Cambridge University Press, 1132 pp; IPCC, 2014: 
Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part B: 
Regional Aspects. Contribution of Working Group II to the Fifth 
Assessment Report of the Intergovernmental Panel on Climate Change 
[Barros, V.R., C.B. Field, D.J. Dokken, M.D. Mastrandrea, K.J. Mach, 
T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. 
Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and 
L.L. White (eds.)]. Cambridge University Press, 688 pp; and IPCC, 
2014: Climate Change 2014: Mitigation of Climate Change. 
Contribution of Working Group III to the Fifth Assessment Report of 
the Intergovernmental Panel on Climate Change [Edenhofer, O., R. 
Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, A. 
Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J. 
Savolainen, S. Schl[ouml]mer, C. von Stechow, T. Zwickel and J.C. 
Minx (eds.)]. Cambridge University Press, 1435 pp.
---------------------------------------------------------------------------

 IPCC's 2012 ``Special Report on Managing the Risks of Extreme 
Events and Disasters to Advance Climate Change Adaptation'' (SREX) 
\107\
---------------------------------------------------------------------------

    \107\ IPCC, 2012: Managing the Risks of Extreme Events and 
Disasters to Advance Climate Change Adaptation. A Special Report of 
Working Groups I and II of the Intergovernmental Panel on Climate 
Change [Field, C.B., V. Barros, T.F. Stocker, D. Qin, D.J. Dokken, 
K.L. Ebi, M.D. Mastrandrea, K.J. Mach, G.-K. Plattner, S.K. Allen, 
M. Tignor, and P.M. Midgley (eds.)]. Cambridge University Press, 582 
pp.
---------------------------------------------------------------------------

 USGCRP's 2014 ``Climate Change Impacts in the United States: 
the Third National Climate Assessment'' (NCA3) \108\
---------------------------------------------------------------------------

    \108\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. 
Yohe, Eds., 2014: Climate Change Impacts in the United States: The 
Third National Climate Assessment. U.S. Global Change Research 
Program, 841 pp.
---------------------------------------------------------------------------

 NRC's 2010 ``Ocean Acidification: A National Strategy to Meet 
the Challenges of a Changing Ocean'' (Ocean Acidification) \109\
---------------------------------------------------------------------------

    \109\ NRC, 2010: Ocean Acidification: A National Strategy to 
Meet the Challenges of a Changing Ocean. The National Academies 
Press, 188 pp.
---------------------------------------------------------------------------

 NRC's 2011 ``Climate Change, the Indoor Environment, and 
Health'' (Indoor Environment) \110\
---------------------------------------------------------------------------

    \110\ NRC Institute of Medicine, 2011: Climate Change, the 
Indoor Environment, and Health. Washington, DC: The National 
Academies Press, 272 pp.
---------------------------------------------------------------------------

 NRC's 2011 ``Report on Climate Stabilization Targets: 
Emissions, Concentrations, and Impacts over Decades to Millennia'' 
(Climate Stabilization Targets) \111\
---------------------------------------------------------------------------

    \111\ NRC 2011: Climate Stabilization Targets: Emissions, 
Concentrations, and Impacts over Decades to Millennia. The National 
Academies Press, 298 pp.
---------------------------------------------------------------------------

 NRC's 2011 ``National Security Implications for U.S. Naval 
Forces'' (National Security Implications) \112\
---------------------------------------------------------------------------

    \112\ NRC, 2011: National Security Implications of Climate 
Change for U.S. Naval Forces. The National Academies Press, 226 pp.
---------------------------------------------------------------------------

 NRC's 2011 ``Understanding Earth's Deep Past: Lessons for Our 
Climate Future'' (Understanding Earth's Deep Past) \113\
---------------------------------------------------------------------------

    \113\ NRC, 2011: Understanding Earth's Deep Past: Lessons for 
Our Climate Future. The National Academies Press, 212 pp.
---------------------------------------------------------------------------

 NRC's 2012 ``Sea-Level Rise for the Coasts of California, 
Oregon, and Washington: Past, Present, and Future'' (Sea Level Rise) 
\114\
---------------------------------------------------------------------------

    \114\ NRC, 2012: Sea-Level Rise for the Coasts of California, 
Oregon, and Washington: Past, Present, and Future. The National 
Academies Press, 201 pp.
---------------------------------------------------------------------------

 NRC's 2013 ``Climate and Social Stress: Implications for 
Security Analysis'' (Climate and Social Stress) \115\
---------------------------------------------------------------------------

    \115\ NRC, 2013: Climate and Social Stress: Implications for 
Security Analysis. The National Academies Press, 280 pp.
---------------------------------------------------------------------------

 NRC's 2013 ``Abrupt Impacts of Climate Change'' (Abrupt 
Impacts) \116\
---------------------------------------------------------------------------

    \116\ NRC, 2013: Abrupt Impacts of Climate Change: Anticipating 
Surprises. The National Academies Press, 250 pp.
---------------------------------------------------------------------------

 NRC's 2014 ``The Arctic in the Anthropocene: Emerging Research 
Questions'' (Arctic) \117\.
---------------------------------------------------------------------------

    \117\ NRC, 2014: The Arctic in the Anthropocene: Emerging 
Research Questions. The National Academies Press, 220 pp.

    From its review, the EPA finds that these new assessments are 
largely consistent with, and in many cases strengthen and add to, the 
already compelling and comprehensive scientific evidence detailing the 
role of the six well-mixed GHGs in driving climate change, explained in 
the 2009 Endangerment Finding.
1. Response to Key Comments on the EPA's Approach to the Science
    Here we summarize key public comments regarding the approach to the 
science--see the Response to Comments document for the Agency's full 
responses to comments. Several commenters agreed and no commenters 
disagreed with the EPA's approach to the science for making an 
endangerment decision specifically with respect to the six well-mixed 
GHGs (see section IV.B.7 for a summary of key public comments and our 
responses to commenters who argued that the science supports expanding 
the scope of the endangerment finding to include other climate forcers 
beyond the six well-mixed GHGs). They specifically mentioned their 
support for the EPA's approach to considering the scientific and 
technical information in the record of the 2009 Endangerment Finding--
primarily the recent, major assessments by the USGCRP, the IPCC, and 
the NRC--as well as the most recent scientific assessments for 
additional support and justification. For the reasons stated in section 
IV.A above, the EPA agrees with the commenters that this approach 
ensures that the Administrator considers the best available scientific 
and technical information.

B. The Air Pollution Consists of Six Key Well-Mixed Greenhouse Gases

    The Administrator must define the scope and nature of the relevant 
air pollution for the endangerment finding under CAA section 
231(a)(2)(A). In this

[[Page 54443]]

final action, the Administrator finds that the air pollution is the 
combined mix of six well-mixed GHGs, which together are the root cause 
and best understood drivers of human-induced climate change and the 
resulting impacts on public health and welfare. These six GHGs--
CO2, methane, nitrous oxide, hydrofluorocarbons, 
perfluorocarbons, and sulfur hexafluoride--are considered an aggregate 
group for purposes of this finding. The Administrator's definition of 
air pollution for purposes of section 231(a)(2)(A) is made in light of 
(1) the evidence, analysis, and conclusions that led to the 2009 
Endangerment Finding; (2) more recent evidence from scientific 
assessments published since 2009; and (3) consideration of public 
comments, for which key comments and responses are summarized in 
sections IV.B.6 and 7 below. The Administrator considered five primary 
reasons in the 2009 Endangerment Finding for focusing on this aggregate 
group as the air pollution: (1) They share common physical properties 
that influence their climate effects; (2) on the basis of these common 
physical properties, they have been determined to be the root cause of 
human-induced climate change, are the best-understood driver of climate 
change, and are expected to remain the primary driver of future climate 
change; (3) they are the common focus of climate change science 
research and policy analyses and discussions; (4) using the combined 
mix of these gases as the definition (versus an individual gas-by-gas 
approach) is consistent with the science, because risks and impacts 
associated with GHG-induced climate change are not assessed on an 
individual gas-by-gas basis; and (5) using the combined mix of these 
gases is consistent with past EPA practice, where separate substances 
from different sources, but with common properties, may be treated as a 
class (e.g., oxides of nitrogen, particulate matter, volatile organic 
compounds).\118\ After consideration of all information before her, 
including public comments, as explained below, the Administrator 
maintains her view that these five reasons for defining the scope and 
nature of the air pollution to be these six well-mixed GHGs remain 
valid and well supported by the current science and are therefore 
reasonable bases for adopting the same definition of ``air pollution'' 
in this section 231(a)(2)(A) finding as that under section 202(a)(1). 
The following subsections summarize the five reasons detailed in the 
2009 Endangerment Finding and as appropriate, summarize additional 
supporting information from the recent scientific assessments published 
since 2009.
---------------------------------------------------------------------------

    \118\ 74 FR at 66517-19.
---------------------------------------------------------------------------

1. Common Physical Properties of the Six Greenhouse Gases
    The six GHGs share common physical properties that are relevant to 
the climate change problem. They all are sufficiently long lived in the 
atmosphere such that, once emitted, concentrations of each gas become 
globally well mixed in the atmosphere.\119\ A well-mixed gas has 
relatively uniform concentrations in the atmosphere anywhere around the 
globe, with little local or regional variation except immediately next 
to sources or sinks. A given amount of a well-mixed gas emitted 
anywhere will have similar impacts on global concentrations regardless 
of the geographic location of emission. All six GHGs trap outgoing heat 
that would otherwise escape to space, and all are directly emitted from 
a source as a GHG rather than becoming a GHG in the atmosphere after 
emission of a precursor gas. This fundamental scientific understanding 
of the intrinsic physical, chemical, and atmospheric properties of the 
six GHGs has not changed and remains supported by the more recent 
climate change assessments.
---------------------------------------------------------------------------

    \119\ The properties ``long lived'' and ``well mixed'' used in 
this document mean that the gas has a lifetime in the atmosphere 
sufficient to become globally well mixed throughout the entire 
atmosphere, which requires a minimum atmospheric lifetime of about 
one year. Atmospheric lifetime is a measure of how long a type of 
molecule is likely to remain in the atmosphere before it breaks 
down, reacts with other gases, or is absorbed by Earth's surface. 
The IPCC often refers interchangeably to the six well-mixed GHGs as 
long-lived GHGs; however, the IPCC and others in the international 
climate change community, such as the United Nations Environment 
Programme, also refer to methane and some HFCs as ``near-term 
climate forcers,'' ``short-lived climate forcers,'' or ``short-lived 
climate pollutants.'' These terms refer to those compounds whose 
impacts on Earth's climate occurs primarily with the first decade 
after their emission. According to the IPCC AR5 (2014), methane has 
an atmospheric lifetime of about 12 years. One of the most commonly 
used hydrofluorocarbons (HFC-134a) has a lifetime of about 13 years. 
Thus, methane and some HFCs are both short- and long-lived GHGs--
i.e., they have lifetimes long enough to become globally well mixed 
in the atmosphere, but short enough to primarily affect Earth's 
climate within a decade after their emission. For comparison, 
nitrous oxide has a lifetime of around 130 years; sulfur 
hexafluoride over 3,000 years; and some perfluorocarbons up to 
10,000 to 50,000 years. CO2 is sometimes approximated as 
having a lifetime of roughly 100 years, but for a given amount of 
CO2 emitted, a better description is that some fraction 
of the atmospheric increase in concentration is quickly absorbed by 
the oceans and terrestrial vegetation, some fraction of the 
atmospheric increase will only slowly decrease over a number of 
years, and a small portion of the increase will remain for many 
centuries or more.
---------------------------------------------------------------------------

2. The Six Well-Mixed Greenhouse Gases Are the Primary and Best 
Understood Driver of Current and Projected Climate Change
    The Administrator judges that the scientific evidence is compelling 
that together the six well-mixed GHGs constitute the largest 
anthropogenic driver of climate change. In addition, the six well-mixed 
GHGs are the best-understood driver of climate change because they have 
well-understood physical properties as described above that govern 
their climate effect (e.g., their radiative forcing, a measure of their 
total net effect on the global energy balance). As explained in more 
detail in the 2009 Endangerment Finding,\120\ the Administrator made 
the judgment that the scientific evidence is compelling that elevated 
concentrations of heat-trapping GHGs are the root cause of recently 
observed climate change and that the scientific record showed that most 
of the observed increase in global average temperatures since the mid-
20th century is very likely due to the observed increase in 
anthropogenic GHG concentrations. The attribution of observed climate 
change to anthropogenic activities was based on multiple lines of 
evidence. The first line of evidence arises from our basic physical 
understanding of the effects of changing concentrations of GHGs, 
natural factors, and other human impacts on the climate system. The 
second line of evidence arises from indirect, historical estimates of 
past climate changes that suggest that the changes in global surface 
temperature over the last several decades are unusual. The third line 
of evidence arises from the use of computer-based climate models to 
simulate the likely patterns of response of the climate system to 
different forcing mechanisms (both natural and anthropogenic). Observed 
increases in global average air temperatures are driving observed 
climate impacts like widespread melting of snow and ice and rising 
global average sea level. The Administrator also considered these 
observed changes as additional evidence of the unequivocal warming of 
the climate system driven primarily by elevated atmospheric GHG 
concentrations because the consistency of these observed changes in 
physical and biological systems and the observed significant warming 
cannot be explained entirely due to natural variability or other 
confounding non-climate factors.
---------------------------------------------------------------------------

    \120\ 74 FR at 66517-18.

---------------------------------------------------------------------------

[[Page 54444]]

    In addition, as described in more detail in the 2009 Endangerment 
Finding,\121\ the Administrator made the judgment that the scientific 
evidence is compelling that six GHGs are expected to remain the primary 
driver of future climate change and that, without substantial and near-
term efforts to significantly reduce emissions, it can be expected that 
atmospheric concentrations of the six GHGs will continue to climb and 
thus lead to ever greater rates of climate change. Given the long 
atmospheric lifetime of the six well-mixed GHGs, which range from 
roughly a decade to centuries, future atmospheric GHG concentrations 
for the remainder of this century and beyond will be influenced not 
only by future emissions but indeed by present-day and near-term 
emissions. Consideration of future plausible scenarios, and how our 
current GHG emissions essentially commit present and future generations 
to cope with an altered atmosphere and climate, reinforces the 
Administrator's judgment that it is appropriate to define the 
combination of the six key greenhouse gases as the air pollution. Most 
future scenarios that assume no explicit GHG mitigation actions (beyond 
those already enacted) project increasing global GHG emissions over the 
century, which in turn result in climbing GHG concentrations. 
Concentrations of the six well-mixed GHGs increase even for those 
scenarios where annual emissions toward the end of the century are 
assumed to be lower than current annual emissions.
---------------------------------------------------------------------------

    \121\ 74 FR at 66518-19.
---------------------------------------------------------------------------

    The EPA has also carefully reviewed the recent assessments of the 
IPCC, USGCRP, and NRC. The EPA finds that these recent assessments 
support and strengthen the evidence cited in the 2009 Endangerment 
Finding that current atmospheric GHG concentrations are now at elevated 
and essentially unprecedented levels primarily as a result of both 
historic and current anthropogenic emissions. The 2014 USGCRP NCA3 
states, ``Atmospheric levels measured at Mauna Loa in Hawai`i and at 
other sites around the world reached 400 parts per million in 2013, 
higher than the Earth has experienced in over a million years.'' \122\ 
Such concentrations are the primary driver of observed changes in 
Earth's climate system, namely increased global average temperatures 
that drive climate impacts like widespread melting of snow and ice and 
rising global average sea level (discussed in more detail in section 
IV.C). The recent assessments of the IPCC, USGCRP, and NRC also 
describe how these six well-mixed GHGs play a dominant role in future 
warming of the climate system. The USGCRP NCA3 makes the following 
finding with very high confidence: ``The magnitude of climate change 
beyond the next few decades depends primarily on the amount of heat-
trapping gases emitted globally, and how sensitive the Earth's climate 
is to those emissions.'' \123\ Key findings from the recent assessments 
regarding global and U.S. trends are described briefly below.
---------------------------------------------------------------------------

    \122\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. 
Yohe, Eds., 2014: Climate Change Impacts in the United States: The 
Third National Climate Assessment. U.S. Global Change Research 
Program, p. 739.
    \123\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. 
Yohe, Eds., 2014: Climate Change Impacts in the United States: The 
Third National Climate Assessment. U.S. Global Change Research 
Program, p.20. See also p. 736: ``Past emissions of heat-trapping 
gases have already committed the world to a certain amount of future 
climate change. How much more the climate will change depends on 
future emissions and the sensitivity of the climate system to those 
emissions.''
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a. Key Observed Trends Driven Primarily by the Six Well-Mixed GHGs
    According to the IPCC AR5, observations of the Earth's globally 
averaged combined land and ocean surface temperature over the period 
1880 to 2012 show a warming of 0.85 [0.65 to 1.06] degrees Celsius or 
1.53 [1.17 to 1.91] degrees Fahrenheit.\124\ The IPCC AR5 concludes 
that the increase in atmospheric GHG concentrations since 1750, plus 
other human activities (e.g., land use change and aerosol emissions), 
has had a radiative forcing effect estimated to be 2.3 Watts per square 
meter (W/m\2\) in 2011.\125\ Radiative forcing is a measure of a 
substance's total net effect on the global energy balance for which a 
positive number represents a warming effect and a negative number 
represents a cooling effect. The IPCC's estimate is an increase from 
the previous 2007 IPCC Fourth Assessment Report (AR4) total net 
estimate of 1.6 W/m\2\ that was referred to in the record for the 2009 
Endangerment Finding. The reasons for this increase include continued 
increases in GHG concentrations, as well as reductions in the estimated 
negative forcing due to aerosol particles. The IPCC AR5 rates the level 
of confidence \126\ in their radiative forcing estimates as ``high'' 
for methane and ``very high'' for CO2 and nitrous oxide.
---------------------------------------------------------------------------

    \124\ ``IPCC, 2013: Summary for Policymakers. In: Climate Change 
2013: The Physical Science Basis. Contribution of Working Group I to 
the Fifth Assessment Report of the Intergovernmental Panel on 
Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, 
S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley 
(eds.)]. Cambridge University Press, 29 pp.
    \125\ Ibid.
    \126\ The IPCC expresses levels of confidence using five 
qualifiers: Very low, low, medium, high, and very high. These levels 
are based on a qualitative evaluation of the robustness of the 
evidence (considering the type, amount, quality, and consistency of 
evidence such as data, mechanistic understanding, theory, models, 
and expert judgment) and the degree of agreement among the findings.
---------------------------------------------------------------------------

    The new assessments also have greater confidence since the 2009 
Endangerment Finding in attributing recent warming to human causes. The 
IPCC AR5 stated that it is extremely likely (>95 percent likelihood) 
that human influences have been the dominant cause of warming since the 
mid-20th century, which is an even stronger statement than the AR4 
conclusion that it is very likely (>90 percent likelihood) that most of 
the increase in temperature since the mid-20th century was due to the 
observed increase in anthropogenic GHG concentrations. The AR4 
conclusion was referred to in the record for the 2009 Endangerment 
Finding. In addition, the IPCC AR5 found that concentrations of 
CO2 and several other of the major GHGs are higher than they 
have been in at least 800,000 years. This is an increase from what was 
reported in IPCC AR4, which found higher concentrations than in at 
least 650,000 years.
    The USGCRP NCA3 states that there is very high confidence \127\ 
that the global climate change of the past 50 years is primarily due to 
human activities. Human activities are affecting climate through 
increasing atmospheric levels of heat-trapping GHGs, through changing 
levels of various particles that can have either a heating or cooling 
influence on the atmosphere, and through activities such as land use 
changes that alter the reflectivity of the Earth's surface and cause 
climatic warming and cooling effects. The USGCRP concludes that 
``considering all known natural and human drivers of climate since 
1750, a strong net warming from long-lived greenhouse gases produced by 
human activities dominates the recent climate record.'' \128\
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    \127\ The NCA expresses levels of confidence using four 
qualifiers: low, medium, high, and very high. These levels are based 
on the strength and consistency of the observed evidence; the skill, 
range, and consistency of model projections; and insights from peer-
reviewed sources.
    \128\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. 
Yohe, Eds., 2014: Climate Change Impacts in the United States: The 
Third National Climate Assessment. U.S. Global Change Research 
Program, p. 741.
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    These recent and strong conclusions attributing recent observed 
global warming to human influence have been made despite what some have 
termed a

[[Page 54445]]

warming slowdown or ``hiatus'' over the past 15 years or so. The IPCC 
AR5 notes that global mean surface temperature exhibits substantial 
natural decadal and interannual variability. Short-term variability 
does not alter conclusions about the long-term climate trend that the 
IPCC AR5 finds after its review of independently verified observational 
records: ``Each of the past three decades has been successively warmer 
at the Earth's surface than all the previous decades in the 
instrumental record, and the first decade of the 21st century has been 
the warmest.'' 129 130
---------------------------------------------------------------------------

    \129\ IPCC, 2013: Climate Change 2013: The Physical Science 
Basis. Contribution of Working Group I to the Fifth Assessment 
Report of the Intergovernmental Panel on Climate Change [Stocker, 
T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. 
Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)].Cambridge University 
Press, p. 161.
    \130\ Furthermore, we note that according to both NOAA and NASA, 
2015 was the warmest year in the modern instrumental record for 
globally averaged surface temperature, breaking the record 
previously held by 2014. This now means that the last fifteen years 
have been fifteen of the sixteen warmest years on record. Available 
at https://www.ncdc.noaa.gov/sotc/global/201513 (last accessed April 
11, 2016).
---------------------------------------------------------------------------

    Temperature trends at the global level have also been observed 
regionally and in the United States. In the Northern Hemisphere, the 
IPCC AR5 finds that the last 30 years were likely the warmest 30-year 
period of the last 1400 years. The USGCRP NCA3 states with very high 
confidence that ``U.S. average temperature has increased by 1.3 [deg]F 
to 1.9 [deg]F since record keeping began in 1895; most of this increase 
has occurred since about 1970. The most recent decade was the nation's 
warmest on record.'' \131\ The USGCRP also notes that the rate of U.S. 
temperature increase over the past 4 to 5 decades has been greater than 
the rate observed in earlier decades.
---------------------------------------------------------------------------

    \131\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. 
Yohe, Eds., 2014: Climate Change Impacts in the United States: The 
Third National Climate Assessment. U.S. Global Change Research 
Program, p. 28.
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b. Key Projections Based Primarily on Future Scenarios of the Six Well-
Mixed GHGs
    Future temperature changes will depend on what path the world 
follows with respect to GHG emissions and associated levels of GHG 
concentrations in the atmosphere. The NRC Climate Stabilization Targets 
assessment concludes that CO2 emissions are currently 
altering the atmosphere's composition and will continue to alter 
Earth's climate for thousands of years. The NRC Understanding Earth's 
Deep Past assessment finds that ``the magnitude and rate of the present 
greenhouse gas increase place the climate system in what could be one 
of the most severe increases in radiative forcing of the global climate 
system in Earth history.'' \132\ A key future projection of this 
assessment is that by the end of the century, if no emissions 
reductions are made, CO2 concentrations are projected to 
increase to levels that Earth has not experienced for more than 30 
million years. In its high emission scenario, the IPCC AR5 projects 
that global temperatures by the end of the century will likely be 2.6 
to 4.8 degrees Celsius (4.7 to 8.6 degrees Fahrenheit) warmer than 
today. Temperatures on land and in northern latitudes will likely warm 
even faster than the global average.
---------------------------------------------------------------------------

    \132\ NRC, 2011: Understanding Earth's Deep Past: Lessons for 
Our Climate Future. The National Academies Press, p. 138.
---------------------------------------------------------------------------

    For the United States, the USGCRP NCA3 concludes, ``Warming is 
ultimately projected for all parts of the nation during this century. 
In the next few decades, this warming will be roughly 2 [deg]F to 4 
[deg]F in most areas. By the end of the century, U.S. warming is 
projected to correspond closely to the level of global emissions: 
roughly 3 [deg]F to 5 [deg]F under lower emissions scenarios (B1 or RCP 
4.5) involving substantial reductions in emissions, and 5 [deg]F to 10 
[deg]F for higher emissions scenarios (A2 or RCP 8.5) that assume 
continued increases in emissions; the largest temperature increases are 
projected for the upper Midwest and Alaska.'' \133\
---------------------------------------------------------------------------

    \133\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. 
Yohe, Eds., 2014: Climate Change Impacts in the United States: The 
Third National Climate Assessment. U.S. Global Change Research 
Program, p. 29.
---------------------------------------------------------------------------

3. The Six Well-Mixed GHGs Are Currently the Common Focus of the 
Climate Change Science and Policy Communities
    The six well-mixed GHGs are currently the common focus of climate 
science and policy analyses and discussions. Grouping them is 
consistent with the focus of international and domestic climate science 
research enterprises like the IPCC and USGCRP. The IPCC and USGCRP 
assessment reports assess the climate change effects on health, 
society, and the environment as a result of human-induced climate 
change driven primarily by the group of six gases.
    Grouping them is also consistent with the focus of climate policy. 
The United Nations Framework Convention on Climate Change (UNFCCC), 
signed and ratified by the United States in 1992, requires its 
signatories to ``develop, periodically update, publish and make 
available . . . national inventories of anthropogenic emissions by 
sources and removals by sinks of all greenhouse gases not controlled by 
the Montreal Protocol, using comparable methodologies . . .'' \134\ To 
date, the primary focus of UNFCCC actions and discussions has been on 
the six well-mixed GHGs, including the recent Paris Agreement in which 
Parties agreed to undertake nationally determined contributions to 
achieving the goal of ``global peaking of GHG emissions as soon as 
possible'' in order to reach a long-term global temperature 
target.\135\ Domestically, the EPA has been developing standards for 
GHG emissions from mobile and stationary sources under the Clean Air 
Act since finalizing the 2009 Endangerment Finding.
---------------------------------------------------------------------------

    \134\ United Nations Framework Convention on Climate Change, 
1992: Article 4(1)(a) of the United Nations Framework Convention on 
Climate Change, p. 10. Available at https://unfccc.int/files/essential_background/background_publications_htmlpdf/application/pdf/conveng.pdf (last accessed April 11, 2016).
    \135\ United Nations Framework Convention on Climate Change, 
2015: Adoption of the Paris Agreement Conference of the Parties 
Twenty-first session Paris, FCCC/CP/2015/L.9/Rev.1, 12 December 
2015, Available at: https://unfccc.int/resource/docs/2015/cop21/eng/l09r01.pdf (last accessed April 8, 2016).
---------------------------------------------------------------------------

4. Defining Air Pollution as the Aggregate Group of Six GHGs Is 
Consistent With Evaluation of Risks and Impacts Due to Human-Induced 
Climate Change
    Based on her review of the science described in detail above in 
section IV.B.2, the Administrator judges that the six well-mixed GHGs 
constitute the largest anthropogenic driver of climate change and play 
a dominant role in observed and projected changes in Earth's climate 
system. Thus, the Administrator finds, as she did in the 2009 
Endangerment Finding, that because the six well-mixed GHGs are 
collectively the primary driver of current and projected human-induced 
climate change, the current and future risks (here described in section 
IV.C below) due to human-induced climate change--whether these risks 
are associated with increases in temperature, changes in precipitation, 
a rise in sea levels, changes in the frequency and intensity of weather 
events, or more directly with the elevated GHG concentrations 
themselves--can be associated with this definition of air pollution. 
Due to the cumulative purpose of the statutory language, even if the 
Administrator were to look at the atmospheric

[[Page 54446]]

concentration of each GHG individually, she would still consider the 
impact of the concentration of a single GHG in combination with that 
caused by the other GHGs.
5. Defining Air Pollution as the Aggregate Group of Six GHGs Is 
Consistent With Past EPA Practice
    Treating the air pollution as the aggregate of the well-mixed GHGs 
is consistent with other provisions of the CAA and previous EPA 
practice under the CAA, where separate emissions from different sources 
but with common properties may be treated as a class (e.g., particulate 
matter (PM)). This approach addresses the total, cumulative effect that 
the elevated concentrations of the six well-mixed GHGs have on climate 
and, thus, on different elements of health, society, and the 
environment. The EPA treats, for example, PM as a common class of air 
pollution; PM is a complex mixture of extremely small particles and 
liquid droplets. Particle pollution is made up of a number of 
components, including acids (such as nitrates and sulfates), organic 
chemicals, metals, and soil or dust particles.
6. Response to Key Comments on Defining the Air Pollution as the 
Aggregate Group of the Six Well-Mixed Greenhouse Gases
    Many commenters agreed with the EPA that the ``air pollution'' for 
purposes of the endangerment finding under section 231(a)(2)(A) of the 
CAA should be defined as the six well-mixed GHGs. Several commenters 
discussed the fact that aircraft engines emit only two of the six well-
mixed GHGs. Commenters pointed out that the majority of aircraft 
emissions are CO2, while nitrous oxide emissions are 
described as ``nominal (<1%)'' or ``trace.'' Some commenters ultimately 
concluded that the EPA's approach to defining the air pollution as an 
aggregate group of six gases is acceptable, but that the scope of 
future regulations should be limited to CO2. One commenter 
agreed with the Agency's evaluation of the six GHGs based on their 
common attributes, but questioned the EPA's decision to aggregate the 
six gases rather than considering them individually for purposes of 
making the findings. Other commenters disagreed with the EPA and 
requested limiting the definition of air pollution in this action to 
CO2 or to CO2 and nitrous oxide.
    The EPA disagrees with comments regarding changing the definition 
of the air pollution to limit it to only those GHGs that are emitted 
from aircraft or to CO2 only. The EPA has explained both in 
the 2009 Endangerment Finding and in the proposed findings under CAA 
section 231(a)(2)(A) that the definition of the air pollution is based 
on shared characteristics and common attributes relevant to climate 
change science and policy \136\--which is not affected by the identity 
of the source(s) of the emissions contributing to the air pollution. 
The EPA recognized in the proposed findings that aircraft emit two of 
the six well-mixed GHGs but stated that nonetheless it is entirely 
reasonable and appropriate, and in keeping with the 2009 Endangerment 
Finding and past EPA practice, for the Administrator to group into a 
single class those substances that possess shared relevant properties, 
even though they are not all emitted from the classes of sources before 
her.\137\ After considering all the comments, this continues to be the 
EPA's view. Moreover, this approach to defining air pollution (and air 
pollutant, as described below) as a grouping of many substances is not 
unique to GHGs but rather is common practice under the CAA, for example 
for particulate matter and volatile organic compounds.
---------------------------------------------------------------------------

    \137\ 80 FR at 37774, 37785 and 37787.
---------------------------------------------------------------------------

    The five primary reasons for grouping the six well-mixed GHGs are 
explained in detail above in sections IV.B.1 through IV.B.5. Because 
the well-mixed GHGs are collectively the primary driver of current and 
projected human-induced climate change, all current and future risks 
due to human-induced climate change can be associated with this 
definition of air pollution. Thus, this grouping is consistent with 
evaluation of the scientific issues that the EPA is required to examine 
in this endangerment finding, namely the risks and impacts due to 
human-induced climate change. As discussed above, the key scientific 
evidence and observations that are the basis of this finding focus on 
the combined six well-mixed GHGs, and did not assess risks and impacts 
associated with greenhouse gas-induced climate change using an 
individual gas approach. Accordingly, we are not undertaking a separate 
endangerment analysis for each of the six well-mixed gases 
individually.
    The question of limits to the scope of future regulations is 
outside of the scope of this action because the EPA has neither 
proposed nor is finalizing in this action any such regulatory 
standards. This final action does not itself impose any requirements on 
source categories under CAA section 231. Thus, the EPA anticipates that 
this question could be raised and considered, as needed, in the 
standard-setting phase of the regulatory process, and the EPA will 
consider comments submitted on the issue of the appropriate form of 
emission standards in response to EPA's anticipated future notice of 
proposed rulemaking on standards. Although this final action 
establishes a duty for the EPA to promulgate standards for the GHG 
emissions from engines used by covered aircraft, the findings do not 
pre-judge the form that such standards may take.
    Another commenter expressed concern about EPA's proposed 
endangerment finding because it does not differentiate between 
CO2 emissions that result from combustion of fossil fuels 
and those that result from ``combustion of biomass or biofuels derived 
from herbaceous crops or crop residues, as well as biogenic 
CO2 emissions associated with the production, gathering and 
processing of crops or crop residues used in bio-based products 
including fuels.'' \138\ The commenter argues that such crop-related 
biogenic CO2 emissions should be excluded from the 
endangerment finding because the CO2 released back to the 
atmosphere when emitted from crop-derived biogenic sources contains the 
same carbon that was previously removed or sequestered from 
CO2 in the atmosphere and thus does not contribute to 
elevated atmospheric concentrations of the six well-mixed GHGs.
---------------------------------------------------------------------------

    \138\ Biogenic CO2 Coalition, 2015: Comments on EPA's 
Proposed Finding That Greenhouse Gas Emissions From Aircraft Cause 
or Contribute to Air Pollution That May Reasonably Be Anticipated To 
Endanger Public Health and Welfare, 80 FR 37757 (July 1, 2015). 
Docket ID number EPA-HQ-OAR-2014-0828-0916. Available at 
www.regulations.gov (last accessed April 11, 2016).
---------------------------------------------------------------------------

    The EPA reiterates that the Administrator defines the relevant air 
pollution considered in the endangerment finding as the aggregate group 
of the six well-mixed GHGs based on shared physical characteristics and 
common attributes relevant to climate change science and policy, which 
is not affected by consideration of the sources of the emissions 
contributing to the air pollution. In the record for the 2009 
Endangerment Finding, the Agency stated that ``all CO2 
emissions, regardless of source, influence radiative forcing equally 
once it reaches the atmosphere and therefore there is no distinction 
between biogenic and non-biogenic CO2 regarding the 
CO2 and the other well-mixed GHGs within the definition of 
air pollution that is reasonably anticipated to endanger public health 
and welfare.'' \139\ The EPA continues to hold that position in these

[[Page 54447]]

findings, which is supported by the evidence before it. First, the fact 
that these CO2 emissions originate from combustion of 
carbon-based fuels created through different processes is not relevant 
to defining the air pollution that is reasonably anticipated to 
endanger public health and welfare. The origin and constitution of a 
fuel prior to its combustion and subsequent emission into the 
atmosphere has no bearing on the fact that CO2 and the other 
well-mixed GHGs are all sufficiently long lived to become well mixed in 
the atmosphere, directly emitted, of well-known radiative forcing, and 
generally grouped and considered together in climate change scientific 
and policy forums as the primary driver of climate change. Moreover, as 
explained in section IV.C of this document, the endangerment arises 
from the elevated concentrations of the six well-mixed GHGs in the 
atmosphere. A molecule of biogenic CO2 has the same 
radiative forcing effect as a molecule of fossil-fuel derived 
CO2. In other words, no matter the original source of the 
CO2, the behavior of the CO2 molecules in the 
atmosphere in terms of radiative forcing, chemical reactivity, and 
atmospheric lifetime is effectively the same. Any differential 
treatment of biogenic CO2 in the context of the endangerment 
finding would be inconsistent with the primary scientific basis for the 
grouping of the six well-mixed GHGs as a single class for purposes of 
identifying the air pollution (and air pollutant, as explained below). 
A more detailed response to the issues raised in this comment can be 
found in the Response to Comments document in the docket.
---------------------------------------------------------------------------

    \139\ EPA, 2009. Response to Comments document, Volume 9: The 
Endangerment Finding, EPA-HQ-OAR-2009-0171-11676. Available at 
www.regulations.gov (last accessed April 11, 2016).
---------------------------------------------------------------------------

7. Other Climate Forcers Not Being Included in the Definition of Air 
Pollution for This Finding
    Both in the 2009 Endangerment Finding and in this action, the 
Administrator recognizes that there are other substances in addition to 
the six well-mixed GHGs that are emitted from human activities and that 
affect Earth's climate (referred to as climate forcers). However, as 
described in more detail in the 2009 Endangerment Finding and in the 
proposed findings under CAA section 231(a)(2)(A),\140\ these substances 
do not fit within one or more of the five primary reasons for focusing 
on this aggregate group as the air pollution. As described in the 
following subsections, we received comments on the omission of water 
vapor, NOX, and aerosol particles emitted from aircraft from 
the proposed definition of air pollution for this finding, but not on 
the omission of other climate forcers. After considering public 
comments and additional information in the new assessments regarding 
the climate-relevant substances outside the group of the six well-mixed 
GHGs, it is the Administrator's view that the reasons stated in the 
2009 Endangerment Finding \141\ for not including these substances in 
the scope of the GHG air pollution still apply at this time.
---------------------------------------------------------------------------

    \140\ 74 FR at 66519-21 and 80 FR at 37781-84.
    \141\ 74 FR at 66519-21.
---------------------------------------------------------------------------

    As the EPA acknowledged in the proposed findings,\142\ some short-
lived substances--namely water vapor, NOX emitted at high 
altitude, and aerosol particles including black carbon--have physical 
properties that result in their having different, and often larger, 
climate effects when emitted at high altitudes. For example, the 
assessment literature indicates that aerosol particles, including black 
carbon, emitted at high altitudes have more interactions with clouds 
and therefore have different effects on the global energy balance than 
do particles emitted at the surface. However, the very properties that 
lead to differential climate effects depending on the altitude of 
emission--properties that are different from those of the six well-
mixed GHGs--lead to more uncertainty in the scientific understanding of 
these short-lived substances' total effect on Earth's climate. The 
short-lived nature of these substances means that, unlike GHGs that are 
sufficiently long lived to become well mixed in the atmosphere, the 
climatic impact of the substance is dependent on a number of factors 
such as the location and time of its emission. The magnitude, and often 
the direction (positive/warming or negative/cooling), of the globally 
averaged climate impact will differ depending on the location of the 
emission due to the local atmospheric conditions (e.g., due to 
differing concentrations of other compounds with which the emissions 
can react, background humidity levels, or the presence or absence of 
clouds). In addition, for emissions at any given location, the spatial 
and temporal pattern of the climate forcing will be heterogeneous, 
again often differing in direction (for example, in the case of 
NOX emissions, the near-term effect in the hemisphere in 
which the emissions occur is usually warming due to increased ozone 
concentrations, but the longer term effects, and effects in the other 
hemisphere, are often cooling due to increased destruction of methane). 
More detail on the uncertainties relating to the climate effects of 
these short-lived substances is provided in the subsections below in 
response to public comments and in the Response to Comments document.
---------------------------------------------------------------------------

    \142\ 80 FR at 37781-84.
---------------------------------------------------------------------------

    Overall, the state of the science as represented in the assessment 
literature at present continues to highlight significant scientific 
uncertainties regarding the total net forcing effect of water vapor, 
NOX, and aerosol particles when emitted at high altitudes. 
The dependence of the effects on where the substance is emitted, and 
the complex temporal and spatial patterns that result, mean that the 
current level of understanding regarding these short-lived substances 
is much lower than for the six well-mixed GHGs. Given the 
aforementioned scientific uncertainties at present, the Agency is not 
including these constituents in the definition of air pollution for 
purposes of the endangerment finding under section 231(a)(2)(A) of the 
CAA.
    Many public comments either supported or opposed inclusion of other 
substances in addition to the six well-mixed GHGs in the definition of 
air pollution, and some specifically suggested water vapor, 
NOX, and aerosol particles as additional substances to 
include in that definition. The Agency's full responses to those 
comments can be found in the Response to Comments document; key 
comments and responses are summarized below.
a. Response to Key Comments on Including Other Climate Forcers in the 
Definition of Air Pollution
    Some commenters argued that the proposed findings under CAA section 
231(a)(2)(A) did not demonstrate careful examination of the scientific 
issues with regard to those short-lived substances that have different 
climate effects when emitted at high altitudes, and that a more 
thorough analysis should lead the EPA to conclude that water vapor, 
NOX, and black carbon also drive climate change in addition 
to the six well-mixed GHGs. These comments stated that the EPA should 
have quantified and included the effect of high-altitude water vapor, 
NOX, and black carbon in the Agency's discussion of drivers 
of climate change. Another commenter argued that the EPA should include 
metal particulates (specifically lead, barium, and aluminum) in the 
definition of air pollution for this finding because of their role in 
aviation-induced cloudiness, which the commenter argues has a larger 
effect on climate change than the six well-mixed GHGs.
    Although the EPA is not at this time taking final action to 
determine whether these other climate forcers should be found to 
represent air pollution within

[[Page 54448]]

the meaning of CAA section 231(a)(2)(A), the EPA disagrees with these 
comments suggesting that the Agency did not carefully examine the 
scientific issues and information supporting its current endangerment 
finding in regard to these substances. Consistent with the approach 
described in the proposed findings and for the reasons discussed above, 
the Administrator considers the major peer-reviewed scientific 
assessments of the IPCC and NRC as the primary scientific and technical 
basis informing the endangerment finding and providing the current 
state of scientific understanding of the differential climate effects 
that water vapor, NOX, and aerosols such as black carbon 
have when emitted at high altitudes. The EPA has considered the 
following assessment reports to obtain the best estimates of these 
substances' net impact on the climate system, which is generally 
discussed in terms of radiative forcing: The IPCC AR5, the IPCC 2007 
Fourth Assessment Report (AR4),\143\ the IPCC Special Report: Aviation 
and the Global Atmosphere (IPCC 1999),\144\ the NRC's Advancing the 
Science of Climate Change (NRC 2010),\145\ and the NRC's Atmospheric 
Effects of Aviation: A Review of NASA's Subsonic Assessment Project 
(NRC 1999).\146\ The USGCRP assessments have not dealt specifically 
with emissions at high altitude.
---------------------------------------------------------------------------

    \143\ IPCC, 2007: Climate Change 2007: The Physical Scientific 
Basis. Contribution of Working Group I to the Fourth Assessment 
Report of the Intergovernmental Panel on Climate Change [Solomon, 
S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor 
and H.L. Miller (eds.)] Cambridge University Press, 996 pp.
    \144\ IPCC, 1999: Aviation and the Global Atmosphere, Special 
Report to the Intergovernmental Panel on Climate Change [Penner, 
J.E., D.H. Lister, D.J. Griggs, D.J.Dokken, M.McFarland (eds.)] 
Cambridge University Press, 373 pp.
    \145\ NRC, 2010: Advancing the Science of Climate Change. The 
National Academies Press, 528 pp.
    \146\ NRC, 1999: Atmospheric Effects of Aviation: A Review of 
NASA's Subsonic Assessment Project. The National Academies Press, 54 
pp.
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    As described previously in section IV.A of this document, the 
Administrator's consideration of the major scientific assessments 
provides assurance that the Administrator is basing her judgment on the 
best available, well-vetted science that reflected the consensus of the 
climate science research community. These scientific assessments 
addressed the scientific issues that the EPA was required to examine, 
were comprehensive in their coverage of the GHG and climate change 
issues, and underwent rigorous and exacting peer review by the expert 
community, as well as rigorous levels of U.S. government review, in 
which the EPA took part. The commenters provide no compelling arguments 
against this approach, which underwent judicial review and was upheld 
as described in section IV.A of this document. The assessments 
synthesize literally thousands of individual studies to convey the 
consensus conclusions on what the body of scientific literature tells 
us, and the commenters did not provide evidence that we had missed or 
mischaracterized conclusions of the assessments regarding aviation 
impacts.
    The state of the science as represented in the assessment 
literature supports the EPA's reasons for defining the air pollution as 
the aggregate group of the six well-mixed GHGs, which include their 
common physical properties relevant to climate change (i.e., directly 
emitted and sufficiently long lived to become well mixed in the 
atmosphere), the fact that these gases are considered the primary 
drivers of climate change, and the fact that these gases remain the 
best understood drivers of anthropogenic climate change. Water vapor, 
NOX, aerosol particles, or aviation-induced cloudiness 
associated with metal particulates do not share these common 
attributes, and are each associated with substantial scientific 
uncertainty. Accordingly, although the EPA is not making a final 
determination on whether these additional substances should be found to 
be air pollution within the meaning of CAA section 231(a)(2)(A), the 
EPA is not at this time changing or expanding the definition of the air 
pollution to include these additional substances. The following 
subsections provide additional discussion of the state of the science 
as represented in the assessment literature regarding the climatic 
effects of these substances when emitted at high altitudes.
b. Responses to Key Comments on Changes in Clouds From High Altitude 
Emissions of Water Vapor and Particles
    Some commenters supported the EPA's summary of the scientific 
assessment literature and agreed that there are substantial scientific 
uncertainties regarding net climate effects of aviation-induced 
cloudiness from high altitude emissions of water vapor and particles. 
Other commenters disagreed and argued that there is clear scientific 
evidence that aviation-induced cloudiness associated with high altitude 
emissions of water vapor drives climate change and should be included 
in the definition of air pollution. One commenter disagrees and argues 
that, due to their effect on aviation-induced cloudiness and climate 
change, metal particulates should be included in the definition of air 
pollution.
    The EPA disagrees with the comments regarding changing or expanding 
the definition of the air pollution employed in this endangerment 
finding to include these additional substances. For the reasons stated 
above, the Administrator considers the scientific assessment literature 
as the primary scientific and technical basis informing the 
endangerment finding and providing the state of climate science on 
aviation-induced cloudiness. Section IV.B.4 of the proposed findings 
under CAA section 231(a)(2)(A) \147\ explained that aviation-induced 
cloudiness (sometimes called AIC) refers to all changes in cloudiness 
associated with aviation operations, which are primarily due to the 
effects of high altitude emissions of water vapor and particles 
(primarily sulfates and black carbon). Changes in cloudiness affect the 
climate by both reflecting solar radiation (cooling) and trapping 
outgoing longwave radiation (warming). Unlike the warming effects 
associated with GHGs that are sufficiently long lived to become well 
mixed in the atmosphere, the climate effects associated with changes in 
cloud cover are more regional and temporal in nature. The assessment 
literature describes three main components of aviation-induced 
cloudiness--persistent contrails, contrail-induced cirrus, and induced 
cirrus. Aircraft engine emissions of water vapor at high altitudes 
during flight can lead to the formation of condensation trails, or 
contrails, under certain conditions such as ice-supersaturated air 
masses with specific humidity levels and temperature.
---------------------------------------------------------------------------

    \147\ 80 FR at 37782-83.
---------------------------------------------------------------------------

    The NRC estimated that persistent contrails increased cloudiness 
above the United States by two percent between 1950 and 1988, with 
similar results reported over Europe.\148\ As stated above, clouds can 
have both warming and cooling effects, and persistent contrails were 
once considered to have significant net warming effects. However, more 
recent estimates suggest a smaller overall climate forcing effect of 
persistent contrails. The IPCC AR5 best estimate for the global mean 
radiative forcing from contrails is 0.01 W/m\2\ (medium confidence and 
with an uncertainty range of 0.005 to 0.03 W/m\2\). \149\ To put both 
the magnitude and

[[Page 54449]]

large uncertainty range of this number for the first of the three 
components of aviation-induced cloudiness into context, some examples 
of other IPCC AR5 best estimates for global mean radiative forcing 
include: 1.68 W/m\2\ for CO2 (very high confidence and with 
an uncertainty range of 1.33 to 2.03 W/m\2\), 0.97 W/m\2\ for methane 
(high confidence and with an uncertainty range of 0.74 to 1.20 W/m\2\), 
and 0.17 W/m\2\ for nitrous oxide (very high confidence and with an 
uncertainty range of .013 to 0.21 W/m\2\).\150\ In addition, the NRC 
(2010) assessment suggested that contrails may affect regional diurnal 
temperature differences, but this has been called into question by the 
recent findings presented in the IPCC AR5, which suggests that aviation 
contrails do not have an effect on mean or diurnal range of surface 
temperatures (medium confidence).
---------------------------------------------------------------------------

    \148\ NRC, 1999: Atmospheric Effects of Aviation: A Review of 
NASA's Subsonic Assessment Project. The National Academies Press, 54 
pp.
    \149\ IPCC, 2013: Climate Change 2013: The Physical Science 
Basis. Contribution of Working Group I to the Fifth Assessment 
Report of the Intergovernmental Panel on Climate Change [Stocker, 
T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. 
Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)].Cambridge University 
Press, 1535 pp.
    \150\ IPCC, 2013: Summary for Policymakers. In: Climate Change 
2013: The Physical Science Basis. Contribution of Working Group I to 
the Fifth Assessment Report of the Intergovernmental Panel on 
Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, 
S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley 
(eds.)]. Cambridge University Press, 29 pp.
---------------------------------------------------------------------------

    Persistent contrails also sometimes lose their linear form and 
develop into cirrus clouds, an effect referred to as contrail-induced 
cirrus. Studies to date have been unable to isolate this second of 
three main climate forcing components of aviation-induced cloudiness, 
but the IPCC AR5 provides a combined contrail and contrail-induced 
cirrus best estimate of 0.05 W/m\2\ (low confidence and with an 
uncertainty range of 0.02 and 0.15 W/m\2\).\151\
---------------------------------------------------------------------------

    \151\ IPCC, 2013: Climate Change 2013: The Physical Science 
Basis. Contribution of Working Group I to the Fifth Assessment 
Report of the Intergovernmental Panel on Climate Change [Stocker, 
T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. 
Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)].Cambridge University 
Press, 1535 pp.
---------------------------------------------------------------------------

    Particles emitted or formed in the atmosphere as a result of 
aircraft emissions (primarily sulfates and black carbon) may also act 
as ice nuclei and modify naturally forming cirrus clouds, an effect 
referred to as ``induced cirrus.'' This third of three main climate 
forcing components of aviation-induced cloudiness is an area of active 
research, and there are significant challenges in estimating the 
climatic impacts of cirrus cloud modification. Neither IPCC AR4 nor AR5 
provided global or regional estimates related to this forcing, with the 
AR5 stating that ``it is deemed too uncertain to be further assessed 
here.''\152\ The 2007 IPCC AR4 characterizes our knowledge of the 
natural freezing modes in cirrus conditions as ``poor'' and notes that 
cirrus cloud processes are not well represented in global models.\153\
---------------------------------------------------------------------------

    \152\ Ibid.
    \153\ IPCC, 2007: Climate Change 2007: The Physical Scientific 
Basis. Contribution of Working Group I to the Fourth Assessment 
Report of the Intergovernmental Panel on Climate Change [Solomon, 
S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor 
and H.L. Miller (eds.)] Cambridge University Press, 996 pp.
---------------------------------------------------------------------------

    Given differences in scientific understanding of the three main 
components of aviation-induced cloudiness, the more recent assessments 
have not provided quantitative estimates of the overall net climate 
forcing effect of changes in clouds from high altitude emissions of 
water vapor and particles. Going back to the 1999 IPCC assessment's 
quantitative estimates, the science is characterized as ``very 
uncertain'' with a range for the best estimate between 0 to 0.040 W/
m\2\.\154\ Thus, based on its consideration of the scientific evidence 
and all the comments on this issue, the EPA agrees with those 
commenters that indicate there are substantial scientific uncertainties 
regarding net effects of the three components of aviation-induced 
cloudiness on the climate system. These uncertainties result in the 
Agency's not being prepared at this time to determine whether these 
additional substances are air pollution within the meaning of CAA 
section 231(a)(2)(A) and not including them within the definition of 
``air pollution'' being employed in this endangerment finding.
---------------------------------------------------------------------------

    \154\ IPCC, 1999: Aviation and the Global Atmosphere, Special 
Report to the Intergovernmental Panel on Climate Change [Penner, 
J.E., D.H. Lister, D.J. Griggs, D.J.Dokken, M.McFarland (eds.)] 
Cambridge University Press, 373 pp.
---------------------------------------------------------------------------

c. Responses to Key Comments on Direct Radiative Forcing Effects of 
High Altitude Particle Emissions
    Some commenters supported the EPA's summary of the scientific 
uncertainties regarding the net direct radiative forcing effects of 
aviation-induced particles including black carbon. Other commenters 
disagreed and argued that there is clear scientific evidence that black 
carbon in particular drives climate change and should be included in 
the definition of air pollution.
    The EPA disagrees with comments regarding changing or expanding the 
definition of the air pollution employed in this endangerment finding 
to include aviation-induced particles like black carbon. For the 
reasons stated above, the Administrator considers the scientific 
assessment literature as the primary scientific and technical basis 
informing the endangerment finding and providing the state of climate 
science regarding the direct radiative forcing effects of high altitude 
emissions of the two primary aviation-induced particles, sulfates and 
black carbon. Section IV.B.4 of the proposed findings under CAA section 
231(a)(2)(A) \155\ explained that aircraft emit precursor gases that 
convert to sulfate particles in the atmosphere, such as sulfur dioxide. 
Sulfate particles have direct effects on the climate by scattering 
solar radiation, which is a negative radiative forcing that ultimately 
results in cooling. The more recent assessments have not identified a 
quantitative best estimate for this negative radiative forcing effect 
specifically from aviation, as it is an active area of scientific study 
with large uncertainties. Going back to the 1999 IPCC assessment's 
quantitative estimates, the direct radiative forcing effect of sulfate 
aerosols from aviation for the year 1992 is estimated at -0.003 W/m\2\ 
with an uncertainty range between -0.001 and -0.009 W/m\2\.\156\
---------------------------------------------------------------------------

    \155\ 80 FR at 37783.
    \156\ IPCC, 1999: Aviation and the Global Atmosphere, Special 
Report to the Intergovernmental Panel on Climate Change [Penner, 
J.E., D.H. Lister, D.J. Griggs, D.J.Dokken, M.McFarland (eds.)] 
Cambridge University Press, 373 pp.
---------------------------------------------------------------------------

    Similarly, the proposed findings under CAA section 231(a)(2)(A) 
explained that black carbon emissions from aviation, which are produced 
by the incomplete combustion of jet fuel, primarily absorb solar 
radiation and heat the surrounding air, resulting in a warming effect 
(positive radiative forcing). The more recent assessments have not 
identified a quantitative best estimate for this effect specifically 
from aviation, as it is an area of active scientific study with large 
uncertainties. Going back to the 1999 IPCC assessment's quantitative 
estimates, the global mean radiative forcing of black carbon emissions 
from aircraft is estimated to be 0.003 W/m\2\ with uncertainty spanning 
0.001 to 0.009 W/m\2\.\157\ The IPCC 1999 assessment suggests that 
because the contribution of black carbon in the stratosphere (which 
actually contributes to cooling of the Earth's surface rather than 
warming) was not included in its calculations, its estimates of 
radiative forcing were likely to be too high.
---------------------------------------------------------------------------

    \157\ Ibid.
---------------------------------------------------------------------------

    In addition, the 2009 Endangerment Finding did not include aerosols 
in the

[[Page 54450]]

definition of air pollution, noting that much of the uncertainty range 
surrounding the best estimate of total net forcing due to all human 
activities was due to uncertainties about the cooling and warming 
effects of aerosols \158\ (though from all sources, not just aircraft). 
The 2009 Endangerment Finding also stated that the magnitude of aerosol 
effects can vary immensely with location and season of emissions, 
noting that estimates of its total climate forcing effect have a large 
uncertainty range.\159\ Regarding black carbon specifically, the 2009 
Endangerment Finding noted that it does not share common physical and 
chemical attributes with the six well-mixed GHGs because it is an 
aerosol particle (not a gas) that has different physical, chemical, and 
atmospheric properties. Black carbon affects the climate differently 
than GHGs that are sufficiently long lived to become well mixed in the 
atmosphere. In contrast to its indirect warming and cooling effects via 
clouds, black carbon causes a direct warming effect primarily by 
absorbing incoming and reflected sunlight (whereas GHGs that are 
sufficiently long lived to become well mixed in the atmosphere cause 
warming by trapping outgoing, infrared heat), and by darkening bright 
surfaces such as snow and ice, which reduces reflectivity. Black carbon 
is short-lived, remaining in the atmosphere for only about a week, and 
does not become well-mixed in the atmosphere. There are also concerns 
in the international climate science and policy communities about how 
to treat the short-lived black carbon emissions alongside GHGs--for 
example, what are the appropriate metrics to compare the warming and/or 
climate effects of the different substances, given that, unlike GHGs 
that are sufficiently long lived to become well mixed in the 
atmosphere, the magnitude of aerosol effects can vary immensely with 
location and season of emissions.
---------------------------------------------------------------------------

    \158\ 74 FR at 66517.
    \159\ 74 FR at 66520.
---------------------------------------------------------------------------

    Thus, although the EPA is not at this time prepared to make a final 
determination on whether black carbon should be found to be air 
pollution within the meaning of CAA section 231(a)(2)(A), based on its 
consideration of the scientific evidence and all the comments on this 
issue, and consistent with its conclusion in the 2009 Endangerment 
Finding, the EPA disagrees with commenters that ask for black carbon to 
be included in the definition of the air pollution as part of this 
endangerment finding. Because aerosols such as black carbon and 
sulfates are fundamentally different from and do not share the relevant 
properties that support grouping the six well-mixed GHGs together as a 
class, and scientific uncertainties remain regarding the net radiative 
forcing effects of these substances (whether in general or when emitted 
at high altitudes), the EPA is not at this time including them in the 
definition of air pollution employed in this finding. However, because 
of these uncertainties the Agency is not at this time taking final 
action to determine whether these additional substances should be found 
to represent air pollution within the meaning of CAA section 
231(a)(2)(A).
d. Responses to Key Comments on Changes in Atmospheric Chemistry From 
High Altitude Nitrogen Oxides Emissions
    Most commenters supported the EPA's summary of the scientific 
uncertainties regarding the changes in atmospheric chemistry from high 
altitude NOX emissions. At least one commenter disagreed and 
argued that there is clear scientific evidence that the effects of 
NOX emissions on ozone production have a significant climate 
forcing effect. They concluded that NOX should therefore be 
included in an endangerment finding.
    The EPA disagrees with comments to the extent that they suggest 
including NOX in this endangerment finding by changing or 
expanding the definition of the air pollution. NOX emissions 
have different, and potentially larger, climate effects when emitted at 
high altitudes and about 90 percent of aircraft NOX is 
emitted in flight (not during landing and takeoff),\160\ meaning its 
relevance for climate change is primarily in relation to emissions at 
high altitude. The atmospheric lifetime of NOX emitted near 
the surface is on the order of a few hours, while in the upper 
troposphere, or roughly the cruise altitude for jet aircraft, it is on 
the order of several days.
---------------------------------------------------------------------------

    \160\ FAA, System for Assessing Aviation's Global Emissions, 
Version 1.5, Global Aviation Emissions Inventories for 2000 through 
2004, FAA-EE-2005-02, September 2005, revised March 2008, available 
at https://www.faa.gov/about/office_org/headquarters_offices/apl/researc/models/sage/ (Last accessed April 14, 2016).
---------------------------------------------------------------------------

    Section IV.B.4 of the proposed findings under CAA section 
231(a)(2)(A) \161\ explained that emissions of NOX do not 
themselves have warming or cooling effects, but affect the climate 
through catalyzing changes in the chemical equilibrium of the 
atmosphere. High altitude emissions of NOX increase the 
concentration of ozone, which has a warming effect in the short term. 
Elevated NOX concentrations also lead to an increased rate 
of destruction of methane, which has a cooling effect in the long-term. 
The reduced methane concentrations eventually contribute to decreases 
in ozone, which also decreases the long-term net warming effect. Thus, 
the net radiative impact of NOX emissions depends on the 
balance between the reductions in methane versus the production of 
ozone, which in turn depends on the time scale under consideration.
---------------------------------------------------------------------------

    \161\ 80 FR at 37783-84.
---------------------------------------------------------------------------

    For the reasons stated above, the Administrator considers the 
scientific assessment literature as the primary scientific and 
technical basis informing the endangerment finding and providing the 
state of climate science regarding how emissions of NOX 
affect the climate system. Quantifying these impacts is an area of 
active scientific study with large uncertainties. The quantification of 
the net global effect of NOX is difficult because the 
atmospheric chemistry effects are heavily dependent on highly localized 
atmospheric properties and mixing ratios. Because the background 
atmospheric concentration of NOX is important for 
quantifying the impact of NOX emissions on ozone and methane 
concentrations, the location of aircraft emissions is an important 
additional factor. Going back to the IPCC 1999 assessment since no more 
recent quantitative estimates are available, the globally averaged 
radiative forcing estimates for high-altitude aircraft emissions of 
NOX in 1992 were 0.023 W/m\2\ for ozone-induced changes 
(uncertainty range of 0.011 to 0.046 W/m\2\), and -0.014 W/m\2\ for 
methane-induced changes (uncertainty range of -0.005 to -0.042 W/
m\2\).\162\
---------------------------------------------------------------------------

    \162\ IPCC, 1999: Aviation and the Global Atmosphere, Special 
Report to the Intergovernmental Panel on Climate Change [Penner, 
J.E., D.H. Lister, D.J. Griggs, D.J. Dokken, M. McFarland (eds.)] 
Cambridge University Press, 373 pp.
---------------------------------------------------------------------------

    The IPCC AR5 presents the impact of aviation high-altitude 
NOX emissions using a different metric, global warming 
potential (GWP), which is a measure of the warming impact of a pulse of 
emissions of a given substance over 100 years relative to the same mass 
of CO2. The AR5 presents a range from -21 to +75 for GWP of 
aviation NOX.\163\ The uncertainty in sign indicates 
uncertainty

[[Page 54451]]

whether the net effect is one of warming or cooling. This report 
further suggests that at cruise altitude there is strong regional 
sensitivity of ozone and methane to NOX, particularly 
notable at low latitudes.
---------------------------------------------------------------------------

    \163\ IPCC, 2013: Climate Change 2013: The Physical Science 
Basis. Contribution of Working Group I to the Fifth Assessment 
Report of the Intergovernmental Panel on Climate Change [Stocker, 
T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. 
Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge 
University Press, 1535 pp.
---------------------------------------------------------------------------

    Thus, although the EPA is not prepared to determine whether 
NOX emissions at high altitude should be found to be air 
pollution within the meaning of CAA section 231(a)(2)(A), based on its 
consideration of the scientific evidence and all the comments on this 
issue, and consistent with its conclusion in the 2009 Endangerment 
Finding, the EPA disagrees with commenters that assert that 
NOX should be included at this time in the definition of the 
air pollution for this finding. NOX does not share the 
relevant properties that support grouping the six well-mixed GHGs 
together as a class. NOX is not classified as a GHG because 
it influences the climate system indirectly through production of ozone 
rather than directly through trapping outgoing heat. In addition, 
NOX does not have a sufficiently long atmospheric lifetime 
to become well-mixed in the atmosphere and significant scientific 
uncertainties remain regarding its net radiative forcing effects.
    The Administrator notes that NOX emissions are already 
regulated under the EPA's rules implementing CAA section 231, at 40 CFR 
part 87, due to their impacts during landing and take-off operations 
(LTO). The prerequisite endangerment and cause or contribute findings 
that formed the basis for these standards, however, did not rely upon 
any conclusions regarding the climate forcing impacts of 
NOX, but rather the role of LTO NOX emissions as 
a precursor to ozone formation in areas that did not meet the NAAQS for 
ozone.\164\ The continuing significant uncertainties regarding high 
altitude NOX emissions, which are emitted during cruise 
operations rather than during LTO, as a climate forcer do not undermine 
the Agency's prior conclusion under CAA section 231(a)(2)(A) that 
emissions of NOX from aircraft engines cause or contribute 
to air pollution which may reasonably be anticipated to endanger public 
health or welfare due to their contribution to ozone concentrations 
that exceed the NAAQS. This final finding does not revise or reopen the 
Agency's prior findings under CAA section 231(a)(2)(A) that emissions 
of NOX from aircraft engines cause or contribute to air 
pollution which may reasonably be anticipated to endanger public health 
or welfare due to their contribution to ozone concentrations that 
exceed the NAAQS.
---------------------------------------------------------------------------

    \164\ U.S. EPA, ``Control of Air Pollution from Aircraft and 
Aircraft Engines, Emission Standards and Test Procedures for 
Aircraft.'' Final Rule, 38 FR 19088 (July 17, 1973).
---------------------------------------------------------------------------

C. The Air Pollution is Reasonably Anticipated To Endanger Both Public 
Health and Welfare

    The Administrator finds that elevated atmospheric concentrations of 
the six well-mixed GHGs may reasonably be anticipated to endanger the 
public health and welfare of current and future generations within the 
meaning of CAA section 231(a)(2)(A). This section describes the major 
pieces of scientific evidence supporting the Administrator's 
endangerment finding, discusses both the public health and welfare 
aspects of the endangerment finding, and addresses a number of key 
issues the Administrator considered when evaluating the state of the 
science.
    The EPA is informed by and places considerable weight on the 
extensive scientific and technical evidence in the record supporting 
the 2009 Endangerment Finding, including the major, peer-reviewed 
scientific assessments used to address the question of whether GHGs in 
the atmosphere endanger public health and welfare, and on the 
analytical framework and conclusions upon which the EPA relied in 
making that finding. This final finding under CAA section 231(a)(2)(A) 
accounts for the EPA's careful consideration of the scientific and 
technical record for the 2009 Endangerment Finding, of the new, major 
scientific assessments issued since closing the administrative record 
for the 2009 Endangerment Finding, and of public comments. No recent 
information or assessments published since late 2009 or provided by 
commenters suggest that it would be reasonable for the EPA to now reach 
a different or contrary conclusion for purposes of CAA section 
231(a)(2)(A) than the one the EPA reached in 2009 under CAA section 
202(a). Rather, they provide further support for this final finding 
under section 231(a)(2)(A). In particular, the new assessments 
discussed in this document provide additional detail regarding public 
health impacts, particularly on groups and people especially vulnerable 
to climate change, including children, the elderly, low-income 
communities and individuals, indigenous groups, and communities of 
color.
    Following the same decision framework and analysis that we followed 
for the 2009 Endangerment Finding, as detailed in section IV.B of that 
finding,\165\ here we summarize the general approach used by the 
Administrator in reaching the judgment that a positive endangerment 
finding should be made for purposes of CAA section 231(a)(2)(A), as 
well as the specific rationale for finding that the GHG air pollution 
may reasonably be anticipated to endanger both public health and 
welfare. First, the Administrator finds the scientific evidence linking 
anthropogenic emissions and resulting elevated atmospheric 
concentrations of the six well-mixed GHGs to observed global and 
regional temperature increases and other climate changes to be 
sufficiently robust and compelling. The Administrator is basing her 
finding on the total weight of scientific evidence and what the science 
has to say regarding the nature and potential magnitude of the risks 
and impacts across all climate-sensitive elements of public health and 
welfare, now and projected out into the foreseeable future. The 
Administrator has considered the state of the science on how 
anthropogenic emissions and the resulting elevated atmospheric 
concentrations of the six well-mixed GHGs may affect each of the major 
risk categories, include human health, air quality, food production and 
agriculture, forestry, water resources, sea level rise and coastal 
areas, the energy sector, infrastructure and settlements, and 
ecosystems and wildlife. The Administrator understands that the nature 
and potential severity of impacts can vary across these different 
elements of public health and welfare, and that they can vary by 
region, as well as over time.
---------------------------------------------------------------------------

    \165\ 74 FR at 66523-36.
---------------------------------------------------------------------------

    The Administrator is therefore aware that, because human-induced 
climate change has the potential to be far-reaching and multi-
dimensional, not all risks and potential impacts can be characterized 
with a uniform level of quantification or understanding, nor can they 
be characterized with uniform metrics. Thus, the Administrator is not 
necessarily placing the greatest weight on those risks and impacts 
which have been the subject of the most study or quantification. 
Rather, given this variety in not only the nature and potential 
magnitude of risks and impacts, but also in our ability to 
characterize, quantify and project into the future such impacts, the 
Administrator must use her judgment to weigh the threat in each of the 
risk categories, weigh the potential benefits where relevant, and 
ultimately to judge whether these risks and

[[Page 54452]]

benefits, when viewed in total, endanger public health and/or welfare.
    First, the Administrator has not established a specific threshold 
metric for the different categories of risk and impacts, which are 
referred to as impact sectors. The potential for both adverse and 
beneficial effects is considered, as well as the relative magnitude of 
such effects, to the extent that the relative magnitudes can be 
quantified or characterized. Furthermore, given the multiple ways in 
which the buildup of anthropogenic GHG emissions in the atmosphere can 
cause effects (e.g., via elevated CO2 concentrations, 
temperature increases, precipitation increases, sea level rise, and 
changes in extreme events), these multiple pathways are considered. The 
Administrator has balanced and weighed the varying risks and effects 
for each impact sector. She has judged whether there is a pattern 
across the sector that supports or does not support an endangerment 
finding, and if so whether the support is of more or less weight. In 
cases where there is a potential for both benefits and risks of harm, 
the Administrator has balanced these factors by determining whether 
there appears to be any directional trend in the overall evidence that 
would support placing more weight on one than the other, taking into 
consideration all that is known about the likelihood of the various 
risks and effects and their seriousness. In all of these cases, the 
judgment is largely qualitative in nature and is not reducible to 
precise metrics or quantification.
    Regarding the timeframe for the endangerment test, it is the 
Administrator's view that both current and future conditions must be 
considered. The Administrator is thus taking the view that the 
endangerment period of analysis extend from the current time to the 
next several decades and in some cases to the end of this century. This 
consideration is also consistent with the timeframes used in the 
underlying scientific assessments. The future timeframe under 
consideration is consistent with the atmospheric lifetime and climate 
effects of the six well-mixed GHGs and also with our ability to make 
reasonable and plausible projections of future conditions. The 
Administrator acknowledges that some aspects of climate change science 
and the projected impacts are more certain than others. Our state of 
knowledge is strongest for recently observed, large-scale changes. 
Uncertainty tends to increase in characterizing changes at smaller 
(regional) scales relative to large (global) scales. Uncertainty also 
increases as the temporal scales move away from the present, either 
backward or more importantly forward in time. Nonetheless, the current 
state of knowledge of observed and past climate changes and their 
causes enables projections of plausible future changes under different 
scenarios of anthropogenic forcing for a range of spatial and temporal 
scales. The subsections below summarize the scientific information on 
climate change impacts to public health and welfare that inform the 
Administrator's judgment, as well as the key public comments and Agency 
responses. The Agency's full responses to public comments can be found 
in the Response to Comments document.
1. The Air Pollution is Reasonably Anticipated To Endanger Public 
Health
    The Administrator finds under CAA section 231(a)(2)(A) that the 
well-mixed GHG air pollution is reasonably anticipated to endanger 
public health, for both current and future generations. The 
Administrator finds that the public health of current generations is 
endangered and that the threat to public health for both current and 
future generations will mount over time as GHGs continue to accumulate 
in the atmosphere and result in ever greater rates of climate change. 
The Administrator continues to find robust scientific evidence in the 
assessment literature that climate change can increase the risk of 
morbidity and mortality and believes that these public health impacts 
can and should be considered when determining endangerment to public 
health under CAA section 231(a)(2)(A). As described in section IV.B.1 
of the 2009 Endangerment Finding, the Administrator is not limited to 
only considering whether there are any direct health effects such as 
respiratory or toxic effects associated with exposure to GHGs.
    Here we summarize information from the scientific assessment 
literature cited in the 2009 Endangerment Finding showing that climate 
change resulting from anthropogenic GHG emissions threatens multiple 
aspects of public health.\166\ In determining that the well-mixed GHG 
air pollution is reasonably anticipated to endanger public health for 
current and future generations under CAA section 202(a), the 
Administrator noted her view that climate change can increase the risk 
of morbidity and mortality. In making that public health determination, 
the Administrator considered direct temperature effects, air quality 
effects, the potential for changes in vector-borne diseases, and the 
potential for changes in the severity and frequency of extreme weather 
events. In addition, the Administrator considered whether and how 
susceptible populations may be particularly at risk. As explained in 
more detail in the 2009 Endangerment Finding, with respect to direct 
temperature effects, by raising average temperatures, climate change 
increases the likelihood of heat waves, which are associated with 
increased deaths and illnesses. Climate change is also expected to lead 
to reductions in cold-related mortality. The 2009 Endangerment Finding, 
while noting uncertainty about how heat and cold related mortality 
would change in the future, also pointed to a USGCRP assessment report 
discussion that increases in heat-related mortality due to global 
warming in the United States were unlikely to be compensated for by 
decreases in cold-related mortality. With regard to air quality 
effects, climate change is expected to increase ozone pollution over 
broad areas of the country, including large metropolitan population 
centers, and thereby increase the risks of respiratory infection, 
aggravation of asthma, and premature death. Other public health threats 
stem from the potential for increased deaths, injuries, infectious and 
waterborne diseases, stress-related disorders, and other adverse 
effects associated with increased hurricane intensity and increased 
frequency of intense storms and heavy precipitation associated with 
climate change. In addition, climate change is expected to be 
associated with an increased risk of food-, water-, and vector-borne 
diseases in susceptible populations. Climate change also has the 
potential to change aeroallergen production (for example, through 
lengthening the growing season for allergen-producing plants), and 
subsequent human exposures could increase allergenic illnesses. 
Children, the elderly, and the poor are among the most vulnerable to 
climate-related health risks and impacts. The Administrator placed 
weight on the fact that these certain groups are most vulnerable to 
these climate-related health effects.
---------------------------------------------------------------------------

    \166\ 74 FR at 66524-30.
---------------------------------------------------------------------------

    The EPA concludes that the 2009 Endangerment Finding's discussion 
under CAA section 202(a) is equally persuasive for purposes of CAA 
section 231(a)(2)(A). In addition, the EPA has carefully reviewed the 
key conclusions in the recent assessments regarding public health risks 
and the current and projected health impacts from human-

[[Page 54453]]

induced climate change. The EPA finds that the new assessments are 
consistent with or strengthen the underlying science considered in the 
2009 Endangerment Finding regarding public health effects from changes 
in temperature, air quality, extreme weather, and climate-sensitive 
diseases and aeroallergens, further supporting an endangerment finding 
under CAA section 231(a)(2)(A). These key findings are described 
briefly here.
    The USGCRP NCA3 finds that, ``Climate change threatens human health 
and well-being in many ways, including impacts from increased extreme 
weather events, wildfire, decreased air quality, threats to mental 
health, and illnesses transmitted by food, water, and diseases carriers 
such as mosquitoes and ticks. Some of these health impacts are already 
underway in the United States.'' \167\ Regarding temperature effects, 
the USGCRP NCA3 states, ``The effects of temperature extremes on human 
health have been well documented for increased heat waves, which cause 
more deaths, hospital admissions and population vulnerability.'' \168\ 
The conclusions of the assessment literature cited in the 2009 
Endangerment Finding were uncertain with respect to the balance of 
future heat- versus cold-related mortality associated with climate 
change, but they noted that the available evidence suggested that the 
increased risk from heat would exceed the decreased risk from cold in a 
warming climate. The most recent assessments now have greater 
confidence that increases in heat-related mortality likely will be 
larger than the decreases in cold-related mortality, further supporting 
this endangerment finding under CAA section 231(a)(2)(A). The USGCRP 
NCA3 concludes, ``While deaths and injuries related to extreme cold 
events are projected to decline due to climate change, these reductions 
are not expected to compensate for the increase in heat-related 
deaths.'' \169\ The IPCC AR5 also notes a potential benefit of climate 
change could include ``modest reductions in cold-related mortality and 
morbidity in some areas due to fewer cold extremes (low confidence),'' 
\170\ but that, ``[o]verall, we conclude that the increase in heat-
related mortality by mid-century will outweigh gains due to fewer cold 
periods.'' \171\
---------------------------------------------------------------------------

    \167\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. 
Yohe, Eds., 2014: Climate Change Impacts in the United States: The 
Third National Climate Assessment. U.S. Global Change Research 
Program, p. 221.
    \168\ Ibid at p. 252.
    \169\ Ibid at p. 224.
    \170\ IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and 
Vulnerability. Part A: Global and Sectoral Aspects. Contribution of 
Working Group II to the Fifth Assessment Report of the 
Intergovernmental Panel on Climate Change [Field, C.B., V.R. Barros, 
D.J. Dokken, K.J. Mach, M.D. Mastrandrea, T.E. Bilir, M. Chatterjee, 
K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. 
Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. 
Cambridge University Press, p. 713.
    \171\ Ibid. at p. 721.
---------------------------------------------------------------------------

    Regarding air quality effects, the assessment literature cited in 
the 2009 Endangerment Finding concluded that climate change is expected 
to increase regional ozone pollution, with associated risks in 
respiratory illnesses and premature death, but that the directional 
effect of climate change on ambient particulate matter levels was less 
certain. One of the more recent assessments, the USGCRP NCA3, similarly 
concludes, ``Climate change is projected to harm human health by 
increasing ground-level ozone and/or particulate matter air pollution 
in some locations. . . . There is less certainty in the responses of 
airborne particles to climate change than there is about the response 
of ozone.'' \172\ The IPCC AR5 finds that ozone and particulate matter 
have been associated with adverse health effects in many locations in 
North America, and that ozone concentrations could increase under 
future climate change scenarios if emissions of precursors were held 
constant. For particulate matter, both the USGCRP NCA3 and IPCC AR5 
discuss increasing wildfire risk under climate change and explain that 
wildfire smoke exposure can lead to various respiratory and 
cardiovascular impacts. The USGCRP NCA3 states, ``The effects of 
wildfire on human health have been well documented with increases in 
wildfire frequency, leading to decreased air quality and negative 
health impacts.'' \173\ The NRC Indoor Environment assessment 
identifies potential adverse health risks associated with climate 
change-induced alterations in the indoor environment, including 
possible exposure to air pollutants due to changes in outdoor air 
quality. Other risks include potential for alterations in indoor 
allergens due to climate change-related increases in outdoor pollen 
levels, potential chemical exposures due to greater use of pesticides 
to address changes in geographic ranges of pest species, and dampness/
mold associated symptoms and illness due to potential flooding and 
water damage in buildings from projected climate change-related 
increases in storm intensity and extreme precipitation events in some 
regions of the United States. Each of these assessments further 
supports finding endangerment under CAA section 231(a)(2)(A).
---------------------------------------------------------------------------

    \172\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. 
Yohe, Eds., 2014: Climate Change Impacts in the United States: The 
Third National Climate Assessment. U.S. Global Change Research 
Program, p. 222.
    \173\ Ibid at p. 252.
---------------------------------------------------------------------------

    Regarding extreme weather events (e.g., storms, heavy 
precipitation, and, in some regions of the United States, floods and 
droughts), the conclusions of the assessment literature cited in the 
2009 Endangerment Finding found potential for increased deaths, 
injuries, infectious and waterborne diseases, and stress-related 
disorders. The more recent assessments further support this conclusion 
for purposes of CAA section 231(a)(2)(A). The USGCRP NCA3 finds that 
``Heavy downpours are increasing nationally, especially over the last 
three to five decades. Largest increases are in the Midwest and 
Northeast. Increases in the frequency and intensity of extreme 
precipitation events are projected for all U.S. regions.'' \174\ The 
USGCRP NCA3 identifies that: ``Elevated waterborne disease outbreaks 
have been reported in the weeks following heavy rainfall, although 
other variables may affect these associations. Water intrusion into 
buildings can result in mold contamination that manifests later, 
leading to indoor air quality problems.'' \175\ Other risks include 
mortality associated with flooding and impacts on mental health, such 
as anxiety and post-traumatic stress disorder. The IPCC AR5 also 
discusses increased risk of death and injury in coastal zones and 
regions vulnerable to inland flooding. The USGCRP NCA3 and the IPCC AR5 
both find that climate change may increase exposure to health risks 
associated with drought conditions, which includes impacts from 
wildfires, dust storms, extreme heat events, and flash flooding. 
Droughts can lead to reduced water quantity and degraded water quality, 
thereby increasing the risk of water-related diseases. The IPCC SREX 
assessment projects further increases in some extreme weather and 
climate events during this century, and it specifically notes that 
changes in extreme weather events have implications for disaster risk 
in the health sector.
---------------------------------------------------------------------------

    \174\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. 
Yohe, Eds., 2014: Climate Change Impacts in the United States: The 
Third National Climate Assessment. U.S. Global Change Research 
Program, p. 36.
    \175\ Ibid at p. 224-225.
---------------------------------------------------------------------------

    The potential for changes in climate-sensitive diseases was also 
cited in the 2009 Endangerment Finding. This included an increase in 
the spread of several food and water-borne pathogens,

[[Page 54454]]

which can affect susceptible populations. Also noted was the potential 
for range expansion of some zoonotic disease carriers such as the Lyme 
disease-carrying tick. The new assessment literature similarly focuses 
on increased exposure risk for some diseases under climate change, 
finding that increasing temperatures may expand or shift the ranges of 
some disease vectors like mosquitoes, ticks, and rodents. The IPCC AR5 
notes that climate change may influence the ``growth, survival, 
persistence, transmission, or virulence of pathogens'' \176\ that cause 
food and water-borne disease. The USGCRP NCA3 notes that uncertainty 
remains regarding future projections of increased human burden of 
vector-borne disease, given complex interacting factors such as 
``local, small-scale differences in weather, human modification of the 
landscape, the diversity of animal hosts, and human behavior that 
affects vector-human contact, among other factors.'' \177\ This new 
assessment literature further supports finding endangerment under CAA 
section 231(a)(2)(A).
---------------------------------------------------------------------------

    \176\ IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and 
Vulnerability. Part A: Global and Sectoral Aspects. Contribution of 
Working Group II to the Fifth Assessment Report of the 
Intergovernmental Panel on Climate Change [Field, C.B., V.R. Barros, 
D.J. Dokken, K.J. Mach, M.D. Mastrandrea, T.E. Bilir, M. Chatterjee, 
K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. 
Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. 
Cambridge University Press, p. 726.
    \177\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. 
Yohe, Eds., 2014: Climate Change Impacts in the United States: The 
Third National Climate Assessment. U.S. Global Change Research 
Program, p. 225.
---------------------------------------------------------------------------

    Regarding aeroallergens, the assessment literature cited in the 
2009 Endangerment Finding found potential for climate change to affect 
the prevalence and severity of allergy symptoms, but definitive data or 
conclusions were lacking on how climate change might impact 
aeroallergens in the United States. Further supporting an endangerment 
finding under CAA section 231(a)(2)(A), the most recent assessments now 
express greater confidence that climate change influences the 
production of pollen, which in turn could affect the incidence of 
asthma and other allergic respiratory illnesses such as allergic 
rhinitis, as well as effects on conjunctivitis and dermatitis. Both the 
USGCRP NCA3 and the IPCC AR5 found that increasing temperature has 
lengthened the allergenic pollen season for ragweed, and that increased 
CO2 by itself can elevate production of plant-based 
allergens. The IPCC AR5 concludes that in North America, there is high 
confidence that ``warming will lead to further changes in the seasonal 
timing of pollen release.'' \178\
---------------------------------------------------------------------------

    \178\ IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and 
Vulnerability. Part B: Regional Aspects. Contribution of Working 
Group II to the Fifth Assessment Report of the Intergovernmental 
Panel on Climate Change [Barros, V.R., C.B. Field, D.J. Dokken, M.D. 
Mastrandrea, K.J. Mach, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. 
Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. 
MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge 
University Press, Cambridge, pp. 1465-1466.
---------------------------------------------------------------------------

a. Health Impacts of Climate Change on Vulnerable Populations
    In the 2009 Endangerment Finding, the EPA cited the assessment 
literature's conclusions regarding the fact that certain populations, 
including children, the elderly, and the poor, are most vulnerable to 
climate change-related health effects. The 2009 Endangerment Finding 
also described climate change impacts facing indigenous peoples in the 
United States, particularly Alaska Natives. The new assessment 
literature strengthens these conclusions and further supports an 
endangerment finding under CAA section 231(a)(2)(A) by providing more 
detailed findings regarding these populations' vulnerabilities and the 
projected impacts they may experience. In addition, the most recent 
assessment reports provide new analysis about how some populations 
defined jointly by ethnic/racial characteristics and geographic 
location may be vulnerable to certain climate change health impacts. 
The following paragraphs summarize information from the most recent 
assessment reports on these vulnerable populations.
    The USGCRP NCA3 finds, ``Climate change will, absent other changes, 
amplify some of the existing health threats the nation now faces. 
Certain people and communities are especially vulnerable, including 
children, the elderly, the sick, the poor, and some communities of 
color.'' \179\ Limited resources make low-income populations more 
vulnerable to ongoing climate-related threats, less able to adapt to 
anticipated changes, and less able to recover from climate change 
impacts. Low-income populations also face higher prevalence of chronic 
health conditions than higher income groups, which increases their 
vulnerability to the health effects of climate change.
---------------------------------------------------------------------------

    \179\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. 
Yohe, Eds., 2014: Climate Change Impacts in the United States: The 
Third National Climate Assessment. U.S. Global Change Research 
Program, p. 221.
---------------------------------------------------------------------------

    According to the USGCRP NCA3 and IPCC AR5, some populations defined 
jointly by ethnic/racial characteristics and geographic location are 
more vulnerable to certain health effects of climate change due to 
factors such as existing health disparities (e.g., higher prevalence of 
chronic health conditions), increased exposure to health stresses, and 
social factors that affect local resilience and ability to recover from 
impacts.
    The USGCRP NCA3 also finds that climate change, in addition to 
chronic stresses such as extreme poverty, is affecting indigenous 
peoples' health in the United States through impacts such as reduced 
access to traditional foods, decreased water quality, and increasing 
exposure to health and safety hazards. The IPCC AR5 finds that climate 
change-induced warming in the Arctic and resultant changes in 
environment (e.g., permafrost thaw, effects on traditional food 
sources) have significant observed and projected impacts on the health 
and well-being of Arctic residents, especially indigenous peoples. 
Small, remote, predominantly indigenous communities are especially 
vulnerable given their ``strong dependence on the environment for food, 
culture, and way of life; their political and economic marginalization; 
existing social, health, and poverty disparities; as well as their 
frequent close proximity to exposed locations along ocean, lake, or 
river shorelines.'' \180\ In addition, increasing temperatures and loss 
of Arctic sea ice increases the risk of drowning for those engaged in 
traditional hunting and fishing.
---------------------------------------------------------------------------

    \180\ IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and 
Vulnerability. Part B: Regional Aspects. Contribution of Working 
Group II to the Fifth Assessment Report of the Intergovernmental 
Panel on Climate Change [Barros, V.R., C.B. Field, D.J. Dokken, M.D. 
Mastrandrea, K.J. Mach, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. 
Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. 
MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge 
University Press, Cambridge, p. 1581.
---------------------------------------------------------------------------

    The USGCRP NCA3 concludes that ``Children, primarily because of 
physiological and developmental factors, will disproportionately suffer 
from the effects of heat waves, air pollution, infectious illness, and 
trauma resulting from extreme weather events.'' \181\ As noted above, 
the IPCC AR5 finds that in North America, climate change will influence 
production of pollen, and that this affects asthma and other allergic 
respiratory diseases to which children are among those especially 
susceptible.

[[Page 54455]]

The IPCC AR5 also identifies children as a susceptible population to 
health effects associated with heat waves, storms, and floods.
---------------------------------------------------------------------------

    \181\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. 
Yohe, Eds., 2014: Climate Change Impacts in the United States: The 
Third National Climate Assessment. U.S. Global Change Research 
Program, p.228.
---------------------------------------------------------------------------

    Both the USGCRP and IPCC conclude that climate change increases 
health risks facing the elderly. Older people are at much higher risk 
of mortality during extreme heat events. Pre-existing health conditions 
also make older adults susceptible to cardiac and respiratory impacts 
of air pollution and to more severe consequences from infectious and 
waterborne diseases. Limited mobility among older adults can also 
increase health risks associated with extreme weather and floods.
    Accordingly, as discussed above, all of these recent assessments 
further support finding endangerment under CAA section 231(a)(2)(A).
b. Responses to Key Comments on Endangerment to Public Health
    Public comments supported the EPA's summary of the scientific 
information and finding that the well-mixed GHG air pollution is 
reasonably anticipated to endanger public health of current and future 
generations under CAA section 231(a)(2)(A). Commenters cited a number 
of examples of climate impacts relevant to public health including 
changes in outdoor and indoor air quality, extreme temperatures, 
floods, fires, and hurricanes. Some commenters also agreed with the 
EPA's summary of health impacts to certain vulnerable populations and 
emphasized that certain populations like the elderly, poor, very young, 
and indigenous groups are more vulnerable to the health impacts of 
climate change for various reasons. No commenters disagreed with the 
EPA's summary of the scientific information or with its conclusion on 
endangerment to public health. The EPA agrees with the commenters that 
this endangerment finding is well supported by the scientific 
assessment literature; that it covers a range of health risks 
associated with climate change-induced changes in air quality, 
increases in temperatures, changes in extreme weather events, increases 
in food and water borne pathogens, and changes in aeroallergens; and 
that certain populations are more vulnerable to climate change health 
risks and impacts.
2. The Air Pollution Is Reasonably Anticipated To Endanger Welfare
    The Administrator finds under CAA section 231(a)(2)(A) that the air 
pollution comprised of the six well-mixed GHGs is reasonably 
anticipated to endanger welfare, for both current and future 
generations. As with public health, the Administrator considered the 
multiple pathways in which the GHG air pollution and resultant climate 
change affect climate-sensitive sectors and the impact this may have on 
welfare. These sectors include food production and agriculture; 
forestry; water resources; sea level rise and coastal areas; energy, 
infrastructure, and settlements; and ecosystems and wildlife. The 
Administrator examined each climate-sensitive sector individually, 
informed by the scientific information in the major assessments 
contained in the administrative record for the 2009 Endangerment 
Finding as well as the newer assessments in the record for this action, 
and weighed the extent to which the risks and impacts within each 
sector support or do not support a positive endangerment finding in her 
judgment. The Administrator then viewed the full weight of evidence 
looking across all sectors to reach her decision regarding endangerment 
to welfare. For each of these sectors, the evidence indicates that the 
risk and the severity of adverse impacts on welfare are expected to 
increase over time, providing compelling support for a finding of 
endangerment to welfare. The Administrator also considered impacts on 
the U.S. population from climate change effects occurring outside of 
the United States, such as national security concerns for the United 
States that may arise as a result of climate change impacts in other 
regions of the world, and finds that this provides additional support 
to the finding of endangerment to welfare of current and future 
generations of the United States population.
    The 2009 Endangerment Finding summarized information from the 
scientific assessment literature showing that climate change resulting 
from anthropogenic GHG emissions also threatens multiple aspects of 
welfare under CAA section 202(a).\182\ In determining that the well-
mixed GHG air pollution is reasonably anticipated to endanger welfare 
for current and future generations, the Administrator considered the 
multiple pathways by which GHG air pollution and resultant climate 
change affect welfare by evaluating the numerous and far-ranging risks 
and impacts associated with food production and agriculture; forestry; 
water resources; widespread snow and ice melt, sea level rise and 
coastal areas; energy, infrastructure, and settlements; and ocean 
acidification, ecosystems, and wildlife. The Administrator also 
considered observed and projected risks and impacts on the U.S. 
population from climate change effects occurring outside of the United 
States. As explained in more detail in the 2009 Endangerment Finding, 
the potential serious adverse impacts of extreme events, such as 
wildfires, flooding, drought, and extreme weather conditions provided 
strong support for the determination. Water resources across large 
areas of the country are at serious risk from climate change, with 
effects on water supplies, water quality, and adverse effects from 
extreme events such as floods and droughts. The severity of risks and 
impacts is likely to increase over time with accumulating GHG 
concentrations and associated temperature increases and precipitation 
changes. Coastal areas are expected to face increased risks from storm 
and flooding damage to property, as well as adverse impacts from rising 
sea level such as land loss due to inundation, erosion, wetland 
submergence and habitat loss. Climate change is expected to result in 
an increase in electricity production for peak electricity demand, and 
extreme weather from climate change threatens energy, transportation, 
and water resource infrastructure. Climate change may exacerbate 
existing environmental pressures in certain settlements. In Alaska, 
indigenous communities are likely to experience disruptive impacts. 
Climate change is also very likely to fundamentally change U.S. 
ecosystems over the 21st century and to lead to predominantly negative 
consequences for biodiversity, ecosystem goods and services, and 
wildlife. Though there may be some benefits for agriculture and 
forestry in the next few decades, the body of evidence points towards 
increasing risks of net adverse impacts on U.S. food production, 
agriculture and forest productivity as average temperature continues to 
rise. Looking across all sectors discussed above, the risk and the 
severity of adverse impacts on welfare are expected to increase over 
time. Lastly, these impacts are global and may exacerbate problems 
outside the United States that raise humanitarian, trade, and national 
security issues for the United States.
---------------------------------------------------------------------------

    \182\ 74 FR at 66530-36.
---------------------------------------------------------------------------

    The Administrator concludes that the discussion in the 2009 
Endangerment Finding under CAA section 202(a) is equally compelling to 
support an endangerment finding under CAA section 231(a)(2)(A). In 
addition, the EPA has carefully reviewed the recent scientific 
conclusions in the assessments regarding human-induced

[[Page 54456]]

climate change impacts on welfare.\183\ The EPA finds that they further 
support finding endangerment under CAA section 231(a)(2)(A), as they 
are largely consistent with or strengthen the underlying science 
supporting the 2009 Endangerment Finding regarding observed and 
projected climate change risks and impacts to food production and 
agriculture; forestry; water resources; widespread snow and ice melt, 
sea level rise, and coastal areas; energy, infrastructure, and 
settlements; ocean acidification, ecosystems, and wildlife; and impacts 
on the U.S. population from climate change effects occurring outside of 
the United States. These key findings are described briefly here.
---------------------------------------------------------------------------

    \183\ The CAA states that ``[a]ll language referring to effects 
on welfare includes, but is not limited to, effects on soils, water, 
crops, vegetation, man-made materials, animals, wildlife, weather, 
visibility, and climate, damage to and deterioration of property, 
and hazards to transportation, as well as effects on economic values 
and on personal comfort and well-being, whether caused by 
transformation, conversion, or combination with other air 
pollutants.'' CAA section 302(h). This language is quite broad. 
Importantly, it is not an exclusive list due to the use of the term 
``includes, but is not limited to . . .'' Effects other than those 
listed here may also be considered effects on welfare.
---------------------------------------------------------------------------

    Regarding agriculture, the assessment literature cited in the 2009 
Endangerment Finding found potential for increased CO2 
levels to benefit yields of certain crops in the short term, but with 
considerable uncertainty. The body of evidence pointed towards 
increasing risk of net adverse impacts on U.S. food production and 
agriculture over time, with the potential for significant disruptions 
and crop failure in the future. The most recent assessments now have 
greater confidence that climate change will negatively affect U.S. 
agriculture over this century, and support finding endangerment under 
CAA section 231(a)(2)(A). Specifically, the USGCRP NCA3 concludes, 
``While some U.S. regions and some types of agricultural production 
will be relatively resilient to climate change over the next 25 years 
or so, others will increasingly suffer from stresses due to extreme 
heat, drought, disease, and heavy downpours. From mid-century on, 
climate change is projected to have more negative impacts on crops and 
livestock across the country.'' \184\ The IPCC AR5 concludes, ``Overall 
yields of major crops in North America are projected to decline 
modestly by mid-century and more steeply by 2100 among studies that do 
not consider adaptation (very high confidence).'' \185\ The IPCC AR5 
notes that in the absence of extreme events, climate change may benefit 
certain regions and crops, but that in North America significant 
harvest losses have been observed due to recent extreme weather events. 
In addition, the IPCC SREX assessment specifically notes that projected 
changes in extreme weather events will increase disaster risk in the 
agriculture sector.
---------------------------------------------------------------------------

    \184\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. 
Yohe, Eds., 2014: Climate Change Impacts in the United States: The 
Third National Climate Assessment. U.S. Global Change Research 
Program, p. 16.
    \185\ IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and 
Vulnerability. Part B: Regional Aspects. Contribution of Working 
Group II to the Fifth Assessment Report of the Intergovernmental 
Panel on Climate Change [Barros, V.R., C.B. Field, D.J. Dokken, M.D. 
Mastrandrea, K.J. Mach, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. 
Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. 
MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge 
University Press, Cambridge, p. 1462.
---------------------------------------------------------------------------

    Regarding forestry, the assessment literature cited in the 2009 
Endangerment Finding found that near-term benefits to forest growth and 
productivity in certain parts of the country from elevated 
CO2 concentrations and temperature increases to date are 
offset by longer-term risks from wildfires and the spread of 
destructive pests and disease that present serious adverse risks for 
forest productivity. The most recent assessments provide further 
support for finding endangerment under CAA section 231(a)(2)(A). Both 
the USGCRP NCA3 and the IPCC AR5 conclude that climate change is 
increasing risks to forest health from fire, tree disease and insect 
infestations, and drought. The IPCC AR5 also notes risks to forested 
ecosystems associated with changes in temperature, precipitation 
amount, and CO2 concentrations, which can affect species and 
ecological communities, leading to ecosystem disruption, 
reorganization, movement or loss. The NRC Arctic assessment states that 
climate change is likely to have a large negative impact on forested 
ecosystems in the high northern latitudes due to the effects of 
permafrost thaw and greater wildfire frequency, extent, and severity. 
The NRC Climate Stabilization Targets assessment found that for an 
increase in global average temperature of 1 to 2 [deg]C above pre-
industrial levels, the area burnt by wildfires in western North America 
will likely more than double.
    Regarding water resources, the assessment literature cited in the 
2009 Endangerment Finding concluded that increasing temperatures and 
increased variability in precipitation associated with climate change 
is expected to have adverse impacts on water quality and is likely to 
further constrain water quantity through changes in snowpack, increased 
risk of floods, drought, and other concerns such as water pollution. 
Similarly, the new assessments further support projections of water 
resource impacts associated with increased floods and short-term 
drought in most U.S. regions, and therefore support an endangerment 
finding under CAA section 231(a)(2)(A). The USGCRP NCA3 also finds 
that, ``[c]limate change is expected to affect water demand, 
groundwater withdrawals, and aquifer recharge, reducing groundwater 
availability in some areas.'' \186\ The IPCC AR5 finds that in part of 
the western United States, ``water supplies are projected to be further 
stressed by climate change, resulting in less water availability and 
increased drought conditions.'' \187\ The IPCC AR5 states, ``Throughout 
the eastern USA, water supply systems will be negatively impacted by 
lost snowpack storage, rising sea levels contributing to increased 
storm intensities and saltwater intrusion, possibly lower streamflows, 
land use and population changes, and other stresses.'' \188\ The IPCC 
AR5 also synthesizes recent studies that project a range of adverse 
climate impacts in North America to surface water quality (including to 
the Great Lakes), drinking water treatment/distribution, and sewage 
collection systems.
---------------------------------------------------------------------------

    \186\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. 
Yohe, Eds., 2014: Climate Change Impacts in the United States: The 
Third National Climate Assessment. U.S. Global Change Research 
Program, p. 70.
    \187\ IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and 
Vulnerability. Part B: Regional Aspects. Contribution of Working 
Group II to the Fifth Assessment Report of the Intergovernmental 
Panel on Climate Change [Barros, V.R., C.B. Field, D.J. Dokken, M.D. 
Mastrandrea, K.J. Mach, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. 
Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. 
MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge 
University Press, Cambridge, pp. 1456-1457.
    \188\ Ibid at p. 1457.
---------------------------------------------------------------------------

    The assessment literature cited in the 2009 Endangerment Finding 
found that the most serious potential adverse effects to coastal areas 
are the increased risk of storm surge and flooding in coastal areas 
from current and projected rates of sea level rise and more intense 
storms. Coastal areas also face other adverse impacts from sea level 
rise such as land loss due to inundation, erosion, wetland submergence, 
and habitat loss. The most recent assessments provide further evidence 
in line with the science supporting the 2009 Endangerment Finding, and 
support finding endangerment under CAA section 231(a)(2)(A). The USGCRP 
NCA3 finds, ``Sea level rise, combined with coastal storms, has 
increased the risk of erosion, storm surge damage, and flooding for

[[Page 54457]]

coastal communities, especially along the Gulf Coast, the Atlantic 
seaboard, and in Alaska.'' \189\
---------------------------------------------------------------------------

    \189\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. 
Yohe, Eds., 2014: Climate Change Impacts in the United States: The 
Third National Climate Assessment. U.S. Global Change Research 
Program, p. 9.
---------------------------------------------------------------------------

    The IPCC AR5 found that global sea levels rose 0.19 m (7.5 inches) 
from 1901 to 2010. Contributing to this rise was the warming of the 
oceans and melting of land ice from glaciers and ice sheets. It is 
likely that 275 gigatons per year of ice melted from land glaciers (not 
including ice sheets) from 1993-2009, and that the rate of loss of ice 
from the Greenland and Antarctic ice sheets increased substantially in 
recent years, to 215 gigatons per year and 147 gigatons per year 
respectively from 2002-2011. For context, 360 gigatons of ice melt is 
sufficient to cause global sea levels to rise one millimeter.
    The IPCC AR5, the USGCRP NCA3, and three of the new NRC assessments 
provide estimates of projected global average sea level rise. These 
estimates, while not always directly comparable as they assume 
different emissions scenarios and baselines, are at least 40 percent 
larger than, and in some cases more than twice as large as, the 
projected rise estimated in the IPCC AR4 assessment, which was referred 
to in the 2009 Endangerment Finding.\190\ The NRC Sea Level Rise 
assessment projects a global average sea level rise of 0.5 to 1.4 
meters by 2100. Change of this magnitude would be sufficient to lead to 
a relative rise in sea level even around the northern coasts of 
Washington State, where the land is still rebounding from the 
disappearance of the great ice sheets.\191\ The NRC National Security 
Implications assessment suggests that ``the Department of the Navy 
should expect roughly 0.4 to 2 meters global average sea-level rise by 
2100.'' \192\ The NRC Climate Stabilization Targets assessment states 
that a global average temperature increase of 3 [deg]C will lead to a 
global average sea level rise of 0.5 to 1 meter by 2100. While these 
NRC and IPCC assessments continue to recognize and characterize the 
uncertainty inherent in accounting for melting ice sheets in sea level 
rise projections, these revised estimates are consistent with the 
assessments underlying the 2009 Endangerment Finding, and support 
finding endangerment under CAA section 231(a)(2)(A).
---------------------------------------------------------------------------

    \190\ The 2007 IPCC AR4 assessment cited in 2009 Endangerment 
Finding estimated a projected sea level rise of between 0.18 and 
0.59 meters by the end of the century, relative to 1990. It should 
be noted that in 2007, the IPCC stated that including poorly 
understood ice sheet processes could lead to an increase in the 
projections.
    \191\ Sea level does not rise uniformly due to changes in winds, 
temperature patterns, land uplift or subsidence, and other factors. 
Therefore, relative sea level rise along any given point on the 
coast can vary from the global average.
    \192\ NRC, 2011: National Security Implications of Climate 
Change for U.S. Naval Forces. The National Academies Press, p. 28.
---------------------------------------------------------------------------

    Regarding climate impacts on energy, infrastructure and 
settlements, the 2009 Endangerment Finding cited the assessment 
literature's findings that temperature increases will change heating 
and cooling demand; that declining water quantity may adversely impact 
the availability of cooling water and hydropower in the energy sector; 
and that changes in extreme weather events will threaten energy, 
transportation, water, and other key societal infrastructure, 
particularly on the coast. The most recent assessments provide further 
evidence in line with the science supporting the 2009 Endangerment 
Finding, to support finding endangerment under CAA section 
231(a)(2)(A). For example, the USGCRP NCA3 finds, ``Coastal 
infrastructure, including roads, rail lines, energy infrastructure, 
airports, port facilities, and military bases, are increasingly at risk 
from sea level rise and damaging storm surges.'' \193\ The NRC Arctic 
assessment identifies threats to human infrastructure in the Arctic 
from increased flooding, erosion, and shoreline ice pile-up, or ivu, 
associated with summer sea ice loss and the increasing frequency and 
severity of storms.
---------------------------------------------------------------------------

    \193\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. 
Yohe, Eds., 2014: Climate Change Impacts in the United States: The 
Third National Climate Assessment. U.S. Global Change Research 
Program, p. 9.
---------------------------------------------------------------------------

    Regarding ecosystems and wildlife, the assessment literature cited 
in the 2009 Endangerment Finding discussed a number of impacts. These 
include a high confidence finding that substantial changes in the 
structure and functioning of terrestrial ecosystems are very likely to 
occur with a global warming greater than 2 to 3 [deg]C above pre-
industrial levels, with predominantly negative consequences for 
biodiversity and the provisioning of ecosystem goods and services. In 
addition, climate change and ocean acidification will likely impair a 
wide range of planktonic and other marine calcifiers such as corals. 
The recent assessments published since 2009 provide additional support 
for finding endangerment under CAA section 231(a)(2)(A). The USGCRP 
NCA3 concluded that ``The oceans are currently absorbing about a 
quarter of the carbon dioxide emitted to the atmosphere annually and 
are becoming more acidic as a result, leading to concerns about 
intensifying impacts on marine ecosystems . . . Over the last 250 
years, the oceans have absorbed 560 billion tons of CO2, increasing the 
acidity of surface waters by 30%. Although the average oceanic pH can 
vary on interglacial timescales, the current observed rate of change is 
roughly 50 times faster than known historical change.'' \194\
---------------------------------------------------------------------------

    \194\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. 
Yohe, Eds., 2014: Climate Change Impacts in the United States: The 
Third National Climate Assessment. U.S. Global Change Research 
Program, p. 48.
---------------------------------------------------------------------------

    The NRC Arctic assessment states that major marine and terrestrial 
biomes will likely shift poleward, with significant implications for 
changing species composition, food web structures, and ecosystem 
function. The NRC Climate Stabilization Targets assessment found that 
coral bleaching events will likely increase in frequency and severity 
due warming sea surface temperatures and that ocean acidification will 
likely reduce coral shell and skeleton growth and increase erosion of 
coral reefs. The NRC Understanding Earth's Deep Past assessment notes 
four of the five major coral reef crises of the past 500 million years 
were caused by GHG-induced ocean acidification and warming that 
followed releases of GHGs of similar magnitude to the emissions 
increases expected over the next hundred years. Similarly, the NRC 
Ocean Acidification assessment finds that ``[t]he chemistry of the 
ocean is changing at an unprecedented rate and magnitude due to 
anthropogenic CO2 emissions; the rate of change exceeds any 
known to have occurred for at least the past hundreds of thousands of 
years.'' \195\ The assessment notes that the full range of consequences 
is still unknown, but the risks ``threaten coral reefs, fisheries, 
protected species, and other natural resources of value to society.'' 
\196\ The IPCC AR5 also projects biodiversity losses in marine 
ecosystems, especially in the Arctic and tropics.
---------------------------------------------------------------------------

    \195\ NRC, 2010: Ocean Acidification: A National Strategy to 
Meet the Challenges of a Changing Ocean. The National Academies 
Press, p. 5.
    \196\ Ibid.
---------------------------------------------------------------------------

    The IPCC AR5 found that annual mean Arctic sea ice has been 
declining at 3.5 to 4.1 percent per decade, and Northern Hemisphere 
snow cover extent has decreased at about 1.6 percent per decade for 
March and 11.7 percent per decade for June. The USGCRP NCA3 finds that 
``rising temperatures across the U.S. have reduced lake ice, sea ice, 
glaciers, and seasonal snow cover over the last few decades.'' \197\ 
These changes

[[Page 54458]]

are projected to continue, threatening seasonal water availability and 
ecosystems reliant on ice and snow cover.
---------------------------------------------------------------------------

    \197\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. 
Yohe, Eds., 2014: Climate Change Impacts in the United States: The 
Third National Climate Assessment. U.S. Global Change Research 
Program, p. 46.
---------------------------------------------------------------------------

a. Welfare Impacts of Climate Change on Vulnerable Populations
    In general, climate change impacts related to welfare are expected 
to be unevenly distributed across different regions of the United 
States and are expected to have a greater impact on certain 
populations, such as indigenous peoples and the poor. The USGCRP NCA3 
finds climate change impacts such as the rapid pace of temperature 
rise, coastal erosion and inundation related to sea level rise and 
storms, ice and snow melt, and permafrost thaw are affecting indigenous 
people in the United States. Particularly in Alaska, critical 
infrastructure and traditional livelihoods are threatened by climate 
change, and ``[i]n parts of Alaska, Louisiana, the Pacific Islands, and 
other coastal locations, climate change impacts (through erosion and 
inundation) are so severe that some communities are already relocating 
from historical homelands to which their traditions and cultural 
identities are tied.'' \198\ The IPCC AR5 notes, ``Climate-related 
hazards exacerbate other stressors, often with negative outcomes for 
livelihoods, especially for people living in poverty (high confidence). 
Climate-related hazards affect poor people's lives directly through 
impacts on livelihoods, reductions in crop yields, or destruction of 
homes and indirectly through, for example, increased food prices and 
food insecurity.'' \199\
---------------------------------------------------------------------------

    \198\ Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. 
Yohe, Eds., 2014: Climate Change Impacts in the United States: The 
Third National Climate Assessment. U.S. Global Change Research 
Program, p. 17.
    \199\ IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and 
Vulnerability. Part A: Global and Sectoral Aspects. Contribution of 
Working Group II to the Fifth Assessment Report of the 
Intergovernmental Panel on Climate Change [Field, C.B., V.R. Barros, 
D.J. Dokken, K.J. Mach, M.D. Mastrandrea, T.E. Bilir, M. Chatterjee, 
K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. 
Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. 
Cambridge University Press, p. 796.
---------------------------------------------------------------------------

b. Other Considerations Regarding Endangerment to Welfare
    In the 2009 Endangerment Finding, the Administrator considered 
impacts on the U.S. population from climate change effects occurring 
outside of the United States, such as national security concerns that 
may arise as a result of climate change impacts in other regions of the 
world. The most recent assessments provide further evidence in line 
with the science supporting the 2009 Endangerment Finding, and further 
support finding endangerment under CAA section 231(a)(2)(A). The NRC 
Climate and Social Stress assessment found that it would be ``prudent 
for security analysts to expect climate surprises in the coming decade 
. . . and for them to become progressively more serious and more 
frequent thereafter.'' \200\ The NRC National Security Implications 
assessment recommends preparing for increased needs for humanitarian 
aid; responding to the effects of climate change in geopolitical 
hotspots, including possible mass migrations; and addressing changing 
security needs in the Arctic as sea ice retreats.
---------------------------------------------------------------------------

    \200\ NRC, 2013: Climate and Social Stress: Implications for 
Security Analysis. The National Academies Press, p. 18.
---------------------------------------------------------------------------

    In addition, the NRC Abrupt Impacts report examines the potential 
for tipping points, thresholds beyond which major and rapid changes 
occur in the Earth's climate system, as well as in natural and human 
systems that are impacted by the changing climate. The Abrupt Impacts 
report did find less cause for concern than some previous assessments 
regarding some abrupt events within the next century, such as 
disruption of the oceanic Atlantic Meridional Overturning Circulation 
(AMOC) and sudden releases of high-latitude methane from hydrates and 
permafrost. But, the same report found that the potential for abrupt 
changes in ecosystems, weather and climate extremes, and groundwater 
supplies critical for agriculture now seem more likely, severe, and 
imminent. The assessment found that some abrupt changes were already 
underway (e.g., Arctic sea ice retreat and increases in extinction risk 
due to the speed of climate change), and cautioned that even abrupt 
changes such disruption to the AMOC that are not expected in this 
century can have severe impacts if/when they happen, such as 
interference with the global transport of oceanic heat, salt, and 
carbon.
c. Responses to Key Comments on Endangerment to Welfare
    Public comments supported the EPA's summary of the scientific 
information and finding that the well-mixed GHG air pollution is 
reasonably anticipated to endanger welfare under CAA section 
231(a)(2)(A). Commenters cited a number of examples of climate impacts 
relevant to welfare including sea level rise and coastal erosion, 
species range changes and extinctions, and reduced water availability 
due to changes in snowpack and timing of snow melt. Some commenters 
also agreed with the EPA's summary of welfare impacts to certain 
vulnerable populations and emphasized that certain populations are more 
vulnerable to the welfare impacts of climate change, in particular 
tribes and indigenous groups. No commenters disagreed with the EPA's 
summary of the scientific information or with its conclusion on 
endangerment to welfare. The EPA agrees with the commenters that this 
finding of endangerment to welfare under CAA section 231(a)(2)(A) is 
well supported by the scientific assessment literature; that it covers 
a range of risks associated with climate change threats to food 
production and agriculture, forestry, water resources, sea level rise 
and coastal areas, energy, infrastructure, and settlements, and 
ecosystems and wildlife; and that certain populations are more 
vulnerable to climate change welfare risks and impacts.
D. Summary of the Administrator's Endangerment Finding Under CAA 
Section 231
    In sum, the Administrator finds, for purposes of CAA section 
231(a)(2)(A), that elevated atmospheric concentrations of the six well-
mixed GHGs constitute air pollution that endangers both public health 
and welfare of current and future generations. In this final action 
under CAA section 231(a)(2)(A), the EPA is informed by and places 
considerable weight on the extensive scientific and technical evidence 
in the record supporting the 2009 Endangerment Finding under CAA 
section 202(a), including the major, peer-reviewed scientific 
assessments used to address the question of whether GHGs in the 
atmosphere endanger public health and welfare, and on the analytical 
framework and conclusions upon which the EPA relied in making that 
finding. This final finding under section 231(a)(2)(A) accounts for the 
EPA's careful consideration of the scientific and technical record for 
the 2009 Endangerment Finding, and of the new, major scientific 
assessments issued since closing the administrative record for the 2009 
Endangerment Finding, and consideration of public comments. No recent 
information or assessments published since late 2009 suggest that it 
would be reasonable for the EPA to now reach a different or contrary 
conclusion for purposes of CAA section 231(a)(2)(A) than the Agency 
reached for purposes of section 202(a); instead, the new, major 
scientific assessments

[[Page 54459]]

further support finding endangerment under CAA section 231(a)(2)(A). In 
making this finding for purposes of section 231(a)(2)(A), we are not 
reopening or revisiting the 2009 Endangerment Finding under CAA section 
202(a). To the contrary, in light of the recent judicial decisions 
upholding that finding, the EPA believes the 2009 Endangerment Finding 
is firmly established and well settled.\201\ Moreover, there is no need 
for the EPA to reopen or revisit that finding for purposes of CAA 
section 202(a) in order for the Administrator to rely on its analyses 
and conclusions, supported by more recent studies, in support of making 
an additional endangerment finding under section 231(a)(2)(A) of the 
CAA. Today's final endangerment finding, although significantly 
informed by the scientific information and the EPA's prior discussion 
of that information in the 2009 Endangerment Finding, is solely for 
purposes of CAA section 231(a)(2)(A).
---------------------------------------------------------------------------

    \201\ CRR, 684 F.3d at 117 (D.C. Cir. 2012), reh'g en banc 
denied, 2012 U.S. App. LEXIS 25997, 26313, 26315 (D.C. Cir. 2012); 
see also Utility Air Reg. Group v. EPA, 134 S. Ct. at 2438 (2014).
---------------------------------------------------------------------------

V. The Administrator's Cause or Contribute Finding for Greenhouse Gases 
Emitted by Certain Classes of Engines Used by Covered Aircraft Under 
CAA Section 231

    As noted above, the Administrator defines the air pollution for 
purposes of the endangerment finding under CAA section 231(a)(2)(A) to 
be the aggregate of six well-mixed GHGs in the atmosphere, and finds 
that such air pollution endangers public health and welfare of current 
and future generations. The second step of the two-part endangerment 
test for this finding is for the Administrator to determine whether the 
emission of any air pollutant from certain classes of aircraft engines 
used by certain aircraft causes or contributes to this endangering air 
pollution. This is referred to as the cause or contribute finding, and 
is the second finding by the Administrator in this action under CAA 
section 231(a)(2)(A).
    Section V.A of this document describes the Administrator's 
reasoning for using under CAA section 231(a)(2) the same definition and 
scope of the GHG air pollutant that was used in the 2009 Endangerment 
Finding under CAA section 202(a). Section V.B puts forth the 
Administrator's finding that emissions of well-mixed GHGs from certain 
classes of aircraft engines used in covered aircraft contribute to the 
air pollution which endangers public health and welfare under CAA 
section 231(a)(2)(A). The EPA's responses to some of the most 
significant comments for the cause or contribute finding are provided 
later in section V.C. Responses to all significant issues raised by the 
comments on the cause or contribute finding are contained in the 
Response to Comments document, which is organized by subject area 
(found in docket EPA-HQ-OAR-2014-0828).

A. The Air Pollutant

1. Definition of Air Pollutant
    Under section 231(a)(2)(A), the Administrator is to determine 
whether emissions of any air pollutant from any class or classes of 
aircraft engines cause or contribute to air pollution which may 
reasonably be anticipated to endanger public health or welfare. As with 
the 2009 Endangerment Finding that the EPA conducted for purposes of 
CAA section 202(a), when making a cause or contribute finding under 
section 231(a)(2), the Administrator must first define the air 
pollutant being evaluated. The Administrator has considered the logical 
relationship between the GHG air pollution and air pollutant: While the 
air pollution is the concentration (e.g., stock) of the well-mixed GHGs 
in the atmosphere, the air pollutant is the same combined grouping of 
the well-mixed GHGs, the emissions of which are analyzed for 
contribution (e.g., the flow into the stock). See 74 FR at 66536 
(similar discussion with respect to the finding for CAA section 
202(a)). For purposes of section 231(a)(2)(A), the Administrator is 
defining the air pollutant as the same combined grouping of the six 
well-mixed GHGs that comprises the air pollution. Accordingly, the 
Administrator is using the same definition of the air pollutant that 
was used in the 2009 Endangerment Finding for purposes of CAA section 
202(a), namely, the aggregate group of the same six well-mixed GHGs: 
CO2, methane, nitrous oxide, hydrofluorocarbons, 
perfluorocarbons, and sulfur hexafluoride. See 74 FR at 66536-37 
(discussing the definition of the GHG air pollutant with respect to the 
finding for CAA section 202(a)). That is, as was done for the 2009 
Endangerment Finding, the Administrator is defining a single air 
pollutant made up of these six GHGs in this action under CAA section 
231(a)(2)(A).
    To reiterate what the Agency has previously stated on this subject, 
this collective approach for the contribution test is consistent with 
the treatment of GHGs by those studying climate change science and 
policy, where it is common practice to evaluate GHGs on a collective, 
CO2-equivalent basis.\202\ This collective approach to 
defining the air pollutant is not unique; grouping of many substances 
with common attributes as a single pollutant is common practice under 
the CAA, for example with particulate matter and volatile organic 
compounds (VOC). As noted in section IV.B, these six substances share 
common attributes that support their grouping to define the air 
pollution for purposes of the endangerment finding. These same common 
attributes also support the Administrator grouping these six well-mixed 
GHGs for purposes of defining the air pollutant for this cause or 
contribute finding under CAA section 231(a)(2)(A).
---------------------------------------------------------------------------

    \202\ As detailed in the 2009 Endangerment Finding proposal (74 
FR at 18904) and continuing today, the UNFCCC, the U.S. and other 
Parties report their annual emissions of the six GHGs in 
CO2-equivalent units. This facilitates comparisons of the 
multiple GHGs from different sources and from different countries, 
and provides a measure of the collective warming potential of 
multiple GHGs. Emissions of different GHGs are compared using GWPs, 
which as described in section IV.B of this document are measures of 
the warming impact of a pulse of emissions of a given substance over 
100 years relative to the same mass of CO2. Therefore, 
GWP-weighted emissions are measured in teragrams of CO2 
equivalent (Tg CO2eq). One teragram (Tg) = 1 million 
metric tons = 1 megatonne (Mt). 1 metric ton = 1,000 kilograms = 
1.102 short tons = 2,205 lbs. The EPA's Greenhouse Gas Reporting 
Program (https://www.epa.gov/ghgreporting/ (last accessed 
April 8, 2016)) also reports GHG emissions on a CO2-
equivalent basis, recognizing the common and collective treatment of 
these six well-mixed GHGs.
---------------------------------------------------------------------------

    The Administrator recognizes that in this case, the aircraft 
engines covered by this document emit two of the six gases, but not the 
other four gases. Nonetheless, it is entirely appropriate, and in 
keeping with the 2009 Endangerment Finding and past EPA practice, for 
the Administrator to define the air pollutant under CAA section 
231(a)(2)(A) in a manner that recognizes the shared relevant properties 
of all these six gases, even though they are not all emitted from the 
classes of sources before her.\203\ For example, a source may emit only 
20 of the possible 200-plus chemicals that meet the definition of VOC 
in the EPA's regulations, but that source is evaluated based on its 
emissions of VOC and not on its emissions of the 20 chemicals by name. 
The fact that these six substances within the definition of GHGs share 
common, relevant attributes is true regardless of the type of sources 
being evaluated for

[[Page 54460]]

contribution. Moreover, the reasonableness of grouping these chemicals 
as a single air pollutant does not turn on the particular source 
category. By using the definition of the air pollutant as comprised of 
the six GHGs with common attributes, the Administrator is taking 
account of these shared attributes and how they are relevant to the air 
pollution that endangers public health and welfare.
---------------------------------------------------------------------------

    \203\ In the 2009 Endangerment Finding, the Administrator found 
that four of the six gases that were included in the definition of 
the air pollutant were emitted by section 202 sources. 74 FR at 
66537.
---------------------------------------------------------------------------

    In fact, as explained in the 2009 Endangerment Finding, Congress 
has given the EPA broad discretion to determine that appropriate 
combinations of compounds should be treated as a single air pollutant. 
74 FR at 66537. Section 302(g) of the CAA defines ``air pollutant'' as 
``any air pollutant agent or combination of such agents. . . .'' Thus, 
it is clear that the term ``air pollutant'' is not limited to 
individual chemical compounds. Moreover, in determining that GHGs are 
within the scope of this definition, the Supreme Court described 
section 302(g) as a ``sweeping'' and ``capacious'' definition that 
unambiguously included GHGs, which are ``unquestionably `agents' of air 
pollution.'' Massachusetts v. EPA, 549 U.S. at 528, 532, 529 n. 26. 
Although the Court did not interpret the term ``combination of'' air 
pollution agents, there is no reason to interpret this phrase more 
narrowly in this context. Congress used the term ``any'' and did not 
qualify the kind of combinations that EPA could define as a single air 
pollutant.
2. The Definition of Air Pollutant May Include Substances Not Emitted 
by CAA Section 231(a)(2) Sources.
    Similar to the discussion in section IV.B.6 for the definition of 
``air pollution'' for purposes of the endangerment finding under CAA 
section 231(a)(2)(A), many commenters highlighted the fact that 
aircraft engines emit only two of the six well-mixed GHGs that together 
are defined as the ``air pollutant'' for purposes of the cause or 
contribute finding under section 231(a)(2)(A) of the CAA. Commenters 
point out that the majority of emissions are CO2, while 
nitrous oxide emissions are described as ``nominal (<1%)'' or 
``trace.'' Some commenters ultimately concluded that the EPA's approach 
to defining the air pollutant as an aggregate group of six gases is 
acceptable, but that the scope of future regulations should be limited 
to CO2. One commenter agreed with the Agency's evaluation of 
the six GHGs based on their common attributes, but questioned the EPA's 
decision to aggregate the six gases rather than considering them 
individually for purposes of making the findings. Other commenters 
disagreed with the EPA and requested limiting the definition of air 
pollutant in this action to CO2 or to CO2 and 
nitrous oxide.
    The EPA disagrees with comments regarding changing the definition 
of the air pollutant to limit it to only those GHGs that are emitted 
from aircraft or to CO2 only. The EPA has explained both in 
the 2009 Endangerment Finding under CAA section 202(a) and in the 
proposed findings under CAA section 231(a)(2)(A) that it is reasonable 
and appropriate for the EPA to consider the logical relationship 
between the GHG air pollution and air pollutant when defining the air 
pollutant. The purpose of this cause or contribute inquiry is to 
determine whether emissions of an air pollutant from certain aircraft 
engines cause or contribute to the endangering GHG air pollution. As 
described in section IV.B of this document, the endangering GHG air 
pollution under consideration is defined as the aggregate group of the 
six well-mixed GHGs based on shared characteristics and common 
attributes relevant to climate change science and policy'' \204\--a 
rationale that does not take into consideration emission source(s). 
Similarly, the definition of the air pollutant in this cause or 
contribute inquiry establishes well-mixed GHGs as a single air 
pollutant comprised of six substances with common attributes. The 
Administrator is giving effect to the shared attributes of the six 
well-mixed GHGs and how they are relevant to the air pollution to which 
they contribute. Thus, it is also reasonable for the EPA to evaluate 
contribution for those gases in the aggregate, rather than 
individually, to ensure a like-to-like comparison of aggregate 
emissions contributing to an aggregate stock (atmospheric 
concentration) of endangering GHG air pollution.
---------------------------------------------------------------------------

    \204\ 74 FR at 66517-19; 80 FR at 37774-85.
---------------------------------------------------------------------------

    The EPA recognized in the proposed findings that aircraft emit two 
of the six well-mixed GHGs, but stated that nonetheless it is entirely 
reasonable and appropriate, and in keeping with the 2009 Endangerment 
Finding under CAA section 202(a) and other past EPA practice, for the 
Administrator to group into a single class those substances that 
possess shared relevant properties, even though they are not all 
emitted from the classes of sources before her.\205\ The fact that 
these six substances share these common, relevant attributes is true 
regardless of the source category being evaluated for contribution. 
After considering all the comments, this continues to be the EPA's 
view. Moreover, this approach to defining an air pollutant as a 
grouping of many substances is not unique to GHGs, but rather is common 
practice under the CAA. For example, the EPA has heavy-duty truck 
standards applicable to VOCs and PM, but it is highly unlikely that 
heavy-duty trucks emit every substance that is included in the group 
defined as VOC or PM. See 40 CFR 51.100(s) (defining volatile organic 
compound (VOC) as ``any compound of carbon, excluding carbon monoxide, 
carbon dioxide, carbonic acid, metallic carbides or carbonates, and 
ammonium carbonate, which participates in atmospheric photochemical 
reactions''; a list of exemptions are also included in the definition); 
40 CFR 51.100(oo) (defining particulate matter (PM) as ``any airborne 
finely divided solid or liquid material with an aerodynamic diameter 
smaller than 100 micrometers'').
---------------------------------------------------------------------------

    \205\ 80 FR at 37774-85, and 37787.
---------------------------------------------------------------------------

    Grouping these six substances as one air pollutant is just as 
reasonable for the contribution analysis undertaken for CAA section 
231(a)(2) sources that emit one subset of the six substances as it was 
for the category of sources that emits another subset under CAA section 
202(a). In other words, it is not necessarily the source category, 
motor vehicles or aircraft engines, being evaluated for contribution 
that determines the reasonableness of defining a group air pollutant 
based on the shared attributes of the group's constituent substances. 
Even if the EPA defined the air pollutant as the group of two compounds 
emitted by CAA section 231(a)(2) sources, it would not change the 
result. The Administrator would make the same contribution finding (as 
described later in section V.B.), as it would have no material effect 
on the emissions comparisons discussed in section V.B.
    The question of limits to the scope of future regulations is 
outside of the scope of this action because the EPA has neither 
proposed nor is finalizing in this action any such regulatory 
standards. This final action does not itself impose any requirements on 
source categories under CAA section 231. Thus, the EPA anticipates that 
this question could be raised and considered, as needed, in the 
standard-setting phase of the regulatory process, and invites potential 
commenters to submit their views on this issue in response to EPA's 
anticipated future notice of proposed rulemaking on standards.
    Another commenter expressed concern about the EPA's proposed 
contribution finding because it does not differentiate between 
CO2 emissions that result from combustion of fossil

[[Page 54461]]

fuels and those that result from ``combustion of biomass or biofuels 
derived from herbaceous crops or crop residues, as well as biogenic 
CO2 emissions associated with the production, gathering and 
processing of crops or crop residues used in bio-based products 
including fuels.'' \206\ The commenter argues that such crop-related 
biogenic CO2 emissions should be excluded from the 
contribution finding because the CO2 released back to the 
atmosphere when emitted from crop-derived biogenic sources contains the 
same carbon that was previously removed or sequestered from 
CO2 in the atmosphere, and thus does not contribute to 
elevated atmospheric concentrations of the six well-mixed GHGs.
---------------------------------------------------------------------------

    \206\ Biogenic CO2 Coalition, 2015: Comments on EPA's 
Proposed Finding That Greenhouse Gas Emissions From Aircraft Cause 
or Contribute to Air Pollution That May Reasonably Be Anticipated To 
Endanger Public Health and Welfare, 80 FR 37757 (July 1, 2015). 
Docket ID number EPA-HQ-OAR-2014-0828-0916. Available at 
www.regulations.gov (last accessed April 11, 2016).
---------------------------------------------------------------------------

    Consistent with the previously discussed response to the commenter 
in the discussion of the definition of air pollution being used under 
CAA section 231(a)(2)(A), the EPA reiterates that the Administrator 
defines the relevant air pollutant considered in the contribution 
finding as the aggregate group of the six well-mixed GHGs based on 
shared physical characteristics and common attributes relevant to 
climate change science and policy, and does not include consideration 
of the source of the air pollutant. In the record for the 2009 
Endangerment Finding under CAA section 202(a), the Agency stated that 
``all CO2 emissions, regardless of source, influence 
radiative forcing equally once it reaches the atmosphere and therefore 
there is no distinction between biogenic and non-biogenic 
CO2 regarding the CO2 and the other well-mixed 
GHGs within the definition of air pollution that is reasonably 
anticipated to endanger public health and welfare.'' \207\ The EPA 
continues to hold that position in these findings under CAA section 
231(a)(2)(A), which is supported by the evidence before it. First, the 
fact that these CO2 emissions originate from combustion of 
carbon-based fuels created through different processes is not relevant 
to defining the air pollutant that contributes to the endangering air 
pollution. The origin and constitution of a fuel prior to its 
combustion and subsequent emission into the atmosphere has no bearing 
on the fact that CO2 and the other well-mixed GHGs are all 
sufficiently long lived to become well mixed in the atmosphere, 
directly emitted, of well-known radiative forcing, and generally 
grouped and considered together in climate change scientific and policy 
forums as the primary driver of climate change. A molecule of biogenic 
CO2 has the same radiative forcing effect as a molecule of 
fossil-fuel derived CO2. In other words, no matter the 
original source of the CO2, the behavior of the 
CO2 molecules in the atmosphere in terms of radiative 
forcing, chemical reactivity, and atmospheric lifetime is effectively 
the same. Any differential treatment of biogenic CO2 in the 
context of the contribution finding under CAA section 231(a)(2)(A) 
would be inconsistent with the primary scientific basis for the 
grouping of the six well-mixed GHGs as a single class for purposes of 
identifying the air pollutant (and air pollution, as explained in 
section IV.B.1). A more detailed response to the issues raised in this 
comment can be found in the Response to Comments document in the 
docket.
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    \207\ EPA, 2009. Response to Comments document, Volume 9: The 
Endangerment Finding, EPA-HQ-OAR-2009-0171-11676. Available at 
www.regulations.gov (last accessed April 11, 2016).
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B. The Administrator's Finding Under CAA Section 231(a)(2)(A) That 
Greenhouse Gas Emissions From Certain Classes of Aircraft Engines Used 
in Certain Aircraft Cause or Contribute to Air Pollution That May Be 
Reasonably Anticipated To Endanger Public Health and Welfare

    Under CAA section 231(a)(2)(A), the Administrator finds that 
emissions of the six well-mixed GHGs from classes of engines used in 
U.S. covered aircraft, which are subsonic jet aircraft with a maximum 
takeoff mass (MTOM) greater than 5,700 kilograms and subsonic propeller 
driven (e.g., turboprop) aircraft with a MTOM greater than 8,618 
kilograms, contribute to the air pollution that endangers public health 
and welfare. The Administrator is not at this time making a 
contribution finding regarding GHG emissions from engines not used in 
covered aircraft (i.e., those used in smaller turboprops, smaller jet 
aircraft, piston-engine aircraft, helicopters and military aircraft), 
or regarding the emission of other substances emitted by aircraft 
engines. A detailed discussion of covered aircraft and their GHG 
emissions data is provided below in section V.B.4.
    The Administrator reached her decision after reviewing emissions 
data on the contribution of covered aircraft under CAA section 231(a) 
relative to both U.S. GHG and global GHG emissions inventories. It is 
the Administrator's judgment that the collective GHG emissions from the 
classes of engines used in U.S. covered aircraft clearly contribute to 
endangering GHG pollution, whether the comparison is--as described 
later in Tables V.1 and V.3 of sections V.B.4.a and V.B.4.b 
respectively--to domestic GHG inventories (10 percent of all U.S. 
transportation GHG emissions, representing 2.8 percent of total U.S. 
emissions), to global GHG inventories (26 percent of total global 
aircraft GHG emissions representing 2.7 percent of total global 
transportation emissions and 0.4 percent of all global GHG emissions), 
or if using a combination of domestic and global inventory comparisons. 
Both domestic and global comparisons, independently and jointly, 
support the contribution finding under CAA section 
231(a)(2)(A).208 209 210 Making this cause or contribute 
finding for engines used in U.S. covered aircraft results in the vast 
majority (89 percent) of total U.S. aircraft GHG emissions being 
included in this determination (as described later in Table V.1 of 
section V.B.4.a.). Covered U.S. aircraft GHG emissions are from 
aircraft that operate in and from the U.S. and thus contribute to 
emissions in the U.S. This includes emissions from U.S. domestic 
flights, and emissions from U.S. international bunker flights 
(emissions from the combustion of fuel used by aircraft departing the 
U.S., regardless of whether they are a U.S. flagged carrier--also 
described as emissions from combustion of U.S. international bunker 
fuels \211\). In addition, the Administrator based her decision on all 
the information in the record for this finding, including the public 
comments received on the proposed finding.
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    \208\ U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions 
and Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and 
Radiation, EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed 
June 14, 2016).
    \209\ IPCC, 2014: Climate Change 2014: Mitigation of Climate 
Change. Contribution of Working Group III to the Fifth Assessment 
Report of the Intergovernmental Panel on Climate Change [Edenhofer, 
O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, 
A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J. 
Savolainen, S. Schl[ouml]mer, C. von Stechow, T. Zwickel and J.C. 
Minx (eds.)]. Cambridge University Press, 1435 pp.
    \210\ The domestic inventory comparisons are for the year 2014, 
and global inventory comparisons are for the year 2010. The 
rationale for the different years is discussed later in section 
V.B.4.
    \211\ For example, a flight departing Los Angeles and arriving 
in Tokyo, regardless of whether it is a U.S. flagged carrier, is 
considered a U.S. international bunker flight. A flight from London 
to Hong Kong is not.

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[[Page 54462]]

1. The Administrator's Approach in Making This Finding
    As it did for the 2009 Endangerment Finding under CAA section 
202(a), and consistent with prior practice and current science, under 
this CAA section 231(a)(2)(A) contribution finding the EPA uses annual 
emissions as a reasonable proxy for contributions to the endangering 
air pollution, i.e., the elevated atmospheric concentrations of the six 
well-mixed GHGs. Cumulative anthropogenic emissions are primarily 
responsible for the observed change in GHG concentrations in the 
atmosphere (i.e., the fraction of a country's or an economic sector's 
cumulative emissions compared to global GHG emissions over a long time 
period will be roughly equal to the fraction of the change in 
concentrations attributable to that country or economic sector); 
likewise, annual GHG emissions are a reasonable proxy for annual 
incremental changes in atmospheric GHG concentrations.
    There are a number of possible ways of assessing whether a source's 
emissions of air pollutants cause or contribute to the endangering air 
pollution, and no single approach is required or has been used 
exclusively in previous determinations under the CAA. Because under 
this CAA section 231(a)(2)(A) action the air pollution against which 
the contribution of air pollutant emissions is being evaluated is the 
six well-mixed GHGs, one reasonable starting point for a contribution 
analysis is a comparison of the emissions of the air pollutant from the 
aircraft under consideration to the total U.S. and total global 
emissions of these six GHGs. The Administrator recognizes that there 
are other valid comparisons that can be considered in evaluating 
whether emissions of the air pollutant cause or contribute to the 
combined concentration of these six GHGs. To inform the Administrator's 
assessment, section V.B.4 presents the following types of simple and 
straightforward comparisons of covered U.S. aircraft GHG emissions:
     As a share of current total U.S. GHG emissions;
     As a share of current U.S. transportation GHG emissions;
     As a share of current total global GHG emissions; and
     As a share of the current global transportation GHG 
emissions.
    All annual GHG emissions data are reported on a CO2-
equivalent (CO2eq) basis, which as described above is a 
commonly used metric to convert GHG emissions into standard units so 
they can be compared. This approach is consistent with how the EPA 
determined contribution for GHGs under section 202(a) of the CAA in 
2009.
2. Details of the Administrator's Approach in Making This Cause or 
Contribute Finding
    The Administrator believes that consideration of the global context 
is important for the cause or contribute finding under CAA section 
231(a)(2)(A), but that the analysis should not solely consider the 
global context. GHG emissions from engines used in U.S. covered 
aircraft will become globally well-mixed in the atmosphere, and thus 
will have an effect not only on the U.S. regional climate but also on 
the global climate as a whole, for many decades to come. It is the 
Administrator's view that it is reasonable for the cause or contribute 
analysis conducted under CAA section 231(a)(2)(A) for GHGs emitted by 
covered U.S. aircraft engines to be consistent with the reasoning 
supporting the 2009 GHG cause or contribute finding under CAA section 
202, as the relevant statutory provisions are parallel and as the 
pollutant is the same. Accordingly, the Administrator finds a positive 
cause or contribute finding for GHG emissions from engines used in U.S. 
covered aircraft is justified whether only the domestic context is 
considered, only the global context is considered, or both the domestic 
and global GHG emissions comparisons are viewed in combination. Both 
domestic and global comparisons, independently and jointly, are equally 
important for the finding.
    In the 2009 CAA section 202(a) cause or contribute finding, the 
Administrator considered the totality of the circumstances in order to 
best understand the role played by CAA section 202(a) source categories 
in emitting air pollutants that contribute to endangering GHG air 
pollution, consistent with Congress' intention for EPA to consider the 
cumulative impact of all emissions from sources to the endangering air 
pollution. In that context, the global nature of the air pollution 
problem and the breadth of countries and sources emitting GHGs meant 
that no single country or source category dominated contribution to the 
endangering air pollution on the global scale.\212\ As was the case in 
2009, it is still true that no single country or GHG source category 
dominates contribution to the collective stock of endangering GHG air 
pollution on the global scale, and contributions from individual GHG 
source categories may appear small in comparison to the total stock, 
when, in fact, they are very important contributors in terms of both 
absolute emissions or in comparison to GHG emissions from other source 
categories, globally or within the United States. That is, because 
climate change is a global problem that results from global GHG 
emissions, it is more the result of numerous and varied sources each 
emitting what may seem to be smaller percentages of GHG pollutants 
compared to the total stock of GHG pollution, than typically might be 
encountered when tackling solely regional or local environmental issues 
for different kinds of pollutants that may have more of a direct impact 
on receptors located in the relative vicinity of the polluting sources 
(such as emissions of lead, for example, or sulfur dioxide without 
consideration of its role as possible precursor to particulate matter). 
It is reasonable for the Administrator to take these circumstances into 
account in making a contribution determination regarding emissions from 
sources of GHGs, as the impacts from GHGs are not spatially or 
temporally limited.\213\ Therefore, in order to address the risks 
associated with global climate change, it is less likely that a single 
``majority'' contributing source category could be identified and 
controlled such that the risks could be eliminated, without the need to 
consider contributions to the endangering stock of air pollution from 
``minority'' source categories that may present smaller percentages of 
contribution than may sometimes be encountered when tackling regional 
or local environmental threats presented by a single or limited set of 
dominant sources. Thus, in addressing GHG risks, it will be, as the 
Supreme Court suggested in Massachusetts v. EPA, necessary for agencies 
to take an incremental approach to resolving the larger GHG 
endangerment issue, as ``[a]gencies, like legislatures, do not 
generally resolve massive problems in one fell regulatory swoop. . . . 
They instead whittle away at them over time, refining their preferred 
approach as circumstances change and as they develop a more nuanced 
understanding of how best to proceed.'' 549 U.S. 497, 524 (2007) 
(citations omitted). The Administrator continues to believe that the 
unique, global aspects of the climate change problem--including that 
from a percentage perspective there are no dominating sources or 
countries for GHG emissions contributing to the endangering GHG air 
pollution and that the global problem is due more to the GHG emissions 
contributed from

[[Page 54463]]

numerous and varied sources--justify consideration of contribution to 
the endangering air pollution at lower percentage levels than the EPA 
typically might encounter when analyzing contribution towards a more 
localized air pollution problem. This is not to suggest, however, that 
all or even most local or regional air pollution problems are due to a 
single or small set of sources. For example, regional haze and ambient 
concentrations of concern for ozone, carbon monoxide, and particulate 
matter are commonly the result of a variety and great number of 
contributing sources, and the EPA has frequently approached such 
problems by incrementally regulating a set of sources that, in 
isolation, is not contributing the dominant share of air pollutants to 
the stock of air pollution, but is contributing a meaningful share. 
This approach has been affirmed by reviewing courts as reasonable and 
lawful under the CAA. See, e.g., Bluewater Network v. EPA, 370 F.3d 1 
(D.C. Cir. 2004). Thus, the Administrator, similar to the approach 
taken in the 2009 GHG cause or contribute finding under CAA section 
202(a), is under CAA section 231(a)(2)(A) placing weight on the fact 
that engines used in U.S. covered aircraft, as discussed in detail in 
sections V.B.4.a of this document, contribute the single largest share 
of GHG emissions from transportation sources in the United States that 
have not yet been regulated for GHG emissions, and that such GHG 
emissions from U.S. covered aircraft are a meaningful contribution to 
total U.S. and total global GHG emissions inventories.
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    \212\ 74 FR at 66538.
    \213\ 74 FR at 66543.
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3. Additional Considerations
    The Administrator also considered information that showed that 
reasonable estimates of GHG emissions from engines used in U.S. covered 
aircraft are projected to grow over the next 20 to 30 years, in making 
her contribution finding under CAA section 231(a)(2)(A). Given the 
projected growth in aircraft emissions compared to other sectors, it is 
reasonable for the Administrator to consider future emissions 
projections as further supporting her assessment of historical annual 
emissions (recent emissions from the current fleet) and informing her 
contribution determination. As described with further detail later in 
section V.B.4.c, recent FAA projections reveal that by 2036 GHG 
emissions from all aircraft and from U.S. covered aircraft are likely 
to increase by 43 percent (from 191 Tg CO2eq to 272 Tg 
CO2eq for the years 2010 to 2036).\214\ By contrast, it is 
estimated that by 2036 the light-duty vehicle sector is projected to 
see a 25 percent reduction in GHG emissions (1,133 Tg CO2eq 
to 844 Tg CO2eq) from the 2010 baseline, while the freight 
trucks sector is projected to experience a 23 percent increase in GHG 
emissions (390 Tg CO2eq to 478 Tg CO2eq) from the 
2010 baseline (this projected increase does not reflect the impact of 
GHG reductions on the freight trucks sector anticipated from the Phase 
2 heavy-duty GHG standards that have not yet been promulgated). In 
addition, by 2036 the rail sector is projected to experience a 3 
percent reduction in GHG emissions (44 Tg CO2eq to 43 Tg 
CO2eq) from the 2010 baseline.\215\ Because the projected 
growth in aircraft engine GHG emissions from U.S. covered aircraft 
through 2036 is more than 80 Tg CO2eq,\216\ this 
consideration of projected future emissions adds further support to the 
Administrator's finding under CAA section 231(a)(2)(A) that emissions 
of the six well-mixed greenhouse gases from classes of engines used in 
U.S. covered aircraft contribute to the GHG air pollution that 
endangers public health and welfare.\217\
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    \214\ As discussed in section V.B.4.c, fuel burn growth rates 
for air carriers and general aviation aircraft operating on jet fuel 
are projected to grow by 43 percent from 2010 to 2036 and this 
provides a scaling factor for growth in projected GHG emissions, 
which are projected to increase at a similar rate as the fuel burn 
by 2030, 2036, and 2040.
    FAA, 2016: FAA Aerospace Forecast Fiscal Years 2016-2036, 94 pp. 
Available at https://www.faa.gov/data_research/aviation/aerospace_forecasts/media/FY2016-36_FAA_Aerospace_Forecast.pdf (last 
accessed March 29, 2016).
    \215\ U.S. Energy Information Administration (EIA), 2015: Annual 
Energy Outlook (AEO) 2015 with projections to 2040, DOE/EIA-0383, 
154 pp. For the years 2010 to 2014, the baseline emissions for each 
sector are from the 2016 Inventory of U.S. Greenhouse Gas Emissions 
and Sinks Report, and after 2014 we utilize projections from the 
2015 EIA AEO report. Available at https://www.eia.gov/forecasts/aeo/ 
(last accessed May 12, 2015).
    \216\ In addition, we expect aircraft engine GHG emissions from 
U.S. covered aircraft to continue contributing to the endangering 
pollution in the future and to be a bigger percentage of 
transportation emissions, since these emission are projected to 
increase at a faster rate than other transportation sources.
    \217\ In 2010, U.S covered aircraft were responsible for 10 
percent of U.S. transportation sector GHG emissions, and in 2036, 
U.S. covered aircraft are projected to be the source of 15 percent 
of U.S. transportation GHG emissions. In 2010, light-duty vehicles 
were responsible for 58 percent of U.S. transportation GHG 
emissions, and in 2036 they are projected to be the source of 46 
percent of such emissions. In 2010, heavy-duty vehicles emitted 20 
percent of U.S. transportation GHG emissions, and in 2036, they are 
projected to emit 26 percent (this projection does not reflect the 
impact from the Phase 2 heavy-duty GHG standards that have not yet 
been promulgated). In 2010, the rail sector contributed 2 percent of 
U.S. transportation GHG emissions, and in 2036, they are projected 
to contribute the same percentage.
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4. Overview of Greenhouse Gas Emissions
    Atmospheric concentrations of CO2 and other GHGs are now 
at essentially unprecedented levels compared to the distant and recent 
past.\218\ This is the unambiguous result of human-activity emissions 
of these gases. See section IV.B.2 for more information on elevated 
atmospheric GHG concentrations and anthropogenic drivers of climate 
change. Global emissions of well-mixed GHGs have been increasing, and 
are projected to continue increasing for the foreseeable future. 
According to the IPCC AR5, total global (when using inventories from 
all anthropogenic emitting sources including forestry and other land 
use) emissions of GHGs in 2010 were 49,000 Tg CO2eq.\219\ 
This represents an increase in global GHG emissions of 29 percent since 
1990 and of 23 percent since 2000. In 2010, total U.S. GHG emissions 
were responsible for 13 percent of global GHG emissions (when comparing 
inventories from all anthropogenic emitting sources including forestry 
and other land use).\220\
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    \218\ IPCC, 2013: Summary for Policymakers. In: Climate Change 
2013: The Physical Science Basis. Contribution of Working Group I to 
the Fifth Assessment Report of the Intergovernmental Panel on 
Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, 
S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley 
(eds.)]. Cambridge University Press, p. 11.
    \219\ IPCC, 2014: Climate Change 2014: Mitigation of Climate 
Change. Contribution of Working Group III to the Fifth Assessment 
Report of the Intergovernmental Panel on Climate Change [Edenhofer, 
O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, 
A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J. 
Savolainen, S. Schl[ouml]mer, C. von Stechow, T. Zwickel and J.C. 
Minx (eds.)]. Cambridge University Press, 1435 pp.
    \220\ IPCC, 2014: Climate Change 2014: Mitigation of Climate 
Change. Contribution of Working Group III to the Fifth Assessment 
Report of the Intergovernmental Panel on Climate Change [Edenhofer, 
O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, 
A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J. 
Savolainen, S. Schl[ouml]mer, C. von Stechow, T. Zwickel and J.C. 
Minx (eds.)]. Cambridge University Press, 351-411 pp.
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    We are also providing 2012 estimates from other widely used and 
recognized global datasets, the World Resources Institute's (WRI) 
Climate Analysis Indicators Tool (CAIT) and the International Energy 
Agency (IEA).\221\ We are providing these data for several reasons; 
first, there is value in looking at multiple data sources to see if 
estimates are generally in line with one another. Second, there are 
more recent

[[Page 54464]]

data available in the WRI/CAIT and IEA datasets (2010 IPCC data vs. 
2012 WRI/CAIT and IEA data). Third and finally, these other datasets 
provide additional utility for examining different disaggregations of 
the data (by country, sector, and with or without forestry and other 
land use emissions). Unless otherwise noted, we are presenting data 
points from these other datasets without including data regarding 
forestry and other land use inventories to enable straightforward 
comparisons of gross emission estimates from transportation sources 
specifically. The total global GHG emissions in 2012 from WRI/CAIT were 
44,816 Tg of CO2eq, representing an increase in global GHG 
emissions of 47 percent since 1990 and 32 percent since 2000. In 
comparison, WRI/CAIT's estimate of total global GHG emissions in 2012 
when including forestry and other land use inventories were 47,599 Tg 
of CO2eq (representing an increase in global GHG emissions 
of 40 percent since 1990 and 30 percent since 2000). In past years, 
WRI/CAIT estimates have generally been consistent with those of IPCC. 
In 2012, WRI/CAIT data indicate that total U.S. GHG emissions were 
responsible for 15 percent of global emissions, which is also generally 
in line with the percentages using IPCC's 2010 estimate described 
above. According to WRI/CAIT, current U.S. GHG emissions rank only 
behind China's, and China was responsible for 24 percent of total 
global GHG emissions.
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    \221\ World Resources Institute (WRI) Climate Analysis 
Indicators Tool (CAIT) Data Explorer (Version 2.0). Available at 
https://cait.wri.org (last accessed January 19, 2016). International 
Energy Agency, Data Services. Available at https://data.iea.org (last 
accessed January 21, 2016).
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    As described earlier in section IV.A, in the proposed finding and 
this final finding, the Administrator considers the recent, major 
scientific assessments of the IPCC, USGCRP, and the NRC as the primary 
scientific and technical basis informing her judgment. Thus, the 
Administrator is informed by and places considerable weight upon the 
IPCC's data on global GHG emissions. She also considers but places less 
emphasis on the WRI/CAIT and IEA emissions data, which in comparison 
have a different aggregation of underlying data but are available for 
more recent years (2010 IPCC data vs. 2012 WRI/CAIT and IEA data).
    The approach of considering the major scientific assessments, 
including IPCC's assessment, provides assurance that the 
Administrator's judgment is informed by the best available, well-vetted 
science that reflects the consensus of the climate science research 
community. The major findings of the assessments, including IPCC's 
assessment, support the Administrator's findings in this action. While 
the EPA uses the IPCC data as the primary data source for informing 
this contribution finding, it has reasonably used additional data 
sources from widely used and recognized global datasets to provide 
context and information from more recent years. These additional data 
supplement and confirm the IPCC data, as they are generally in line 
with IPCC. Comparing their 2010 total global GHG emissions, IPCC data 
are 49,000 Tg CO2eq, and WRI/CAIT data indicates 42,968 Tg 
CO2eq (a 12 percent difference).\222\ Also, comparing their 
2010 global aircraft GHG emissions estimates, IPCC data are 743 Tg 
CO2eq, and IEA data indicate 749 Tg CO2eq (a 1 
percent difference).\223\ Ultimately, whether the Agency utilizes the 
IPCC data alone or the WRI/CAIT dataset (and IEA data) alone, or both 
datasets together, it would have no material effect on the emissions 
comparisons discussed in section V.B and the Administrator would make 
the same contribution finding.
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    \222\ Comparing their 2010 total global GHG emissions, IPCC data 
are 49,000 Tg CO2eq, and WRI/CAIT data, including 
forestry and land use inventories, indicates 45,748 Tg 
CO2eq (a 7 percent difference).
    \223\ Comparing 2012 WRI/CAIT to 2010 IPCC data, WRI/CAIT data 
for total global GHG emissions indicates 44,816 Tg CO2eq 
for 2012 (a 9 percent difference), and including forestry and land 
use inventories WRI/CAIT data indicates 47,599 Tg CO2eq 
for 2012 (a 3 percent difference). Comparing 2012 IEA data to 2010 
IPCC data, IEA data for global aircraft GHG emissions indicates 775 
Tg CO2eq for 2012 (a 4 percent difference).
---------------------------------------------------------------------------

    The Inventory of U.S. Greenhouse Gas Emissions and Sinks Report 
\224\ (hereinafter ``U.S. Inventory''), in which 2014 is the most 
recent year for which data are available, indicates that total U.S. GHG 
emissions increased by 7.3 percent from 1990 to 2014 (or by 7.8 percent 
when using inventories that include forestry and other land use), and 
emissions increased from 2013 to 2014 by 1.1 percent.\225\ This 2013 to 
2014 increase was attributable to multiple factors including an 
increase in vehicle miles traveled and vehicle fuel use, a colder 
winter resulting in an increased demand for heating fuel, and an 
increase in industrial production across multiple sectors. The U.S. 
Inventory also shows that while overall U.S. GHG emissions grew between 
1990 and 2014, transportation GHG emissions grew at a significantly 
higher rate, 16 percent, more rapidly than any other U.S. sector. 
Within the transportation sector, aircraft remain the single largest 
source of GHG emissions not yet subject to any GHG regulations (U.S. 
covered aircraft GHG emissions grew by 15 percent between 1990 and 
2014, and total U.S. aircraft GHG emissions decreased by 3 percent over 
this same time period).\226\
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    \224\ U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions 
and Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and 
Radiation, EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed 
June 14, 2016). The EPA has determined that the U.S. Inventory has 
been adequately reviewed in accordance with the EPA's Peer Review 
Handbook. For the presentation of emissions inventory information in 
this contribution finding, the EPA disaggregated the existing data 
in one area of the U.S. Inventory (for the General Aviation Jet Fuel 
Category) and had the disaggregation methodology peer reviewed in 
accordance with the EPA's Peer Review Handbook. The EPA Science 
Advisory Board reviewed this approach to the underlying technical 
and scientific information supporting this action, and concluded 
that the approach had precedent and the action will be based on 
well-reviewed information. All relevant peer review documentation is 
located in the docket for today's final action (EPA-HQ-OAR-2014-
0828).
    \225\ As described later in detail, total U.S. GHG emissions, 
include emissions from combustion of U.S. international bunker 
fuels, which are fuels used for transport activities from aviation 
(both commercial and military) and marine sources.
    \226\ As described later in detail, total U.S. GHG emissions, 
U.S. transportation GHG emissions, total U.S. aircraft GHG 
emissions, and U.S. covered aircraft GHG emissions include emissions 
from combustion of U.S. international bunker fuels. More 
specifically, total U.S. aircraft GHG emissions include 
international bunker fuel emissions from both commercial and 
military aviation. U.S. covered aircraft GHG emissions include 
international bunker fuel emissions from only commercial aviation.
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    Section V.B.4.a which follows describes U.S. aircraft GHG emissions 
within the domestic context, while section V.B.4.b describes these same 
GHG emissions in the global context. Section V.B.4.c addresses future 
projections of aircraft GHG emissions.
a. U.S. Aircraft GHG Emissions Relative to U.S. GHG Transportation and 
Total U.S. GHG Inventory
    Relying on data from the U.S. Inventory, we compare total U.S. 
aircraft GHG emission and U.S. covered aircraft GHG emissions to the 
transportation sector and to total U.S. GHG emissions as an indication 
of the role this source plays in the total domestic portion of the air 
pollution that is endangering by causing climate change. We are 
providing information about total U.S. aircraft GHG emissions for 
purposes of giving context for the discussion of GHG emissions from 
U.S. covered aircraft, which are included in this contribution finding 
under CAA section 231(a)(2)(A). As explained in more detail below, the 
contribution finding under CAA section 231(a)(2)(A) in this action does 
not include GHG emissions from all aircraft that operate in and from 
the U.S. and thus emit GHGs in the U.S.
    In 2014, total U.S. GHG emissions from all sources were 6,975 Tg 
CO2eq. As stated above, total U.S. GHG emissions have 
increased by 7.3 percent

[[Page 54465]]

between 1990 and 2014, while U.S. transportation GHG emissions from all 
categories have grown 16 percent since 1990. The U.S. transportation 
sector was the second largest GHG-emitting sector (behind electricity 
generation), contributing 1,919 Tg CO2eq or 28 percent of 
total U.S. GHG emissions in 2014. This sectoral total and the total 
U.S. GHG emissions include emissions from combustion of U.S. 
international bunker fuels, which are fuels used for transport 
activities from aviation (both commercial and military) and marine 
sources. Following the IPCC guidelines for common and consistent 
accounting and reporting of GHGs, the UNFCCC requires countries to 
report both total national GHG emissions and international bunker fuel 
emissions (aviation and marine international bunker fuel emissions), 
and though these emissions are reported separately, both are assigned 
to the reporting country. In meeting the UNFCCC reporting requirements, 
the U.S. Inventory calculates international bunker fuel GHG emissions 
in a consistent manner with domestic GHG emissions. In this final 
contribution finding, the EPA maintains its approach used in the 
proposed findings to include aviation international bunker fuel 
emissions attributable to the United States with the national emissions 
number from the U.S. Inventory as reported to the UNFCCC. It is the 
EPA's view that it is reasonable and appropriate for the analysis in 
the contribution finding to reflect the full contribution of U.S. 
emissions from certain classes of aircraft engines, including those 
from domestic flights of U.S. aircraft and those associated with 
international aviation bunker fuel emissions. Consistent with IPCC 
guidelines for common and consistent accounting and reporting of GHGs 
under the UNFCCC, the ``U.S. international aviation bunker fuels'' 
category includes emissions from combustion of fuel used by aircraft 
departing from the United States, regardless of whether they are a U.S. 
flagged carrier. Total U.S. aircraft GHG emissions (which include 
emissions from international commercial and military aviation bunker 
fuels) clearly are included in the U.S. transportation sector's GHG 
emissions, accounting for 222 Tg CO2eq or 12 percent of such 
emissions (see Table V.1). In 2014, total U.S. aircraft GHG emissions 
(222 Tg CO2eq) were the third largest transportation source 
of GHGs within the United States, behind GHG emissions from light-duty 
vehicles and medium- and heavy-duty trucks (totaling 1,508 Tg 
CO2eq).
    For purposes of making this cause or contribute finding, the EPA 
includes a set of aircraft engine classes used in types of aircraft as 
described below, which corresponds to the scope of the international 
CO2 emissions standard agreed to by ICAO. These emissions 
are from what we have previously described as ``covered aircraft'' 
(which include emissions from international commercial aviation bunker 
fuels).
    As mentioned earlier in section II.D, traditionally the U.S. 
government (EPA and FAA) participates at ICAO in the development of 
international standards, and then where appropriate, the EPA 
establishes domestic aircraft engine emission standards under CAA 
section 231 of at least equivalent stringency to ICAO's standards. An 
international CO2 emissions standard was agreed to in 
February 2016, and we expect to proceed with proposing emissions 
standards of at least equivalent stringency domestically as soon as is 
practicable. The thresholds of applicability for the international 
CO2 emissions standard are based on weight as follows: For 
subsonic jet aircraft, a maximum takeoff mass (MTOM) greater than 5,700 
kilograms; and for subsonic propeller driven (e.g., turboprop) 
aircraft, a MTOM greater than 8,618 kilograms.\227\ Applying these 
weight thresholds, our contribution finding applies to GHG emissions 
from classes of engines used in covered aircraft that meet these MTOM 
criteria. For purposes of the contribution finding, examples of covered 
aircraft include smaller jet aircraft such as the Cessna Citation CJ3+ 
and the Embraer E170, up to the largest commercial jet aircraft--the 
Airbus A380 and the Boeing 747. Other examples of covered aircraft 
include larger turboprop aircraft, such as the ATR 72 and the 
Bombardier Q400. The scope of the contribution finding corresponds to 
the aircraft engine GHG emissions that are from aircraft that match the 
applicability thresholds for the international aircraft CO2 
standard. We have also identified aircraft that are not covered 
aircraft for purposes of this contribution finding. That includes 
aircraft that fall below the international applicability thresholds: 
Smaller turboprop aircraft, such as the Beechcraft King Air 350i, and 
smaller jet aircraft, such as the Cessna Citation M2. In addition, ICAO 
(with U.S. participation) has agreed to exclude ``piston-engine 
aircraft,'' ``helicopters,'' and ``military aircraft'' \228\ from the 
types of aircraft that will be subject to the ICAO standards.\229\ As 
these aircraft will not be subject to the ICAO standards, in this 
contribution finding we are also not including GHG emissions from 
classes of engines used in these types of aircraft. We stress that our 
exclusion of these aircraft does not reflect a final scientific or 
technical determination regarding their GHG emissions. Rather, 
consistent with how the endangerment finding does not include various 
other climate forcers within the scope of the ``air pollution'' defined 
in this final action, we are not prepared to make final decisions 
regarding the GHG emissions from these excluded aircraft.
---------------------------------------------------------------------------

    \227\ ICAO, 2013: CAEP/9 Agreed Certification Requirement for 
the Aeroplane CO2 Emissions Standard, Circular (Cir) 337, 40 pp., 
AN/192, Available at https://www.icao.int/publications/catalogue/cat_2016_en.pdf (last accessed April 8, 2016). The ICAO Circular 337 
is found on page 87 of the ICAO Products & Services 2016 catalog and 
is copyright protected; Order No. CIR337.
    \228\ ICAO regulations only apply to civil aviation (aircraft 
and aircraft engines); consequently, ICAO regulations do not apply 
to military aircraft.
    \229\ The applicability of the international CO2 
standard is limited to subsonic aircraft, and does not extend to 
supersonic aircraft.
---------------------------------------------------------------------------

    The majority of the GHG emissions from all classes of aircraft 
engines are within the scope of this contribution finding, which 
corresponds to that agreed to by ICAO. Below we describe the 
contribution of these U.S. covered aircraft GHG emissions to U.S. GHG 
emissions, and later in section V.B.4.b we discuss the contribution of 
these U.S. covered aircraft emissions to global GHG emissions, in 
support of our conclusion that GHG emissions from engines used by U.S. 
covered aircraft contribute to endangering GHG air pollution.
    In 2014, GHG emissions from U.S. covered aircraft (197 Tg 
CO2eq), which includes non-military GHG emissions from 
combustion of U.S. international aviation bunker fuels,\230\ comprised 
89 percent of total U.S. aircraft GHG emissions \231\ (222 Tg 
CO2eq) and 10 percent of total U.S. transportation sector 
GHG emissions (1,919 Tg CO2eq) (See Table V.1). Overall, 
U.S. covered aircraft comprised the third largest source of GHG 
emissions in the U.S. transportation sector behind only the light-duty 
vehicle and medium- and heavy-duty truck sectors (totaling 1,508 Tg 
CO2eq),\232\ which is the same ranking

[[Page 54466]]

as total U.S. aircraft.\233\ The U.S. covered aircraft also represent 
2.8 percent of total U.S. GHG emissions (6,975 Tg CO2eq), 
which is approximately equal to the contribution from total U.S. 
aircraft of 3.2 percent (Table V.1).\234\ Also, in Table V.2 for 
background information and context, we provide similar information, but 
excluding GHG emissions from aviation combustion of U.S. international 
bunker fuels.\235\
---------------------------------------------------------------------------

    \230\ U.S. covered aircraft does not include military aircraft 
that use U.S. international bunker fuels.
    \231\ Eastern Research Group, Incorporated (ERG), 2015: U.S. Jet 
Fuel Use and CO2 Emissions Inventory for Aircraft Below ICAO CO2 
Standard Thresholds, Final Report, EPA Contract Number EP-D-11-006, 
38 pp.
    \232\ In 2014, the U.S. light-duty vehicle (passenger cars and 
light-duty trucks) GHG emissions were 1,101 Tg CO2eq and 
the medium- and heavy-duty truck GHG emissions were 407 Tg 
CO2eq.
    \233\ Compared independently, total U.S. aircraft GHG emissions 
and U.S. covered aircraft GHG emissions are both ranked the third 
largest source in the U.S. transportation sector, behind only light-
duty vehicle and medium- and heavy-duty truck sectors.
    \234\ Total U.S. aircraft GHG emissions and U.S. covered 
aircraft GHG emissions were from 12 to 31 percent greater in 2000 
and 2005 than in 1990. These increases in aircraft GHG emissions are 
primarily because aircraft operations (or number of flights) grew by 
similar amounts during this time period. Also, total U.S. aircraft 
GHG emissions and U.S. covered aircraft GHG emissions were from 10 
to 15 percent greater in 2000 and 2005 than in 2014. These decreases 
in aircraft GHG emissions are partly because aircraft operations 
decreased by similar amounts during this time period. In addition, 
the decreases in aircraft emissions are due in part to improved 
operational efficiency that results in more direct flight routing, 
improvements in aircraft and engine technologies to reduce fuel burn 
and emissions, and the accelerated retirement of older, less fuel 
efficient aircraft. Also, the U.S. transportation GHG emissions were 
changing at similar rates as total U.S. aircraft GHG emissions and 
U.S. covered aircraft GHG emissions for these same time periods, and 
thus, the aircraft GHG emissions share of U.S. Transportation 
remains approximately constant (over these time periods). (U.S. EPA, 
2016: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-
2014, 558 pp. Available at https://www3.epa.gov/climatechange/Downloads/ghgemissions/US-GHG-Inventory-2016-Main-Text.pdf (last 
accessed April 22, 2016)).
    \235\ For Table V.2, total U.S. aircraft GHG emissions and U.S. 
covered aircraft GHG emissions exclude emissions from aviation 
combustion of U.S. international bunker fuels. The U.S. 
transportation sector GHG emissions and total U.S. GHG emissions (in 
Table V.2) exclude emissions from both aviation and marine 
combustion of U.S. international bunker fuels.
---------------------------------------------------------------------------

    It is important to note that in regard to the six well-mixed GHGs 
(CO2, methane, nitrous oxide, hydrofluorocarbons, 
perfluorocarbons, and sulfur hexafluoride), only two of these gases--
CO2 and nitrous oxide--are reported as non-zero emissions 
for total aircraft and covered aircraft.\236\ CO2 represents 
99 percent of all GHGs from both total U.S. aircraft (220 Tg 
CO2eq) and U.S. covered aircraft (195 Tg CO2eq), 
and nitrous oxide represents 1 percent from total aircraft (2.1 Tg 
CO2eq) and covered aircraft (1.9 Tg CO2eq). 
Modern aircraft do not emit methane,\237\ and hydrofluorocarbons, 
perfluorocarbons, and sulfur hexafluoride are not products of aircraft 
engine combustion.
---------------------------------------------------------------------------

    \236\ U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions 
and Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and 
Radiation, EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed 
June 14, 2016).
    \237\ Emissions of methane from jet fuels are no longer 
considered to be emitted (based on the latest studies) across the 
time series from aircraft gas turbine engines burning jet fuel A at 
higher power settings (EPA, Recommended Best Practice for 
Quantifying Speciated Organic Gas Emissions from Aircraft Equipped 
with Turbofan, Turbojet and Turboprop Engines, EPA-420-R-09-901, May 
27, 2009 (see https://www3.epa.gov/otaq/regs/nonroad/aviation/420r09901.pdf (last accessed April 22, 2016)). Based on this data, 
methane emissions factors for jet aircraft were reported as zero to 
reflect the latest emissions testing data. Also, the 2006 IPCC 
Guidelines indicate the following: ``Methane (CH4) may be 
emitted by gas turbines during idle and by older technology engines, 
but recent data suggest that little or no CH4 is emitted 
by modern engines.'' (IPCC, 2006: IPCC Guidelines for National 
Greenhouse Gas Inventories, The National Greenhouse Gas Inventories 
Programme, The Intergovernmental Panel on Climate Change, H.S. 
Eggleston, L. Buendia, K. Miwa, T. Ngara, and K. Tanabe (eds.). 
Hayama, Kanagawa, Japan.) The EPA uses an emissions factor of zero 
to maintain consistency with the IPCC reporting guidelines, while 
continuing to stay abreast of the evolving research in this area. 
For example, one recent study has indicated that modern aircraft jet 
engines operating at higher power modes consume rather than emit 
methane (Santoni et al., 2011: Aircraft Emissions of Methane and 
Nitrous Oxide during the Alternative Aviation Fuel Experiment, 
Environ. Sci. Technol., 45 pp. 7075-7082).
    \238\ U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions 
and Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and 
Radiation, EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed 
June 14, 2016).
    \239\ ERG, 2015: U.S. Jet Fuel Use and CO2 Emissions Inventory 
for Aircraft Below ICAO CO2 Standard Thresholds, Final Report, EPA 
Contract Number EP-D-11-006, 38 pp.
    \240\ U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions 
and Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and 
Radiation, EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed 
June 14, 2016).

  Table V.1 238 239--Comparisons of U.S. Aircraft GHG Emissions to Total U.S. Transportation and Total U.S. GHG
                                                    Emissions
----------------------------------------------------------------------------------------------------------------
                                        1990       2000       2005       2010       2012       2013       2014
----------------------------------------------------------------------------------------------------------------
Total U.S. Aircraft GHG emissions          228        262        254        216        212        216        222
 (Tg CO2eq)........................
    Share of U.S. Transportation...        14%        13%        12%        11%        11%        11%        12%
    Share of total U.S. Inventory..       3.5%       3.6%       3.4%         3%       3.1%       3.1%       3.2%
U.S. Covered Aircraft GHG emissions        171        223        218        191        190        195        197
 (Tg CO2eq)........................
    Share of U.S. aircraft GHG             75%        85%        86%        88%        90%        90%        89%
     emissions.....................
    Share of U.S. Transportation...        10%        11%        10%       9.8%        10%        10%        10%
    Share of total U.S. Inventory..       2.6%         3%       2.9%       2.7%       2.8%       2.8%       2.8%
U.S. Transportation GHG emissions        1,659      2,029      2,119      1,950      1,891      1,895      1,919
 (Tg CO2eq)........................
    Share of total U.S. Inventory..        26%        28%        28%        28%        28%        28%        28%
Total U.S. GHG emissions (Tg CO2eq)      6,502      7,362      7,493      7,104      6,750      6,901      6,975
----------------------------------------------------------------------------------------------------------------


  Table V.2 240 241--Comparisons of U.S. Aircraft GHG Emissions to Total U.S. Transportation and Total U.S. GHG
                            Emissions--Excluding U.S. International Bunker Fuels 242
----------------------------------------------------------------------------------------------------------------
                                        1990       2000       2005       2010       2012       2013       2014
----------------------------------------------------------------------------------------------------------------
Total U.S. Aircraft GHG emissions          190        200        194        155        147        151        152
 (Tg CO2eq)........................
    Share of U.S. Transportation...        12%        10%       9.7%       8.5%       8.2%       8.4%       8.4%
    Share of total U.S. Inventory..         3%       2.8%       2.6%       2.2%       2.2%       2.2%       2.2%
U.S. Covered Aircraft GHG emissions        141        166        162        133        128        132        130
 (Tg CO2eq)........................
    Share of U.S. aircraft GHG             74%        83%        84%        86%        87%        88%        86%
     emissions.....................
    Share of U.S. Transportation...         9%       8.6%       8.1%       7.3%       7.2%       7.4%       7.2%
    Share of total U.S. Inventory..       2.2%       2.3%       2.2%       1.9%       1.9%       1.9%       1.9%
U.S. Transportation GHG emissions        1,554      1,927      2,004      1,832      1,784      1,794      1,815
 (Tg CO2eq)........................
    Share of total U.S. Inventory..        24%        27%        27%        26%        27%        26%        26%
Total U.S. GHG emissions (Tg CO2eq)      6,397      7,259      7,379      6,986      6,643      6,800      6,871
----------------------------------------------------------------------------------------------------------------


[[Page 54467]]

b. U.S. Aircraft GHG Emissions Relative to Global Aircraft GHG 
Inventory and the Total Global GHG Inventory
---------------------------------------------------------------------------

    \241\ ERG, 2015: U.S. Jet Fuel Use and CO2 Emissions Inventory 
for Aircraft Below ICAO CO2 Standard Thresholds, Final Report, EPA 
Contract Number EP-D-11-006, 38 pp.
    \242\ International bunker fuels emissions are emissions 
resulting from the combustion of fuels used for international 
transport activities, which includes aviation and marine. U.S. 
international bunker fuels includes aviation and marine bunker fuels 
allocated to the U.S. The U.S. international aviation bunker fuels 
category includes emissions from combustion of fuel used by aircraft 
departing from the United States, regardless of whether they are a 
U.S. flagged carrier. The U.S. international marine bunker fuels 
category includes emissions from the combustion of fuel used by 
vessels of all flags (that are engaged in international water-borne 
navigation) departing from the United States.
---------------------------------------------------------------------------

    For background information and context, we first provide 
information on the portion of GHG emissions from global aircraft and 
the global transportation sector to total global GHG emissions, and 
describe how this compares to the emissions from aircraft covered by 
the ICAO CO2 standard. We then compare U.S. aircraft GHG 
emissions to the global aircraft sector, to the global transport 
sector, and to total global GHG emissions as an indication of the role 
this source plays in the total global portion of the air pollution that 
is causing climate change. As in the preceding section, we present 
comparisons from both total U.S. aircraft GHG emissions and U.S. 
covered aircraft GHG emissions.
    According to IPCC AR5, global aircraft GHG emissions in 2010 were 
11 percent of global transport GHG emissions and 1.5 percent of total 
global GHG emissions. Data from ICAO's 2013 Environmental Report 
indicate that the vast majority of global emissions from the aircraft 
sector are emitted by the types of aircraft that are covered by the 
ICAO CO2 standard (``ICAO covered aircraft''), which was 
agreed to in February 2016.\243\ When compared to global data from IPCC 
AR5, worldwide GHG emissions from ICAO covered aircraft represented 93 
percent (688 Tg CO2eq) of global aircraft GHG 
emissions,\244\ 9.8 percent of global transport GHG emissions, and 1.4 
percent of total global GHG emissions in 2010.
---------------------------------------------------------------------------

    \243\ ICAO CAEP, 2013: ICAO Environmental Report 2013, Aviation 
and Climate Change, 224 pp. Available at https://cfapp.icao.int/Environmental-Report-2013/ (last accessed April 8, 2016).
    \244\ Worldwide GHG emissions from ICAO covered aircraft include 
emissions from both international and domestic aircraft operations 
around the world.
---------------------------------------------------------------------------

    Comparing data from the U.S. Inventory to IPCC AR5, we find that 
total U.S. aircraft GHG emissions represented 29 percent of global 
aircraft GHG emissions, 3.1 percent of global transport GHG emissions, 
and 0.5 percent of total global GHG emissions in 2010 (see Table V.3). 
U.S. covered aircraft in 2010 GHG emissions represented 26 percent of 
global aircraft GHG emissions, 2.7 percent of global transport GHG 
emissions, and 0.4 percent of total global GHG emissions (see Table 
V.3).\245\ For reasons described above in section V.B.4, we also made 
comparisons using 2012 estimates from WRI/CAIT and the IEA and found 
that they yield very similar results.\246\ Also, in Table V.4 for 
background information and context in regard to the global GHG 
inventory, we provide similar information, but excluding aviation GHG 
emissions from combustion of U.S. international bunker fuels.
---------------------------------------------------------------------------

    \245\ We are providing information about total U.S. aircraft GHG 
emissions for purposes of giving context for the discussion of GHG 
emissions from U.S. covered aircraft, which are included in this 
contribution finding under CAA section 231(a)(2)(A). As explained in 
more detail below, the contribution finding under CAA section 
231(a)(2)(A) in this action does not include GHG emissions from all 
aircraft that operate in and from the U.S and thus emit GHGs in the 
U.S.
    \246\ Data from WRI/CAIT (that excludes forestry and other land 
use inventories) and IEA show that, in 2012, total U.S. aircraft 
emissions represented 27 percent of global aircraft GHG emissions, 
2.9 percent of global transport GHG emissions, and 0.5 percent of 
total global GHG emissions. U.S. covered aircraft represented 25 
percent of global aircraft GHG emissions, 2.6 percent of global 
transport GHG emissions, and 0.4 percent of total global GHG 
emissions in 2012.
    \247\ IPCC, 2014: Climate Change 2014: Mitigation of Climate 
Change. Contribution of Working Group III to the Fifth Assessment 
Report of the Intergovernmental Panel on Climate Change [Edenhofer, 
O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, 
A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J. 
Savolainen, S. Schl[ouml]mer, C. von Stechow, T. Zwickel and J.C. 
Minx (eds.)]. Cambridge University Press, 1435 pp.
    U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions and 
Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and Radiation, 
EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed 
June 14, 2016).
    \248\ ERG, 2015: U.S. Jet Fuel Use and CO2 Emissions Inventory 
for Aircraft Below ICAO CO2 Standard Thresholds, Final Report, EPA 
Contract Number EP-D-11-006, 38 pp.
    \249\ IPCC, 2014: Climate Change 2014: Mitigation of Climate 
Change. Contribution of Working Group III to the Fifth Assessment 
Report of the Intergovernmental Panel on Climate Change [Edenhofer, 
O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, 
A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J. 
Savolainen, S. Schl[ouml]mer, C. von Stechow, T. Zwickel and J.C. 
Minx (eds.)]. Cambridge University Press, 1435 pp. U.S. EPA, 2016: 
Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2014, 
1,052 pp., U.S. EPA Office of Air and Radiation, EPA 430-R-16-002, 
April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed June 14, 2016).
    \250\ ERG, 2015: U.S. Jet Fuel Use and CO2 Emissions Inventory 
for Aircraft Below ICAO CO2 Standard Thresholds, Final Report, EPA 
Contract Number EP-D-11-006, 38 pp.

  Table V.3 \247\--Comparisons of U.S. Aircraft GHG Emissions to Total Global Greenhouse Gas Emissions in 2010
----------------------------------------------------------------------------------------------------------------
                                                                    Total U.S.     U.S. covered       Global
                                                  2010 (Tg CO2    aircraft share  aircraft share  aircraft share
                                                       eq)             (%)           (%) \248\          (%)
----------------------------------------------------------------------------------------------------------------
Global Aircraft GHG emissions..................             743               29              26  ..............
Global Transport GHG emissions.................           7,000              3.1             2.7              11
Total Global GHG emissions.....................          49,000              0.5             0.4             1.5
----------------------------------------------------------------------------------------------------------------


 Table V.4 \249\--Comparisons of U.S. Aircraft GHG Emissions to Total Global Greenhouse Gas Emissions in 2010--
 Excluding Aviation GHG Emissions From Combustion of U.S. International Bunker Fuels From the U.S. Aircraft GHG
                                                    Emissions
----------------------------------------------------------------------------------------------------------------
                                                                    Total U.S.     U.S. covered       Global
                                                  2010 (Tg CO2    aircraft share  aircraft share  aircraft share
                                                       eq)             (%)           (%) \250\          (%)
----------------------------------------------------------------------------------------------------------------
Global Aircraft GHG emissions..................             743               21              18  ..............
Global Transport GHG emissions.................           7,000              2.2             1.9              11
Total Global GHG emissions.....................          49,000              0.4             0.3             1.5
----------------------------------------------------------------------------------------------------------------


[[Page 54468]]

    For additional background information and context, we used 2012 
WRI/CAIT and IEA data to make comparisons between the aircraft sector 
and the emissions inventories of entire countries and regions. When 
compared to entire countries, total global aircraft GHG emissions in 
2012 ranked 8th overall, behind only China, United States, India, 
Russian Federation, Japan, Brazil, and Germany, and ahead of about 177 
other countries. Total U.S. aircraft GHG emissions have historically 
been and continue to be by far the largest contributor to global 
aircraft GHG emissions. Total U.S. aircraft GHG emissions are about 6 
times higher than aircraft GHG emissions from China, which globally is 
the second ranked country for aircraft GHG emissions, and about 4 times 
higher than aircraft GHG emissions from all of Asia. U.S. covered 
aircraft GHG emissions are about 5 times more than total aircraft GHG 
emissions from China, and about 4 times more than total aircraft GHG 
emissions from all of Asia. If U.S. covered aircraft emissions of GHGs 
were ranked against total GHG emissions for entire countries, these 
covered aircraft emissions would rank ahead of Belgium, Czech Republic, 
Ireland, Sweden, Switzerland and about 150 other countries in the 
world.
c. Aircraft GHG Emissions Are Projected To Increase in the Future
    Global and U.S. covered aircraft GHG emissions have increased 
between 1990 and 2010, and are predicted to continue to increase in 
future years. While overall GHG emissions from U.S. covered aircraft 
increased by 12 percent from 1990 to 2010, the portion attributable to 
combustion of U.S. international aviation bunker fuels \251\ increased 
by 91 percent.\252\ During this same time period, global aircraft GHG 
emissions grew by 40 percent, and the portion attributable to 
combustion of global international aviation bunker fuels increased by 
80 percent.253 254 Notwithstanding the substantial growth in 
GHG emissions from combustion of U.S. international aviation bunker 
fuels, U.S. covered aircraft emissions have not increased as much as 
global aircraft emissions from 1990 to 2010, primarily because the U.S. 
aviation market was relatively mature compared to the markets in Europe 
and other emergent markets, and because during this time period the 
U.S. commercial air carriers suffered several major shocks that reduced 
demand for air travel.\255\ In fact, U.S. covered aircraft emissions 
decreased from 2000 to 2010 (13 percent), but then have increased from 
2010 to 2014 (3 percent).\256\ After consolidation and restructuring in 
recent years, the U.S. commercial air carriers have regained 
profitability and are forecasted by the FAA to grow more over the next 
20 to 30 years.\257\ With regard to global aircraft GHG emissions, the 
aviation markets in Asia/Pacific, Europe (where airline deregulation 
has stimulated significant new demands in this period), and the Middle 
East (and other emerging markets) have been growing rapidly, and the 
global market is expected to continue to grow significantly over the 
next 20 to 30 years.\258\
---------------------------------------------------------------------------

    \251\ The U.S. international aviation bunker fuels category 
includes emissions from combustion of fuel used by aircraft 
departing from the United States, regardless of whether they are a 
U.S. flagged carrier. GHG emissions from U.S. international aviation 
bunker fuels are a subset of GHG emissions from U.S. covered 
aircraft. From 1990 to 2010, GHG emissions from U.S. covered 
aircraft increased from 171 to 191 Tg CO2eq, and GHG 
emissions from the portion attributable to U.S. international 
aviation bunker fuels grew from 30 to 58 Tg CO2eq during 
this same time period. From 1990 to 2011, GHG emissions from U.S. 
covered aircraft increased from 171 to 193 Tg CO2eq (13 
percent), and GHG emissions from the portion attributable to U.S. 
international aviation bunker fuels grew from 30 to 62 Tg 
CO2eq (110 percent). From 1990 to 2012, GHG emissions 
from U.S. covered aircraft increased from 171 to 190 Tg 
CO2eq (11 percent), and GHG emissions from the portion 
attributable to U.S. international aviation bunker fuels grew from 
30 to 62 Tg CO2eq (110 percent).
    \252\ U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions 
and Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and 
Radiation, EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed 
June 14, 2016).
    \253\ IPCC, 2014: Climate Change 2014: Mitigation of Climate 
Change. Contribution of Working Group III to the Fifth Assessment 
Report of the Intergovernmental Panel on Climate Change [Edenhofer, 
O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, 
A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J. 
Savolainen, S. Schl[ouml]mer, C. von Stechow, T. Zwickel and J.C. 
Minx (eds.)]. Cambridge University Press, pp. 599-670.
    \254\ According to IEA, from 1990 to 2012, global aircraft GHG 
emissions grew by 53 percent, and global international aviation 
bunker fuels increased by 86 percent. International Energy Agency 
Data Services, Available at https://data.iea.org (last accessed 
January 21, 2016).
    \255\ According to the FAA Aerospace Forecast 2014-2034, these 
shocks include the September 11, 2001, terror attacks, significant 
increases in fuel prices, debt restructuring in Europe and U.S., and 
a global recession. FAA, 2014: FAA Aerospace Forecast Fiscal Years 
2014-2034, 129 pp. Available at https://www.faa.gov/data_research/aviation/aerospace_forecasts/media/2014_faa_aerospace_forecast.pdf 
(last accessed April 8, 2016).
    \256\ U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions 
and Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and 
Radiation, EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed 
June 14, 2016).
    \257\ According to the FAA Aerospace Forecast 2016-2036, in 2015 
U.S. air carriers were profitable for the sixth consecutive year.
    FAA, 2016: FAA Aerospace Forecast Fiscal Years 2016-2036, 94 pp. 
Available at https://www.faa.gov/data_research/aviation/aerospace_forecasts/media/FY2016-36_FAA_Aerospace_Forecast.pdf (last 
accessed March 29, 2016).
    \258\ According to the FAA Aerospace Forecast 2014-2034, the 
International Air Transport Association (IATA) reports that world 
air carriers (including U.S. airlines) are expected to register an 
operating profit for 2013. Based on financial data compiled by ICAO 
and IATA, between 2004 and 2013 world airlines produced cumulative 
operating profits (with nine years out of ten posting gains) and net 
profits (with six years out of ten posting gains).
---------------------------------------------------------------------------

    Recent studies estimate that both ICAO covered aircraft and U.S. 
covered aircraft will experience substantial growth over the next 20 to 
30 years in their absolute fuel burn,\259\ and that this will translate 
into increased GHG emissions. ICAO estimates that the global fuel burn 
from ICAO covered aircraft will increase by about 120 percent from 2010 
to 2030 and by about 210 percent from 2010 to 2040 (for a scenario with 
moderate technology and operational improvements).\260\ The FAA 
projects that the fuel consumption from U.S. air carriers and general 
aviation aircraft operating on jet fuel will grow by 43 percent from 
2010 to 2036, corresponding to an average annual increase rate in fuel 
consumption of 1.4 percent.\261\ These aircraft groups (U.S. air 
carriers and general aviation aircraft operating on jet fuel) are of 
similar scope to the U.S. covered aircraft whose engine GHG emissions 
are the subject of this contribution finding. Using fuel burn growth 
rates provided above as a scaling factor for growth in GHG emissions 
(globally and nationally), it is estimated that GHG emissions from ICAO 
covered aircraft and U.S. covered aircraft will increase at a similar 
rate as the fuel burn by 2030, 2036, and 2040.
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    \259\ FAA, 2016: FAA Aerospace Forecast Fiscal Years 2016-2036, 
94 pp. Available at https://www.faa.gov/data_research/aviation/aerospace_forecasts/media/FY2016-36_FAA_Aerospace_Forecast.pdf (last 
accessed March 29, 2016).
    ICAO CAEP, 2013: ICAO Environmental Report 2013, Aviation and 
Climate Change, 224 pp. Available at https://cfapp.icao.int/Environmental-Report-2013/ (last accessed April 8, 2016).
    \260\ ICAO CAEP, 2013: ICAO Environmental Report 2013, Aviation 
and Climate Change, 224 pp. Available at https://cfapp.icao.int/Environmental-Report-2013/ (last accessed April 8, 2016).
    \261\ FAA, 2016: FAA Aerospace Forecast Fiscal Years 2016-2036, 
94 pp. Available at https://www.faa.gov/data_research/aviation/aerospace_forecasts/media/FY2016-36_FAA_Aerospace_Forecast.pdf (last 
accessed March 29, 2016).
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C. Response to Key Comments on the Administrator's Cause or Contribute 
Finding

    EPA received numerous comments regarding the Administrator's 
proposed cause or contribute finding. Below is a brief discussion of 
some of the key comments. Responses to comments on

[[Page 54469]]

this topic (and further details for the key comments) are also 
contained in the Response to Comments document.
1. The Administrator Reasonably Defined the Scope of the Cause or 
Contribute Finding
a. Applicability Weight Thresholds Match Those of International 
CO2 Standard
    Several commenters stated that the EPA should undertake another 
cause or contribute finding for a broader range of aircraft not covered 
in our proposed finding, including smaller turboprop aircraft (such as 
the Beechcraft King Air 350i), smaller jet aircraft (such as the Cessna 
Citation M2), piston-engine aircraft, and helicopters. These commenters 
stated, however, that this comment did not affect the validity of the 
conclusions in the proposed finding. Numerous commenters stated their 
support for our proposed finding's scope matching the applicability 
(weight or MTOM) thresholds of the international CO2 
standard.
    As described earlier, at this time and for the purposes of this 
cause or contribute finding under CAA section 231(a)(2)(A), the EPA is 
including emissions of the six well-mixed greenhouse gases from classes 
of engines used in U.S. covered aircraft which are subsonic jet 
aircraft with a maximum takeoff mass (MTOM) greater than 5,700 
kilograms and subsonic propeller driven (e.g., turboprop) aircraft with 
a MTOM greater than 8,618 kilograms. We are not at this time taking 
final action with respect to the GHG emissions from aircraft other than 
those included in the scope of this finding.\262\ The cause or 
contribute finding is a prerequisite under CAA section 231 for EPA to 
adopt standards that are of at least equivalent stringency to those set 
by ICAO. Accordingly, in this finding, the EPA is focusing on matching 
the scope of our contribution finding to the applicability thresholds 
of the international standard. The covered aircraft match the 
applicability (or MTOM) thresholds of the international aircraft 
CO2 standard. This is a reasonable approach for this first 
finding regarding the contribution of aircraft GHG emissions to the 
endangering air pollution, as the vast majority of U.S. emissions from 
all classes of aircraft engines (89 percent of U.S. aircraft GHG 
emissions) will be covered by this scope of applicability, which 
corresponds to 26 percent of global aircraft GHG emissions. This 
approach is also consistent with our past practice in promulgating 
aircraft engine NOX standards. In ruling on a petition for 
judicial review of the 2005 rule for further stringency of aircraft 
engine NOX standards,\263\ the D.C. Circuit held that the 
EPA's approach in that action of tracking the applicability criteria of 
the ICAO standards was reasonable and permissible under the CAA. NACAA 
v. EPA, 489 F.3d 1221, 1230-32 (D.C. Cir. 2007). (The Court also held 
that section 231 of the CAA confers a broad degree of discretion on the 
EPA to adopt aircraft emission standards that the Agency determines are 
reasonable. Id.) Also, by using the phrase ``any class or classes of 
aircraft engines which in [her] judgment causes, or contributes to,'' 
the endangering air pollution, section 231(a)(2)(A) gives the EPA 
discretion to determine which class or classes of aircraft engines to 
evaluate in making a cause or contribute finding, and whether to focus 
on a single class or multiple classes of aircraft engines in satisfying 
the requirements of section 231(a)(2)(A).
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    \262\ Consequently, this final action does not restrict the 
EPA's future discretion to address GHG emissions from aircraft that 
are not included in the scope of this finding, or prejudge how the 
Agency would respond to a petition to address those GHG emissions 
should one be submitted in the future.
    \263\ U.S. EPA, 2005: Control of Air Pollution from Aircraft and 
Aircraft Engines; Emission Standards and Test Procedures; Final 
Rule, 70 FR 69664 (November 17, 2005).
    In 2005, we promulgated more stringent NOX emission 
standards for newly certified commercial turbofan engines. That 
final rule brought the U.S. standards closer to alignment with ICAO 
CAEP/4 requirements that became effective in 2004.
---------------------------------------------------------------------------

    In response to the commenters who asked the EPA to undertake an 
additional cause and contribute finding regarding GHG emissions from 
non-covered U.S. aircraft, the Agency will take that request under 
advisement and consideration among its other duties and priorities, but 
is not prepared at this time to either reject or grant that request. At 
this point, given the nearly complete process for ICAO's adoption of an 
international standard, which will under the Chicago Convention trigger 
the duties of the U.S. and other member states to adopt domestically 
standards that are of at least equal stringency, it is most important 
for the EPA to prepare for having to meet that nearly certain duty by 
expeditious completion of the pre-requisite endangerment and cause or 
contribute findings, without possibly delaying final action to consider 
the possibility of proposing a broader cause or contribute finding 
before taking final action.
b. The Administrator Reasonably Defined U.S. Covered Aircraft
    A commenter stated that they understand that the scope of the 
finding corresponds to the aircraft engine GHG emissions that are from 
aircraft that match the applicability thresholds (or MTOM thresholds) 
for the international aircraft CO2 standard; however, they 
requested clarification on the difference between ``U.S. covered 
aircraft'' and non-U.S. covered aircraft. This commenter requested 
clarification on whether U.S. covered aircraft means aircraft made in 
the U.S., registered in the U.S., operated by an entity holding an air 
carrier certificate issued by the U.S., operated by an air carrier in 
the National Air Space, or operated by anyone in the U.S. (National) 
Air Space. The commenter expressed that the EPA must explain the basis 
for its definition, and its claimed authority to regulate U.S. covered 
aircraft.
    As described earlier in section V.B.4, U.S. covered aircraft for 
this cause or contribute finding refers to aircraft that are a subset 
of all aircraft that meet the applicability thresholds of the 
international aircraft CO2 standard, namely those that fly 
domestically with starting and ending points within the U.S. and those 
that depart the U.S. for international destinations. U.S. covered 
aircraft include aircraft that operate in the U.S., and thus contribute 
to GHG emissions in the U.S. This includes emissions from U.S. domestic 
flights of these aircraft. In addition, the scope of this finding 
reaches GHG emissions from non-military aircraft combusting U.S. 
international bunker fuels departing the U.S., regardless of whether 
they are a U.S. flagged carrier--also described as emissions from 
combustion of U.S. international bunker fuels.\264\ Similar to 
statements earlier in section V.B.4, in defining U.S. covered aircraft 
for this specific contribution finding, in advance of needing to meet 
the expected duties imposed by the ICAO standards, the EPA is focused 
on the GHG emissions that the atmosphere receives as a result of 
aviation activities occurring inside the U.S. and originating from the 
U.S., in order to capture the full contribution of covered aircraft to 
U.S. GHG emissions, consistent with the scope of the ICAO international 
standard. It is important for the EPA's finding to reach the subset of 
aircraft that meet the definition of U.S. covered aircraft, and that 
subset

[[Page 54470]]

will not necessarily be covered by any other member state with 
responsibilities to meet the ICAO standard under the Chicago 
Convention. For U.S. covered aircraft, the EPA has chosen to combine 
GHG emissions from all flights both domestic and those reflected in 
international bunker fuel inventories to determine the contribution of 
U.S. covered aircraft GHG emissions to the endangering air pollution. 
We additionally note that the IPCC and UNFCCC guidance states that for 
an international bunker flight the entire flight's emissions are 
calculated and reported (for the country from where the flight 
departed), and the GHG emission calculation methodologies are the same 
for both domestic and international aviation bunker fuel flights. We 
have followed this guidance in our calculation methodologies for this 
contribution finding.\265\ Ultimately, GHG emissions inventories from 
U.S. covered aircraft with or without GHG emissions from combustion of 
U.S. international aviation bunker fuels are sufficient to support the 
Administrator's cause or contribute finding in this action, whether we 
consider the inventories both together, or just the inventory from 
domestic flights of U.S. covered aircraft.
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    \264\ For example, a flight departing Los Angeles and arriving 
in Tokyo--regardless of whether it is a U.S. flagged carrier--is 
considered a U.S. international bunker flight. A flight from London 
to Hong Kong is not.
    \265\ As described earlier, following the IPCC guidelines for 
common and consistent accounting and reporting of GHGs, the UNFCCC 
requires countries to report both total national GHG emissions and 
international bunker fuel emissions (aviation and marine 
international bunker fuel emissions), and though these emissions are 
reported separately, both are assigned to the reporting country. In 
meeting the UNFCCC reporting requirements, the U.S. Inventory 
calculates international bunker fuel GHG emissions in a consistent 
manner with domestic GHG emissions. In this final contribution 
finding, the EPA maintains its approach used in the proposed 
findings to include aviation international bunker fuel emissions 
attributable to the United States with the national emissions number 
from the U.S. Inventory as reported to the UNFCCC. It is the EPA's 
view that it is reasonable and appropriate for the analysis in the 
contribution finding to reflect the full contribution of U.S. 
emissions from certain classes of aircraft engines, including those 
from domestic flights of U.S. aircraft and those associated with 
international aviation bunker fuel emissions. Consistent with IPCC 
guidelines for common and consistent accounting and reporting of 
GHGs under the UNFCCC, the ``U.S. international aviation bunker 
fuels'' category includes emissions from combustion of fuel used by 
aircraft departing from the United States, regardless of whether 
they are a U.S. flagged carrier.
---------------------------------------------------------------------------

    In response to the comment that EPA must explain its claimed 
authority to regulate U.S. covered aircraft, as described earlier, the 
endangerment and cause or contribute findings are a prerequisite under 
CAA section 231(a)(2)(A) for EPA to adopt standards (that are of at 
least equivalent stringency to those set by ICAO). If the Administrator 
makes these findings in the affirmative, she must issue standards under 
section 231(a)(2)(A).
c. It Is Reasonable for the Administrator To Limit the Contribution 
Finding to U.S. Covered Aircraft
    Some commenters stated that the EPA should issue a broader 
contribution finding and wait until the standard setting phase to 
exercise discretion as to what classes of aircraft engines should be 
covered by standards. These commenters stated that the EPA has 
authority to set aircraft engine GHG emission standards, following a 
cause or contribute finding, that do not impose requirements on every 
engine or class of aircraft engine within the scope of that finding. 
They also argued that in this instance there does not seem to be a 
sufficiently reasoned basis for EPA to exclude the non-covered aircraft 
for purposes of making the cause or contribute finding.
    As described earlier in section III, the endangerment and 
contribution findings for aircraft GHG emissions under section 
231(a)(2)(A) of the CAA are a necessary first step to begin to address 
GHG emissions from the aviation sector, the highest-emitting category 
of transportation GHG sources that the EPA has not yet addressed. As 
presented in more detail in section V.B.4 of this preamble, covered 
U.S. aircraft GHG emissions in 2014 represented 10 percent of GHG 
emissions from the U.S. transportation sector,\266\ and in 2010, the 
latest year with complete global emissions data, U.S. covered aircraft 
GHG emissions represented 26 percent of global aircraft GHG 
emissions.267 268 U.S. covered aircraft GHG emissions are 
projected to increase by 43 percent over the next two decades.\269\
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    \266\ U.S. EPA, 2016: Inventory of U.S. Greenhouse Gas Emissions 
and Sinks: 1990-2014, 1,052 pp., U.S. EPA Office of Air and 
Radiation, EPA 430-R-16-002, April 2016. Available at: www3.epa.gov/climatechange/ghgemissions/usinventoryreport.html (last accessed 
June 14, 2016).
    \267\ Ibid.
    \268\ IPCC, 2014: Climate Change 2014: Mitigation of Climate 
Change. Contribution of Working Group III to the Fifth Assessment 
Report of the Intergovernmental Panel on Climate Change [Edenhofer, 
O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, 
A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J. 
Savolainen, S. Schl[ouml]mer, C. von Stechow, T. Zwickel and J.C. 
Minx (eds.)]. Cambridge University Press, 599-670 pp.
    \269\ As discussed in section V.B.4.c, fuel burn growth rates 
for air carriers and general aviation aircraft operating on jet fuel 
are projected to grow by 43 percent from 2010 to 2036, and this 
provides a scaling factor for growth in GHG emissions which would 
increase at a similar rate as the fuel burn by 2030, 2036, and 2040. 
FAA, 2016: FAA Aerospace Forecast Fiscal Years 2016-2036, 94 pp. 
Available at https://www.faa.gov/data_research/aviation/aerospace_forecasts/media/FY2016-36_FAA_Aerospace_Forecast.pdf (last 
accessed March 29, 2016).
---------------------------------------------------------------------------

    Section III of this preamble summarizes the legal framework for 
this action under CAA section 231. As discussed there, section 
231(a)(2)(A) of the CAA states that ``The Administrator shall, from 
time to time, issue proposed emission standards applicable to the 
emission of any air pollutant from any class or classes of aircraft 
engines which in [her] judgment causes, or contributes to, air 
pollution which may reasonably be anticipated to endanger public health 
or welfare.'' Before the Administrator may issue standards addressing 
emissions of GHGs under section 231, the Administrator must satisfy a 
two-step test. First, the Administrator must decide whether, in her 
judgment, the air pollution under consideration may reasonably be 
anticipated to endanger public health or welfare. Second, the 
Administrator must decide whether, in her judgment, emissions of an air 
pollutant from the classes of aircraft engines under consideration 
cause or contribute to this air pollution.\270\ If the Administrator 
answers both questions in the affirmative, she must issue standards 
under section 231. While we agree that the EPA has significant 
discretion in the standard-setting phase, we disagree with the comment 
to the extent that it suggests the standard-setting phase is the only 
appropriate place for the EPA to exercise discretion as to the scope of 
covered aircraft engine classes in this first instance of findings 
regarding aircraft GHG emissions. By using the phrase ``any class or 
classes of aircraft engines which in [her] judgment causes, or 
contributes to,'' the endangering air pollution, section 231(a)(2)(A) 
gives the EPA discretion to determine which class or classes of 
aircraft engines to evaluate in making a cause or contribute finding, 
and whether to focus on a single class or multiple classes of aircraft 
engines in satisfying the requirements of section 231(a)(2)(A). Because 
the scope of the first international CO2 standard adopted by 
ICAO is limited to aircraft over the specified MTOM levels, and the 
U.S. will have a duty to set domestic standards in order to meet its 
obligations under the Chicago Convention, it is reasonable in this case 
to similarly limit the scope of and issue this first aircraft GHG 
contribution

[[Page 54471]]

finding and not delay this determination in order to possibly 
additionally consider and re-propose our finding to reach a broader 
scope. We do not necessarily disagree with the commenters who suggested 
that we could issue a broader contribution finding and then narrow the 
scope of future standards at that stage, but doing so in this action 
would require further analysis and development of an additional 
proposed finding, which could impede expeditious final issuance of the 
finding we proposed and thereby possibly impede prompt development of 
domestic standards that are of at least equivalent stringency as 
ICAO's. We expect to proceed with promulgating a domestic 
CO2 standard (or GHG standard) of at least equivalent 
stringency to the international CO2 standard as soon as it 
is practicable, and to begin to take action along this expected path, 
we are exercising our discretion in matching the applicability 
thresholds of the international CO2 standard. The majority 
of the GHG emissions from all classes of aircraft engines would be 
covered by these applicability thresholds. We are not making either 
positive or negative contribution findings regarding GHG emissions from 
engines used in non-covered aircraft at this time, but nothing prevents 
us from doing so in the future.
---------------------------------------------------------------------------

    \270\ To clarify the distinction between air pollution and air 
pollutant, the air pollution is the atmospheric concentrations and 
can be thought of as the total, cumulative stock of GHGs in the 
atmosphere. The air pollutants, on the other hand, are the emissions 
of GHGs and can be thought of as the flow that changes the size of 
the total stock.
---------------------------------------------------------------------------

2. The Administrator's Cause or Contribute Analysis Is Reasonable
a. It Is Reasonable To Include GHG Emissions From Combustion of 
International Aviation Bunker Fuels in the U.S. Aircraft GHG Inventory
    Some commenters stated that the EPA's choice of data for the cause 
or contribute analysis was selective and biased. They contended that 
emissions resulting from combustion of the international aviation 
bunker fuels should not be part of the U.S. covered aircraft GHG 
inventory or of the total U.S. aircraft GHG inventory, since the EPA's 
own U.S. inventory for UNFCCC reporting purposes does not include 
emissions from combustion of these fuels in the national GHG totals and 
reports them separately to the UNFCCC, pursuant to UNFCCC inventory 
reporting guidelines.\271\ Consequently, they asserted that the total 
emissions from domestic commercial aircraft accounts for less than 2 
percent (1.7%) of total U.S. aircraft GHG emissions. Because of this, 
commenters believe that EPA inappropriately specified that the U.S. 
covered aircraft GHG emissions represent 3 percent of the total U.S. 
GHG emissions.
---------------------------------------------------------------------------

    \271\ EPA GHG Emissions Inventory at A-31 (reporting and 
methods) is available at: https://www.epa.gov/climatechange/Downloads/ghgemissions/US-GHG-Inventory-2015-Annex-2-Emissions-Fossil-Fuel-Combustion.pdf (last accessed April 8, 2016).
---------------------------------------------------------------------------

    The EPA disagrees with this comment. As stated earlier in this 
section, U.S. covered aircraft GHG emissions \272\ (and total U.S. 
aircraft GHG emissions) in this cause or contribute finding include 
those GHG emissions resulting from combustion of international aviation 
bunker fuel because we want to capture the full contribution of GHG 
emissions from aircraft that are attributable to covered aircraft 
activity in or originating from the U.S. In tracking aircraft GHG 
emissions, the EPA is focused on the U.S.'s contributions from this 
sector to the atmosphere. Accordingly, the EPA includes GHG emissions 
for all aircraft departing from U.S. airports in a calendar year 
(domestic and international flights) in determining total U.S. GHG 
emissions and total U.S. aircraft GHG emissions. Thus, consistent with 
that practice, for assessing GHG emissions from U.S. covered aircraft, 
EPA has chosen to combine all flights, both those with domestic takeoff 
and landing points, and those with domestic takeoff points and 
international landing points. In addition, guidance from the IPCC and 
UNFCCC states that for an international bunker fuel-combusting flight 
the entire flight's emissions are calculated and reported, and the GHG 
emission calculation methodologies are the same for both domestic and 
international bunker fuel-combusting flights. The U.S. calculates and 
reports emissions resulting from combustion of international bunker 
fuels in accordance with this guidance. However, pursuant to UNFCCC 
reporting guidelines, emissions from combustion of international bunker 
fuels are reported separately from other aircraft emissions in the U.S. 
Inventory, in order to meet the reporting commitments under the UNFCCC. 
We follow the IPCC and UNFCC guidance in our calculation and reporting 
methodologies.\273\
---------------------------------------------------------------------------

    \272\ As described earlier in section V.B.4, U.S. covered 
aircraft do not include military aircraft that use U.S. 
international aviation bunker fuels.
    \273\ As described earlier, following the IPCC guidelines for 
common and consistent accounting and reporting of GHGs, the UNFCCC 
requires countries to report both total national GHG emissions and 
international bunker fuel emissions (aviation and marine 
international bunker fuel emissions), and though these emissions are 
reported separately, both are assigned to the reporting country. In 
meeting the UNFCCC reporting requirements, the U.S. Inventory 
calculates international bunker fuel GHG emissions in a consistent 
manner with domestic GHG emissions. In this final contribution 
finding, the EPA maintains its approach used in the proposed 
findings to include aviation international bunker fuel emissions 
attributable to the United States with the national emissions number 
from the U.S. Inventory as reported to the UNFCCC. It is the EPA's 
view that it is reasonable and appropriate for the analysis in the 
contribution finding to reflect the full contribution of U.S. 
emissions from certain classes of aircraft engines, including those 
from domestic flights of U.S. aircraft and those associated with 
international aviation bunker fuel emissions. Consistent with IPCC 
guidelines for common and consistent accounting and reporting of 
GHGs under the UNFCCC, the ``U.S. international aviation bunker 
fuels'' category includes emissions from combustion of fuel used by 
aircraft departing from the United States, regardless of whether 
they are a U.S. flagged carrier.
---------------------------------------------------------------------------

b. The Administrator Does Not Need To Find Significant Contribution, or 
Establish a Bright Line
    One comment letter stated that aircraft GHG emissions are extremely 
small relative to both domestic and global GHG emissions in the 
aggregate, and questioned whether there is a reasoned basis for EPA to 
find that GHG emissions from U.S. aircraft cause or contribute to air 
pollution that endangers public health and welfare when assessed not 
only relative to contributions from other sectors, but also relative to 
climate impacts. For example, this commenter indicated the EPA 
estimates that total U.S. aircraft GHG emissions accounted for about 
0.5 percent of total global GHG emissions in 2010. Thus, the commenter 
stated that the total U.S. aircraft GHG emission contributions from the 
U.S. aviation sector are extremely small relative to total global GHG 
emissions, or negligible as a percentage of total global GHG emissions.
    The EPA disagrees with this comment and has fully explained the 
reasoning for this contribution finding in section V.B. In addition, 
the Administrator interprets CAA section 231(a)(2)(A) to require some 
level of contribution that, while more than de minimis or trivial, does 
not need to rise to the level of significance to support a contribution 
finding. By its terms, section 231(a)(2)(A) does not contain a modifier 
on its use of the term ``contribute,'' which contrasts with some other 
provisions of the CAA, such as sections 213(a)(2) and (4), and 
110(a)(2)(D)(i)(I), that expressly require a ``significant'' 
contribution. The Administrator's interpretation is consistent with the 
interpretation of parallel language in CAA section 202(a), which was 
described in the 2009 Findings,\274\ and is also supported by past 
court decisions. For example, the D.C. Circuit's opinion in Catawba 
County v. EPA, 571 F.3d 20 (D.C. Cir. 2009),

[[Page 54472]]

discusses the concept of contribution in the area designations context 
under section 107(d)(1)(A), which, like section 231(a)(2)(A), does not 
include the term ``significant'' to modify ``contribute.'' This 
decision, along with others, supports the Administrator's 
interpretation that CAA section 231(a)(2)(A) does not require a 
significant contribution, but rather, in the absence of specific 
language regarding the degree of contribution, provides the EPA 
discretion such that a positive finding may be based on a determination 
that the air pollutant emissions from the relevant class or classes of 
aircraft engines merely ``contribute to'' the air pollution which may 
reasonably be anticipated to endanger public health or welfare. In 
addition, similar to the interpretation of section 202(a) described in 
the 2009 Findings, the Administrator is not required under section 
231(a)(2)(A) to establish a bright-line, objective test for 
contribution, but is to exercise her judgment in determining 
contribution.\275\ As explained above, and similar to the approach used 
in the 2009 Findings, when exercising her judgment under section 
231(a)(2)(A), in this context the Administrator considers both the 
cumulative impact and also the totality of the circumstances. It is 
reasonable for the Administrator to apply a ```totality-of-the-
circumstances test to implement a statute that confers broad 
discretionary authority, even if the test lacks a definite `threshold' 
or `clear line of demarcation to define an open-ended term.' '' Id. at 
39 (citations omitted).
---------------------------------------------------------------------------

    \274\ 74 FR at 66541-42.
    \275\ 74 FR at 66542.
---------------------------------------------------------------------------

    In Catawba County the D.C. Circuit upheld the EPA's 
PM2.5 area designation decisions and analyzed CAA section 
107(d), which requires the EPA to designate an area as nonattainment if 
it ``contributes to ambient air quality in a nearby area'' not meeting 
the national ambient air quality standards. Id. at 35. CAA section 
107(d)(1), as mentioned above, like section 231(a)(2)(A), does not use 
the term ``significant'' in establishing this duty, or set forth any 
other bright-line benchmark that must be met for the EPA to find 
``contribution.'' The court noted that it had previously held that the 
term ``contributes'' is ambiguous in the context of CAA language. See 
EDF v. EPA, 82 F.3d 451, 459 (D.C. Cir. 1996). ``[A]mbiguities in 
statutes within an agency's jurisdiction to administer are delegations 
of authority to the agency to fill the statutory gap in reasonable 
fashion.'' 571 F.3d at 35 (citing Nat'l Cable & Telecomms. Ass'c v. 
Brand X Internet Servs, 545 U.S. 967, 980 (2005)).
    The D.C. Circuit then proceeded to consider and reject petitioners' 
argument that the verb ``contributes'' in CAA section 107(d) 
necessarily connotes a significant causal relationship. Specifically, 
the court again noted that the term is ambiguous, leaving it to the EPA 
to interpret in a reasonable manner. In the context of this discussion, 
the court noted that ``a contribution may simply exacerbate a problem 
rather than cause it . . .'' 571 F.3d at 39. This is consistent with 
the D.C. Circuit's decision in Bluewater Network v. EPA, 370 F.3d 1 
(D.C. Cir. 2004), in which the court, in evaluating EPA's judgment that 
emissions from a specific class or category of nonroad engines 
contribute to air pollution for which findings of ``significant'' 
contribution had already been made with respect to nonroad engines' 
emissions in the aggregate, noted that the term ``contribute'' in CAA 
section 213(a)(3) ``[s]tanding alone, . . . has no inherent connotation 
as to the magnitude or importance of the relevant `share' in the 
effect; certainly it does not incorporate any `significance' 
requirement.'' 370 F.3d at 13. In that context, the court found that 
the bare term ``contribute'' invests the Administrator with discretion 
to exercise judgment regarding what constitutes a sufficient 
contribution for the purpose of making a contribution finding. Id. at 
14.
    Finally, in Catawba County, the D.C. Circuit also rejected 
``petitioners' argument that the EPA violated the statute by failing to 
articulate a quantified amount of contribution that would trigger'' the 
regulatory action. 571 F.3d at 39. Although petitioners preferred that 
the EPA establish a bright-line test, the court recognized that the 
statute did not require that EPA ``quantify a uniform amount of 
contribution.'' Id.
    Given this context, it is entirely reasonable for the Administrator 
to interpret CAA section 231(a)(2)(A) to require some level of 
contribution that, while more than de minimis or trivial, need not be 
significant. It is also reasonable for the EPA to find contribution 
without establishing a ``bright-line `objective' test of 
contribution.'' 571 F.3d at 39. As in the 2009 Endangerment Finding, 
when exercising her judgment under CAA section 231(a)(2)(A), the 
Administrator not only considers the cumulative impact, but also looks 
at the totality of the circumstances (e.g., the air pollutant, the air 
pollution, the nature of the endangerment, the type of source category, 
the number of sources in the source category, and the number and type 
of other source categories that may emit the air pollutant) when 
determining whether the emissions justify regulation under the CAA. See 
id. (finding it reasonable for an agency to adopt a totality-of-the-
circumstances test under similar circumstances). In the context of GHG 
emissions, which come from many different sectors no single one of 
which is primarily responsible as their source, and which aggregate 
together into a common pollution stock that itself impacts public 
health and welfare, it is particularly reasonable to address those 
emissions from contributing sectors, even if looked at individually a 
sector may not be considered dominant. Therefore, in the specific 
context of making a contribution finding regarding GHG emissions from 
aircraft engines under CAA section 231, it is reasonable for the EPA to 
interpret that provision to not require some level of contribution that 
rises to a pre-determined numerical level or percentage- or mass-based 
portion of the overall endangering GHG air pollution.
    In addition, the EPA disagrees with the assertion that we do not 
have a reasoned basis to make this contribution finding. As described 
earlier in section V.B.4, the collective GHG emissions from the classes 
of engines used in U.S. covered aircraft (197 Tg CO2eq) clearly 
contribute to the endangering GHG air pollution, whether the comparison 
is domestic (89 percent of total U.S. aircraft GHG emissions, 10 
percent of all U.S. transportation GHG emissions, representing 2.8 
percent of total U.S. GHG emissions), global (26 percent of total 
global aircraft GHG emissions representing 2.7 percent of total global 
transportation GHG emissions and 0.4 percent of all global GHG 
emissions), or a combination of domestic and global. Both domestic and 
global comparisons, independently and jointly, support the finding. 
Moreover, these comparisons also support the finding even if GHG 
emissions from combustion of U.S. international aviation bunker fuels 
are excluded. Making this cause or contribute finding for engines used 
in U.S. covered aircraft will result in the vast majority of total U.S. 
aircraft GHG emissions being included in this determination.
    Also, even if the EPA were required to determine that a 
contribution met or exceeded a level of significance to make a 
contribution finding, for the reasons discussed above, the EPA would 
find that the contribution to the U.S. and global stocks of GHG air 
pollution from GHG emissions from classes of engines

[[Page 54473]]

used in U.S. covered aircraft is significant. As discussed in more 
detail above, their GHG emissions are larger than those from the great 
majority of emitting countries, they are larger than those of several 
major emitting countries, and they constitute one of the largest 
remaining unregulated contributing parts of the U.S. GHG emissions 
inventory.
    Finally, in response to the suggestion in the comments that a 
positive contribution finding is not supportable unless the EPA finds 
that GHG emissions from covered aircraft themselves cause climate 
impacts, without consideration of the impacts caused by the larger 
aggregate stock of GHG air pollution, we stress that the comment 
conflates the endangerment and contribution steps of the analysis. In 
making the contribution finding, the EPA need not additionally and 
separately find whether the contribution alone causes endangerment. 
That endangerment finding has already been made with respect to the 
stock of GHG air pollution to which covered aircraft GHG emissions 
contribute. The only remaining issue at the second step of the analysis 
is whether the analyzed GHG source sector in fact emits GHG air 
pollutants that contribute to the air pollution that has already been 
found to endanger public health and welfare. The covered aircraft, as 
we have shown and explained, clearly do emit GHG air pollutants that 
measurably contribute to that stock.
c. The Administrator Reasonably Provided Context in Comparing Aircraft 
GHG Emissions to Other Sector GHG Emissions
    Some commenters asserted that the EPA did not show important 
context in comparing covered aircraft GHG emissions to other mobile 
source categories' GHG emissions. The EPA does not describe the very 
low level of aircraft emissions in general relative to emissions from 
other sources. The commenters assert that, for example, the EPA does 
not point out that the growth in emissions from U.S. medium-duty and 
heavy-duty trucks since 1990 is 53 percent greater than the GHG 
emissions from the U.S. commercial aircraft sector today, and 18 
percent higher than the total U.S. aircraft (or entire U.S. aviation 
sector) GHG emissions today.
    In the proposed finding and this final finding, the EPA provides 
context for covered aircraft GHG emissions relative to other sectors' 
GHG emissions, including other categories within the transportation 
sector. As described earlier in section V.B.4, from a national 
perspective, the EPA provided tables to compare total U.S. aircraft and 
U.S. covered aircraft GHG emissions to U.S. transportation and total 
U.S. inventory GHG emissions, over an extended timeframe (1990-2014). 
We also noted that overall U.S. covered aircraft comprised the third 
largest source of GHG emissions in the U.S. transportation sector 
behind only the light-duty vehicle sector and medium- and heavy-duty 
truck sectors. This is the same ranking as total U.S. aircraft, if U.S. 
covered aircraft and total U.S. aircraft are compared to the other 
transportation sectors independent of one another. Finally, we note 
that the U.S. inventory also shows that while overall U.S. GHG 
emissions grew between 1990 and 2014, transportation GHG emissions grew 
at a notably higher rate, 16 percent, more rapidly than any other U.S. 
sector. U.S. covered aircraft GHG emissions grew by 15 percent in this 
time period.\276\ Within the transportation sector, aircraft remain the 
single largest source of GHG emissions not yet subject to any GHG 
standards.
---------------------------------------------------------------------------

    \276\ Total U.S. aircraft GHG emissions decreased by 3 percent 
from 1990 to 2014. U.S. non-covered aircraft GHG emissions decreased 
by 56 percent in this same time period.
---------------------------------------------------------------------------

    In our proposal and again in this finding in section V.B.4, the 
Administrator also stated her concern that recent projections indicate 
that by 2036 GHG emissions both from all aircraft and from U.S. covered 
aircraft are likely to increase by 43 percent (from 191 Tg 
CO2eq to 272 Tg CO2eq for the years 2010 to 
2036).\277\ This was contrasted with projections of GHG emissions 
changes in other transportation sectors in the same timeframe. For 
example, projections estimate that by 2036 the light-duty vehicle 
sector is projected to see a 25 percent reduction in GHG emissions 
(from 1,133 Tg CO2eq to 844 Tg CO2eq) from the 
2010 baseline, while the freight trucks sector is projected to 
experience a 23 percent increase in GHG emissions (from 390 Tg 
CO2eq to 478 Tg CO2eq) from the 2010 baseline. 
(However, this projected increase does not reflect the impact of GHG 
reductions on the freight trucks sector anticipated from the Phase 2 
heavy-duty GHG standards that have not yet been promulgated.) In 
addition, by 2036 the rail sector is projected to experience a 3 
percent reduction in GHG emissions (44 Tg CO2eq to 43 Tg 
CO2eq) from the 2010 baseline.\278\ Therefore, in the context of 
projected growth it appears that U.S. covered aircraft GHG emissions 
through 2036 are estimated to increase by more than 80 Tg 
CO2eq.279 280
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    \277\ As discussed in section V.B.4.c, fuel burn growth rates 
for air carriers and general aviation aircraft operating on jet fuel 
are projected to grow by 43 percent from 2010 to 2036 and this 
provides a scaling factor for growth in GHG emissions which would 
increase at a similar rate as the fuel burn by 2030, 2036, and 2040.
    FAA, 2016: FAA Aerospace Forecast Fiscal Years 2016-2036, 94 pp. 
Available at https://www.faa.gov/data_research/aviation/aerospace_forecasts/media/FY2016-36_FAA_Aerospace_Forecast.pdf (last 
accessed March 29, 2016).
    \278\ U.S. Energy Information Administration (EIA), 2015: Annual 
Energy Outlook (AEO) 2015 with projections to 2040, DOE/EIA-0383, 
154 pp. For the years 2010 to 2014, the baseline emissions for each 
sector are from the 2016 Inventory of U.S. Greenhouse Gas Emissions 
and Sinks Report, and after 2014 we utilize projections from the 
2015 EIA AEO report. Available at https://www.eia.gov/forecasts/aeo/ 
(last accessed April 8, 2016).
    \279\ As described earlier in section V.B.3, in 2010, U.S. 
covered aircraft were 10 percent of U.S. transportation sector GHG 
emissions, and in 2036, U.S. covered aircraft are projected to be 15 
percent of U.S. transportation GHG emissions. In 2010, light-duty 
vehicles were 58 percent of U.S. transportation GHG emissions, and 
in 2036 they are projected to be 46 percent. In 2010, heavy-duty 
vehicles were 20 percent of U.S. transportation GHG emissions, and 
in 2036, they are projected to be 26 percent (does not reflect the 
impact from the Phase 2 heavy-duty GHG standards that have not been 
promulgated). In 2010, the rail sector was 2 percent of U.S. 
transportation GHG emissions, and in 2036, they are projected to be 
the same percentage.
    \280\ Some commenters stated that section 231(a)(2)(A) of the 
CAA does not give the EPA the authority to legally base the 
contribution finding on future emission projections. As described 
earlier in section V.B, the EPA considered future emission 
projections as information to further support our assessment of 
annual actual emissions (recent emissions from the current fleet) 
for the contribution finding.
---------------------------------------------------------------------------

    Also, the EPA provided a global perspective by showing how total 
U.S. aircraft and U.S. covered aircraft GHG emissions compare to global 
aircraft, global transport, and total global GHG emissions. In 
addition, the EPA shows the ranking of the total U.S. aircraft and U.S. 
covered GHG emissions relative to other global transportation sectors 
and entire country GHG emissions.
    One commenter stated that it is inappropriate and misleading to 
compare U.S. aircraft GHG emissions with those of other, individual 
countries. They indicated that to fairly compare the U.S. airlines' GHG 
emissions contribution, EPA should analyze, as ICAO does, contributions 
from other world regions with comparable land masses and levels of 
economic activity. (In terms of landmass, the U.S. ranks third 
globally, behind only Russia and Canada.) The EPA disagrees with this 
comment. The language of CAA section 231(a)(2)(A) is silent regarding 
how the Administrator is to make her contribution analysis. While it 
requires that the Administrator assess whether emissions of an air 
pollutant cause or contribute to air pollution which may reasonable be 
anticipated to endanger public health or

[[Page 54474]]

welfare, it does not limit how she may undertake that assessment. It 
surely is reasonable that the Administrator look at how total U.S. 
aircraft GHG emissions and U.S. covered aircraft GHG emissions compare 
to U.S. and global GHG emissions on an absolute and relative basis, 
including ranking compared to other transportation sectors and entire 
country emissions. It is entirely appropriate for the Administrator to 
decide that part of understanding how a U.S. source category emitting 
GHGs fits into the bigger picture of global climate change is to 
determine how that source category fits into the contribution from the 
United States as a whole (including U.S. transportation and total U.S. 
inventory GHG emissions), where the United States as a country is a 
major emitter of GHGs. Knowing how total U.S. aircraft GHG emissions 
and U.S. covered aircraft GHG emissions rank compared to entire country 
GHG emissions is relevant to understanding what role they play in the 
global problem and hence whether they ``contribute'' to the global 
problem. Moreover, the Administrator is looking at these emissions 
comparisons as appropriate under the applicable science, facts, and 
law. Therefore, the EPA appropriately compared and provided sufficient 
context for total U.S. aircraft GHG emissions and U.S. covered aircraft 
GHG emissions.
d. The Administrator Reasonably Utilized Multiple Databases for Global 
GHG Emissions
    Some commenters stated that the mix of data from different years 
utilizing emissions data from IPCC, WRI/CAIT, and IEA was confusing and 
potentially misleading. The EPA acknowledges that we presented data 
from a variety of sources, but the EPA does not agree that the analysis 
and presentation was misleading. We note that the global analysis for 
this covered aircraft contribution finding is consistent with the 
analytical approach originally developed and used in the 2009 
Endangerment Finding. As described earlier in section IV.A, in the 
proposed finding and this final finding, the Administrator considers 
the recent, major scientific assessments of the IPCC, USGCRP, and the 
NRC as the primary scientific and technical basis informing her 
judgment. Thus, the Administrator is informed by and places 
considerable weight upon the IPCC's data on global GHG emissions. She 
places less emphasis on the WRI/CAIT and IEA emissions data, which in 
comparison have a different aggregation of underlying data but are 
available for more recent years (in comparison to the IPCC data). As 
described earlier in section V.B.4, the WRI/CAIT data are generally in 
line with the IPCC data. For 2010 total global GHG emissions, IPCC data 
are 49,000 Tg CO2eq, and WRI/CAIT indicates 42,968 Tg 
CO2eq (a 12 percent difference).\281\ Also, for 2010 global 
aircraft GHG emissions, IPCC data are 743 Tg CO2eq, and IEA 
data indicate 749 Tg CO2eq (a 1 percent difference).\282\
---------------------------------------------------------------------------

    \281\ Comparing their 2010 total global GHG emissions, IPCC data 
are 49,000 Tg CO2eq, and WRI/CAIT data, including 
forestry and land use inventories, indicates 45,748 Tg 
CO2eq (a 7 percent difference).
    \282\ Comparing 2012 WRI/CAIT to 2010 IPCC data, WRI/CAIT data 
for total global GHG emissions indicates 44,816 Tg CO2eq 
for 2012 (a 9 percent difference), and including forestry and land 
use inventories WRI/CAIT data indicates 47,599 Tg CO2eq 
for 2012 (a 3 percent difference). Comparing 2012 IEA data to 2010 
IPCC data, IEA data for global aircraft GHG emissions indicates 775 
Tg CO2eq for 2012 (a 4 percent difference).
---------------------------------------------------------------------------

    The approach of considering the major scientific assessments, 
including IPCC's assessment, provides assurance that the 
Administrator's judgment is informed by the best available, well-vetted 
science that reflects the consensus of the climate science research 
community. The major findings of the assessments, including IPCC's 
assessment, support the Administrator's findings in this action. While 
the EPA uses the IPCC data as the primary data source for this 
contribution finding, it has reasonably used additional data sources 
from widely used and recognized global datasets to provide context and 
information from more recent years. These additional data supplement 
and confirm the IPCC data. Ultimately, whether the Agency utilizes the 
IPCC data alone or the WRI/CAIT dataset (and IEA data) alone, or both 
datasets together, it would have no material effect on the emissions 
comparisons discussed in section V.B and the Administrator would make 
the same contribution finding.

VI. Statutory Authority and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review and Executive 
Order 13563: Improving Regulation and Regulatory Review

    This action is a significant regulatory action because it raises 
novel policy issues. Accordingly, it was submitted to the Office of 
Management and Budget (OMB) for review. This action finalizes a finding 
that GHG emissions from aircraft cause or contribute to air pollution 
that may be reasonably anticipated to endanger public health and 
welfare. Any changes made in response to OMB recommendations have been 
documented in the docket for this action.

B. Paperwork Reduction Act (PRA)

    This action does not impose an information collection burden under 
the PRA. The endangerment and cause or contribute findings under CAA 
section 231(a)(2)(A) do not contain any information collection 
activities.

C. Regulatory Flexibility Act (RFA)

    I certify that this action will not have a significant economic 
impact on a substantial number of small entities under the RFA. This 
action will not impose any requirements on small entities. The 
endangerment and cause or contribute findings under CAA section 
231(a)(2)(A) do not in-and-of-themselves impose any new requirements 
but rather set forth the Administrator's determination that GHG 
emissions from certain classes of aircraft engines--those used in U.S. 
covered aircraft--cause or contribute to air pollution that may be 
reasonably anticipated to endanger public health and welfare. 
Accordingly, this action affords no opportunity for the EPA to fashion 
for small entities less burdensome compliance or reporting requirements 
or timetables or exemptions from all or part of the findings.

D. Unfunded Mandates Reform Act (UMRA)

    This action does not contain any unfunded mandate as described in 
UMRA, 2 U.S.C. 1531-1538, and does not significantly or uniquely affect 
small governments. The action imposes no enforceable duty on any state, 
local or tribal governments or the private sector.

E. Executive Order 13132: Federalism

    This action does not have federalism implications. It will not have 
substantial direct effects on the states, on the relationship between 
the national government and the states, or on the distribution of power 
and responsibilities among the various levels of government.

F. Executive Order 13175: Consultation and Coordination With Indian 
Tribal Governments

    This action does not have tribal implications as specified in 
Executive Order 13175. The final endangerment and cause or contribute 
findings under CAA section 231(a)(2)(A) do not in-and-of-themselves 
impose any new requirements but rather set forth the Administrator's 
determination that GHG emissions from certain classes of aircraft 
engines--those used in U.S. covered

[[Page 54475]]

aircraft--cause or contribute to air pollution that may be reasonably 
anticipated to endanger public health and welfare. Thus, Executive 
Order 13175 does not apply to this action.

G. Executive Order 13045: Protection of Children From Environmental 
Health Risks and Safety Risks

    This action is not subject to Executive Order 13045 because it is 
not economically significant as defined in Executive Order 12866. The 
Administrator considered climate change risks to children as part of 
the endangerment and cause or contribute findings under CAA section 
231(a)(2)(A). This action's discussion of climate change impacts on 
public health and welfare is found in section IV of this preamble. 
Specific discussion with regard to children is contained in sections 
IV.C.1.a of the preamble. A copy of all documents pertaining to the 
impacts on children's health from climate change have been placed in 
the public docket for this action.

H. Executive Order 13211: Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution or Use

    This action is not a ``significant energy action'' because it is 
not likely to have a significant adverse effect on the supply, 
distribution or use of energy. Further, we have concluded that this 
action is not likely to have any adverse energy effects because the 
endangerment and cause or contribute findings under section 
231(a)(2)(A) do not in-and-of themselves impose any new requirements 
but rather set forth the Administrator's determination that GHG 
emissions from certain classes of aircraft engines--those used in U.S. 
covered aircraft--cause or contribute to air pollution that may be 
reasonably anticipated to endanger public health and welfare.

I. National Technology Transfer and Advancement Act (NTTAA)

    This action does not involve technical standards.

J. Executive Order 12898: Federal Actions To Address Environmental 
Justice in Minority Populations and Low-Income Populations

    The EPA believes this action will not have potential 
disproportionately high and adverse human health or environmental 
effects on minority, low-income, or indigenous populations because this 
action does not affect the level of protection provided to human health 
or the environment. The Administrator considered climate change risks 
to minority, low-income, and indigenous populations as part of these 
endangerment and cause or contribute findings under CAA section 
231(a)(2)(A). This action's discussion of climate change impacts on 
public health and welfare is found in section IV.C of the preamble. 
Specific discussion with regard to minority, low-income, and indigenous 
populations are found in sections IV.C.1.a and IV.C.2.a of this 
preamble. A copy of all documents pertaining to the impacts on these 
communities from climate change have been placed in the public docket 
for this action.

K. Congressional Review Act (CRA)

    The EPA will submit a rule report to each House of the Congress and 
to the Comptroller General of the United States. This action is not a 
``major rule'' as defined by 5 U.S.C. 804(2).

L. Determination Under Section 307(d)

    Section 307(d)(1)(V) of the CAA provides that the provisions of 
section 307(d) apply to ``such other actions as the Administrator may 
determine.'' Pursuant to section 307(d)(1)(V), the Administrator 
determines that this action is subject to the provisions of section 
307(d).

VII. Statutory Provisions and Legal Authority

    Statutory authority for this action comes from 42 U.S.C. 7571, 7601 
and 7607.

List of Subjects

40 CFR Part 87

    Environmental protection, Air pollution control, Aircraft, Aircraft 
engines.

40 CFR Part 1068

    Environmental protection, Administrative practice and procedure, 
Confidential business information, Imports, Motor vehicle pollution, 
Penalties, Reporting and recordkeeping requirements, Warranties.

    Dated: July 25, 2016.
Gina McCarthy,
Administrator.
[FR Doc. 2016-18399 Filed 8-12-16; 8:45 am]
 BILLING CODE 6560-50-P