Proposed Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Section 202(a) of the Clean Air Act, 18886-18910 [E9-9339]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 74, Number 78 (Friday, April 24, 2009)]
[Proposed Rules]
[Pages 18886-18910]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E9-9339]



[[Page 18885]]

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Part III





Environmental Protection Agency





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40 CFR Chapter 1



Proposed Endangerment and Cause or Contribute Findings for Greenhouse 
Gases Under Section 202(a) of the Clean Air Act; Proposed Rule

Federal Register / Vol. 74 , No. 78 / Friday, April 24, 2009 / 
Proposed Rules

[[Page 18886]]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Chapter 1

[EPA-HQ-OAR-2009-0171; FRL-8895-5]
RIN 2060-ZA14


Proposed Endangerment and Cause or Contribute Findings for 
Greenhouse Gases Under Section 202(a) of the Clean Air Act

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: Today the Administrator is proposing to find that greenhouse 
gases in the atmosphere endanger the public health and welfare of 
current and future generations. Concentrations of greenhouse gases are 
at unprecedented levels compared to the recent and distant past. These 
high atmospheric levels are the unambiguous result of human emissions, 
and are very likely the cause of the observed increase in average 
temperatures and other climatic changes. The effects of climate change 
observed to date and projected to occur in the future--including but 
not limited to the increased likelihood of more frequent and intense 
heat waves, more wildfires, degraded air quality, more heavy downpours 
and flooding, increased drought, greater sea level rise, more intense 
storms, harm to water resources, harm to agriculture, and harm to 
wildlife and ecosystems--are effects on public health and welfare 
within the meaning of the Clean Air Act. In light of the likelihood 
that greenhouse gases cause these effects, and the magnitude of the 
effects that are occurring and are very likely to occur in the future, 
the Administrator proposes to find that atmospheric concentrations of 
greenhouse gases endanger public health and welfare within the meaning 
of Section 202(a) of the Clean Air Act. She proposes to make this 
finding specifically with respect to six greenhouse gases that together 
constitute the root of the climate change problem: carbon dioxide, 
methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and 
sulfur hexafluoride.
    The Administrator is also proposing to find that the combined 
emissions of carbon dioxide, methane, nitrous oxide, and 
hydrofluorocarbons from new motor vehicles and new motor vehicle 
engines are contributing to this mix of greenhouse gases in the 
atmosphere. Thus, she proposes to find that the emissions of these 
substances from new motor vehicles and new motor vehicle engines are 
contributing to air pollution which is endangering public health and 
welfare under section 202(a) of the Clean Air Act.

DATES: Comments on this proposed action must be received on or before 
June 23, 2009. If you submitted comments on the issues raised by this 
proposal in dockets for other Agency efforts (e.g., the Advance Notice 
of Proposed Rulemaking on Regulating Greenhouse Gases under the Clean 
Air Act), you must still submit your comments to the docket for this 
action (EPA-HQ-OAR-2009-0171) by the deadline if you want them to be 
considered.
    There will be two public hearings. One hearing will be held on May 
18, 2009 in Arlington, VA. The other hearing will be on May 21, 2009 in 
Seattle, WA. To obtain information about the public hearings or to 
register to speak at the hearings, please see the SUPPLEMENTARY 
INFORMATION section below or go to https://www.epa.gov/climatechange/endangerment.html.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-
OAR-2009-0171, by one of the following methods:
     Federal eRulemaking Portal: https://www.regulations.gov. 
Follow the online instructions for submitting comments.
     E-mail: GHG-Endangerment-Docket@epa.gov.
     Fax: (202) 566-1741.
     Mail: Environmental Protection Agency, EPA Docket Center 
(EPA/DC), Mailcode 6102T, Attention Docket ID No. EPA-HQ-OAR-2009-0171, 
1200 Pennsylvania Avenue, NW., Washington, DC 20460.
     Hand Delivery: EPA Docket Center, Public Reading Room, EPA 
West Building, Room 3334, 1301 Constitution Avenue, NW., Washington, DC 
20004. Such deliveries are only accepted during the Docket's normal 
hours of operation, and special arrangements should be made for 
deliveries of boxed information.
    Instructions: Direct your comments to Docket ID No. EPA-HQ-OAR-
2009-0171. EPA's policy is that all comments received will be included 
in the public docket without change and may be made available online at 
https://www.regulations.gov, including any personal information 
provided, unless the comment includes information claimed to be CBI or 
other information whose disclosure is restricted by statute. Do not 
submit information that you consider to be CBI or otherwise protected 
through https://www.regulations.gov or e-mail. The https://www.regulations.gov Web site is an ``anonymous access'' system, which 
means EPA will not know your identity or contact information unless you 
provide it in the body of your comment. If you send an e-mail comment 
directly to EPA without going through https://www.regulations.gov your 
e-mail address will be automatically captured and included as part of 
the comment that is placed in the public docket and made available on 
the Internet. If you submit an electronic comment, EPA recommends that 
you include your name and other contact information in the body of your 
comment and with any disk or CD-ROM you submit. If EPA cannot read your 
comment due to technical difficulties and cannot contact you for 
clarification, EPA may not be able to consider your comment. Electronic 
files should avoid the use of special characters, any form of 
encryption, and be free of any defects or viruses.
    Docket: All documents in the docket are listed in the https://www.regulations.gov index. Although listed in the index, some 
information is not publicly available, e.g., CBI or other information 
whose disclosure is restricted by statute. Certain other material, such 
as copyrighted material, will be publicly available only in hard copy. 
Publicly available docket materials are available either electronically 
in https://www.regulations.gov or in hard copy at the Air Docket, EPA/
DC, EPA West, Room B102, 1301 Constitution Ave., NW., Washington, DC. 
This Docket Facility 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: Jeremy Martinich, Climate Change 
Division, Office of Atmospheric Programs (MC-6207J), Environmental 
Protection Agency, 1200 Pennsylvania Ave., NW., Washington, DC 20460; 
telephone number: (202) 343-9927; fax number: (202) 343-2202; e-mail 
address: ghgendangerment@epa.gov. Please use this contact information 
for general questions only. Official comments must be submitted using 
the instructions above.

SUPPLEMENTARY INFORMATION:
    Additional Information on Public Hearings: The two public hearings 
will be held on May 18 in Arlington, VA, and on May 21, 2009, in 
Seattle, WA. Both hearings will begin at 9 a.m. and end at 8 p.m., 
respective local times.
    Addresses: The hearings will be held at the following locations:

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    1. Arlington, VA: One Potomac Yard, 2777 S. Crystal Drive, 
Arlington, VA 22202.
    2. Seattle, WA: Bell Harbor International Conference Center, 2211 
Alaskan Way, Pier 66, Seattle, WA 98121.
    The public hearings will provide interested parties the opportunity 
to present data, views, or arguments concerning the proposed findings. 
The EPA may ask clarifying questions during the oral presentations, but 
will not respond to the presentations at that time. Written statements 
and supporting information submitted during the comment period will be 
considered with the same weight as any oral comments and supporting 
information presented at the public hearings. Written comments must be 
received by the last day of the comment period, as specified in the 
proposal.
    To obtain additional information about the public hearings or to 
register to speak at the hearings, please go to: https://www.epa.gov/climatechange/endangerment.html. Alternatively, contact Jeremy 
Martinich at 202-343-9927. Verbatim transcripts of the hearings and 
written statements will be included in the rulemaking docket.

What Should I Consider as I Prepare My Comments for EPA?

1. Submitting CBI

    Do not submit this information to EPA through www.regulations.gov 
or e-mail. Clearly mark the part or all of the information that you 
claim to be confidential business information (CBI). For CBI 
information in a disk or CD ROM that you mail to EPA, mark the outside 
of the disk or CD ROM as CBI and then identify electronically within 
the disk or CD ROM the specific information that is claimed as CBI. In 
addition to one complete version of the comment that includes 
information claimed as CBI, a copy of the comment that does not contain 
the information claimed as CBI must be submitted for inclusion in the 
public docket. Information so marked will not be disclosed except in 
accordance with procedures set forth in 40 CFR part 2.

2. Tips for Preparing Your Comments

    When submitting comments, remember to:
     Explain your views as clearly as possible.
     Describe any assumptions that you used.
     Provide any technical information and/or data you used 
that support your views.
     Provide specific examples to illustrate your concerns.
     Offer alternatives.
     Make sure to submit your comments by the comment period 
deadline identified.
     To ensure proper receipt by EPA, identify the appropriate 
docket identification number in the subject line on the first page of 
your response. It would also be helpful if you provided the name, date, 
and Federal Register citation related to your comments.

Table of Contents

I. Introduction
    A. Summary
    B. Background Information Helpful to Understanding This Proposal
    1. Greenhouse Gases and Their Effects
    2. Statutory Basis for This Proposal
    3. The Supreme Court's Decision in Massachusetts v. EPA
    a. The Petition of the International Center for Technology 
Assessment
    b. The Supreme Court's Decision
    4. EPA's Advance Notice of Proposed Rulemaking on Regulating 
Greenhouse Gases Under the Clean Air Act
    C. Solicitation of Comments
II. Legal Framework for This Action
    A. Section 202(a)--Endangerment and Cause or Contribute
    1. The Statutory Language
    2. Origin of the Current Statutory Language
    a. Ethyl Corp. v. EPA
    b. The 1977 Clean Air Act Amendments
    3. Additional Considerations for the Cause or Contribute 
Analysis
    4. Comments on Elements of the Endangerment and Cause or 
Contribute Tests Made During the ANPR Public Comment Period
    B. Air Pollutant, Public Health and Welfare
III. The Administrator's Proposed Endangerment Finding
    A. Approach in Utilizing the Best Available Scientific 
Information
    B. The Air Pollution
    1. Common Features of the Six Key Greenhouse Gases
    2. Evidence That the Six Greenhouse Gases Are at Unprecedented 
Levels in the Atmosphere
    3. Evidence That Elevated Atmospheric Concentrations of the Six 
Greenhouse Gases Are the Root Cause of Observed Climate Change
    4. Other Climate Forcers
    a. Water Vapor
    b. The Ozone-Depleting Substances: CFCs, HCFCs and Halons
    c. Tropospheric Ozone
    d. Black Carbon
    e. Fluorinated Ethers and Recently Identified Greenhouse Gases
    C. The Administrator's Proposed Finding That the Air Pollution 
Endangers Public Health and Welfare
    1. Evidence of Currently Observed Climatic and Related Effects
    2. Future Projected Climatic and Related Effects
    3. Impacts on Public Health
    4. Impacts on Public Welfare
    5. The Administrator's Consideration of International Effects
    6. The Administrator's Consideration of Key Uncertainties
    7. Summary
IV. The Administrator's Cause or Contribute Finding
    A. The Air Pollutant(s)
    1. Proposed Definition of Air Pollutant
    2. How the Definition of Air Pollutant in the Endangerment 
Determination Affects Section 202(a) Standards
    B. Proposed Cause or Contribute Finding
    1. Overview of Greenhouse Gas Emissions
    2. Overview of Section 202(a) Source Categories and Cause or 
Contribute Analysis
    3. Proposed Finding That Emissions of the Collective Group of 
Six Greenhouse Gases Contributes to Air Pollution Which May 
Reasonably Be Anticipated To Endanger Public Health and Welfare
    a. Total Greenhouse Gas Emissions From Section 202(a) Source 
Categories
    b. Proposed Contribution Finding for the Single Air Pollutant 
Comprised of the Collective Group of Six Greenhouse Gases
    4. Additional Consideration of Whether Each Greenhouse Gas as a 
Separate Air Pollutant Contributes to Air Pollution Which May 
Reasonably Be Anticipated To Endanger Public Health and Welfare
    a. Carbon Dioxide Emissions From Section 202(a) Source 
Categories
    b. Methane Emissions From Section 202(a) Source Categories
    c. Nitrous Oxide Emissions From Section 202(a) Source Categories
    d. HFC emissions From Section 202(a) Source Categories
V. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review
    B. Paperwork Reduction Act
    C. Regulatory Flexibility Act
    D. Unfunded Mandates Reform Act
    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
    H. Executive Order 13211: Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution, or Use
    I. National Technology Transfer and Advancement Act
    J. Executive Order 12898: Federal Actions To Address 
Environmental Justice in Minority Populations and Low-Income 
Populations

I. Introduction

A. Summary

    Pursuant to section 202(a) of the Clean Air Act (CAA or Act), the 
Administrator proposes to find that the mix of six key greenhouse gases 
in the atmosphere may reasonably be anticipated to endanger public 
health and welfare. Specifically, the Administrator is proposing to 
define the ``air pollution'' referred to in section

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202(a) of the CAA to be the mix of six key directly emitted and long-
lived greenhouse gases: Carbon dioxide (CO2), methane 
(CH4), nitrous oxide (N2O), hydrofluorocarbons 
(HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride 
(SF6). It is the Administrator's judgment that the total 
body of scientific evidence compellingly supports a positive 
endangerment finding for both public health and welfare. The 
Administrator reached this judgment by considering both observed and 
projected future effects, and by considering the full range of risks 
and impacts to public health and welfare occurring within the U.S., 
which by itself warrants this judgment. In addition, the scientific 
evidence concerning risks and impacts occurring outside the U.S., 
including risks and impacts that can affect people in the U.S., 
provides further support for this finding.\1\
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    \1\ As discussed later, EPA does not need to determine, and is 
not determining, whether impacts occurring outside the U.S. would be 
sufficient by themselves to justify the proposed endangerment 
finding. Instead the impacts occurring outside the U.S. are 
considered as providing additional support for the proposed finding, 
in a situation where, as here, the impacts occurring within the U.S. 
are sufficient on their own to warrant the proposed finding. Thus, 
the Administrator does not now take a position on the legal question 
whether international effects, on their own, would be sufficient to 
support an endangerment finding under the Clean Air Act.
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    Under section 202(a) of the CAA, the Administrator is to determine 
whether emissions of any air pollutant from new motor vehicles and 
their engines cause or contribute to air pollution which may reasonably 
be anticipated to endanger public health or welfare. The Administrator 
further proposes to find that combined emissions from new motor 
vehicles and new motor vehicle engines of four of these greenhouse 
gases--carbon dioxide, methane, nitrous oxide, and hydrofluorocarbons--
contribute to this air pollution. The other greenhouse gases that are 
the subject of this proposal (perfluorocarbons and sulfur hexafluoride) 
are not emitted by motor vehicles.
    The Administrator's proposed findings come in response to the 
Supreme Court's decision in Massachusetts v. EPA, 549 U.S. 497 (2007). 
That case involved a petition submitted by the International Center for 
Technology Assessment and 18 other environmental and renewable energy 
industry organizations requesting that EPA issue standards under 
section 202(a) of the Act for the emissions of carbon dioxide, methane, 
nitrous oxide, and hydrofluorocarbons from new motor vehicles and 
engines. The proposed findings are in response to this petition and are 
for purposes of section 202(a). EPA is not proposing or taking action 
under any other provision of the Clean Air Act.

B. Background Information Helpful to Understanding This Proposal

1. Greenhouse Gases and Their Effects
    Greenhouse gases are gases that effectively trap some of the 
Earth's heat that would otherwise escape to space. Greenhouse gases are 
both naturally occurring and anthropogenic. The primary greenhouse 
gases of concern directly emitted by human activities 
include carbon dioxide, methane, nitrous oxide, 
hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride. Of these 
six gases, four (carbon dioxide, methane, nitrous oxide, and 
hydrofluorocarbons) are emitted by motor vehicles.
    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 greenhouse gases from the atmosphere. 
The heating effect caused by the human-induced buildup of greenhouse 
gases in the atmosphere is very likely \2\ the cause of most of the 
observed global warming over the last 50 years. A detailed explanation 
of climate change and its impact on health, society, and the 
environment is included in EPA's technical support document (docket 
OAR-2009-0171) and discussed in the context of the 
Administrator's finding in Section III.
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    \2\ According to Intergovernmental Panel on Climate Change 
(IPCC) terminology, ``very likely'' conveys a 90 to 99 percent 
probability of occurrence. ``Virtually certain'' conveys a greater 
than 99 percent probability, ``likely'' conveys a 66 to 90 percent 
probability, and ``about as likely as not'' conveys a 33 to 66 
percent probability.
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    The U.S. transportation sector is a significant contributor to 
total U.S. and global anthropogenic emissions of greenhouse gases. 
Transportation sources subject to regulation under section 202(a) of 
the Act are the second largest greenhouse gas-emitting sector in the 
U.S., after electricity generation, and accounted for 24 percent of 
total U.S. greenhouse gas emissions in 2006 (see table 1 in section IV 
below) (these emissions are compared on carbon dioxide equivalent 
basis; see footnote 18 for an explanation). Detailed information on 
past, present, and projected greenhouse gas concentrations and 
emissions is provided in the Technical Support Document, and summarized 
in Sections III and IV, respectively.
2. Statutory Basis for This Proposal
    Section 202(a)(1) of the CAA states that ``The Administrator shall 
by regulation prescribe (and from time to time revise) * * * standards 
applicable to the emission of any air pollutant from any class or 
classes of new motor vehicles or new motor vehicle engines, which in 
[her] judgment cause, or contribute to, air pollution which may 
reasonably be anticipated to endanger public health or welfare.''
    Before the Administrator may issue standards addressing emissions 
of greenhouse gases from new motor vehicles or engines under section 
202(a), 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 new motor vehicles or 
engines cause or contribute to this air pollution.\3\ If the 
Administrator answers both questions in the affirmative, she must issue 
standards under section 202(a). Massachusetts v. EPA, 549 U.S. at 533.
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    \3\ 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 problem of 
greenhouse gases in the atmosphere. The air pollutants, on the other 
hand, are the emissions of greenhouse gases and can be thought of as 
the flow that changes the size of the total stock.
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    Typically, the endangerment and cause or contribute findings have 
been proposed concurrently with proposed standards under various 
sections of the CAA, including section 202(a). Comment has been taken 
on these proposed findings as part of the notice and comment process 
for the emission standards. See, e.g., Rulemaking for non-road 
compression-ignition engines under section 213(a)(4) of the CAA, 
Proposed Rule 58 FR 28809, 28813-14 (May 17, 1993), Final Rule 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 65 FR 35430 (June 2, 2000), Final Rule 66 FR 5002 
(Jan. 18, 2001). However, there is no requirement that the 
Administrator propose the endangerment and cause or contribute findings 
with proposed standards. The Administrator is moving forward with this 
proposed endangerment finding and a cause or contribute determination

[[Page 18889]]

while developing proposed standards under section 202(a).
    The Administrator is applying the rulemaking provisions of CAA 
section 307(d) to this action.\4\ Thus, these proposed findings will be 
subject to the same rulemaking requirements that would apply if the 
proposed findings were part of the standard-setting rulemaking. Any 
standard setting rulemaking under section 202(a) will also be subject 
to these notice and comment rulemaking procedures.
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    \4\ Commenters on the Advanced Notice of Proposed Rulemaking on 
Regulating Greenhouse Gases under the Clean Air Act, 73 FR 44354 
(2007), see Section I.B.4 below, argued that EPA is required to 
follow notice and comment requirements for the endangerment and 
cause or contribute findings. Without agreeing or disagreeing with 
the reasoning set forth in those comments, the Administrator is 
applying the rulemaking requirements of CAA section 307(d), 
including notice and comment, to today's action. See, e.g., CAA 
sections 307(d)(1)(K) (applying 307(d) requirements to the 
promulgation or revisions of regulations under section 202), 
307(d)(1)(V) (the provisions of section 307(d) apply to ``such other 
actions as the Administrator may determine.'').
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3. The Supreme Court's Decision in Massachusetts v. EPA
a. The Petition of the International Center for Technology Assessment
    On October 20, 1999, the International Center for Technology 
Assessment and 18 other environmental and renewable energy industry 
organizations filed a ``Petition for Rulemaking and Collateral Relief 
Seeking the Regulation of Greenhouse Gas Emissions from New Motor 
Vehicles under Section 202(a) of the Clean Air Act.'' The thrust of the 
petition was that four greenhouse gases--carbon dioxide, methane, 
nitrous oxide, and hydrofluorocarbons--are air pollutants as defined in 
CAA section 302(g), that emissions of these greenhouse gases contribute 
to air pollution which is reasonably anticipated to endanger public 
health or welfare, that these greenhouse gases are emitted by new motor 
vehicles, and therefore that EPA has a mandatory duty to issue 
regulations under CAA section 202(a) addressing these greenhouse gases.
    After an opportunity for public comment, EPA denied the petition in 
a notice issued on August 8, 2003. The Agency concluded that it lacked 
authority under the CAA to regulate greenhouse gases for purposes of 
global climate change, and that even if it did have the authority to 
set greenhouse gas emission standards for new motor vehicles, it would 
be unwise to do so at that time. The federal appeals court in 
Washington, DC, upheld EPA's denial of the petition.
b. The Supreme Court's Decision
    In Massachusetts v. EPA, the Supreme Court reversed the lower 
court's decision and held that EPA had improperly denied the petition. 
549 U.S. 497 (2007). The Court held that greenhouse gases are air 
pollutants under the CAA, and that the alternative grounds EPA gave for 
denying the petition were ``divorced from the statutory text'' and 
hence improper.
    Specifically, the Court held that carbon dioxide, methane, nitrous 
oxide, and hydrofluorocarbons fit the CAA's ``sweeping definition of 
`air pollutant' '' since they are ``without a doubt `physical [and] 
chemical * * * substances which [are] emitted into * * * the ambient 
air.' The statute is unambiguous.'' Id. at 529. The Court also rejected 
the argument that post-enactment legislative developments even 
``remotely suggest[ed] that Congress meant to curtail [EPA's] power to 
treat greenhouse gases as air pollutants.'' Id.
    The Court further rejected the argument that EPA could not regulate 
motor vehicle emissions of the chief greenhouse gas, carbon dioxide, 
because doing so would essentially require control of vehicle fuel 
economy, and Congress delegated that authority to the Department of 
Transportation in the Energy Policy and Conservation Act. The Court 
held that the fact ``that DOT sets mileage standards in no way licenses 
EPA to shirk its environmental responsibilities. EPA has been charged 
with protecting the public's `health' and `welfare,' 42 U.S.C. 
7521(a)(1), a statutory obligation wholly independent of DOT's mandate 
to promote energy efficiency.'' Id. at 532 (citation omitted). The two 
obligations may overlap ``but there is no reason to think the two 
agencies cannot both administer their obligations and yet avoid 
inconsistency.'' Id.
    Turning to EPA's alternative grounds for denial, the Court held 
that EPA's decision on whether or not to grant the petition must relate 
to ``whether an air pollutant `causes, or contributes to, air pollution 
which may reasonably be anticipated to endanger public health or 
welfare.' '' Id. at 532-33. Thus, ``[u]nder the clear terms of the 
Clean Air Act, EPA can avoid taking further action only if it 
determines that greenhouse gases do not contribute to climate change or 
if it provides some reasonable explanation as to why it cannot or will 
not exercise its discretion to determine whether they do.'' Id. at 533. 
The Court held that three of the four reasons EPA advanced as 
alternative grounds for denying the petition were unrelated to whether 
greenhouse gas emissions from new motor vehicles cause or contribute to 
air pollution that may reasonably be anticipated to endanger public 
health or welfare. Thus, EPA had failed to offer a reasoned explanation 
for its action. For example, the Court held that concerns related to 
foreign policy objectives had ``nothing to do with whether greenhouse 
gas emissions contribute to climate change'' and hence could not 
justify the denial. Id. The Court further held that EPA's generalized 
concerns about scientific uncertainty were likewise insufficient unless 
``the scientific uncertainty is so profound that it precludes EPA from 
making a reasoned judgment as to whether greenhouse gases contribute to 
global warming,'' in which case EPA must so find. Id. at 534.
    The Supreme Court was careful to note that it was not dictating 
EPA's action on remand, and was not deciding whether or not EPA must 
find that greenhouse gases endanger public health or welfare. Nor did 
the Court rule on ``whether policy concerns can inform EPA's actions in 
the event that it makes such a finding.'' Id. at 534-35. The Court also 
observed that under CAA section 202(a), ``EPA no doubt has significant 
latitude as to the manner, timing, content, and coordination of its 
regulations with those of other agencies.'' Id. at 533. Nonetheless, 
any EPA decisions concerning the endangerment and cause or contribute 
criteria must be grounded in the requirements of CAA section 202(a).
    Since the Supreme Court's decision in April 2007, some stakeholders 
have taken the position, including in comments on the Advance Notice of 
Proposed Rulemaking discussed below, that the Supreme Court did not 
foreclose EPA's ability to deny the petition without addressing the 
endangerment question. For example, one industry group argued that EPA 
could deny the rulemaking petition based on statutory factors besides 
scientific uncertainty and those already rejected by the Court, but did 
not describe what those additional statutory factors may be or how they 
would support a denial of the ICTA petition.
    EPA does not agree with these interpretations of the Supreme 
Court's decision. Moreover, commenters have not provided examples of 
additional statutory factors that they believe would justify denying 
the petition without addressing the endangerment and cause or 
contribute criteria. Today the Administrator is addressing these 
criteria, and is proposing to find that the mix of six key greenhouse 
gases in the atmosphere may reasonably be anticipated to endanger 
public health

[[Page 18890]]

and welfare due overwhelmingly to the effects of climate change. 
Furthermore, the Administrator is proposing to find that emissions of 
greenhouse gases by motor vehicles collectively contribute to the air 
pollution that endangers public health and welfare.
4. EPA's Advance Notice of Proposed Rulemaking on Regulating Greenhouse 
Gases Under the Clean Air Act
    On July 30, 2008, EPA published an Advance Notice of Proposed 
Rulemaking on ``Regulating Greenhouse Gas Emissions under the Clean Air 
Act'' (73 FR 44354) (ANPR). The ANPR presented information relevant to, 
and solicited public comment on, a wide variety of issues regarding the 
potential regulation of greenhouse gases under the CAA, including EPA's 
response to the Supreme Court's decision in Massachusetts v. EPA. 
Section V of the ANPR contained an earlier version of much of the 
material in this proposal, including the legal framework, a summary of 
the science of climate change, and an illustration of how the 
Administrator could analyze the cause or contribute element using 
information regarding the greenhouse gas emissions of the portion of 
the U.S. transportation sector covered by section 202(a). A July 2008 
version of the Technical Support Document (TSD) for this proposal was 
also in the docket for the ANPR (EPA-HQ-OAR-2008-0318).
    The ANPR also contained a summary of much of the work EPA had done 
in 2007 regarding draft greenhouse gas emission standards for light 
duty vehicles and trucks under section 202(a) of the Act. As noted 
earlier, EPA is currently developing proposed emissions standards 
related to today's proposal. EPA expects that these proposed standards 
will be ready to propose for public comment several months from now.
    Finally, the ANPR also discussed pending petitions under various 
sections of the Act requesting that EPA regulate greenhouse gas 
emissions from other mobile sources, as well as stationary source 
rulemakings (recently completed, ongoing or remanded) in which 
commenters suggested EPA regulate greenhouse gas emissions. EPA is 
continuing to evaluate its response to those other pending petitions 
and rulemakings and will address them in later actions.

C. Solicitation of Comments

    The Administrator requests comments on all aspects of this action. 
She requests comment on the data on which the proposed findings are 
based, the methodology used in obtaining and analyzing the data, and 
the major legal interpretations and policy considerations underlying 
the proposed findings.

II. Legal Framework for This Action

    Two provisions of the CAA govern today's proposal. Section 202(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 202(a). These statutory provisions are discussed below.

A. Section 202(a)--Endangerment and Cause or Contribute

    As noted above, section 202(a) of the CAA calls for the 
Administrator to exercise her judgment and make two separate 
determinations: first, whether air pollution may reasonably be 
anticipated to endanger public health or welfare, and second whether 
emissions of any air pollutant from new motor vehicles or engines cause 
or contribute to this air pollution.
    Based on the text of this provision and its legislative history, 
the Administrator interprets the two-part test as follows. 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. The 
Administrator is thus to consider both current and future risks. 
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. 
Under either scenario, the Administrator is permitted to find 
endangerment. If the harm would be catastrophic, the Administrator is 
permitted to find endangerment even if the likelihood is small. In the 
context of climate change, for example, the Administrator should take 
account of the most catastrophic scenarios and their probabilities. As 
explained below, however, it is not necessary to rely on low-
probability outcomes in order to find endangerment here.\5\
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    \5\ Cf. Massachusetts v. EPA, 549 U.S. at 525 n.23, citing 
Mountain States Legal Foundation v. Glickman, 92 F.3d 1228, 1234 
(D.C. Cir. 1996) (``The more drastic the injury that government 
action makes more likely, the lesser the increment in probability to 
establish standing''); Village of Elk Grove Village v. Evans, 997 
F.2d 328, 329 (7th Cir. 1993) (``[E]ven a small probability of 
injury is sufficient to create a case or controversy--to take a suit 
out of the category of the hypothetical--provided of course that the 
relief sought would, if granted, reduce the probability.'').
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    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 welfare may involve the frontiers of 
scientific or medical knowledge. At the same time, the Administrator 
must exercise reasoned decision making, and avoid speculative or 
crystal ball inquiries. Third, 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. Fourth, 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 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, and here too, catastrophic 
scenarios and their probabilities should be considered. As explained 
below, vulnerable subpopulations face serious health risks as a result 
of climate change.
    This framework recognizes that regulatory agencies such as 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.'' See 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.' '' See Massachusetts v. EPA, 549 U.S. at 506, 
n.7 (citing Ethyl Corp.). To be sure, the concept of ``expected value'' 
has its limitations in this context, but it is useful insofar as it 
suggests that when severe risks to the public health and welfare are 
involved, the Administrator need not wait as evidence continues to 
accumulate.
    The Administrator recognizes that the context for this action is 
unique. There is a very large and comprehensive base of scientific 
information that has been

[[Page 18891]]

developed over many years through a global consensus process involving 
numerous scientists from many countries and representing many 
disciplines. She also recognizes that there are varying degrees of 
uncertainty across many of these scientific issues. It is in this 
context that she is exercising her judgment and applying the statutory 
framework. Further discussion of the language in section 202(a) and its 
legislative history is provided below, to explain more fully the basis 
for this interpretation.
1. The Statutory Language
    The interpretation described above flows from the statutory 
language itself. The phrase ``may reasonably be anticipated'' and the 
term ``endanger'' 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. Moreover, 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 group of sources are the sole or even 
the major part of an air pollution problem. The use of the term 
contribute clearly indicates that a lower threshold than a finding that 
such emissions are the sole or major cause is a sufficient basis to 
make the required finding. Finally, 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. When exercising her judgment 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. Origin of the Current Statutory Language
    When Congress revised section 202(a) and other provisions of the 
CAA as part of the 1977 amendments to the CAA, it was responding to an 
opinion issued by the D.C. Circuit regarding the pre-1977 version of 
section 211(c) of the Act. The legislative history of those amendments, 
particularly the report by the House Committee on Interstate and 
Foreign Commerce, demonstrate that EPA's interpretation is fully 
consistent with Congress' intention in crafting this a provision 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'').
a. Ethyl Corp. v. EPA
    In revising the statutory language, Congress relied heavily on the 
en banc decision in Ethyl Corp. v. EPA, which reversed a 3-judge panel 
opinion regarding an EPA rule restricting the content of lead in leaded 
gasoline.\6\ 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.'' 
Id. at 7.
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    \6\ 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 211(c)(1)(A) (1970) (emphasis added). The italicized 
language in the above quote is the relevant language revised by the 
1977 amendments.
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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 held, regulatory 
action would not only precede, but prevent, a perceived threat. Id.
    The court also rejected petitioner's 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 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 EPA that even without the language in 
section 202(a) regarding ``cause or contribute to,'' it was appropriate 
for 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.
b. The 1977 Clean Air Act Amendments
    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. In 
particular, the Committee believed the Ethyl Corp. decision posed 
several ``crucial policy questions'' regarding the protection of public 
health and welfare.'' Id. \7\ The Committee addressed those questions 
with the language that now appears in section 202(a) and several other 
CAA provisions--``emission of any air pollutant * * * , which in [the 
Administrator's] judgment cause, or contribute to, air pollution which 
may reasonably be anticipated to endanger public health or welfare.''
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    \7\ The Supreme Court recognized that the current language in 
section 202(a)(1) is ``more-protective'' than the 1970 version that 
was similar to the section 211 language before the DC Circuit in 
Ethyl Corp. Massachusetts v. EPA, 549 U.S. at 506, fn 7.
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    The legislative history clearly indicates that the Committee 
intended the language to serve several purposes consistent with the en 
banc decision in Ethyl Corp. In particular, the language (1) emphasizes 
the preventive or precautionary nature of the CAA \8\; (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 at 2516-17.\9\
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    \8\ 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'').
    \9\ 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 
CAA Amendments of 1977.
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    As noted above, 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

[[Page 18892]]

the effects in reaching her judgment. The Committee emphasized that 
``judgment'' is different from a factual ``finding.'' \10\ The 
Administrator may make projections, assessments and estimates that are 
reasonable, as compared to a `` `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 below. H.R. Rep. 95-294 at 
50-51, 4 LH at 2517-18.
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    \10\ \\ Throughout this Notice 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 exercise of judgment in applying the scientific 
information to the statutory criteria is solely a factual finding; 
while grounded squarely in the science of climate change, these 
judgments also embody policy considerations.
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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 difficulties inherent in information on public 
health and welfare. H.R. Rep. 95-294 at 51, 4 LH at 2518.\11\
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    \11\ Thus, contrary to the position set forth by at least one 
commenter on the Greenhouse Gas ANPR, the statutory language does 
not require that 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.
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    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 
group 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, the statutory 
language in section 202(a) does not contain a modifier on its use of 
the term contribute. Unlike other CAA provisions, it does not require 
``significant'' contribution. See, e.g., CAA sections 111(b); 
213(a)(2), (4). Congress made it clear that the Administrator is to 
exercise her judgment in determining contribution, and 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 EPA to identify 
and then address what may well be many different sectors or groups of 
sources that are each part of the problem.
    The DC Circuit Court of Appeals has discussed 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 (DC Cir. 2004), 
industry argued that section 213(a)(3) requires a finding of a 
significant contribution before EPA can regulate, while EPA's view was 
that the CAA requires a finding only of contribution. Id. at 13. 
Section 213(a)(3), like section 202(a), is triggered by a finding that 
certain sources ``cause, or contribute to,'' air pollution, while an 
adjacent provision, section 213(a)(2), is triggered by a finding of a 
``significant'' contribution. The court looked at the ``ordinary 
meaning of `contribute' '' when upholding EPA's reading. 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.\12\ The court found that the bare ``contribute'' language 
invests the Administrator with discretion to exercise judgment 
regarding what constitutes a sufficient contribution for the purpose of 
making an endangerment finding. Id. at 14.\13\
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    \12\ 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.
    \13\ 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 section 213(a)(3), section 202(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 threshold to be met; a truly trivial or 
de minimis ``contribution'' might not count as such. 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.\14\ In the past, the 
Administrator has evaluated the emissions of the source or sources in 
different ways, based on the particular circumstances involved. For 
instance, in some mobile source rulemakings, the Administrator has used 
the percent of emissions from the regulated mobile source category 
compared to the total mobile source inventory for that air pollutant as 
the best way to evaluate contribution. See, e.g., 66 FR 5001 (2001) 
(heavy duty engine and diesel sulfur rule). In other instances the 
Administrator has looked at the percent of emissions compared to the 
total nonattainment area inventory of the air pollution at issue. See, 
e.g., 67 FR 68,242 (2002) (snowmobile rule). EPA has found that air 
pollutant emissions that amount to 1.2 percent of the total inventory 
``contribute.'' Bluewater Network, 370 F.3d at 15 (``For Fairbanks, 
this contribution was equivalent to 1.2 percent of the total daily CO 
inventory for 2001.'').
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    \14\ Section IV discusses the evidence in this case that 
supports the proposed finding of contribution. 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.
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    While these prior actions are instructive, they do not establish 
bright line emission levels above which a positive contribution 
determination must be made, or below which a contribution determination 
could not be made. The Administrator may determine that emissions at a 
certain level or percentage contribute to air pollution in one set of 
circumstances, while also judging that the same level or percentage of 
another air pollutant in a different circumstances and involving 
different air pollution does not contribute. When exercising her 
judgment, 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. Further discussion of this issue can be 
found in Section IV.

[[Page 18893]]

4. Comments on Elements of the Endangerment and Cause or Contribute 
Tests Made During the ANPR Public Comment Period
    Certain comments submitted on the ANPR \15\ argued that when 
evaluating endangerment and cause or contribute, the Administrator is 
limited to considering only those impacts that can be traced to the 
amount of air pollution directly attributable to the greenhouse gases 
emitted by new motor vehicles and engines. Such an approach collapses 
the two prongs of the test by requiring that any climate change impacts 
upon which an endangerment determination is made result solely from the 
greenhouse gas emissions of motor vehicles. It essentially eliminates 
the ``contribute'' part of the ``cause or contribute'' portion of the 
test. This approach was clearly rejected by the en banc court in Ethyl 
Corp. 541 F.2d at 29 (rejecting the argument that the emissions of the 
fuel additive to be regulated must ``in and of itself, i.e. considered 
in isolation, endanger[s] public health.''). Moreover, it conflicts 
with an enumerated purpose of the 1977 CAA Amendments: ``To assure 
consideration of the cumulative impact of all sources of a pollutant in 
setting ambient and emission standards, not just the extent of the risk 
from the emissions from a single source or class of sources of the 
pollutant; * * *'' H.R. Rep. 95-294 at 49-50, 4 LH at 2516-17.
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    \15\ Numerous comments on the ANPR discussed the endangerment 
and cause or contribute findings, and set forth how various 
stakeholders believe EPA is compelled to make those findings. EPA 
has reviewed the comments on the ANPR, and EPA appreciates the work 
that went into them. While we are not responding to every comment 
received in today's proposal, the Agency is taking this opportunity 
to respond to a few key comments related to the test that some 
stakeholders believe guides the Administrator when undertaking an 
endangerment analysis and cause or contribute evaluation. As noted 
above, commenters should submit to the docket for today's action any 
comments they want EPA to consider as it makes a decision on this 
proposed determination.
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    Nor does EPA agree with comments that argue the Administrator 
cannot make a positive endangerment or contribution determination 
unless the emissions reductions required by the resulting standards 
would ``effectively mitigate'' or ``fruitfully attack'' the impacts 
underlying the endangerment determination. Again, such an approach 
fails to appreciate the holistic approach that Congress adopted in 
1977. Moreover, as the Supreme Court recognized, ``[a]gencies, like 
legislatures, do not generally resolve massive problems in one fell 
regulatory swoop.'' Massachusetts v. EPA, 549 U.S. at 524 (citations 
omitted).\16\ 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.
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    \16\ EPA also rejects the comment that EPA has defined 
``contribute'' as resulting in a ``humanly perceptible'' difference. 
See Regional Haze Regulations and Guidelines for Best Available 
Retrofit Technology [BART] Determinations, 70 FR 39104 (2005). In 
that rule, EPA noted that a 1.0 deciview change in visibility is 
humanly perceptible in virtually all situations. Based on this, EPA 
concluded that for a state making a contribution finding for an 
individual source under section 169A(b)(2)(A), it would be 
unreasonable to determine that a source emitting pollution that 
resulted in a 0.5 deciview change in visibility did not 
``contribute'' to visibility impairment. Id. at 39120. In fact, EPA 
noted that ``[i]f `causing' visibility impairment means causing a 
humanly perceptible change in visibility, * * * then `contributing' 
to visibility impairment must mean having some lesser impact * * * 
that need not rise to the level of human perception.'' Id. at 39120, 
fn 32. The Agency did not establish a test that required human 
perception before contribution could be found.
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    Importantly, these various narrow approaches to the endangerment 
and cause or contribute criteria would effectively preclude the 
Administrator from ever making a positive finding for a global 
phenomenon like climate change because the regulatory actions would 
always be limited to just part of the picture. Indeed, they would 
preclude the Administrator from making a positive finding for any 
complex pollution problem that cannot be solved by one regulatory 
action alone. This is contrary to Congress' direction that the 
Administrator consider the whole picture when exercising her judgment 
about the critical issues of cause or contribute and endangerment to 
public health and welfare.

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, 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). Greenhouse gases 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 IV below contains 
further discussion on today's proposed definition of ``air pollutant'' 
for purposes of the contribution 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, 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 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 can include 
impacts from changes in temperature and precipitation as well as from 
the spreading of invasive species or insects. Prior welfare effects 
evaluated by EPA include impacts on vegetation generally, and changes 
in crop and forestry specifically, 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 National Ambient Air Quality Standard for Ozone, 73 FR 16436 
(2007); Control of Emissions from Nonroad Large Spark Ignition Engines 
and Recreational Engines (Marine and Land-Based), 67 FR 68242 (2002); 
Final Heavy-Duty Engine and Vehicle Standards and Highway Diesel Sulfur 
Control Requirements, 66 FR 5002 (2001).
    There is no definition of public health in the Clean Air Act. The 
Supreme Court has discussed the concept in the context of whether costs 
can be considered when setting National Ambient Air Quality Standards. 
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.