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Proposed Rule2026-19072

Rescission of the Greenhouse Gas Findings for Fossil Fuel-Fired Power Plants and Repeal of Regulations for Power Plant Greenhouse Gas Emissions Under Clean Air Act Section 111

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Published

September 17, 2026

Issuing agencies

Environmental Protection Agency

Abstract

In this action, the U.S. Environmental Protection Agency (EPA) is supplementing its proposal to repeal all greenhouse gas (GHG) emission standards for fossil fuel-fired electric generating units (EGUs) to effectuate the best reading of Clean Air Act (CAA) section 111. We propose that CAA section 111 does not authorize the EPA to regulate emissions from power plants in response to global climate change concerns. For the multiple and independent reasons described herein, this additional rationale would also require rescinding the Administrator's contrary findings and determinations in 2015 and repealing all associated 2015 and 2024 GHG standards for the fossil fuel-fired EGU source category. In a separate action published concurrently with this supplemental notice, the EPA is finalizing the repeal of certain 2024 GHG standards for the fossil fuel-fired EGU source category on distinct legal and technical grounds. We are not reopening that final rule. Nor are we soliciting further comment on those issues through this supplemental notice, except to the extent that commenters believe the final rule bears on the distinct questions of statutory authority addressed herein.

Full Text

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[Federal Register Volume 91, Number 179 (Thursday, September 17, 2026)]
[Proposed Rules]
[Pages 59002-59046]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2026-19072]

[[Page 59001]]

Vol. 91

Thursday,

No. 179

September 17, 2026

Part III

Environmental Protection Agency

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40 CFR Part 60

Rescission of the Greenhouse Gas Findings for Fossil Fuel-Fired Power
Plants and Repeal of Regulations for Power Plant Greenhouse Gas
Emissions Under Clean Air Act Section 111; Proposed Rule

Federal Register / Vol. 91, No. 179 / Thursday, September 17, 2026 /
Proposed Rules

[[Page 59002]]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 60

[EPA-HQ-OAR-2025-0124; FRL-12674.1-01-OAR]
RIN 2060-AX00

Rescission of the Greenhouse Gas Findings for Fossil Fuel-Fired
Power Plants and Repeal of Regulations for Power Plant Greenhouse Gas
Emissions Under Clean Air Act Section 111

AGENCY: Environmental Protection Agency (EPA).

ACTION: Supplemental notice of proposed rulemaking.

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SUMMARY: In this action, the U.S. Environmental Protection Agency (EPA)
is supplementing its proposal to repeal all greenhouse gas (GHG)
emission standards for fossil fuel-fired electric generating units
(EGUs) to effectuate the best reading of Clean Air Act (CAA) section
111. We propose that CAA section 111 does not authorize the EPA to
regulate emissions from power plants in response to global climate
change concerns. For the multiple and independent reasons described
herein, this additional rationale would also require rescinding the
Administrator's contrary findings and determinations in 2015 and
repealing all associated 2015 and 2024 GHG standards for the fossil
fuel-fired EGU source category. In a separate action published
concurrently with this supplemental notice, the EPA is finalizing the
repeal of certain 2024 GHG standards for the fossil fuel-fired EGU
source category on distinct legal and technical grounds. We are not
reopening that final rule. Nor are we soliciting further comment on
those issues through this supplemental notice, except to the extent
that commenters believe the final rule bears on the distinct questions
of statutory authority addressed herein.

DATES: Comments must be received on or before November 2, 2026.
Comments on the information collection provisions submitted to the
Office of Management and Budget (OMB) under the Paperwork Reduction Act
(PRA) are best assured of consideration by OMB if OMB receives a copy
of your comments on or before October 19, 2026. Please refer to the PRA
section under ``Statutory and E.O. Reviews'' in this preamble for
specific instructions.
Public Hearing. The EPA will hold a virtual public hearing on
October 1, 2026. Please refer to the SUPPLEMENTARY INFORMATION section
for information on registering for the public hearing.

ADDRESSES: You may send comments, identified by Docket ID No. EPA-HQ-
OAR-2025-0124, by any of the following methods:
<bullet> Federal eRulemaking Portal: <a href="https://www.regulations.gov">https://www.regulations.gov</a>
(our preferred method) website. Follow the online instructions for
submitting comments.
<bullet> Email: <a href="/cdn-cgi/l/email-protection#f190dc909f95dc83dc959e929a9485b1948190df969e87">[email&#160;protected]</a>. Include Docket ID No. EPA-
HQ-OAR-2025-0124 in the subject line of the message.
<bullet> Mail: U.S. Environmental Protection Agency, EPA Docket
Center, Docket ID No. EPA-HQ-OAR-2025-0124, Mail Code 28221T, 1200
Pennsylvania Avenue NW, Washington, DC 20460.
<bullet> Hand/Courier Delivery: EPA Docket Center, WJC West
Building, Room 3334, 1301 Constitution Avenue NW, Washington, DC 20004.
The Docket Center's hours of operation are 8:30 a.m. to 4:30 p.m.
Eastern Time (ET), Monday through Friday (except Federal holidays).
Instructions: All submissions received must include the Docket ID
No. for this rulemaking. Comments received may be posted without change
to <a href="https://www.regulations.gov">https://www.regulations.gov</a>, including any personal information
provided. For detailed instructions on sending comments and additional
information on the rulemaking process, see the SUPPLEMENTARY
INFORMATION section of this document.

FOR FURTHER INFORMATION CONTACT: For information about this proposed
rule, contact Ms. Lisa Thompson, Industrial Processing and Power
Division (D243-02), Office of Clean Air Programs, U.S. Environmental
Protection Agency, Research Triangle Park, North Carolina 27711;
telephone number: (919) 541-5158 and email address:
<a href="/cdn-cgi/l/email-protection#17637f787a67647879397b7e64765772677639707861">[email&#160;protected]</a>.

SUPPLEMENTARY INFORMATION:
Participation in virtual public hearing. The hearing will be held
via virtual platform on October 1, 2026. The EPA will announce further
details at <a href="https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power">https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power</a>.
The EPA will begin pre-registering speakers for the hearing no
later than 1 business day after a request has been received. To
register to speak at the virtual hearing, please use the online
registration form available at <a href="https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power">https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power</a> or contact the public hearing team at (888) 372-8699 or by
email at <a href="/cdn-cgi/l/email-protection#b5fce5e5f1c5c0d7d9dcd6ddd0d4c7dcdbd2f5d0c5d49bd2dac3">[email&#160;protected]</a>. The last day to pre-register to
speak at the hearing will be September 29, 2026. Prior to the hearing,
the EPA will post a general agenda that will list pre-registered
speakers at: <a href="https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power">https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power</a>.
The EPA will make every effort to follow the schedule as closely as
possible on the day of the hearing; however, please plan for the
hearings to run either ahead of schedule or behind schedule. The EPA
may close a session 15 minutes after the last pre-registered speaker
has testified if there are no additional speakers.
Each commenter will have 4 minutes to provide oral testimony. The
EPA encourages commenters to submit a copy of their oral testimony as
written comments electronically to the rulemaking docket.
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 oral testimony and
supporting information presented at the public hearing.
Please note that any updates made to any aspect of the hearing will
be posted online at <a href="https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power">https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power</a>. While the EPA expects the hearing to go forward as set forth
above, please monitor our website or contact the public hearing team at
(888) 372-8699 or by email at <a href="/cdn-cgi/l/email-protection#4e071e1e0a3e3b2c22272d262b2f3c2720290e2b3e2f60292138">[email&#160;protected]</a> to determine if
there are any updates. The EPA does not intend to publish a document in
the Federal Register announcing updates.
If you require special accommodations such as audio description,
please pre-register for the hearing with the public hearing team and
describe your needs by September 24, 2026. The EPA may not be able to
arrange accommodations without advanced notice.
Docket. The EPA established a docket for this action under Docket
ID No. EPA-HQ-OAR-2025-0124. The docket lists all documents at <a href="https://www.regulations.gov">https://www.regulations.gov</a>. Although listed, some information is not publicly
available, e.g., Confidential Business Information (CBI) or other
information whose disclosure is restricted by statute. The EPA does not
place certain other material, such as copyrighted material, on the
internet; this material is publicly available only as portable document
format (PDF) versions accessible only on

[[Page 59003]]

EPA computers in the docket office reading room. The public cannot
download certain databases and physical items from the docket but may
request these items by contacting the docket office at (202) 566-1744.
The docket office has 10 business days to respond to such requests.
With the exception of such material, publicly available docket
materials are available electronically at <a href="https://www.regulations.gov">https://www.regulations.gov</a>
or on EPA computers in the docket office reading room at the EPA Docket
Center, WJC West Building, Room Number 3334, 1301 Constitution Ave. NW,
Washington, DC. The Public Reading Room hours of operation are 8:30
a.m. to 4:30 p.m. ET, Monday through Friday (except for Federal
holidays). The telephone number for the Public Reading Room is (202)
566-1744, and the telephone number for the EPA Docket Center is (202)
566-1742.
Written Comments. Direct your comments to Docket ID No. EPA-HQ-OAR-
2025-0124. Under the EPA's policy, the Agency includes all comments in
the public docket without change and makes them available online at
<a href="https://www.regulations.gov">https://www.regulations.gov</a>, including any personal information
provided, unless a submission contains information claimed as CBI or
other information for which a statute restricts disclosure. Do not
submit electronically to <a href="https://www.regulations.gov">https://www.regulations.gov</a> any information
that you consider to be CBI or other information for which a statute
restricts disclosure. Submit such information as described in the
Submitting CBI section of this preamble.
The EPA may publish any comment it receives to the public docket. A
written comment must accompany any multimedia submission (e.g., audio
or video). The EPA considers the written comment the official comment
and expects it to address all points the commenter wishes to make. The
EPA will generally not consider comments or supporting materials that
appear outside the primary submission (i.e., on websites, cloud
storage, or other file-sharing systems). For additional submission
methods, the EPA's full public comment policy, information about CBI or
multimedia submissions, and guidance on making effective comments,
visit <a href="https://www.epa.gov/dockets/commenting-epa-dockets">https://www.epa.gov/dockets/commenting-epa-dockets</a>.
The <a href="https://www.regulations.gov">https://www.regulations.gov</a> website allows commenters to submit
comments anonymously, which means the EPA will not know the commenter's
identity or contact information unless the commenter provides it in the
body of the comment. If a commenter emails a comment directly to the
EPA rather than using <a href="https://www.regulations.gov">https://www.regulations.gov</a>, the EPA's system
automatically captures the sender's email address, and the Agency
includes that address in the public docket and makes it available
online. If a commenter submits an electronic comment, the EPA
recommends including the commenter's name and other contact information
in the body of the comment and with any digital storage media
submitted. If the EPA cannot read a comment due to technical
difficulties and cannot contact the commenter for clarification, the
Agency may be unable to consider the comment. Submit electronic files
without special characters, encryption, defects, or viruses. For
additional information about the EPA's public docket, visit the EPA
Docket Center homepage at <a href="https://www.epa.gov/dockets">https://www.epa.gov/dockets</a>.
The EPA solicits comment on numerous aspects of this proposed rule.
The EPA indexes each comment solicitation with an identifier (e.g.,
``C-1, C-2, . . .'') to provide a consistent framework for effective,
efficient commenting. Accordingly, the EPA asks commenters to include
the corresponding identifier when submitting comments relevant to that
solicitation. Include the identifier in a heading or within the text of
each comment (e.g., ``In response to C-1, . . .'') to make clear which
solicitation the commenter is addressing. The EPA emphasizes that the
Agency is not limiting comment to these identified areas and encourages
commenters to provide any other comments relevant to this supplemental
proposal.
Submitting CBI. Do not submit information containing CBI to the EPA
through <a href="https://www.regulations.gov">https://www.regulations.gov</a>. Clearly mark the part or all the
information that you claim to be CBI. For CBI information on any
digital storage media that you mail to the EPA, note the docket ID,
mark the outside of the digital storage media as CBI, and identify
electronically within the digital storage media the specific
information that is claimed as CBI. In addition to one complete version
of the comments that includes information claimed as CBI, you must
submit a copy of the comments that does not contain the information
claimed as CBI directly to the public docket through the procedures
outlined in the Written Comments section of this preamble. If you
submit any digital storage media that does not contain CBI, mark the
outside of the digital storage media clearly that it does not contain
CBI and note the docket ID. Information not marked as CBI will be
included in the public docket and the EPA's electronic public docket
without prior notice. Information marked as CBI will not be disclosed
except in accordance with procedures set forth in 40 Code of Federal
Regulations (CFR) part 2.
Our preferred method to receive CBI is for it to be transmitted
electronically using email attachments, File Transfer Protocol (FTP),
or other online file sharing services (e.g., Dropbox, OneDrive, Google
Drive). Electronic submissions must be transmitted directly to the
Office of Clean Air Programs (OCAP) at the email address:
<a href="/cdn-cgi/l/email-protection#ef808c8e9f8c8d86af8a9f8ec1888099">[email&#160;protected]</a> and, as described earlier in this preamble, should
include clear CBI markings and note the docket ID. If assistance is
needed with submitting large electronic files that exceed the file size
limit for email attachments, and if you do not have your own file
sharing service, please contact the person listed in the FOR FURTHER
INFORMATION CONTACT section of this preamble to receive instructions.
Preamble acronyms and abbreviations. Throughout this document the
use of ``we,'' ``us,'' or ``our'' is intended to refer to the EPA. We
use multiple acronyms and terms in this preamble. While this list may
not be exhaustive, to ease the reading of this preamble and for
reference purposes, the EPA defines the following terms and acronyms
here:

ACE Affordable Clean Energy [rule]
BSER best system of emission reduction
CAA Clean Air Act
CCS carbon capture and sequestration/storage
CO<INF>2</INF> carbon dioxide
CPP Clean Power Plan
CPS Carbon Pollution Standards rule
EGU electric generating unit
EIA economic impact analysis
E.O. Executive Order
EPA Environmental Protection Agency
FR Federal Register
GHG greenhouse gas
GMST global mean surface temperature
GSLR global sea level rise
HAP hazardous air pollutant
HFC hydrofluorocarbons
IGCC integrated gasification combined cycle
IRA Inflation Reduction Act
NAAQS National Ambient Air Quality Standards
NPRM Notice of Proposed Rulemaking
NSPS new source performance standards
OMB Office of Management and Budget

Table of Contents

I. General Information
A. Does this action apply to me?
B. Where can I get a copy of this document and other related
information?
II. Executive Summary
A. Introduction
B. Need for Regulatory Action
III. Background

[[Page 59004]]

A. Statutory Authority Under CAA Section 111
B. Legislative and Regulatory History of CAA Section 111
C. Regulation of Greenhouse Gases Under CAA Section 111
D. Legislation Concerning CAA Section 111
IV. Legal Framework for Action
V. Rescission of the 2015 Findings
A. Best Reading of CAA Section 111(b)(1)(A)
B. Lack of Clear Congressional Authorization
C. Eliminating GHG Emissions From Fossil Fuel-Fired Power Plants
Would Be Futile
VI. Repeal of GHG Standards of Performance for Fossil Fuel-Fired
EGUs Under CAA Section 111
A. Scope of Repeal of GHG Standards of Performance
B. Impacts of Repeal of GHG Standards of Performance
VII. Requests for Comment
VIII. Statutory and E.O. Reviews
A. E.O. 12866: Regulatory Planning and Review
B. E.O. 14192: Unleashing Prosperity Through Deregulation
C. Paperwork Reduction Act (PRA)
D. Regulatory Flexibility Act (RFA)
E. Unfunded Mandates Reform Act (UMRA)
F. E.O. 13132: Federalism
G. E.O. 13175: Consultation and Coordination With Indian Tribal
Governments
H. E.O. 13045: Protection of Children From Environmental Health
Risks and Safety Risks
I. E.O. 13211: Actions Concerning Regulations That Significantly
Affect Energy Supply, Distribution, or Use
J. National Technology Transfer and Advancement Act (NTTAA) and
1 CFR Part 51

I. General Information

A. Does this action apply to me?

Fossil fuel-fired electric utility steam generating units and
stationary combustion turbine EGUs that provide electricity to the
electric grid (a utility power distribution system) comprise the source
category that is subject to this action. The 2022 North American
Industry Classification System (NAICS) code for the source category is
221112. The EPA does not intend this identification to be exhaustive
but rather to provide a guide for readers regarding the entities that
this proposed action is likely to affect.
The proposed repeal of 40 CFR part 60, subpart TTTT, once
promulgated, would be applicable to stationary combustion turbines that
commenced construction or modification after January 8, 2014, or
reconstruction after June 18, 2014, and on or before May 23, 2023, and
any steam generating unit or integrated gasification combined cycle
(IGCC) facility that commenced construction after January 8, 2014, or
commenced modification or reconstruction after June 18, 2014. The
proposed repeal of 40 CFR part 60, subpart TTTTa, once promulgated,
would be applicable to stationary combustion turbines that began
construction or reconstruction after May 23, 2023, and any steam
generating unit that commenced modification after May 23, 2023.

B. Where can I get a copy of this document and other related
information?

In addition to the docket, an electronic copy of this proposed
action will be on the internet. Following signature by the
Administrator, the EPA will post a copy of this proposed action at
<a href="https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power">https://www.epa.gov/stationary-sources-air-pollution/greenhouse-gas-standards-and-guidelines-fossil-fuel-fired-power</a>. Following publication
in the Federal Register (FR), the EPA will post the FR version at this
same website.

II. Executive Summary

A. Introduction

On June 17, 2025, the EPA published a Notice of Proposed Rulemaking
(NPRM) in the Federal Register entitled ``Repeal of Greenhouse Gas
Emissions Standards for Fossil Fuel-Fired Electric Generating Units.''
90 FR 25752 (``June 2025 NPRM''). In that action, we proposed two
independent pathways for revisiting the GHG standards of performance
for the fossil fuel-fired EGU source category established in the 2015
New Source Performance Standards, 80 FR 64510 (Oct. 23, 2015) (``2015
NSPS''), and 2024 Carbon Pollution Standards, 89 FR 39798 (May 9, 2024)
(``2024 CPS''). The primary pathway proposed to repeal all GHG
standards of performance for fossil fuel-fired EGUs for lack of
authority based on the conclusion that such power plants do not
``contribute significantly'' to air pollution that endangers public
health or welfare. The alternative pathway proposed to repeal many
requirements in the 2024 CPS based on a reconsideration of the best
system of emission reduction (BSER) determinations supporting the
requirements.
In a final rule issued concurrently with this supplemental notice,
the EPA is finalizing the repeal of the majority of the 2024 CPS
requirements based on a reassessment of the BSER for the relevant
subcategories.\1\ The EPA notes in that final rule that it is seeking
additional public comment in a separate action (i.e., in this
supplemental notice) on the underlying question raised in the primary
basis of the June 2025 NPRM: Whether the EPA lacks statutory authority
to regulate GHG emissions from power plants under CAA section 111.\2\
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\1\ See Partial Repeal of the Carbon Pollution Standards for
Fossil Fuel-Fired Electric Generating Units, available in Docket ID
EPA-HQ-OAR-2025-0124.
\2\ The EPA is not reopening or soliciting further comment on
the distinct issues addressed in the contemporaneous final rule.
Commenters are welcome to articulate whether and why they believe
the actions and rationales adopted in the final rule are relevant to
the distinct question addressed in this supplemental proposal, but
the EPA generally will not respond to comments that are limited to
the issues resolved in the final rule. Interested parties were
invited to comment on those issues in connection with the
alternative basis presented in the June 2025 NPRM and may review the
EPA's summary of comments and responses thereto in the final rule
preamble and associated response to comments (RTC).
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This supplemental notice proposes additional approaches to that
question in light of the Agency's intervening final action entitled
``Rescission of the Greenhouse Gas Endangerment Finding and Motor
Vehicle Greenhouse Gas Emission Standards Under the Clean Air Act,'' 91
FR 7686 (Feb. 18, 2026) (``Endangerment Finding Rescission''). In that
final rule, the EPA rescinded the Administrator's 2009 findings of
endangerment and contribution, and repealed all GHG emission standards,
for new motor vehicles and engines based on the conclusion that the
Agency lacks statutory authority under CAA section 202(a)(1) to
regulate in response to global climate change concerns. In this
supplemental notice, we propose that the EPA lacks authority under CAA
section 111 to regulate power plants in response to global climate
change concerns for multiple, independent reasons. The approach and
rationales proposed in this supplemental notice would require the same
regulatory actions contemplated in the primary proposal in the June
2025 NPRM--the repeal of all fossil fuel-fired EGU GHG standards for
lack of authority--but for different reasons. Whereas the primary
proposal in the June 2025 NPRM sought public comment on, among other
things, whether fossil fuel-fired EGUs ``contribute significantly'' to
air pollution, this supplemental notice seeks public comment on the
distinct question whether global climate change concerns satisfy the
threshold requirement in CAA section 111(b)(1)(A) that the source
category emissions contribute significantly to ``air pollution which
may reasonably be anticipated to endanger public health or welfare.''
We will evaluate both proposed approaches and rationales in taking
final action, as both issues--

[[Page 59005]]

contribution and endangerment--were the subject of significant
interpretive and policy changes in the 2009 Endangerment Finding and
the 2015 NSPS and 2024 CPS that extended the Agency's novel approach to
power plant stationary sources.\3\
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\3\ The EPA is not soliciting further comment on the primary
proposal in the June 2025 NPRM. Commenters are welcome to articulate
whether and why they believe the distinct rationales presented in
this supplemental proposal are or are not preferable to the
rationale presented in the June 2025 NPRM, but the EPA generally
will not respond to comments that are limited to the primary
proposal in the June 2025 NPRM. Interested parties were invited to
comment on those issues in connection with the primary proposal in
the June 2025 NPRM, and the Agency will address such comments as
appropriate in a forthcoming final rule addressing the rationales
presented in both the primary proposal in the June 2025 NPRM and
this supplemental proposal.
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In 2009, the EPA took the unprecedented step of asserting authority
to regulate GHG emissions in a standalone action that launched the
Agency into a course of regulation that fundamentally reshaped many
aspects of the Nation's economic and social life. 74 FR 66496 (Dec. 15,
2009) (``2009 Endangerment Finding'').\4\ In the 2009 Endangerment
Finding, we interpreted CAA section 202(a)(1) for the first time to
authorize regulation of domestic emissions from new motor vehicles and
engines based on global climate change concerns rather than air
pollution that endangers public health or welfare through local or
regional exposure. 74 FR 66526-27. We relied on that interpretation to
define both the relevant ``air pollution'' and the relevant ``air
pollutant'' as the combination of six ``well-mixed GHGs''--carbon
dioxide (CO<INF>2</INF>), methane, nitrous oxide (N<INF>2</INF>O),
hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur
hexafluoride (SF<INF>6</INF>)--while reserving the right to include
additional ``climate forcers'' in these definitions in the future. 74
FR 66516-17, 66536-37.
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\4\ See also ``Endangerment and Cause or Contribute Findings for
Greenhouse Gases Under Section 202(a) of the Clean Air Act: EPA's
Response to Public Comments'' (``EF RTC''), available in a
Memorandum to Docket entitled ``EPA's Response to Public Comments on
the 2009 Endangerment and Cause or Contribute Findings for
Greenhouse Gases: Volumes 1-11,'' Document ID EPA-HQ-OAR-2025-0194-
31053.
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The EPA subsequently relied on the 2009 Endangerment Finding as the
foundation for a new regulatory construct that subjected an increasing
number of sectors to controls in the name of addressing global climate
change concerns. In 2015, we extended the GHG initiative to power plant
stationary sources regulated under CAA section 111 by promulgating GHG
emissions standards for new, modified, and reconstructed fossil fuel-
fired EGUs in the 2015 NSPS, 80 FR 64510, and GHG emission guidelines
for existing fossil fuel-fired EGUs, 80 FR 64662 (``Clean Power Plan''
or ``2015 CPP'').\5\ In these related actions, we applied the expansive
reading of CAA section 202(a)(1) adopted in the 2009 Endangerment
Finding to conclude for the first time that a source category could be
subject to additional regulatory controls under CAA section 111 based
on global climate change concerns. We also made a finding in the
alternative, again relying on the 2009 Endangerment Finding, that
global GHG concentrations in the atmosphere constitute air pollution
that endangers public health and welfare and that GHG emissions from
power plants cause or contribute significantly to that air pollution.
After the Supreme Court largely vacated these regulatory efforts in
West Virginia v. EPA, 597 U.S. 697 (2022), we responded by promulgating
more stringent GHG standards for new sources and reissuing emission
guidelines for existing sources in the 2024 CPS. Meanwhile, global GHG
concentrations in the upper atmosphere have continued to rise, driven
primarily by increased emissions from foreign sources,\6\ all without
producing the degree of adverse impacts to public health and welfare in
the U.S. anticipated in the 2009 Endangerment Finding and 2015 NSPS and
2015 CPP.
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\5\ References to ``GHG standards'' here and elsewhere include
new source performance standards (NSPS) promulgated under CAA
section 111(b) and emission guidelines for existing sources
promulgated under CAA section 111(d). See 42 U.S.C. 7411(b), (d).
\6\ Crippa, M. et al. (2023). GHG emissions of all world
countries. Publications Office of the European Union: <a href="https://doi.org/10.2760/953322">https://doi.org/10.2760/953322</a>.
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Upon further review, and in light of subsequent developments since
2009 and 2015, the EPA is seeking further public comment on its
statutory authority to regulate GHG emissions from fossil fuel-fired
EGUs in response to global climate change concerns. The Supreme Court
has significantly clarified the limits on the EPA's authority in recent
years, including in West Virginia, Utility Air Regulatory Group v. EPA,
573 U.S. 302 (2014) (``UARG''), and Michigan v. EPA, 576 U.S. 743
(2015), and made clear in Loper Bright Enterprises v. Raimondo, 603
U.S. 369 (2024), that Federal agencies can no longer rely on statutory
silence or ambiguity to expand regulatory power. The EPA recently
considered these issues in the Endangerment Finding Rescission, in
which we concluded that CAA section 202(a)(1) is best read as
authorizing regulation of air pollution that threatens health and
welfare through local and regional exposure and does not authorize
regulation in the name of global climate change concerns. We further
concluded that Congress had not provided the requisite clear
authorization for our GHG emissions program under CAA section
202(a)(1), which had resulted in an unprecedented expansion of
regulatory power with adverse effects on the economy and American
households. And we concluded that attempting to address global climate
change through regulation under CAA section 202(a)(1) was futile based
on modeling showing that new motor vehicle and engine GHG emission
standards would have no more than a de minimis impact on key indicators
of the health and welfare concerns animating regulation. We thus
rescinded the 2009 Endangerment Finding and repealed all associated GHG
emission standards to ensure that the EPA exercised ``only those powers
given to [it] by Congress'' \7\ and to follow ``the best reading of the
statute,'' which is fixed at the time of enactment.\8\
---------------------------------------------------------------------------

\7\ 91 FR 7686, 7688 (Feb. 18, 2026) (quoting West Virginia, 597
U.S. at 723).
\8\ Id. (quoting Loper Bright, 603 U.S. at 400-01).
---------------------------------------------------------------------------

Informed by these conclusions, the EPA in this supplemental
proposal seeks additional public comment on the Agency's statutory
authority to regulate GHG emissions from power plants. We propose that
the text, structure, and history of CAA section 111, the applicability
and implications of the major questions doctrine, and the futility of
power plant GHG standards in relation to the unique and global scale of
the underlying problem similarly support the conclusion that the EPA
lacks authority to impose additional controls on power plants in
response to global climate change concerns under the statutory standard
for regulation.
The remainder of this section describes the need for regulatory
action and the scope of this proposed action. These interests emphasize
the need for urgent action to avoid further expenditures in reliance on
a potentially unlawful regulatory framework that may not further public
health or welfare in any material respect relevant to the global
climate change concerns identified and relied upon by the EPA since
2015.
Section III of this preamble sets out relevant background,
including the EPA's statutory authority under CAA section 111, our
historical approach to regulating emissions from new and existing
stationary sources, our changes in position with respect to regulating
in response to global climate change

[[Page 59006]]

concerns in 2009 and 2015, as well as relevant litigation, and our
recent reconsideration and rescission of the 2009 Endangerment Finding.
Section IV of this preamble describes our legal authority for the
proposed rescissions and repeals of the 2015 NSPS, 2024 CPS, and any
underlying listings, findings, and determinations with respect to GHG
emissions from fossil fuel fired-EGUs under CAA section 111. We propose
that CAA section 111 authorizes these proposed actions, together with
agencies' authority to revise or rescind prior actions by acknowledging
the change, providing a reasonable explanation, and considering
legitimate reliance interests. In the June 2025 NPRM, we acknowledged
that our prior decisions to regulate GHG emissions from fossil fuel-
fired EGUs have caused significant expenditure of resources by Federal,
State, local, and private-sector entities and solicited comment on any
legitimate reliance interests relevant to the proposed rescissions and
repeals. In this supplemental proposal, we solicit comment on whether
the additional bases set out in this supplemental proposal implicate
distinct reliance interests and how the EPA should consider such
interests consistent with applicable legal principles and limits on our
statutory authority.
Section V.A of this preamble discusses the EPA's additional
statutory interpretation rationale for the proposed rescissions and
repeals. First, we propose that EPA lacks authority to retain these
standards under CAA section 111(b)(1)(A), which subjects a source
category's emissions to regulation when the Administrator determines
that the source category causes or contributes significantly to ``air
pollution which may reasonably be anticipated to endanger public health
or welfare.'' Specifically, we propose that ``air pollution'' is best
read as that which itself threatens health or welfare through local or
regional exposure, consistent with the ordinary meaning of the term at
the time of enactment, the surrounding language of the provision, the
statute's structure and amendment history, and the EPA's longstanding
practice prior to 2015. For these reasons, we propose that the 2015
NSPS and 2024 CPS erred in listing and regulating fossil fuel-fired
EGUs based on global climate change concerns that fall outside the
scope of ``air pollution'' within the meaning of the CAA section 111.
Second, we propose that additional flaws in the Agency's findings and
determinations in the 2015 NSPS, as endorsed by the 2024 CPS, render
them independently unlawful and reinforce the proposed conclusions
previously discussed. These flaws include the effective listing of a
new source category without undertaking a new listing under CAA section
111(b)(1)(A) and reliance on the flawed 2009 Endangerment Finding.
Section V.B discusses the EPA's major questions doctrine rationale
for the proposed rescissions and repeals. We propose that, consistent
with the Supreme Court's decision in West Virginia, the major questions
doctrine applies to the Agency's economically and politically
significant assertion of authority to regulate power plant emissions
based on global climate change concerns. We further propose that
Congress did not clearly authorize the EPA to regulate power plants in
response to global climate change concerns when it enacted the standard
for regulation in CAA section 111(b)(1)(A) and authorized the
Administrator to determine whether emissions satisfy that standard.
That is, Congress did not clearly provide that global climate change
concerns may trigger regulation under CAA section 111(b)(1)(A) and
therefore did not clearly authorize the Administrator to invoke that
standard to subject power plant emissions to additional regulatory
controls commensurate with the unique and global nature of the problem.
Rather, we propose that the appropriate policy response to global
climate change concerns is a decision vested in Congress, and that
Congress did not decide that the Nation's policy response to these
concerns would include regulating power plants when it enacted CAA
section 111.
Section V.C discusses the EPA's proposed futility rationale for the
proposed rescissions and repeals. In developing this supplemental
proposal, the Agency used generally accepted models to estimate the
impacts on global mean surface temperature (GMST) and global sea level
rise (GSLR) of eliminating all GHG emissions from the U.S. power sector
as an overly conservative proxy for the potential impacts of GHG
emission restrictions under CAA section 111. The EPA proposes that the
results of this modeling demonstrate that even the complete elimination
of GHG emissions from the U.S. power sector, and at minimum, any
plausible reduction in GHG emissions from the U.S. power sector that
could result from application of CAA section 111, would have no more
than de minimis impacts on the key indicators of adverse impacts
attributed to global climate change. On this basis, the EPA proposes
that the futility of regulation supports the conclusion that global
climate change concerns cannot satisfy the prerequisite for imposing
regulatory controls under CAA section 111. The EPA further propose that
the inability of GHG standards to address global climate change
supports the conclusion that GHG emissions from fossil fuel-fired EGUs
do not ``contribute significantly'' to air pollution. Finally, the EPA
proposes that retaining futile GHG standards for fossil fuel-fired EGUs
under CAA section 111 would be unreasonable given the significant costs
they impose on regulated parties, consumers, and the economy.
Section VI of this preamble discusses the proposed repeals of all
GHG regulations for fossil fuel-fired EGUs under CAA section 111,
including the relationship of these repeals to distinct regulatory
programs and Federal preemption. We propose that absent emissions
satisfying the statutory prerequisite for regulation under CAA section
111(b)(1)(A), the EPA must fully repeal the 2015 NSPS and 2024 CPS,
which listed (and retained) a combined source category of fossil fuel-
fired EGUs for the purpose of regulating GHG emissions. We explain that
these repeals would not disturb criteria-pollutant standards or other
requirements applicable to power plants currently listed in the fossil
fuel-fired EGU source category. Nor would returning to the pre-2015
status quo alter the CAA's displacement of Federal common law or the
CAA's preemptive force with respect to State law.
Section VII of this preamble specifically requests comment on key
aspects of this supplemental notice and indexes comment solicitation to
promote public participation and facilitate our review of public
comments. The EPA is not limiting public participation to the issues
raised in this section and will respond to all significant comments
within the scope of this supplemental proposal. Rather, we are
highlighting aspects of this supplemental proposal for which public
input would be particularly helpful in determining whether to finalize
the additional rationales proposed in this supplemental notice.

B. Need for Regulatory Action

Immediately upon taking office in 2025, President Trump established
as the policy of the United States new Executive Branch priorities for
energy, transportation, and consumer choice and committed agencies to
ensuring regulations remain within constitutional and statutory bounds.
On January 20, 2025, President Trump issued Executive Order (E.O.)
14154,

[[Page 59007]]

``Unleashing American Energy.'' \9\ In that E.O., the President
established that it is ``the policy of the United States to ensure that
all regulatory requirements related to energy are grounded in clearly
applicable law,'' \10\ and directed Federal agencies, including the
EPA, to review existing regulations ``to identify those agency actions
that impose an undue burden on the identification, development, or use
of domestic energy resources--with particular attention to oil, natural
gas, coal, hydropower, biofuels, critical mineral, and nuclear energy
resources.'' \11\ The President also directed the Administrator to
submit recommendations to the Director of the Office of Management and
Budget (OMB) on the legality and continuing applicability of the 2009
Endangerment Finding.\12\
---------------------------------------------------------------------------

\9\ 90 FR 8353 (Jan. 29, 2025).
\10\ Id. section 2.
\11\ Id. section 3(a).
\12\ Id. section 6(f).
---------------------------------------------------------------------------

On February 19, 2025, President Trump issued E.O. 14219, ``Ensuring
Lawful Governance and Implementing the President's `Department of
Government Efficiency' Deregulatory Initiative.'' \13\ This E.O.
established a national policy requiring agencies, including the EPA, to
``focus the executive branch's limited enforcement resources on
regulations squarely authorized by constitutional Federal statutes''
and to ``initiate a process to review all regulations subject to their
sole or joint jurisdiction for consistency with law and Administration
policy.'' \14\ Among other things, the E.O. instructed agencies to
identify regulations that are based on anything other than the best
reading of the underlying statutory authority or prohibition and
regulations that implicate matters of social, political, or economic
significance that are not authorized by clear statutory authority. In
the course of this review, the EPA identified GHG standards for power
plants as regulations that may be based on interpretations that are
inconsistent with the best reading of CAA section 111 and address a
significant issue without clear statutory authorization.
---------------------------------------------------------------------------

\13\ 90 FR 10583 (Feb. 25, 2025).
\14\ Id. sections 1, 2.
---------------------------------------------------------------------------

On April 8, 2025, President Trump issued E.O. 14261,
``Reinvigorating America's Beautiful Clean Coal Industry and Amending
Executive Order 14241.'' \15\ This E.O. states that ``coal is essential
to our national and economic security'' and establishes ``a national
priority to support the domestic coal industry by removing Federal
regulatory barriers that undermine coal production.'' \16\ The E.O.
finds that ``coal resources will be critical to meeting the rise in
electricity demand due to the resurgence of domestic manufacturing and
the construction of artificial intelligence data processing centers''
and to increasing ``energy supply,'' lowering ``electricity costs,''
stabilizing the power grid, creating ``high paying jobs,'' supporting
``burgeoning industries,'' and assisting allies abroad.\17\
Accordingly, the E.O. directs the EPA, among other Federal agencies, to
identify regulatory actions that seek to transition the Nation away
from coal production and electricity generation and consider revising
or rescinding such actions consistent with applicable law.\18\
---------------------------------------------------------------------------

\15\ 90 FR 15517 (Apr. 14, 2025).
\16\ Id. section 2.
\17\ Id. section 1.
\18\ Id. section 6(a)-(b).
---------------------------------------------------------------------------

Upon confirmation by the Senate, Administrator Lee Zeldin committed
the EPA to prioritizing its core statutory missions and ensuring that
all regulatory actions are clearly grounded in statutory authority and
the best reading of the law. As part of these efforts, and consistent
with E.O. 14154, E.O. 14219, and E.O. 14261, the Administrator
initiated a review of the 2009 Endangerment Finding and related
regulations bearing on the energy sector, including power plant GHG
emission standards. On February 19, 2025, the Administrator submitted a
memorandum to the OMB Director recommending that the EPA reconsider the
2009 Endangerment Finding to address legal and scientific developments
that appeared to undermine the bases for that action and subsequent
regulations. The Administrator noted that recent Supreme Court
decisions, including Loper Bright, West Virginia, UARG, and Michigan,
provided further instruction as to how we should interpret and apply
the statutes Congress entrusted us to administer. The Administrator
further noted that the 2009 Endangerment Finding recognized significant
uncertainties in its conclusions and assumptions that should be
evaluated in light of more recent empirical data and scientific
evidence. Accordingly, the Administrator announced on March 12, 2025,
that the EPA would reconsider the 2009 Endangerment Finding and
subsequent regulations under CAA section 202(a)(1) to determine whether
our GHG regulations have an adequate statutory basis and to seek public
input on developments since 2009.\19\ That same day, the Administrator
announced that the EPA would initiate a rulemaking to reconsider our
GHG emission standards for power plants under CAA section 111.\20\
---------------------------------------------------------------------------

\19\ Memorandum from Lee Zeldin, Administrator, U.S.
Environmental Protection Agency, to Russell Vought, Director, Office
of Management and Budget (Feb. 19, 2025) (Feb. 19, 2025 Memo),
Docket ID No, EPA-HQ-OAR-2025-0194-0059.
\20\ Trump EPA Announces Reconsideration of Biden-Harris Rule,
``Clean Power Plan 2.0,'' That Prioritized Shutting Down Power
Plants While Raising Costs on American Families (Mar. 12, 2025),
available at <a href="https://www.epa.gov/newsreleases/trump-epa-announces-reconsideration-biden-harris-rule-clean-power-plan-20-prioritized">https://www.epa.gov/newsreleases/trump-epa-announces-reconsideration-biden-harris-rule-clean-power-plan-20-prioritized</a>.
---------------------------------------------------------------------------

In June 2025, the EPA completed its initial review of GHG emission
standards for power plants under CAA section 111. Based on a
reassessment of the legal and technical conclusions in the 2015 NSPS
and 2024 CPS, we sought public comment in the June 2025 NPRM on a
primary proposal and an alternative proposal.\21\ The primary proposal
involved repealing all GHG emissions standards for new and existing
sources in the fossil fuel-fired EGU source category. Specifically, we
proposed to determine that CAA section 111 requires the Agency to make
a finding that GHG emissions from fossil fuel-fired power plants
``cause[ ], or contribute significantly'' to ``air pollution which may
reasonably be anticipated to endanger public health or welfare'' (which
we shorthanded as ``dangerous air pollution'') as a predicate to
regulating GHG emissions from those power plants. We further proposed
to find that GHG emissions from fossil fuel-fired power plants do not
contribute significantly to dangerous air pollution. The alternative
proposal was based on the EPA's reexamination of the BSER
determinations and associated requirements for fossil fuel-fired power
plants in the 2024 CPS. Specifically, we proposed to repeal
requirements in the 2024 CPS predicated on the Agency's prior
determinations that 90 percent carbon capture and storage (CCS) and/or
40 percent natural gas co-firing were BSER for the relevant
subcategories.
---------------------------------------------------------------------------

\21\ 90 FR 25752 (June 17, 2025).
---------------------------------------------------------------------------

In August 2025, the EPA completed its initial review of GHG
emission standards for new motor vehicles and engines under CAA section
202(a)(1). Based on substantial concerns with the legal and scientific
underpinnings of these regulations and the associated findings, we
proposed to rescind the 2009 Endangerment Finding and repeal associated
GHG emission standards on several alternative legal, policy, and
scientific bases.
In February 2026, the EPA took final action to rescind the 2009

[[Page 59008]]

Endangerment Finding and repeal associated GHG emission standards for
new motor vehicles and engines under CAA section 202(a)(1). We
concluded in the Endangerment Finding Rescission that the EPA lacks
statutory authority under CAA section 202(a)(1) to regulate in response
to global climate change concerns for the legal reasons discussed at
proposal. Specifically, we concluded that global climate change
concerns associated with GHG emissions are not ``air pollution which
may reasonably be anticipated to endanger public health or welfare''
within the meaning of CAA section 202(a)(1), that Congress had not
clearly authorized such an economically and politically significant
assertion of authority, and that the futility of emission standards
further supported the rescission and repeals in multiple respects.
In today's actions, the EPA is returning to the issues raised in
the June 2025 NPRM regarding our statutory authority to regulate GHG
emissions from power plants under CAA section 111. Concurrently with
this supplemental notice, the EPA is taking final action to repeal most
of the provisions of the 2024 CPS based on a record-focused
reevaluation of the BSER determinations for the relevant subcategories.
That concurrent final rule repeals the associated aspects of the 2024
CPS, consistent with the alternative proposal in the June 2025 NPRM,
while taking no action on the primary proposal in the June 2025 NPRM.
The EPA responded to comments received on the alternative proposal in
the RTC for the final rule. The EPA is not reopening the record for the
final rule in this supplemental notice and is not seeking further
public comment on the record-based considerations addressed in the
final rule.
This supplemental proposal seeks public comment on the question
whether the EPA lacks authority under CAA section 111 to regulate GHG
emissions from power plants in response to global climate change
concerns given CAA section 111(b)(1)(A)'s predicate requirement that
their emissions contribute significantly to ``air pollution which may
reasonably be anticipated to endanger public health or welfare.'' The
rationale proposed in this supplemental notice is distinct from the
rationale presented in the primary proposal of the June 2025 NPRM,
which sought public comment on whether the EPA has authority to
regulate GHG emissions from power plants based on the significance of
the fossil fuel-fired EGU source category's contribution. The EPA is
not seeking additional comment on the primary proposal in the June 2025
NPRM in this supplemental notice. Rather, we are rather soliciting
public comment on distinct statutory authority rationales in light of
the Endangerment Finding Rescission: the best reading of CAA section
111 with respect to fossil fuel-fired EGUs; the applicability and
implications of the major questions doctrine; the futility of GHG
emission standards for power plants in addressing global climate change
concerns; and several additional issues, including the ongoing validity
of the Agency's endangerment and significant contribution findings in
the alternative in the 2015 NSPS, as reaffirmed in the 2024 CPS. In
contrast to the record-based issues related to BSER determinations
addressed in the concurrent final rule, this supplemental proposal
analyzes the text and structure of the CAA to ascertain its best
reading, bolstered by statutory and legislative history and the body of
regulatory history relevant to the scope of the Agency's legal
authority, including all aspects of the 2015 NSPS, the vacated 2015
CPP, and the 2024 CPS, as well as regulatory actions that predated the
Agency's 2015 changes in position. This information is relevant to how
the statute has been applied and, for major questions doctrine
purposes, to the permissibility of the scope of the authority we first
asserted in 2015.
Should the EPA finalize its proposed conclusion that the Agency
lacks statutory authority to regulate GHG emissions from power plants
based on global climate change concerns under the statutory standard
for regulation in CAA section 111(b)(1)(A), that final action would
remove the legal basis for all prior actions taken under CAA section
111 to regulate GHG emissions from these sources in response to global
climate change. This conclusion would require the EPA to rescind its
findings and determinations in the 2015 NSPS and repeal all GHG
regulations and requirements for power plants under CAA section 111,
including those in the 2015 NSPS and those in the 2024 CPS that are not
being repealed on other grounds in the concurrent final rule. With
respect to the aspects of the 2024 CPS being repealed on other grounds
in the concurrent final rule, this conclusion would independently
reinforce the basis for repeal based on a lack of statutory
authority.\22\
---------------------------------------------------------------------------

\22\ Because the Supreme Court invalidated the 2015 CPP in West
Virginia by reversing the D.C. Circuit's vacatur of the EPA's
subsequent repeal of the 2015 CPP, any similar findings or
determinations in the 2015 CPP are no longer in effect. 597 U.S.
697; see Am. Lung Ass'n v. EPA, No. 19-1140, Order (D.C. Cir. Oct.
27, 2022). Nevertheless, as with the concurrently repealed aspects
of the 2024 CPS, finalizing that the EPA lacks statutory authority
to regulate GHG emissions from power plants in response to global
climate change would necessarily contradict and invalidate any such
findings or determinations in the 2015 CPP.
---------------------------------------------------------------------------

III. Background

This section discusses the EPA's statutory authority under CAA
section 111, relevant statutory, legislative, and regulatory history,
and the Agency's prior changes in position with respect to the
regulation of GHGs under CAA section 111.

A. Statutory Authority Under CAA Section 111

CAA section 111 authorizes the EPA to list and regulate a category
of stationary sources if the Administrator, ``in his judgment,'' finds
that it ``causes, or contributes significantly to, air pollution which
may reasonably be anticipated to endanger public health or welfare.''
\23\ The listing of a source category triggers the Agency's authority
to promulgate ``standards of performance'' for new sources and, under
limited circumstances, to prescribe regulations under which States
submit plans that establish standards of performance for existing
sources.\24\
---------------------------------------------------------------------------

\23\ 42 U.S.C. 7411(b)(1)(A).
\24\ 42 U.S.C. 7411(b), (d).
---------------------------------------------------------------------------

1. Regulation of Emissions From New Sources
CAA section 111(b)(1)(A) authorizes the Administrator to publish,
and from time-to-time revise, a list of categories of stationary
sources that the Administrator, ``in his judgment,'' finds ``causes, or
contributes significantly to, air pollution which may reasonably be
anticipated to endanger public health or welfare.'' Once the EPA lists
a source category under CAA section 111(b)(1)(A), the EPA must, under
CAA section 111(b)(1)(B), establish ``standards of performance'' for
``new sources'' in the source category. These standards are referred to
as new source performance standards, or NSPS. The NSPS are national
requirements that apply directly to new sources within the relevant
source category.
As discussed later in this section, Congress enacted the NSPS
regulatory scheme to work together with the geography-based national
ambient air quality standards (NAAQS) program in CAA sections 107-110.
Similar to national emission standards for hazardous air pollutants
(NESHAPs) that limit emissions of hazardous air pollutants (HAPs)
listed and regulated

[[Page 59009]]

under CAA section 112, NSPS under CAA section 111 apply to a new source
regardless whether the area in which the new source is located is
attaining the NAAQS (and therefore subject to limited NAAQS-related
restrictions) or not attaining the NAAQS (and therefore subject to
additional NAAQS-related restrictions). Accordingly, CAA section
111(a)(2) defines a ``new source'' as ``any stationary source, the
construction or modification of which is commenced after the
publication of regulations (or, if earlier, proposed regulations)
prescribing a standard of performance under this section, which will be
applicable to such source.''
CAA section 111(a)(1) defines ``standard of performance'' as ``a
standard for emissions of air pollutants'' that must be promulgated or
revised in a specified manner. When the EPA establishes or revises a
standard of performance, CAA section 111(a)(1) provides that such
standard must ``reflect[ ] the degree of emission limitation achievable
through the application of the best system of emission reduction which
(taking into account the cost of achieving such reduction and any
nonair quality health and environmental impact and energy requirements)
the Administrator determines has been adequately demonstrated.'' Thus,
the term ``standard of performance'' as used in CAA section 111 makes
clear that the foundation for the regulatory requirements for the
source category is the EPA's determination of the ``best system of
emission reduction'' (BSER) that is ``adequately demonstrated'' for
emissions of the relevant air pollutants.\25\ The EPA has discretion in
determining the BSER, and has historically followed a ``technology-
based approach'' that focuses on ``measures that improve the pollution
performance of individual sources,'' such as ``add-on controls.'' \26\
---------------------------------------------------------------------------

\25\ West Virginia, 597 U.S. at 709.
\26\ See id. at 727 (quoting the 2015 CPP).
---------------------------------------------------------------------------

After determining the BSER, the EPA derives the ``degree of
emission limitation achievable'' through application of the BSER. A
standard of performance is ``achievable'' if a technology can
reasonably be projected to be available to an individual source at the
time it is constructed so as to allow it to meet the standard.\27\ The
EPA must then, under CAA section 111(b)(1)(B), promulgate ``standard[s]
for emissions''--the NSPS--that reflect that level of stringency. The
EPA may determine that different sets of sources have different
characteristics relevant for determining the BSER for emissions of the
relevant air pollutants and may subcategorize sources accordingly.\28\
---------------------------------------------------------------------------

\27\ Portland Cement Ass'n v. Ruckelshaus, 486 F.2d 375, 391
(D.C. Cir. 1973).
\28\ 42 U.S.C. 7411(b)(2).
---------------------------------------------------------------------------

2. Regulation of Emissions From Existing Sources
The EPA has generally used CAA section 111 to establish NSPS for
emissions of specified air pollutants from new sources within a
category. In the rare instances in which the new stationary source
standards concern air pollutant emissions that are not regulated under
the NAAQS program pursuant to CAA sections 108-110, or the NESHAP
program pursuant to CAA section 112, the statute provides a separate
authority for addressing such emissions from existing sources in the
source category.\29\
---------------------------------------------------------------------------

\29\ 42 U.S.C. 7411(d)(1)(A)(i)-(ii); see West Virginia, 597
U.S. at 710 (``Section 111(d) thus `operates as a gap-filler,'
empowering EPA to regulate harmful emissions not already controlled
under the Agency's other authorities . . . . Reflecting the
ancillary nature of Section 111(d), EPA has used it only a handful
of times since the enactment of the statute in 1970.'').
---------------------------------------------------------------------------

In contrast to the national regime for new sources under CAA
section 111(b), CAA section 111(d) establishes a framework of
``cooperative federalism for the regulation of existing sources.'' \30\
CAA section 111(d)(1) provides that when air pollutants covered by an
NSPS for a source category are not already encompassed within the NAAQS
program or NESHAP program, the EPA ``shall prescribe regulations which
shall establish a procedure similar to that provided by'' CAA section
110 ``under which each State shall submit to the Administrator'' a plan
for addressing emissions of such air pollutants by existing sources
within such source category.\31\ Reference to CAA section 110
incorporates the statute's provision for State submission and EPA
review of state implementation plans (SIPs) that provide for the
implementation, maintenance, and enforcement of the NAAQS for the areas
within such State.\32\ In a comparable manner, State plans required by
the regulations authorized in CAA section 111(d) must ``establis[h]
standards of performance for any existing source'' for the air
pollutant emissions at issue and ``provid[e] for the implementation and
enforcement of such standards of performance.''
---------------------------------------------------------------------------

\30\ Am. Lung Ass'n v. EPA, 985 F.3d 914, 931 (D.C. Cir. 2021),
rev'd in part sub nom. West Virginia, 597 U.S. 697.
\31\ 42 U.S.C. 7411(d)(1). CAA section 111(a)(6) defines an
``existing source'' as ``any stationary source other than a new
source.'' 42 U.S.C. 7411(a)(6).
\32\ 42 U.S.C. 7410.
---------------------------------------------------------------------------

In the relatively few instances in which the EPA applies this
provision, the Agency generally promulgates regulations, termed
``emission guidelines,'' that identify the BSER and the degree of
emission limitation achievable through the application of the BSER.
These regulations then require States to establish standards of
performance for emissions of the air pollutant at issue by covered
sources that reflect that level of stringency. Once the EPA approves a
State's plan, its provisions become federally enforceable in the same
manner as the provisions of an approved SIP under the CAA.\33\ If a
State does not submit a plan or the EPA does not find a State's
submission ``satisfactory,'' the Agency is authorized to issue a
Federal plan imposing standards of performance for the State's existing
sources.\34\
---------------------------------------------------------------------------

\33\ 42 U.S.C. 7411(d)(2)(B).
\34\ 42 U.S.C. 7411(d)(2)(A).
---------------------------------------------------------------------------

B. Statutory and Regulatory History of CAA Section 111

Congress enacted CAA section 111 in the 1970 CAA Amendments as part
of title I of Act, which ``establishes three main regulatory programs
to control air pollution from stationary sources such as power
plants.'' \35\ In enacting CAA section 111 in 1970 and revising key
language in the 1977 CAA Amendments and 1990 CAA Amendments, Congress
addressed its requirements as part of a comprehensive scheme including
the NAAQS program under CAA sections 107-110 and the NESHAP program
under CAA section 112. This subsection discusses the statutory history
of CAA section 111, the relation of CAA section 111 to the other
provisions of title I, and regulatory history that reflects the EPA's
contemporary understanding of the statute as informed by Congress's
amendments to key statutory language.
---------------------------------------------------------------------------

\35\ West Virginia, 597 U.S. at 707.
---------------------------------------------------------------------------

1. 1970 CAA Amendments and Subsequent Regulations
Congress enacted CAA section 111 in 1970 as one of three related
provisions directing the EPA to regulate emissions from stationary
sources. The first--CAA sections 107 through 110--addressed what are
commonly referred to as criteria pollutants, which are pollutants,
``the presence of which in the ambient air results from numerous or
diverse mobile or stationary sources'' and are determined to have ``an
adverse effect on public health or welfare.'' \36\ Under

[[Page 59010]]

these provisions, the Federal government would develop air quality
criteria on the health and welfare impacts of criteria pollutants and
promulgate numeric standards--the NAAQS--representing the ambient
concentrations of such pollutants in the air of a particular area that
are adequately protective. States would have primary responsibility for
assuring air quality within their geographic area by developing and
submitting SIPs for ``implementation, maintenance, and enforcement'' of
the NAAQS to the Federal government for review and approval. These
plans would include ``emission limitations, schedules, and timetables
for compliance . . . and such other measures as may be necessary to
insure attainment and maintenance'' of the NAAQS.\37\
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\36\ CAA Amendments of 1970, Public Law 91-604, 84 Stat. 1676,
1678. Congress subsequently amended the ``adverse effect'' criterion
in CAA section 108(a)(1)(A) to refer to pollutants ``which may
reasonably be anticipated to endanger public health or welfare,'' 42
U.S.C. 7408(a)(1)(A), and deliberately added identical phrasing to
statutory provisions granting the EPA authority to regulate
particular sources under certain conditions, see, e.g., 42 U.S.C.
7411(b)(1)(A) (stationary sources), 7521(a)(1) (new motor vehicles
and new motor vehicle engines).
\37\ CAA Amendments of 1970, 84 Stat. at 1680.
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The second prong was CAA section 112, which addressed particularly
dangerous pollutants--HAPs--through the establishment of NESHAPs at a
level that ``provides an ample margin of safety to protect the public
health.'' \38\ All new or modified sources of any HAP would be required
to meet these emission standards unless, for example, an existing
source obtained a waiver or presidential exemption.
---------------------------------------------------------------------------

\38\ Id. at 1685.
---------------------------------------------------------------------------

The third prong was CAA section 111, which addressed air pollutant
emissions on a source category basis. Under CAA section 111(b), as
enacted in 1970, the EPA would list source categories which
``contribute significantly to air pollution which causes or contributes
to the endangerment of public health or welfare'' and then establish
``standards of performance'' for new sources in the listed
category.\39\ The relevant Committee Report explained that the
provision would apply to ``[m]ajor new facilities such as electric
generating plants, kraft pulp mills, petroleum refineries, steel mills,
primary smelting plants, and various other commercial and industrial
operations'' along with ``any other categories of major stationary
sources from which emissions would cause or contribute to endangerment
of public health and welfare.'' \40\ The legislation's Senate sponsor,
Senator Edmund Muskie, explained that CAA section 111 was designed to
apply across the country to level the playing field among States,
thereby avoiding ```shopping around' for open sites'' in areas that
were subject to fewer local restrictions under the NAAQS program.\41\
In this way, the national standards for new sources would reduce an
incentive to shift operations from nonattainment areas required to
improve air quality to attainment areas that already had acceptable air
quality that should be maintained. For existing sources in a listed
source category, CAA section 111(d) set out procedures for the
establishment of federally enforceable ``emission standards'' of any
pollutant not otherwise controlled under the CAA's NAAQS provisions or
CAA section 112.
---------------------------------------------------------------------------

\39\ Id. at 1684.
\40\ S. Rep. No. 91-1196, at 16 (1970). The Committee Report
added ``New stationary sources which the administration has advised
the committee to expect would be subject to the provisions of this
section include'' 19 industries, ranging from ``[c]ement
manufacturing'' and ``[c]oal cleaning operations'' to ``[m]unicipal
incinerators'' and ``[s]team electric powerplants.'' Id.
\41\ 91 Cong. Rec. 32902 (Sept. 21, 1970) (statement of Sen.
Muskie, during the Senate debate on S. 4358).
---------------------------------------------------------------------------

These provisions grew out of different bills adopted by the House
and Senate and reconciled by a conference committee to create what
became CAA sections 107-112. The relevant committees and bill sponsors
drafted these provisions to address contemporary air pollution problems
causing or threatening harm through exposure at the local and regional
level.\42\ These included the criteria pollutants addressed by what
became CAA sections 107-110; \43\ various ``hazardous,'' \44\
``extremely hazardous'' \45\ or ``extra-hazardous'' \46\ air
pollutants, which were subject to what became CAA section 112; and
``selected air pollution agents,'' which could also be criteria
pollutants and were subject to what became CAA section 111.\47\ The
Senate Report described the air pollutants subject to the language
later adopted at conference as CAA section 111 as ``agents which are
not emitted in such quantities or are not of such a character as to be
widely present or readily detectable on a continuous basis with
available technology in the ambient air'' and specified that ``[t]he
presence of these agents is generally confined, at least for detection
purposes, to the area of the emission source.'' \48\ The Senate Report
further specified that ``[t]he information available at this time
indicates that the following list of substances are most likely to be
considered as the agents to be covered under this section: Arsenic,
chlorine gas, hydrogen chloride, copper, manganese, nickel, vanadium,
zinc, barium, boron, chromium, selenium, pesticides, [and] radioactive
substances.'' \49\
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\42\ See S. Rep. No. 91-1196, at 18 (1970) (describing the
various sets of air pollutants subject to the stationary source
provisions of the Senate bill).
\43\ Prior to 1970, the Secretary of Health, Education, and
Welfare issued air quality criteria under an earlier version of the
CAA for SO<INF>2</INF>, PM, CO, ozone (photochemical oxidants), and
hydrocarbons. See, e.g., 36 FR 1502 (Jan. 30, 1971) (citing 35 FR
4768 and 34 FR 1988). Congress anticipated that these pollutants,
along with certain precursors, would be the foundation of the NAAQS
program for criteria pollutants under CAA sections 107-110. See,
e.g., 91 Cong. Rec. 32902 (Sept. 21, 1970) (Exhibit II to statement
of Sen. Boggs during the Senate debate on S. 4358).
\44\ S. 4358, 91st Cong. section 6 (1970).
\45\ H.R. 17255, 91st Cong. section 5 (1970).
\46\ H.R. Rep. No. 1146, at 3 (1970).
\47\ S. Rep. No. 91-1196, at 93-94 (1970).
\48\ S. Rep. No. 91-1196, at 18 (1970).
\49\ Id.
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In response to the 1970 CAA Amendments, the EPA began listing
source categories under CAA section 111(b)(1)(A) and promulgating
standards of performance under CAA section 111(b)(1)(B). Between 1970
and 1977, the EPA listed at least 31 source categories in brief notices
that did not solicit public comment.\50\ In 1975, EPA published
regulations that established the process for promulgating standards of
performance for new sources and emission guidelines for existing
sources \51\ and established requirements for modified and
reconstructed sources.\52\ By 1977, the EPA generally proposed
standards of performance for a source category at the same time as the
listing and discussed the basis for the listing in the preamble to the
proposed standards, including the amount of emissions of relevant air
pollutants from the source category.\53\
---------------------------------------------------------------------------

\50\ See, e.g., 36 FR 5931 (Mar. 31, 1971) (first five source
categories, including steam-fired EGUs); 42 FR 22510 (May 3, 1977)
(listing lime manufacturing).
\51\ 40 FR 53340 (Nov. 17, 1975).
\52\ 40 FR 58416 (Dec. 16, 1975).
\53\ See, e.g., 42 FR 22510 (May 3, 1977) (listing lime
manufacturing); 42 FR 22506 (May 3, 1977) (proposing standards for
lime manufacturing and explaining that ``[l]ime manufacturing plants
have been shown to be a significant source of particulate matter
emissions'').
---------------------------------------------------------------------------

2. 1977 CAA Amendments and Subsequent Regulations
Congress revisited the CAA in 1977 to address growing concerns
related to the energy and environmental impacts of the 1973 oil embargo
and resolve issues associated with implementing the statutory programs
enacted in 1970.\54\ The EPA advised relevant committees at

[[Page 59011]]

the time that increased coal combustion to generate power in response
to the oil crisis meant that ``vigorous and effective control'' of air
emissions was ``even more urgent.'' \55\ Congress responded by adding
new statutory provisions setting out the prevention of significant
deterioration (PSD) program, visibility protections known as the
regional haze program, and additional requirements for nonattainment
areas under the NAAQS program. As with the 1970 CAA Amendments, the
provisions added in the 1977 CAA Amendments required further steps to
combat air pollution by reducing emissions of criteria pollutants and
other air pollutants that cause or threaten adverse impacts from local
or regional exposure.\56\
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\54\ CAA Amendments of 1977, Public Law 95-95, 91 Stat. 685.
\55\ See Senate Hearings on S. 272, S. 273, S. 977, and S. 1469
(1977), reprinted in Library of Congress, 5 A Legislative History of
the Clean Air Amendments of 1977 (``1977 CAA Legis. Hist.'') at 3532
(statement of Administrator Costle).
\56\ For example, Congress recognized that many air pollutants
had not been regulated despite ``mounting evidence'' that these
pollutants ``are associated with serious health hazards.'' H.R. Rep.
No. 94-1175, at 22 (1976). Because the EPA ``failed to promulgate
regulations to institute adequate control measures,'' Congress
directed the EPA to regulate four specific pollutants that had
``been found to be cancer-causing or cancer-promoting.'' Id. at 23.
This directive, reflected in CAA section 122, specifically added
radioactive pollutants, cadmium, arsenic, and polycyclic organic
matter ``under the various provisions of the Clean Air Act and
allows their regulation as criteria pollutants under ambient air
quality standards, as hazardous air pollutants, or under new source
performance standards, as appropriate.'' H.R. Rep. No. 95-564, at
142 (1977); 42 U.S.C. 7422(a).
---------------------------------------------------------------------------

Congress further amended the endangerment and contribution language
in CAA section 111, CAA section 202(a)(1), and additional regulatory
provisions to provide a comparable standard for invoking each
regulatory authority. As amended in 1977, CAA section 111(b)(1)(A) read
as it currently does: the Administrator ``shall include a category of
sources in such list if in his judgment it causes, or contributes
significantly, to air pollution which may reasonably be anticipated to
endanger public health or welfare.'' \57\ The House Report for the
relevant bill language explained that these related amendments were
designed to provide ``the same standard of proof for regulation of any
air pollutant, whether that pollutant comes from stationary or mobile
sources, or both'' that allowed for precautionary regulation,
consistent with the D.C. Circuit's en banc decision in Ethyl Corp. v.
EPA, 541 F.2d 1 (D.C. Cir. 1976).\58\
---------------------------------------------------------------------------

\57\ CAA Amendments of 1977, section 109(a), 91 Stat. at 791;
compare 42 U.S.C. 7411(b)(1)(A), with 42 U.S.C. 7521(a)(1) (the
Administrator ``shall by regulation prescribe . . . 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 his judgment cause, or contribute to, air pollution which
may reasonably be anticipated to endanger public health or
welfare'').
\58\ H.R. Rep. No. 95-294 at 43 (1977). The House Report further
explained that the language eventually enacted set out ``a
standardized basis for future rulemakings'' and the ``same basic
formula'' in CAA sections 108 (defining criteria for NAAQS), 111
(NSPS), 112 (HAP, ``although the nature of risk must be more
serious''), 202 (new motor vehicle emission standards), 211
(regulation of fuels and fuel additives), and 231 (aircraft emission
standards). Id. at 50.
---------------------------------------------------------------------------

Congress also enacted further amendments specific to CAA section
111. First, it amended the definition of ``standard of performance'' in
CAA section 111 to require ``all new sources to meet emission standards
based on the reductions achievable through the use of the `best
technological system of continuous emission reduction.' '' \59\ Second,
for fossil fuel-fired stationary sources, Congress required a
percentage reduction in emissions from the use of fuels.\60\ Together,
this was designed to ``force new sources to burn high-sulfur fuel thus
freeing low-sulfur fuel for use in existing sources where it is harder
to control emissions and where low-sulfur fuel is needed for
compliance.'' \61\ This change responded to the oil shortage, the
resulting energy legislation that restricted power plant use of oil or
gas to generate electricity, and the consequent increase in coal
combustion by power plants. This increase in coal combustion gave rise
to the need to limit low-sulfur coal to existing power
plants.62 63 Third, Congress added CAA section 111(f), which
required the EPA to list categories of major stationary sources not
already listed and imposed a schedule for establishing standards of
performance for those source categories. Finally, Congress added CAA
section 111(f)(4), which specifically allowed States to petition the
Administrator for new or revised (and more stringent) standards.\64\
---------------------------------------------------------------------------

\59\ Id. at 192. Congress separately defined ``technological
system of continuous emission reduction'' as ``(A) a technological
process for production or operation by any source which is
inherently low-polluting or nonpolluting, or (B) technological
system for continuous reduction of the pollution generated by a
source before such pollution is emitted into the ambient air,
including precombustion cleaning or treatment of fuels.'' CAA
Amendments of 1977, 91 Stat. at 700; see 42 U.S.C. 7411(a)(7).
\60\ CAA Amendments of 1977, 91 Stat. at 700.
\61\ 44 FR 33580, 33581-82 (June 11, 1979) (promulgating NSPS
for electric utility steam generating units).
\62\ H.R. Rep. No. 95-294, at 185-86, 188-89, 190-93.
\63\ Congress also amended CAA section 111(b)(1)(B) to require
the Administrator to periodically review and, if appropriate, revise
new source standards of performance; further amended the definition
of a standard of performance in section 111(a)(1) to require the
consideration of ``nonair quality health and environmental impact
and energy requirements,'' along with cost; amended CAA section
111(d) to require States to promulgate ``standards of performance,''
as defined under 111(a)(1), in lieu of ``emission standards'' and to
clarify that States could consider ``the remaining useful life'' of
a source when applying a standard of performance to a particular
existing source; and added CAA section 111(h), which authorized
alternative standards in limited circumstances. CAA Amendments of
1977, 91 Stat. at 699-700.
\64\ Id. at 697.
---------------------------------------------------------------------------

The EPA responded to the 1977 CAA Amendments by increasing the pace
of stationary source regulation. Consistent with CAA section 111(f),
the Agency promulgated a list of 59 source categories in 1979 with each
assigned a priority for action.\65\ The EPA based the list on the
source categories' emissions of nine air pollutants: volatile organic
compounds (VOC), nitrogen oxides (NO<INF>X</INF>), particulate matter
(PM), sulfur dioxide (SO<INF>2</INF>), carbon monoxide (CO), lead,
fluorides, acid mist, and hydrogen sulfide.\66\ The EPA proceeded to
promulgate standards of performance for these air pollutants applicable
to new sources in the listed categories.\67\
---------------------------------------------------------------------------

\65\ 44 FR 49225-26 (Aug. 21, 1979).
\66\ 44 FR 49222 (Aug. 21, 1979).
\67\ See, e.g., 50 FR 26122 (June 24, 1985) (promulgating NSPS
for SO<INF>2</INF> emissions from natural gas processing plants).
---------------------------------------------------------------------------

3. 1990 CAA Amendments and Subsequent Regulations
In the 1990 CAA Amendments, Congress overhauled the CAA by
strengthening the NAAQS program, thoroughly revising CAA section 112,
and adding several new titles to the Act to address emerging problems
not adequately encompassed within the design of title I for regulating
stationary sources.\68\ The newly enacted title IV addressed acid rain,
which forms when SO<INF>2</INF> and NO<INF>X</INF> emissions transform
in the atmosphere and return to the earth as precipitation, by
requiring the EPA to impose strict limits on SO<INF>2</INF> emissions
from existing power plants and other sources. The newly enacted title V
established a consolidated permitting program for certain stationary
sources intended to improve efficiency, compliance, and enforceability
of existing permitting and emission requirements. And the newly enacted
title VI provided the EPA with new regulatory authorities and
obligations to phase out certain ozone depleting substances in response
to rising concerns that anthropogenic emissions were contributing to a
global weakening of the stratospheric ozone layer's capacity to deflect
radiation from the sun associated with skin cancer and

[[Page 59012]]

other adverse health and environmental impacts worldwide.
---------------------------------------------------------------------------

\68\ CAA Amendments of 1990, Public Law 101-549, 104 Stat. 2399.
---------------------------------------------------------------------------

Congress also made several further changes to CAA section 111. For
the CAA section 111(a)(1) definition of ``standard of performance,''
Congress repealed the percentage reduction requirement added in the
1977 CAA Amendments, which had come to be understood as unduly
restrictive, and returned the definition to how it read after the 1970
CAA Amendments while retaining the 1977 language providing that the EPA
must consider nonair quality environmental impacts and energy
requirements.\69\ In connection with the newly enacted title IV,
Congress directed the EPA to revise its NSPS for SO<INF>2</INF>
emissions from fossil fuel-fired power plants and required the revised
standards to be at least as stringent as earlier regulations.\70\ And
Congress revised CAA section 111(f) to update the schedule for
regulating listed source categories according to a prioritization
scheme that reinforced the provision's design: establishing national
minimum standards for emitting sources that may shift over time from
one area of the country to another.\71\
---------------------------------------------------------------------------

\69\ Congress designed this repeal to apply only so long as the
SO<INF>2</INF> cap in the newly established acid rain program of
title IV remained in effect. CAA Amendments of 1990, 104 Stat. at
2631.
\70\ Id.
\71\ See id. at 2467. Specifically, Congress instructed the EPA
to prioritize regulation based the quantity of a source category's
emissions, the extent to which each emitted pollutant may endanger
public health or welfare, and ``the mobility and competitive nature
of each such category of sources and the consequent need for
nationally applicable new source standards of performance.'' 42
U.S.C. 7411(f)(2).
---------------------------------------------------------------------------

In response to the 1990 CAA Amendments, the EPA began implementing
the new programs in title IV, title V, and title VI, continued to
promulgate standards of performance for new sources in listed source
categories under CAA section 111(b), and, in limited instances,
promulgated regulations addressing existing-source emissions under CAA
section 111(d).

C. Regulation of Greenhouse Gases Under CAA Section 111

1. The EPA's Historical Approach to CAA Section 111
During the first four decades of regulatory activity under CAA
section 111 and related provisions, the EPA listed and regulated source
categories to address air pollution with adverse impacts from local and
regional exposure and never attempted to list or regulate in response
to global climate change concerns. In the limited instances in which
the Agency addressed emissions of what have since been labeled GHGs,
the justifications for and requirements of the regulatory action were
based on such local and regional impacts. For example, in 1996, we
listed the municipal solid waste (MSW) landfills source category
primarily to regulate nonmethane organic compound (NMOC) emissions but
also included limited requirements for methane emissions.\72\ In the
1991 proposal, we explained that there is a ``well-documented danger of
fires and explosions, both on- and off-site'' from methane emitted from
MSW landfills.\73\ After surveying multiple additional bases for
regulating methane and other emissions form that source category, we
also noted that ``[a]n ancillary benefit from regulating air emissions
from MSW landfills is a reduction in the contribution of MSW landfill
emissions to global emissions of methane,'' \74\ and that methane was
``under discussion by the Intergovernmental Negotiating Committee for a
Framework Convention on Climate Change, convened by the United
Nations.'' \75\ The 1996 final rule further discussed these issues,\76\
again making it clear that our justification for listing the MSW
landfill source category and regulating landfill gases was not
contingent on global climate change concerns.\77\
---------------------------------------------------------------------------

\72\ 61 FR 9905 (Mar. 12, 1996).
\73\ 56 FR 24468, 24474 (May 30, 1991).
\74\ Id.
\75\ Id. at 24473.
\76\ See, e.g., 61 FR at 9906 (Mar. 12, 1996).
\77\ See id. (analyzing the health and welfare impacts of local
and regional exposure to landfill gas emissions that constitute the
basis for listing and regulating the source category, as well as
discussing methane's role as a GHG); see also id. at 9914, 9916,
9917 (explaining that the methane-related requirements function in
part to response to the EPA's obligations under President Clinton's
1993 ``Climate Change Action Plan'' and repeating that global
climate change benefits are ``[a]n ancillary benefit'' of the
regulation).
---------------------------------------------------------------------------

In 2003, the EPA expressly took the position that CAA section
202(a)(1) did not authorize the Agency to regulate GHG emissions in
response to global climate change concerns in denying 1999 petitions
for rulemaking on mobile-source emissions of CO<INF>2</INF>, methane,
N<INF>2</INF>O, and HFCs. 68 FR 52922 (Sept. 8, 2003) (``2003
Denial''). In the 2003 Denial, the EPA asserted three primary reasons
for denying the petitions. First, after ``examin[ing] the fundamental
issue of whether the CAA authorizes the imposition of control
requirements'' to ``reduce the risk of global climate change,'' we
concluded that ``CO<INF>2</INF> and other GHGs cannot be considered
`air pollutants' subject to the CAA's regulatory provisions for any
contribution they may make to global climate change.'' 68 FR 52925.
Citing the Supreme Court's decision in FDA v. Brown & Williamson
Tobacco Corp., 529 U.S. 120 (2000), we noted that the CAA does not
address GHGs as a regulatory matter, including in then-recent
amendments, and that the ``EPA has used these provisions to address air
pollution problems that occur primarily at ground level or near the
surface of the earth.'' 68 FR 52926. On this basis, we concluded that
GHGs ``are not air pollutants under the CAA's regulatory provisions,
including sections 108, 109, 111, 112, and 202'' because they
categorically are not ``air pollutant[s]'' under the Act-wide
definition in CAA section 302(g). 68 FR 52928.
Second, we raised several policy reasons for declining to regulate
GHG emissions, including that regulating GHG emissions from motor
vehicles and engines under the CAA would interfere with the National
Highway Traffic Safety Administration's authority to implement fuel
economy standards. 68 FR 52929. We also asserted that regulating GHG
emissions from motor vehicles and engines under the CAA would undermine
then-President Bush's policy approach of addressing global climate
change concerns multilaterally. 68 FR 52930-31. That is, we reasoned
that establishing GHG emission standards through unilateral action
would ``result in an inefficient, piecemeal approach to addressing the
climate change issue'' because ``all significant sources and sinks of
GHG emissions'' should be considered in deciding the best way to
achieve emission reductions. 68 FR 52931.
In Massachusetts v. EPA, 549 U.S. 497 (2007), the Supreme Court
narrowly reversed the D.C. Circuit's decision upholding the EPA's
denial of the 1999 petitions for rulemaking.\78\ The Court took
particular issue with the EPA's reading of the Act-wide definition in
CAA section 302(g), ruling that ``[t]he Clean Air Act's sweeping
definition of `air pollutant' . . . embraces all airborne compounds of
whatever stripe'' and provided no textual basis for excluding
CO<INF>2</INF> or the three other GHGs raised in the petitions for
rulemaking. 549 U.S. at 528-29. The Court also addressed the EPA's
reliance on Brown & Williamson, which the majority construed as having
found no congressional intent to ban the

[[Page 59013]]

sale of tobacco products outright because such an application of the
relevant statute would have been highly unlikely given the Food and
Drug Administration (FDA)'s refusal to assert such authority in the
past. Id. at 530-31. In contrast, in Massachusetts, the Court found
that the CAA did not reflect a congressional intent to categorically
exclude GHGs from the ``sweeping definition of `air pollutant''' and,
citing several EPA memoranda, that we had not similarly foresworn all
authority to regulate GHGs as a categorical matter. Id. at 528, 530-31.
Notably, the Court expressly declined to decide whether the EPA was
required to issue an endangerment finding as to GHG emissions under the
standard set out in CAA section 202(a)(1). Id. at 534 (``We need not
and do not reach the question whether on remand EPA must make an
endangerment finding.''). Nor did the Court address ``whether policy
concerns can inform EPA's actions in the event that it makes such a
finding.'' Id. at 534-35. Rather, the Court emphasized that the scope
of its review of the denial of a rulemaking petition was ``extremely
limited,'' id. at 527-28 (citation omitted), and held that we must
respond to the petitions by deciding whether GHG emissions from new
motor vehicles and engines meet the standard for regulation in CAA
section 202(a)(1) or whether the science was too uncertain to make any
determination, and that, in doing so, we must ``ground [our] reasons
for action or inaction in the statute,'' id. at 535.\79\
---------------------------------------------------------------------------

\78\ The D.C. Circuit majority had upheld the denial on the
merits because ``the EPA Administrator properly exercised his
discretion under section 202(a)(1) in denying the petition for
rulemaking.'' Massachusetts v. EPA, 415 F.3d 50, 58 (D.C. Cir.
2005). The dissent argued that CAA section 202(a)'s breadth provided
the EPA sufficient authority to regulate GHGs, that more specific
authorization was not required, and that the Agency's policy
justifications were inadequate reasons to deny the petitions. Id. at
67-82 (Tatel, J., dissenting).
\79\ Writing for four members of the Court, Chief Justice
Roberts would have dismissed the petitions for review for lack of
Article III standing. 549 U.S. at 535 (Roberts, C.J., joined by
Scalia, Thomas, and Alito, J.J., dissenting). Writing for the same
four members of the Court, Justice Scalia would have denied the
petitions on the grounds that the Administrator reasonably exercised
judgment in declining to regulate and that CAA section 302(g)'s
definition of ``air pollutant'' does not clearly encompass
CO<INF>2</INF> and other GHGs that naturally occur in the ambient
air. Id. at 549 (Scalia, J., joined by Roberts, C.J., and Thomas and
Alito, J.J., dissenting).
---------------------------------------------------------------------------

The EPA responded in 2008 by issuing an advanced notice of proposed
rulemaking titled ``Regulating Greenhouse Gas Emissions Under the Clean
Air Act,'' 73 FR 44354 (July 30, 2008) (``2008 ANPRM''), which analyzed
the extent to which various CAA provisions could address GHGs. The
Agency noted that the CAA was not specifically designed to address
GHGs, 73 FR 44397, and that the Agency had traditionally used its air
pollution authorities to address local and regional problems, 73 FR
44408. The EPA further noted that CAA section 111 provided significant
discretion over which stationary sources should be regulated and in
determining the appropriate technologies and costs. 73 FR 44486-93.
The EPA subsequently retained this position in implementing CAA
section 111. In June 2008, the EPA promulgated revised standards of
performance for petroleum refineries, including NO<INF>X</INF>
standards for certain types of facilities.\80\ In response to comments
asserting that the EPA was required to promulgate standards for
CO<INF>2</INF> and methane emissions because they contribute
significantly to dangerous air pollution, we stated that ``it is
reasonable for EPA not to promulgate performance standards for GHG
emissions as part of this 8-year review cycle'' because ``we believe
that the nature of GHG emissions renders them readily distinguishable
from other air pollutants for which we have previously promulgated new
performance standards concurrent with an 8-year review of the existing
standards.'' \81\ We further stated that ``[i]ndeed, GHG emissions
present issues that we have never had to address in the context of even
an initial NSPS rulemaking for a source category,'' and that ``[t]hese
differences warrant proceeding initially through a more deliberate
process, i.e., the announced [2008 ANPRM], than in this source
category-specific rulemaking.'' \82\
---------------------------------------------------------------------------

\80\ 73 FR 35838, 35846 (June 24, 2008).
\81\ Id. at 35859.
\82\ Id.
---------------------------------------------------------------------------

2. Developments Between 2009 and 2015
In 2009, following a change in administration, the EPA adopted a
new position on its authority to regulate in response to global climate
change concerns under CAA section 202(a)(1). President Obama and the
Administrator at the time initially urged Congress to amend the Act to
provide additional statutory authority. As discussed later in this
section, Congress considered legislation that would have added a new
title to the Act specific to GHGs and global climate change, similar to
the approach taken in the 1990 CAA Amendments with respect to title
IV's acid rain program and title VI's provisions for phasing out ozone-
depleting substances. When this legislation stalled, however, the EPA
finalized a new interpretation of its existing authority under CAA
section 202(a)(1) in the 2009 Endangerment Finding.
In the 2009 Endangerment Finding, the Administrator found that
``the science [was] sufficiently certain'' to compel a determination
and interpreted Massachusetts as ``allow[ing] for the consideration
only of science.'' 74 FR 66501. The Administrator interpreted
Massachusetts as holding not only that ``GHGs fall within the
definition of `air pollutant' under the CAA,'' but also as standing for
the proposition ``that EPA may regulate GHGs if required findings were
made.'' EF RTC 11:5. The EPA based the endangerment determination on
the Intergovernmental Panel on Climate Change's (IPCC) Assessment
Report 4 projections concerning global mean surface temperature and
linked that warming to indirect health risks driven by, among other
things, more frequent heat waves, air quality effects and extreme
weather events, 74 FR 66525, as well as welfare effects related to
global sea level rise, and other downstream impacts, including, among
other things, food production and agriculture and water resources, 74
FR 66531-35.\83\ Importantly, the Administrator acknowledged that the
understanding of public health and welfare in the Endangerment Finding
was atypical, particularly with respect to considering indirect effects
and because ``[n]one of th[e] human health effects are associated with
direct exposure to [GHGs],'' but asserted the approach was necessary
given the ``unique'' challenge presented by global climate change. 74
FR 66527. The EPA subsequently issued GHG standards for multiple new
motor vehicle and engine categories under CAA section 202(a)(1) and
attempted to expand its regulatory program to stationary sources by
establishing GHG emission thresholds for stationary source permitting
under the PSD program and title V.\84\
---------------------------------------------------------------------------

\83\ The EPA acknowledged that the identified welfare impact
pathways involved multiple causal steps, unlike more typical
situations analyzed in the past. 74 FR 66531.
\84\ Reconsideration of Interpretation of Regulations That
Determine Pollutants Covered by Clean Air Act Permitting Programs,
75 FR 17004 (Apr. 2, 2010) (``Triggering Rule''); Prevention of
Significant Deterioration and Title V Greenhouse Gas Tailoring Rule,
75 FR 31514 (June 3, 2010) (``Tailoring Rule'').
---------------------------------------------------------------------------

The EPA did not immediately apply the new legal interpretation
developed in the 2009 Endangerment Finding with respect to CAA section
202(a)(1) to CAA section 111. In October 2009, for example, we
promulgated NSPS for SO<INF>2</INF>, NO<INF>X</INF>, and CO from the
coal preparation and processing plants source category for the first
time.\85\ Commenters again argued that we were required to, or at least
should, regulate GHG emissions--CO<INF>2</INF>, N<INF>2</INF>O, and
black carbon--from the

[[Page 59014]]

source category to address global climate change concerns. We declined
to regulate such emissions, stating: ``At this time EPA is not aware of
any emissions or mitigation data for the pollutants noted by the
commenter for this source category. Hence, we lack sufficient
information on which to base an NSPS for emissions of CO<INF>2</INF>,
N<INF>2</INF>O, and black carbon from the source category at this
time.'' \86\
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\85\ 74 FR 51950 (Oct. 8, 2009). The EPA had listed the source
category in 1974, 39 FR 37807 (Oct. 24, 1974), and regulated PM
emissions from the source category in 1976, 39 FR 2232 (Jan. 15,
1976).
\86\ 74 FR 51957-58.
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Litigation by proponents of regulations seeking other avenues for
controlling GHG emissions from power plants continued during this
period. In Connecticut v. American Electric Power Co., 582 F.3d 309 (2d
Cir. 2009), the Second Circuit held (among other things) that litigants
could seek pollution controls under the Federal common law because the
EPA had not yet taken regulatory action with respect to GHG emissions
from stationary sources.\87\ The Supreme Court unanimously reversed
this holding in American Electric Power Co. v. Connecticut, 564 U.S.
410 (2011) (``AEP'').\88\ In AEP, the Court found that CAA section 111,
together with the Act's avenues for enforcement, rulemaking petitions,
and judicial review, ``provides a means to seek limits on emissions of
carbon dioxide from domestic powerplants--the same relief the
plaintiffs seek by invoking federal common law.'' Id. at 425. The Court
held that the Act's preclusive effect does not turn on whether the EPA
actually exercises its regulatory authority: ``The critical point is
that Congress delegated to EPA the decision whether and how to regulate
carbon-dioxide emissions from powerplants; the delegation is what
displaces federal common law.'' Id. at 426. Further, ``were EPA to
decline to regulate carbon-dioxide emissions altogether,'' the courts
``would have no warrant to employ the federal common law of nuisance to
upset the Agency's expert determination.'' Id.
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\87\ See 582 F.3d at 379-80 (``In sum, at least until EPA makes
the requisite findings, for the purposes of our displacement
analysis the CAA does not (1) regulate greenhouse gas emissions or
(2) regulate such emissions from stationary sources. . . . We
express no opinion at this time as to whether the actual regulation
of greenhouse gas emissions under the CAA by EPA, if and when such
regulation should come to pass, would displace Plaintiffs' cause of
action under the federal common law.'').
\88\ The Supreme Court affirmed by an equally divided court the
Second Circuit's holding that plaintiffs had standing to maintain
the lawsuit. See AEP, 564 U.S. at 420.
---------------------------------------------------------------------------

Separate litigation addressed aspects of the EPA's GHG regulatory
initiative without definitively resolving important questions regarding
the scope of the Agency's statutory authority. In Coalition for
Responsible Regulation v. EPA, 684 F.3d 102 (D.C. Cir. 2012), the D.C.
Circuit rejected certain challenges to the 2009 Endangerment Finding
and the suite of rules promulgated under CAA section 202(a)(1) and the
Act's stationary source permitting provisions. Among other things, the
court read Massachusetts as precluding us from declining to regulate
for policy reasons that ``were not part of the calculus'' and, citing
generally to the entirety of the opinion, as holding that the ``EPA
indeed wields the authority to regulate greenhouse gases under the
CAA.'' 684 F.3d at 118. Applying this reading, the court rejected
petitioners' arguments that we should have considered the `` 'absurd'
'' results for stationary source permitting when issuing the 2009
Endangerment Finding. Id. The court understood the interpretation of
the statutory definition of ``air pollutant'' in Massachusetts to apply
anywhere that term is used in the substantive provisions of the CAA.
Id. at 134-44. The court acknowledged that ``nothing in the CAA
requires regulation of a substance simply because it qualifies as an
`air pollutant' under this broad definition.'' Id. at 135. Applying its
broad understanding of Massachusetts, however, the court held that
reading ``air pollutant'' as ``any regulated air pollutant'' was
``compelled by the statute'' and rejected petitioners' arguments that
the PSD provisions should be read in context as focusing on localized
``air pollution'' problems. Id. at 134, 138.\89\
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\89\ The D.C. Circuit subsequently denied rehearing en banc. See
Coal. for Responsible Regulation v. EPA, 2012 U.S. App. LEXIS 25997
(Dec. 20, 2012). Judge Brown dissented, arguing that the CAA was
designed to address ``the harmful effects of poisoned air on human
beings and their local environs,'' that such important policy
decisions were for Congress to decide, and that the panel had
overread ``dicta'' in Massachusetts. Id. at *29-62. Then-Judge
Kavanaugh also dissented, arguing that the EPA exceeded its
statutory authority in regulating GHG emissions under the PSD
program by failing to read the term ``air pollutant'' in context and
that the issue was ``plainly one of exceptional importance'' that
Congress should decide. Id. at *62-93.
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In UARG, the Supreme Court granted review of the D.C. Circuit's
decision in Coalition and revisited issues related to those it had
addressed seven years earlier in Massachusetts and three years earlier
in AEP. The Court disagreed with the D.C. Circuit's reasoning and held
that the EPA's approach to extending PSD permitting to GHG emissions
exceeded the Agency's statutory authority. 573 U.S. at 316. The Court
rejected the D.C. Circuit's application of Massachusetts in this
context as a ``flawed syllogism,'' id. at 319 (citation omitted),
holding that ``while Massachusetts rejected EPA's categorical
contention that greenhouse gases could not be `air pollutants' for any
purposes of the Act, it did not embrace EPA's current, equally
categorical position that greenhouse gases must be air pollutants for
all purposes regardless of the statutory context,'' id. Rather,
``Massachusetts does not foreclose the Agency's use of statutory
context to infer that certain of the Act's provisions use `air
pollutant' to denote not every conceivable airborne substance, but only
those that may sensibly be encompassed within the particular regulatory
program.'' Id. The Court rejected the EPA's attempt to require a permit
based on GHG emissions as `` `incompatible' with `the substance of
Congress' regulatory scheme' '' and contrary to the principle that
``Congress . . . speak[s] clearly if it wishes to assign to an agency
decisions of vast `economic and political significance.' '' Id. at 322-
24 (quoting Brown & Williamson, 529 U.S. at 159).
3. The EPA's Regulation of GHGs Under CAA Section 111 Since 2015
In August 2015, the EPA announced ``a historic and important first
step in reducing carbon pollution from power plants.'' \90\ This
``first step'' consisted of two related final rules that, for the first
time since 1970, regulated stationary source emissions in response to
global climate change concerns. This watershed moment fundamentally
changed what and how the EPA regulates under CAA section 111.
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\90\ <a href="https://archive.epa.gov/epa/cleanpowerplan/fact-sheet-overview-clean-power-plan.html">https://archive.epa.gov/epa/cleanpowerplan/fact-sheet-overview-clean-power-plan.html</a>.
---------------------------------------------------------------------------

a. Regulation of CO<INF>2</INF> Emissions From Fossil Fuel-Fired Power
Plants
i. 2015 NSPS for CO<INF>2</INF> Emissions From New Power Plants
In the 2015 NSPS, the EPA laid out a novel legal basis for
regulating GHG emissions under CAA section 111 based on global climate
change concerns. The EPA explained that CAA section 111(b)(1)(A)
requires the Administrator to list any source category that ``causes,
or contributes significantly to, air pollution which may reasonably be
anticipated to endanger public health or welfare.'' The EPA posited
that, unlike other CAA provisions, CAA section 111(b)(1)(A) does not
require the EPA to make endangerment and significant contribution
findings for individual pollutants. Rather, the EPA asserted that once
such findings are made for any pollutant emitted by a source category,
the Agency has discretion to regulate all pollutants emitted by the
source

[[Page 59015]]

category subject only to rational basis constraints. 80 FR 64529-30.
Using this framework, the EPA created a new source category
consisting of the type of power plants previously listed in the 1970s
under several source categories. The source category encompassed all
fossil fuel-fired EGUs and focused on CO<INF>2</INF> emissions on the
understanding that subject power plants did not emit substantial
quantities of the additional GHGs encompassed within the 2009
Endangerment Finding.\91\ The Agency maintained, however, that it was
not listing a new source category and therefore was not required to
make any endangerment or significant contribution finding for the
fossil fuel-fired EGU source category to promulgate NSPS. The EPA
determined that it had a rational basis for concluding that emissions
of CO<INF>2</INF> from fossil fuel-fired power plants merit regulation
under CAA section 111. In reaching that conclusion, the Agency stated
that it had determined in the 2009 Endangerment Finding that GHG
emissions may reasonably be anticipated to endanger public health or
welfare and that more recent information confirmed this determination.
The EPA explained that the approach it was taking to endangerment from
GHG emissions from the fossil fuel-fired EGU source category was
``substantially similar to that reflected in the 2009 Endangerment
Finding and the 2010 denial of petitions to reconsider.'' 80 FR
64531.\92\ The EPA added that ``the high level of GHG emissions from
fossil fuel-fired EGUs makes clear that it is rational for the EPA to
regulate GHG emissions from this sector.'' 80 FR 64530.
---------------------------------------------------------------------------

\91\ Specifically, referencing the determination in the 2009
Endangerment Finding that GHGs constitute both the relevant ``air
pollutant'' and ``air pollution'' for purposes of regulating in
response to global climate change, the EPA stated in the 2015 NSPS
that ``[t]he air pollutant regulated in this final action is
greenhouse gases. However, the standards in this rule are expressed
in the form of limits on only emissions of CO<INF>2</INF>, and not
the other constituent gases of the air pollutant GHGs.'' 80 FR
64537.
\92\ See 75 FR 49556 (Aug. 13, 2010) (denying petitions for
reconsideration of the 2009 Endangerment Finding).
---------------------------------------------------------------------------

Nevertheless, the EPA purported to make separate endangerment and
significant contribution findings in the alternative pursuant to CAA
section 111(b)(1)(A). While maintaining that no pollutant-specific
contribution findings were required, the EPA asserted that the
information and conclusions in the preamble to the 2015 NSPS would
suffice for such findings. 80 FR 64530-31. That is, the EPA took the
position in the 2015 NSPS that regardless whether the Agency needed
only a rational basis to regulate CO<INF>2</INF> emissions from fossil
fuel-fired EGUs or whether the Agency was instead required to make new
endangerment and contribution findings, it had made the requisite
determinations based on the 2009 Endangerment Finding and the
additional information presented in the preamble to the 2015 NSPS.
The standards of performance in the 2015 NSPS limited
CO<INF>2</INF> emissions based on several different BSER
determinations. For new coal-fired steam boilers, the EPA based the
standards on a BSER of 16 to 23 percent (depending on the type of coal
combusted) carbon capture and storage (CCS). 80 FR 64548. For new
natural gas-fired combustion turbines, the EPA based the standards on a
BSER of efficiency measures. 80 FR 64515. The EPA subsequently denied
multiple petitions for reconsideration,\93\ and several States and
industry groups filed petitions for review in the D.C. Circuit.\94\
---------------------------------------------------------------------------

\93\ 81 FR 27442 (May 6, 2016). The EPA deferred action on one
petition with respect to the treatment of biomass. Id. at 27443.
\94\ North Dakota v. EPA, No. 15-1381 (D.C. Cir.). These
petitions have been held in abeyance since 2016 given intervening
developments.
---------------------------------------------------------------------------

ii. Emission Guidelines for CO<INF>2</INF> From Existing Power Plants
(A) 2015 Clean Power Plan
In the 2015 CPP, issued the same day as the 2015 NSPS, the EPA
promulgated emissions guidelines under CAA section 111(d) establishing
presumptive standards of performance for existing fossil fuel-fired
EGUs and requiring States to submit plans for implementation and
enforcement. 80 FR 64661. The Agency asserted that its authority under
CAA section 111(d) derived from the 2015 NSPS under CAA section 111(b)
and noted that GHGs, and CO<INF>2</INF> in particular, are not
separately regulated through the NAAQS program under CAA sections 107-
110 or the NESHAP program under CAA section 112.
The Agency based the emission guidelines for existing coal-fired
steam plants on a BSER that consisted of a set of measures, including
heat-rate improvements (i.e., the amount of fuel that must be burned to
generate a unit of electricity) and substituting fossil fuel-based
power generation with lower-emitting power generation, such as
renewable sources. 80 FR 64667. The latter type of measure is known as
``generation shifting.'' 80 FR 64728-29. The emission guidelines
authorized the States to include trading or averaging programs in their
State plans. 80 FR 64840. In February 2016, the Supreme Court stayed
the 2015 CPP after the D.C. Circuit denied preliminary relief.\95\
---------------------------------------------------------------------------

\95\ West Virginia v. EPA, 577 U.S. 1126 (2016). The D.C.
Circuit held the litigation in abeyance and later dismissed in light
of subsequent developments. See Am. Lung Ass'n, 985 F.3d at 937.
---------------------------------------------------------------------------

(B) 2019 ACE Rule and Clean Power Plan Repeal
In 2019, following a change in administration, the EPA repealed and
replaced the 2015 CPP in the Affordable Clean Energy (ACE) Rule, 84 FR
32529 (July 8, 2019). In the 2019 ACE Rule, the Agency determined that
the statutory ``text and reasonable inferences from it'' indicate that
the best ``system'' of emission reduction as defined in CAA section
111(a)(1) ``is limited to measures that can be applied to and at the
level of the individual source,'' meaning the BSER must be control
measures for reducing emissions at individual sources. 84 FR 32523-24.
The Agency concluded that generation shifting is not such a control
measure. 84 FR 32546. In addition, the EPA concluded that the 2015 CPP
was a ``major rule'' subject to the major questions doctrine and
therefore must be supported by ``a clear statement from Congress.''
Because the statutory phrase ``best system of emission reduction'' does
not clearly speak to generation shifting, the Agency reasoned that CAA
section 111 should not be read to encompass generation-shifting
measures. 84 FR 32529. To replace the 2015 CPP, the EPA promulgated as
part of the 2019 ACE Rule a new set of emission guidelines for existing
coal-fired steam-generating EGUs. 84 FR 32532.
In American Lung Association, a divided panel of the D.C. Circuit
vacated the 2019 ACE Rule, including the CPP Repeal. First, the panel
majority held that CAA section 111(d) does not limit the EPA, in
determining the BSER, to measures applied at and to an individual
source. 985 F.3d at 944. Second, the panel majority rejected in the
strongest terms the argument that generation-shifting implicated ``the
so-called `major questions' doctrine'' based on its interpretation of
the Supreme Court's decisions in Massachusetts and AEP. Id. at 959. The
panel majority reasoned that the EPA had ``complied'' with
Massachusetts by issuing the 2009 Endangerment Finding and that in AEP,
``the Court [ ] told the EPA directly that it is the Agency's job to
regulate power plants' emissions of greenhouse gases under Section
[111].'' Id. at 959-60. Therefore, the panel majority concluded, all
questions as to ``what,''

[[Page 59016]]

``whom,'' and ``how'' the Agency may regulate ``have all been resolved
and so do not trigger the major questions doctrine.'' Id. at 962.\96\
Finally, the panel majority rejected certain additional challenges to
the findings (or lack thereof) supporting the 2015 NSPS and therefore
the 2015 CPP as well as arguments that coal power plants could not be
regulated under CAA section 111(d) given the EPA's regulation of
mercury emissions from coal plants under CAA section 112. Id. at 971-
88. Ultimately the panel majority vacated the 2019 ACE Rule, including
the CPP Repeal, thereby placing the 2015 CPP back into effect.\97\
---------------------------------------------------------------------------

\96\ The panel majority further held that the major questions
doctrine ``does not apply'' to the interpretation of ``best system
of emission reduction'' because, among other reasons, ``the
regulatory authority and its reach have been affirmed and enforced
by the Supreme Court'' and generation shifting was an ``already-in-
use'' system. 985 F.3d at 963-68.
\97\ In a partial dissent, Judge Walker argued that the 2015 CPP
(and aspects retained in the 2019 ACE Rule) violated the major
questions doctrine because CAA section 111 does not include a clear
statement of authority to regulate GHG emissions from power plants.
Id. at 995-1003 (pointing to failed legislation in 2009 that would
have provided the requisite authority to regulate GHG emissions from
power plants).
---------------------------------------------------------------------------

In West Virginia, the Supreme Court reversed the D.C. Circuit's
treatment of the major questions doctrine and held that the 2015 CPP
exceeded the EPA's authority under CAA section 111(d). First, the Court
surveyed its precedents to confirm that an agency must have more than
``a colorable textual basis'' to assert `` `unheralded' regulatory
power over `a significant portion of the American economy.' '' 597 U.S.
at 721-23 (quoting UARG, 573 U.S. at 324). In such cases, ``both
separation of power principles and a practical understanding of
legislative intent'' require the agency to ``point to `clear
congressional authorization' for the power it claims.'' Id. at 723
(quoting UARG, 573 U.S. at 324). The Court explained that its decision
in UARG ``addressed another question regarding EPA's authority--namely,
whether EPA could construe the term `air pollutant,' in a specific
provision of the Clean Air Act, to cover greenhouse gases,'' and held
that despite the ``textual plausibility'' of the interpretation
supporting the Agency's assertion of authority, the significant
consequences involved required more than a ``plausib[le]'' statutory
basis. Id. at 722. Next, the Court held that our reliance on CAA
section 111(d) to regulate GHG emissions was ``a major questions case''
because we had asserted the power ``to substantially restructure the
American energy market.'' Id. at 724. That provision ``had rarely been
used in the preceding decades,'' and we had used it in an
``unprecedented'' manner ``to adopt a regulatory program that Congress
had conspicuously and repeatedly declined to enact itself.'' Id. at
724-28. The Court specifically rejected the argument that AEP precluded
application of the major questions doctrine, stating that the case
involved the question ``whether Congress wanted district court judges
to decide, under unwritten federal nuisance law, `whether and how to
regulate carbondioxide emissions from powerplants' '' and ``said
nothing about the ways in which Congress intended EPA to exercise its
power under that provision.'' Id. at 730 (quoting AEP, 564 U.S. at
426). Finally, the Court concluded that we lacked statutory authority
for the 2015 CPP based on a lack of statutory authorization to require
generation shifting. Id. at 732-35.\98\
---------------------------------------------------------------------------

\98\ In dissent, Justice Kagan argued that the Court had
obstructed the EPA's efforts to regulate GHG emissions: ``Today, the
Court strips the [EPA] of the power Congress gave it to respond to
`the most pressing environmental challenge of our time.''' West
Virginia, 597 U.S. at 753 (Kagan, J., joined by Breyer and
Sotomayor, J.J., dissenting) (quoting Massachusetts, 549 U.S. at
505); see also id. at 755 (``This Court has obstructed EPA's effort
from the beginning.'').
---------------------------------------------------------------------------

In October 2022, the D.C. Circuit recalled its mandate for the
vacatur of the 2019 ACE Rule, revised its judgment to place the CPP
Repeal back into effect, and stayed further proceedings. Am. Lung Ass'n
v. EPA, No. 19-1140, Order (Oct. 27, 2022).
(C) 2024 Carbon Pollution Standards Rule
In May 2024, the EPA responded to the Supreme Court's decision in
West Virginia by promulgating more stringent requirements for fossil
fuel-fired EGUs than those contained in the 2015 NSPS or vacated 2015
CPP. 89 FR 39798. The 2024 CPS included several related components.
First, the EPA repealed the 2019 ACE Rule (aside from its repeal of the
2015 CPP) after determining that the BSER for existing coal-fired power
plants was not the suite of heat-rate improvements identified in the
2019 ACE Rule. Second, the EPA promulgated new emission guidelines for
GHG emissions from existing fossil fuel-fired power plants
subcategorized into coal-fired units, oil-fired units, and gas-fired
units. For existing coal-fired units, the EPA based the requirements on
a new BSER of either 90 percent CCS or 40 percent gas cofiring. For
existing natural gas- and oil-fired steam generating units, the EPA
based the requirements on BSERs of either routine methods of operation
and maintenance or uniform fuels. Finally, the Agency promulgated NSPS
for new and reconstructed combustion turbines, based on efficiency
measures, 90 percent CCS, or use of lower-emitting fuels. In addition,
the EPA revised the standards of performance for coal-fired steam
generating units that undertake a large modification to be based on the
BSER of 90 percent CCS.\99\
---------------------------------------------------------------------------

\99\ In the 2024 CPS, the EPA also withdrew the separate
proposed revisions to the New Source Review (NSR) regulations that
were included the ACE Rule proposal (see 83 FR 44746, 44773-83 (Aug.
31, 2018)).
---------------------------------------------------------------------------

Following promulgation of the 2024 CPS, States and industry groups
filed petitions for review in the D.C. Circuit, and many subsequently
filed motions to stay the rule. The D.C. Circuit denied the stay
motions on July 19, 2024,\100\ and the Supreme Court denied them on
October 16, 2024.\101\ These challenges have been held in abeyance
since the change in administration.
---------------------------------------------------------------------------

\100\ West Virginia v. EPA, No. 2420, Order, 2024 U.S. App.
LEXIS 17856 (July 19, 2024).
\101\ West Virginia v. EPA, 145 S. Ct. 2 (2024). Justice Thomas
would have granted a stay, and Justice Kavanaugh, joined by Justice
Gorsuch, wrote separately that ``the applicants have shown a strong
likelihood of success on the merits as to at least some of their
challenges to the [EPA's] rule.'' Id.
---------------------------------------------------------------------------

D. Recent Developments

1. Rescission of the 2009 Endangerment Finding
In February 2025, the Administrator initiated reconsideration of
the 2009 findings of endangerment and contribution under CAA section
202(a)(1) that launched the EPA's GHG regulatory initiative across
multiple statutory programs. The Administrator explained that the
Agency would address legal and scientific developments that presented
reason to question the ongoing validity and reliability of the
conclusions in the 2009 Endangerment Finding and to seek public comment
on these important issues for the first time since 2009.\102\ These
efforts culminated in a proposed rule issued on July 29, 2025,\103\
followed by a public comment period in which we received hundreds of
thousands of comments from a variety of perspectives.
---------------------------------------------------------------------------

\102\ See Feb. 19, 2025 Memo at 1.
\103\ See 90 FR 36288 (Aug. 1, 2025).
---------------------------------------------------------------------------

On February 12, 2026, the Administrator signed a final rule
rescinding the 2009 Endangerment Finding and repealing all associated
GHG emission standards for new motor vehicles and engines under CAA
section 202(a)(1).\104\ The EPA concluded in the Endangerment Finding
Rescission that we lack statutory authority to regulate GHG emissions
from new motor

[[Page 59017]]

vehicles and motor vehicle engines based on global climate change
concerns. We further concluded that the appropriate policy response to
global climate change concerns is a decision vested in Congress, and
that Congress did not give the EPA the authority to decide the Nation's
policy response to these concerns when it enacted CAA section 202(a)(1)
to address domestic air pollution problems. And we concluded, based on
an analysis of commonly accepted climate impact modeling, including
models and arguments received from multiple perspectives during the
public comment period, that the inability of GHG emission standards for
new motor vehicles and engines to have more than a de minimis impact on
phenomena attributed to global climate changes rendered the standards
futile.\105\
---------------------------------------------------------------------------

\104\ See 91 FR 7586 (Feb. 18, 2026).
\105\ This discussion summarizes the bases of the Endangerment
Finding Rescission for informational purposes, only, and does not
reopen that final rule or seek additional comment on issues
addressed in that final rule. For more information, see the final
rule preamble, accompanying RTC, and supporting documentation for
the Endangerment Finding Rescission.
---------------------------------------------------------------------------

2. Proposed Repeal of GHG Standards for Fossil Fuel-Fired EGUs
On June 17, 2025, the EPA issued a proposed rule to repeal GHG
standards for fossil fuel-fired EGUs. The June 2025 NPRM included a
primary proposal, which would repeal all such GHG standards, and an
alternative proposal, which would repeal most of the GHG standards
promulgated in the 2024 CPS. This subsection summarizes the June 2025
NPRM for informational purposes only; as noted above, the EPA is not
soliciting additional comment on issues addressed in the concurrently
issued final rule based on the alternative proposal in the June 2025
NPRM and will address comments received on the primary proposal in the
June 2025 NPRM in a final action addressing that proposal and this
supplemental proposal.
The primary proposal in the June 2025 NPRM proposed to conclude
that CAA section 111 is best read to require, or at least authorize the
EPA to require, an Administrator's determination that an air pollutant
emitted by a source category causes, or contributes significantly to,
air pollution which may reasonably be anticipated to endanger public
health or welfare as a predicate to establishing emission standards for
that pollutant. As such, we proposed to conclude that the Administrator
must make a significant contribution finding before issuing GHG
emission standards for a new source category even if covered sources
had previously been listed under a distinct category. We further
proposed to determine, in a change from the 2015 NSPS and 2024 CPS,
that GHG emissions from fossil fuel-fired EGUs do not contribute
significantly to air pollution as required for the promulgation of new
and existing source standards. We proposed that a determination of
significant contribution must consider whether such determination would
have an influence or effect on the targeted air pollution and the
public health or welfare impacts attributed to such air pollution, and
that this inquiry entails considering the policies that would inform
the resulting regulation. Based on this understanding, we proposed to
find that regulation of GHG emissions from fossil fuel-fired EGUs under
CAA section 111 would not have a significant effect on GHG air
pollution and the public health or welfare impacts attributed to such
air pollution, and that the contribution of this source category is
therefore not significant for a host of reasons. The EPA thus proposed
to repeal all GHG emissions standards for the power sector under CAA
section 111, including the 2015 NSPS, codified in 40 CFR part 60,
subpart TTTT, and the 2024 CPS, codified in 40 CFR part 60, subparts
TTTTa and UUUUb.
The alternative proposal in the June 2025 NPRM proposed to
reconsider the BSER determinations in the 2024 CPS through a record-
based evaluation and in light of applicable requirements for
determining an appropriate BSER. The EPA proposed to rescind the
requirements for existing coal-fired units on grounds that 90 percent
CCS and 40 percent natural gas co-firing do not qualify as the BSER for
existing coal-fired units. The EPA is finalizing that proposal
concurrently with this supplemental proposal. The EPA is not taking
further action at this time on the primary proposal in the June 2025
NPRM and will consider and respond to comments on that proposal
together with comments submitted on this supplemental notice in a
forthcoming final action.
3. Relevant Legislative Action
Both before and since the 2009 Endangerment Finding, `` `Congress
considered and rejected' multiple times'' legislation that would have
authorized or required the EPA to regulate GHG emissions from
stationary sources that were subject to CAA section 111 for their non-
GHG emissions, as well as mobile sources. West Virginia, 597 U.S. at
731 (quoting Brown & Williamson, 529 U.S. at 144). This history is
particularly relevant because of the established pattern in the 1970,
1977, and 1990 CAA Amendments of Congress adding requirements for
regulatory action to CAA section 111. From 2007 to 2009, Congress
considered legislation that would have authorized or required the EPA
to prescribe emissions regulations for GHGs. For example, the Safe
Climate Act of 2007 would have adopted findings and policies with
respect to limiting global temperature increase, required participating
in various forms of international cooperation, and added a new title
VII to the CAA instructing the EPA to achieve phased GHG emission
reduction targets and employ a cap-and-trade program to regulate GHG
emissions from sources that EPA determines are appropriate to regulate,
including sources that ``have the largest emissions.'' \106\ Similarly,
the American Clean Energy and Security Act of 2009 would have required
international cooperation and added new titles to the CAA requiring the
EPA to, among other things, regulate through a cap-and-trade program
GHG emissions from large stationary sources and regulate GHG emissions
from other stationary sources under CAA section 111 on a specified
schedule.\107\ Neither bill was enacted, and Congress has since
declined to adopt similar legislation.\108\
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\106\ H.R. 1590, 110th Cong. (2007) (proposed CAA section
703(b)(1)(A)).
\107\ H.R. 2454, 111th Cong. (2009) (proposed CAA section 811).
This bill, introduced on May 15, 2009--a month after the EPA
proposed the 2009 Endangerment Finding--passed the House of
Representatives by a 219-212 vote on June 26, 2009, but never
received a vote in the Senate. <a href="https://www.congress.gov/bill/111th-congress/house-bill/2454">https://www.congress.gov/bill/111th-congress/house-bill/2454</a>. The President and Administrator at the
time expressed a strong preference for legislation but also a
willingness to resolve legislative inaction by administrative means,
and the Agency ultimately finalized the Endangerment Finding on
December 7, 2009. See President Barack Obama, 2013 State of the
Union Address (Feb. 12, 2013) <a href="https://obamawhitehouse.archives.gov/the-press-office/2013/02/12/remarks-President-state-union-address">https://obamawhitehouse.archives.gov/the-press-office/2013/02/12/remarks-President-state-union-address</a>
(``[I]f Congress won't act soon to protect future generations, I
will.'').
\108\ Congress's pattern of declining to provide the EPA such
authority extends long before 2009. See Coal. For Responsible
Regulation, 2012 U.S. App. LEXIS 25997, at *36-37 (Brown, J.,
dissenting from denial of rh'g en banc) (noting Congress expressly
rejected proposals offered during the drafting of the 1990 CAA
Amendments that would have authorized the EPA to regulate GHGs).
---------------------------------------------------------------------------

On several recent occasions, Congress has adopted legislation
bearing on issues similar to those addressed here with respect to the
EPA's authority under CAA section 111. This subsequent legislation
either declined to adopt statutory language endorsing our authority to
regulate GHG emissions from power plants or elected to use non-
regulatory measures.

[[Page 59018]]

In 2022, Congress adopted the Inflation Reduction Act (IRA),\109\
which appropriated funds to the EPA for a low emissions electricity
program (LEEP) that would, among other things, ``assess . . . the
reductions in [GHG] emissions that result from changes in domestic
electricity generation and use that are anticipated to occur'' and
ensure that such reductions ``are achieved through use of the existing
authorities of this chapter, incorporating the assessment'' noted
above.\110\ The version of the IRA adopted by the House of
Representatives would have appropriated funds to EPA ``to remain
available until September 30, 2031, to carry out, with respect to
greenhouse gases, sections 111, 115, 165, 177, 202, 211, 213, 231, and
612 of the Clean Air Act,'' but this provision was eventually dropped
and never enacted.\111\
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\109\ Public Law 117-169, <a href="https://www.govtrack.us/congress/bills/117/hr5376">https://www.govtrack.us/congress/bills/117/hr5376</a>.
\110\ CAA section 135(a)(5)-(6), 42 U.S.C. 7435(a)(5)-(6).
\111\ The EPA issued a comment solicitation in November 2022
seeking input on how to use the funds to promote education,
technical assistance, and partnerships but ultimately did not take
further action. <a href="https://www.regulations.gov/document/EPA-HQ-OAR-2022-0878-0002">https://www.regulations.gov/document/EPA-HQ-OAR-2022-0878-0002</a>.
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In 2025, Congress passed and the President signed into law the One
Big Beautiful Bill Act (OBBBA). This legislation rescinded the
unobligated balance of funding for the LEEP program and the majority of
other programs funded under the IRA, as well as repealing certain IRA
provisions.\112\ Also in 2025, Congress passed, and the President
signed into law, three joint resolutions adopted under the
Congressional Review Act disapproving three waivers EPA granted under
CAA section 209 that allowed California and participating States to
enforce GHG emission regulations for motor vehicles and engines, up to
and including zero-emissions standards that mandated a shift to
electric vehicles.\113\
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\112\ 139 Stat. 155 (``RESCISSION OF FUNDING FOR THE LOW
EMISSIONS ELECTRICITY PROGRAM. The unobligated balances of amounts
made available to carry out section 135 of the Clean Air Act (42
U.S.C. 7435) are rescinded.'') <a href="https://www.congress.gov/bill/119th-congress/house-bill/1/text">https://www.congress.gov/bill/119th-congress/house-bill/1/text</a>.
\113\ H.R.J. Res. 87; H.R.J. Res. 88; H.R.J. Res. 89; see also
Diamond Alt. Energy, LLC v. EPA, 606 U.S.100, 107 n.1 (2025);
Statement by the President (June 12, 2025), <a href="https://www.whitehouse.gov/briefings-statements/2025/06/statement-by-the-president/">https://www.whitehouse.gov/briefings-statements/2025/06/statement-by-the-president/</a>.
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IV. Legal Framework for Action

In the 2015 NSPS and 2015 CPP, the EPA for the first time announced
a legal basis for regulating GHG emissions from power plants under CAA
section 111. The EPA asserted that section 111 authorizes the Agency to
regulate GHG emissions from a listed source category so long as it has
a rational basis for doing so and does not require endangerment or
contribution findings specific to GHG emissions from power plants. The
Agency went on to determine that we had a rational basis for concluding
that emissions of CO<INF>2</INF> from fossil fuel-fired power plants
merit regulation under CAA section 111, in light of the 2009
Endangerment Finding and subsequent information, as well as the amount
of GHG emissions from the source category; and that even if we were
required to make new endangerment and contribution findings, the same
information would justify such findings.\114\
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\114\ 80 FR 64530-31 (Oct. 23, 2015).
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The EPA is now proposing to repeal the suite of determinations,
findings, and actions finalized in the 2015 NSPS for purposes of
regulating GHG emissions from fossil fuel-fired power plants on
statutory authority grounds distinct from those presented in the
primary proposal in the June 2025 NPRM. Regardless whether the EPA must
or can make a GHG-specific significant contribution finding for fossil
fuel-fired power plants, the Agency cannot invoke its CAA section 111
authority to regulate emissions from power plants unless GHG emissions
from such sources and the associated global climate change concerns
used to justify regulation satisfy the statutory prerequisite for
regulation under CAA section 111(b)(1)(A) in the first instance. That
is, GHG emissions from power plants must contribute significantly to
``air pollution that may reasonably be anticipated to endanger public
health or welfare.'' The Agency is proposing in this supplemental
notice that global climate change concerns cannot satisfy that
standard. Thus, the EPA is proposing to rescind the set of
determinations the Agency made in the 2015 NSPS and retained in the
2024 CPS with regard to GHG emissions from fossil fuel-fired power
plants, including the determination that it had a rational basis for
regulating GHG emissions from fossil fuel-fired power plants and the
endangerment and significant contribution findings made in the
alternative (collectively ``the 2015 Findings'').
The statutory authority for this supplemental proposal is the same
as that relied upon to make the 2015 Findings in the first instance:
CAA section 111(b)(1)(A). In addition, unless provided otherwise by
statute, an agency may revise or rescind prior actions so long as it
acknowledges the change in position, provides a reasonable explanation
for the new position, and considers legitimate reliance interests in
the prior position.\115\
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\115\ See FDA v. Wages & White Lion Invs., LLC, 145 S. Ct. 898
(2025) (applying change-in-position doctrine); FCC v. Fox TV
Stations, Inc., 556 U.S. 502 (2009); Motor Vehicle Mfrs. Ass'n v.
State Farm Mut. Auto. Ins. Co., 463 U.S. 29 (1983); see also Clean
Air Council v. Pruitt, 862 F.3d 1, 8 (D.C. Cir. 2017) (``Agencies
obviously have broad discretion to reconsider a regulation at any
time.'').
---------------------------------------------------------------------------

The EPA proposes that nothing in the language of the relevant
statutory provisions prohibits or conditions our general authority to
rescind prior actions through rulemaking. CAA section 111(b)(1)(B)
explicitly calls upon the Administrator to ``revise'' standards of
performance if appropriate and does not require retaining the same
level of stringency when revising or rescinding the existing standards
at issue here. Moreover, the statute does not prohibit the
Administrator from rescinding findings under CAA section 111(b)(1)(A).
The EPA notes that, with regard to the similar statutory provision in
CAA section 202(a)(1), it has consistently assumed that it has the
statutory authority to rescind endangerment and contribution findings.
This is evidenced by both the EPA's review of the merits of petitions
for reconsideration of the Agency's authority to regulate GHG emissions
under CAA section 202(a)(1) and the recent Endangerment Finding
Rescission.\116\
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\116\ See, e.g., 87 FR 25412 (Apr. 29, 2022) (noticing 2022
reconsideration denial documents in which the EPA assumed it could
rescind the findings); 75 FR 49556, 49560-63 (Aug. 13, 2010)
(denying reconsideration without asserting that the EPA lacked
statutory authority to rescind or revise the Endangerment Finding);
see generally 91 FR 7686, 7702-10 (Feb. 18, 2026).
---------------------------------------------------------------------------

The EPA acknowledges that rescinding the 2015 Findings and
repealing associated standards would involve significant changes to the
more recent legal interpretations that we have relied on to regulate
GHG emissions from power plants under CAA section 111. For example, the
interpretation of CAA section 111(b)(1)(A) the EPA is proposing would
reverse the basis for the 2015 Findings by concluding that global
climate change concerns cannot satisfy the statutory standard for
regulation of emissions under CAA section 111(b)(1)(A). Going forward,
the EPA would regulate emissions from power plants that fall within the
meaning of ``air pollution which may reasonably be anticipated to
endanger public health or welfare'' as interpreted in this supplemental
proposal. However, the EPA believes that a reconsideration of these
legal interpretations is necessary to hew to

[[Page 59019]]

the best reading of the statute and in light of recent legal
developments, such as the Supreme Court's landmark decisions in West
Virginia and Loper Bright.
The EPA further acknowledges that the 2015 Findings, and in
particular regulatory requirements under the 2015 NSPS and 2024 CPS,
have imposed significant burdens on Federal, State, and private-sector
entities, including costs already incurred to achieve and demonstrate
compliance with requirements by compliance dates in the past. We also
understand that certain States, municipalities, and third-party
organizations may have relied on the 2015 Findings or associated
regulations in developing additional regulatory or voluntary programs.
The EPA solicited public comment on these and other reliance interests
in connection with the primary proposal in the June 2025 NPRM, which
similarly proposed to rescind and repeal these findings and
regulations. We acknowledge that the additional rationales in this
action could potentially implicate additional and different reliance
interests. Although we do not believe that any such reliance interests
could justify retaining the findings and regulations in the absence of
statutory authorization, we solicit comment on whether the there are
additional reliance interests implicated by the additional rationales
put forward in this supplemental proposal and, if so, why they are
legitimate and significant and how we should consider them when taking
final action.
To a certain extent, the EPA's reexamination of its authority to
regulate GHG emissions under CAA section 111 based on global climate
change concerns is informed by our recent rescission of the 2009
Endangerment Finding under CAA section 202(a)(1). The statutory
provisions governing the endangerment and contribution findings under
CAA sections 111(b)(1)(A) and 202(a)(1) differ in ways, although both
call upon the EPA to regulate when a collection of emitting sources
contributes (or contributes significantly) to ``air pollution which may
reasonably be anticipated to endanger public health or welfare.'' The
2015 Findings were based in significant part on the approach taken in
the 2009 Endangerment Finding, and as such, many of the flaws
identified in the 2009 Endangerment Finding similarly impact the legal
and analytical approach we carried through to stationary sources in the
2015 NSPS and 2024 CPS.
Recent legal developments have also compelled the EPA to take a
harder look at the 2015 Findings. In particular, the Supreme Court's
decision in West Virginia, which explained and applied the major
questions doctrine, has particular bearing on the question whether the
EPA has authority to regulate GHG emissions from fossil fuel-fired
power plants under CAA section 111. The EPA discusses application of
the major questions doctrine to this question in section V of this
preamble. And in June 2024, the Supreme Court announced its decision in
Loper Bright, which overruled Chevron deference to agency statutory
interpretation and clarified that statutes have a single, best meaning,
which is fixed at the time of enactment.\117\ As explained in section V
of this preamble, the EPA's authority to regulate air pollutant
emissions from a source category under CAA sections 111(b)(1)(B) and
111(a)(1) flows from the Administrator's listing of that category upon
finding that it ``causes, or contributes significantly to, air
pollution which may reasonably be anticipated to endanger public health
or welfare.'' Regardless whether CAA section 111(b)(1)(A) requires the
EPA to have only a rational basis for regulating air pollutants from an
already listed source category or whether the Agency must make a
pollutant-specific significant contribution finding, as a threshold
matter, the EPA must demonstrate that the source category emissions
satisfy the statutory prerequisite for regulation--that is, they must
relate to qualifying ``air pollution'' within the meaning of the
statute. And because the EPA is proposing to find that we lack
authority under CAA section 111 to regulate GHG emissions from fossil
fuel-fired power plants based on global climate change concerns, we are
also proposing to repeal all regulations relating to GHG emissions from
fossil fuel-fired power plants that the Agency has promulgated pursuant
to CAA sections 111(b)(1)(B) and 111(a)(1), which are currently
codified in 40 CFR part 60, subparts TTTT and TTTTa.
---------------------------------------------------------------------------

\117\ 603 U.S. at 412-13 (overruling Chevron U.S.A., Inc. v.
NRDC, Inc., 467 U.S. 837 (1984)).
---------------------------------------------------------------------------

The EPA emphasizes that the scope of this supplemental notice is
limited to the treatment of GHG emissions from fossil fuel-fired power
plants under CAA section 111.\118\ While the proposed interpretation of
CAA section 111(b)(1)(A) regarding authority to regulate GHG emissions
could apply more broadly, other components of our analysis, including
the applicability of the major questions doctrine and the evaluation of
the impact of regulating GHG emissions from fossil fuel-fired power
plants based on the identified harms associated with global climate
change, are specific to the fossil fuel-fired power plant source
category.
---------------------------------------------------------------------------

\118\ See UARG, 573 U.S. at 319-20.
---------------------------------------------------------------------------

The EPA acknowledges that we are proposing action in the context of
a subject matter that has generated scientific and technical
literature, including findings and reports of the National Academy of
Sciences (NAS). For example, on July 16, 2026, the NAS released a
consensus study report discussing the attribution of extreme weather
events to global climate change.\119\ The report discusses scientific
methodology and modeling associated with the attribution of extreme
weather events such as heat waves, wildfires, or connective storms to
GHG emissions produced from human activities. The report also discusses
developments in weather event attribution and further steps for
research and improving conclusions regarding event attribution. The
issues raised in this supplemental proposal, however, are legal in
nature and turn on statutory interpretation and the application of
judicial precedent. We propose that this report, and prior information
released by NAS, do not differ in any material respect from or conflict
with the legal rationales set forth in this supplemental notice.
---------------------------------------------------------------------------

\119\ National Academies of Sciences, Engineering, and Medicine.
2026. Attribution of Extreme Weather and Climate Events and Their
Impacts. Washington, DC: National Academies Press. <a href="https://doi.org/10.17226/28590">https://doi.org/10.17226/28590</a>.
---------------------------------------------------------------------------

As discussed throughout this preamble, the EPA is proposing these
changes to comply with limits on our statutory authority under the best
reading of CAA section 111(b)(1)(A), to adhere to the legal limits on
our power to set national policy within our constitutional system of
democratic government, and to realign Agency resources to prioritize
core statutory responsibilities to protect human health and the
environment. Importantly, the Nation's policy response to global
climate change concerns was a major issue in the 2024 presidential
election, in which voters were presented with distinct legal and policy
approaches and elected a candidate promising a change in policy. Under
these circumstances, the election of a new Administration is an
independent and sufficient basis for reassessing and revising legal
interpretations to faithfully adhere to the best reading of the
statute.\120\

[[Page 59020]]

Democratic accountability is essential to the exercise of delegated
authority by administrative agencies,\121\ and retaining the 2015
Findings and associated GHG standards without clear statutory authority
would frustrate, not promote, constitutional values and the rule of
law. The EPA proposes to determine that it lacks authority to retain
the 2015 Findings under the best reading of CAA section 111(b)(1)(A),
and the statute controls regardless of policy preferences.\122\
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\120\ See State Farm, 463 U.S. at 59 (Rehnquist, J., concurring
in part and dissenting in part); PETA v. USDA, 918 F.3d 151, 158
(D.C. Cir. 2019) (``new administrations are entitled to reevaluate
and modify agency practices, even longstanding ones''); Nat'l Ass'n
of Home Builders v. EPA, 682 F.3d 1032, 1043 (D.C. Cir. 2012) (``the
inauguration of a new President and the confirmation of a new EPA
Administrator'' went ``a long way toward explaining why EPA''
changed policy).
\121\ See, e.g., U.S. Telecom Ass'n v. FCC, 855 F.3d 381 (D.C.
Cir. 2017) (Brown, J., dissenting from denial of rehearing en banc);
Elena Kagan, Presidential Administration, 114 Harv. L. Rev. 2245,
2252-53, 2332-34 (2001).
\122\ Loper Bright, 603 U.S. at 403; West Virginia, 597 U.S. at
735; UARG, 573 U.S. at 325.
---------------------------------------------------------------------------

V. Rescission of the 2015 Findings

In this section, the EPA provides its bases for proposing to
rescind the 2015 Findings that purported to provide the authority to
regulate GHG emissions from fossil fuel-fired power plants under CAA
section 111 based on global climate change concerns. We are proposing
to determine that these Findings and regulations exceed the EPA's
statutory authority for multiple, independent reasons.
Section V.A.1 proposes that the best reading of CAA section
111(b)(1)(A), as informed by Loper Bright and principles of statutory
interpretation, precludes the EPA from regulating power plant emissions
based on global climate change concerns because such concerns cannot
satisfy the statutory prerequisite for applying the Agency's regulatory
authority. Rather, the best reading of the requirement to list a source
category ``if in [the Administrator's] judgment it causes, or
contributes significantly to, air pollution which may reasonably be
anticipated to endanger public health or welfare'' is that the ``air
pollution'' to be addressed under CAA section 111 must adversely impact
public health or welfare through local or regional exposure. This
proposed interpretation is based on the language of the statute, canons
of statutory interpretation, statutory context, amendment and
legislative history, and relevant case law, among other considerations.
Because GHG emissions may endanger public health and welfare only by
virtue of elevated global concentrations of GHGs in the atmosphere and
the impacts of second- and third-order phenomena attributed to global
climate change, i.e., not based on local or regional exposure to GHG
emissions, the EPA is proposing to find that they cannot satisfy the
standard in CAA section 111(b)(1)(A). The futility of regulating GHG
emissions from fossil fuel-fired power plants under CAA section 111 in
addressing the public health and welfare impacts attributed to global
climate change further reinforces this proposed interpretation.
Section V.A.2 proposes two further bases for rescinding the 2015
Findings and associated regulations that stem from flaws in the 2015
Findings themselves. First, as an initial step, in 2015 the EPA
combined two separate source categories to create the fossil fuel-fired
EGU source category specifically for the purpose of regulating GHG
emissions from these sources. In doing so, we failed to undertake a new
listing under CAA section 111(b)(1)(A) and instead purported to subject
these sources to additional regulatory controls without grappling fully
with the predicate requirements for taking such an action. The EPA
proposes that this omission renders the 2015 Findings and subsequent
regulations unlawful. Second, the 2015 Findings relied on the same
interpretive approach that underlays the 2009 Endangerment Finding
under CAA section 202(a)(1), as well as on the existence of the
endangerment and contribution findings in the 2009 Endangerment
Finding. The rescission of the 2009 Endangerment Finding has abrogated
the legal framework underlying the 2015 Findings, which the EPA
proposes to find renders the 2015 Findings without legal basis.
Relatedly, the flaws identified in the 2009 Endangerment Finding
similarly render the 2015 Findings insupportable.
Section V.B proposes that the major questions doctrine applies to
the EPA's assertion of authority under CAA section 111 and that the
Agency lacks the clear congressional authorization required for the
unheralded assertion of authority adopted in the 2015 Findings. We
review the Supreme Court's precedents applying the major questions
doctrine, including UARG and West Virginia, to propose that the
Nation's policy response to global climate change concerns is a
question of significant economic and political importance that Congress
did not clearly empower the EPA to decide by authorizing the
Administrator to list a category of sources for regulation ``if in [the
Administrator's] judgment it causes, or contributes significantly to,
air pollution which may reasonably be anticipated to endanger public
health or welfare.'' We further propose that a limiting construction of
CAA section 111(b)(1)(A) is necessary to avoid serious constitutional
concerns with the breadth of the provision required by the logic
adopted in the 2015 Findings.
Section V.C of this preamble explains our proposed determination
that the EPA lacks authority to regulate GHG emissions under CAA
section 111(b)(1)(A) because such regulations have not and cannot
diminish the public health and welfare impacts attributed to global
climate change in any non-de minimis way. As presented below, the
results of commonly accepted models indicate that even the elimination
of all CO<INF>2</INF> emissions from fossil fuel-fired power plants in
the United States (much more than the regulations we propose to repeal
would do if fully implemented) would not yield impacts beyond a level
that is well below the range of inherent variability in measurement for
trends in GMST and GSLR. We propose that these findings further support
the contemplated rescissions and repeals given the language of CAA
section 111(b)(1)(A) and the background principles that Congress does
not require futile efforts or include de minimis concerns in general
statutory terms.
In proposing these rationales, the EPA is mindful that we issued
the 2015 Findings during a transitional period regarding the standards
for statutory interpretation and understandings of agency authority.
The Supreme Court had, in Massachusetts, determined that GHGs fit
within the CAA-wide definition of ``air pollutant.'' At the time we
responded to this decision, both the breadth of agency discretion and
the question whether Congress reserves major policy questions for
itself were sharply disputed. Judicial decisions in the intervening
years have significantly clarified the law. In Loper Bright, the
Supreme Court overruled the Chevron doctrine of deference to agency
statutory interpretation, ruling that statutes ``have a single, best
meaning'' that is `` `fixed at the time of enactment' '' and informed,
but not dictated, by Executive Branch practice. 603 U.S. at 400-01
(quoting Wis. Cent. Ltd. v. United States, 585 U.S. 274, 284 (2018)).
And in West Virginia, the Supreme Court built upon its decisions in
UARG and Brown & Williamson, among others, by confirming that an agency
must have more than ``a colorable textual basis'' to claim authority to
decide major questions of policy that Congress generally reserves for
itself. 597 U.S. at 723.
Each of the legal bases proposed in this action is independent from
the others and would be sufficient to rescind the 2015 Findings and
repeal the associated GHG standards. The EPA

[[Page 59021]]

is proposing that a lack of statutory authority for the 2015 Findings
and related GHG regulations would require the rescissions and repeals
even if the major questions doctrine did not apply. Similarly, we
propose that the major questions doctrine would require finalizing this
action even if the EPA had a plausible textual basis for asserting the
authority to regulate GHG emissions in response to global climate
change concerns. Each of these bases would require finalizing this
action even if the futility of regulating GHG emissions from fossil
fuel-fired power plants was not established in the record or was not an
adequate basis for finalizing these actions. And that futility, in
turn, provides another separate and independent basis for these
proposed actions.

A. Best Reading of CAA Section 111(b)(1)(A)

The EPA is proposing that under the best reading of CAA section
111, fixed at the time of enactment and informed by ordinary principles
of statutory interpretation and relevant history, the Agency's change
in position in the 2015 NSPS (as retained in the 2024 CPS) exceeded the
Agency's statutory authority for multiple reasons. First, we propose
multiple reasons for concluding that CAA section 111(b)(1)(A) sets the
outer bounds of the EPA's regulatory authority and is best read as
authorizing the Agency to regulate emissions that contribute
significantly to air pollution that itself endangers public health or
welfare through local or regional exposure. Second, we propose that
separate and apart from whether the EPA may regulate in response to
global climate change concerns, several errors in the 2015 NSPS
(retained in the 2024 CPS) would independently support rescinding these
prior actions and associated emission standards for fossil fuel-fired
power plants.
1. CAA Section 111(b)(1)(A) Does Not Subject Source Category Emissions
to Regulation Based on Global Climate Change Concerns
The EPA is proposing to determine that CAA section 111(b)(1)(A)
authorizes the Agency to regulate source category emissions that cause
or contribute significantly to air pollution that may itself endanger
health or welfare through local or regional exposure. This reading is
consistent with the ordinary meaning of key terms and the statutory
structure and history, our decades-long implementation of the statute
prior to 2015, and background principles of statutory interpretation,
including default rules for proximate cause. This reading is also
consistent with the Supreme Court's decisions in Massachusetts and AEP,
both of which addressed distinct issues and must be read in harmony
with subsequent decisions bearing on the EPA's authority and statutory
interpretation, including UARG, West Virginia, and Loper Bright.
As an initial matter, we propose that the EPA's authority to list
source categories under CAA section 111(b)(1)(A) informs the overall
regulatory scope of CAA section 111. That is, the Agency's authority to
regulate particular emissions from a given source category is cabined
by whether the associated air pollution is the type that Congress
authorized the EPA to address. This inquiry is informed by the function
CAA section 111(b)(1)(A) plays in the statute's regulatory scheme for
stationary sources. After the Administrator lists a source category
under CAA section 111(b)(1)(A), section 111(b)(1)(B) provides that the
EPA ``shall publish proposed regulations, establishing Federal
standards of performance for new sources within such category.'' The
definition of ``standard of performance'' in CAA section 111(a)(1)
states that it is ``a standard for emissions of air pollutants which
reflects the degree of emission limitation achievable through the
application of the best system of emission reduction . . .'' (emphasis
added). Thus, we propose that the basis for any regulation of
stationary sources under CAA section 111 must be ``air pollution which
may reasonably be anticipated to endanger public health or welfare.''
In the 2015 NSPS, the EPA effectively listed a new source
category--fossil fuel-fired EGUs--when it combined the fossil fuel-
fired steam generating EGU and fossil fuel-fired stationary combustion
turbine source categories.\123\ Consistent with discussion in the June
2025 NPRM, we propose that the Agency erred in failing to undertake a
listing for this new source category. That listing action would have
required analyzing whether the global climate change concerns
associated with power plant GHG emissions qualified as air pollution
within the meaning of CAA section 111 and evaluating whether GHG
emissions from power plants contribute significantly to such air
pollution. Instead, we asserted that the Agency need only have a
``rational basis'' for regulation of GHG emissions from ``a source
category that was previously listed and regulated for other
pollutants.'' \124\ Importantly, however, the rational basis we
identified was the conclusion in the 2009 Endangerment Finding ``that
GHG air pollution may reasonably be anticipated to endanger public
health or welfare.'' \125\ We thus acknowledged in the 2015 NSPS that
regulation is bounded by the statutory requirement that such regulation
involve qualifying air pollution. We propose that even under the
``rational basis'' approach, it would be irrational to regulate
emissions from a source category for purposes other than addressing
``air pollution which may reasonably be anticipated to endanger public
health or welfare.''
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\123\ See 80 FR 64510, 64531 (Oct. 23, 2015).
\124\ Id. at 64530.
\125\ See id. at 64522-24, 64529-31. Specifically, the 2015 NSPS
cited to the 2009 Endangerment Finding, subsequent 2010
reconsideration denials, and additional information that ``len[t]
further credence to the validity of the Endangerment Finding.'' Id.
at 64530.
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a. Extending CAA Section 111(b)(1)(A) Regulation to Global Climate
Change Concerns Is Inconsistent With the Statutory Text and Past
Practice
CAA section 111(b)(1)(A) calls on the Administrator to list a
category of stationary sources ``if in his judgment it causes, or
contributes significantly to, air pollution which may reasonably be
anticipated to endanger public health or welfare.'' \126\ The Act does
not define the term ``air pollution.'' The EPA proposes to interpret
``air pollution'' as that which itself endangers public health or
welfare through local or regional exposure. This interpretation is
supported by the ordinary meaning at the time of enactment of the key
terms ``air pollution,'' ``pollutant,'' and ``pollution,'' the
statutory definitions of ``air pollutant'' and ``welfare'' in CAA
section 302, the context in which these terms appear, and the Agency's
consistent practice prior to 2015 and 2009.
---------------------------------------------------------------------------

\126\ 42 U.S.C. 7411(b)(1)(A).
---------------------------------------------------------------------------

As noted above, the scope of the EPA's authority to list source
categories under CAA section 111(b)(1)(A) informs the overall
regulatory scope of CAA section 111. That is, the Agency's authority to
regulate a given air pollutant from a given source category under CAA
section 111 is cabined by whether the associated air pollution is the
type that Congress intended the EPA to address. At the time Congress
added the terms ``air pollutant'' and ``air pollution'' to CAA section
111, ``pollutant'' was defined as ``[a]nything that pollutes;
especially, any gaseous, chemical, or organic waste that

[[Page 59022]]

contaminates air, soil, or water,'' \127\ and ``pollution'' was defined
as ``[t]he contamination of soil, water or the atmosphere by the
discharge of noxious substances.'' \128\ The definition of the root
word ``pollute''--``[t]o dirty, contaminate''--confirms the
relationship of these terms to concepts of contamination and
toxicity.\129\ The central concept is the addition of a contaminant,
something that ``make[s] impure by contact or mixture.'' \130\ CAA
section 302(g) defines ``air pollutant'' as any ``air pollution agent
or combination of such agents'' that ``is emitted into or otherwise
enters the ambient air.'' \131\ The underlying concept of dangerousness
and contamination reinforces the conclusion that ``air pollution''--
when read in the context of CAA section 111, as the Supreme Court held
the EPA must in UARG--refers to that which itself endangers public
health or welfare through local or regional exposure.
---------------------------------------------------------------------------

\127\ Pollutant, Am. Heritage Dictionary 1015 (1970); see also
Pollutant, 3 Webster's Third New Int'l Dictionary 1756 (1966)
(``something that pollutes: a polluting substance, medium or
agent'').
\128\ Pollution, Am. Heritage Dictionary 1015 (1970); see also
Pollution, 3 Webster's Third New Int'l Dictionary 1756 (1966) (``the
action of polluting or the state of being polluted: defilement,
desecration, impurity, uncleanness'').
\129\ Pollute, Am. Heritage Dictionary 1015 (1970); see also
Pollute, Black's Law Dictionary 1043 (5th ed. 1979) (``To corrupt or
defile. The contamination of soil, air and water by noxious
substances and noises.''); Pollute, 3 Webster's Third New Int'l
Dictionary 1756 (1966) (``to make physically impure or unclean:
befoul, dirty, taint'').
\130\ Contaminate, Am. Heritage Dictionary 156 (1970); see also
Contaminate, 1 Webster's Third New Int'l Dictionary 491 (1966) (``to
soil, stain, corrupt, or infect by contact or association'').
\131\ 42 U.S.C. 7602(g).
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Contemporaneous usage of the term ``air pollution'' in the 1960s
and 1970s supports this reading. Judicial decisions issued around that
time used the term exclusively in reference to local and regional
exposure.\132\ News reports and legislative debates similarly addressed
air pollution problems arising from local and regional exposure,
including smog and health and welfare impacts related to inhalation and
physical contact.\133\
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\132\ See, e.g., Washington v. GM Corp., 406 U.S. 109, 115-16
(1972) (declining to exercise original jurisdiction over complaint
alleging conspiracy to restrain the development of air pollution
control devices for motor vehicles because, although ``Congress has
largely preempted the field with regard to `emissions from new motor
vehicles,' . . . geophysical characteristics which define local and
regional airsheds are often significant considerations in
determining the steps necessary to abate air pollution''); Friends
of Earth v. FCC, 449 F.2d 1164, 1165-66 (D.C. Cir. 1971) (addressing
challenge to the FCC's treatment of automobile advertisements that
petitioners alleged took a position on motor vehicle air pollution
worsening local conditions in New York City, including ``dangerous
hydrocarbons in the air'').
\133\ See, e.g., Coal. for Responsible Regulation, 2012 U.S.
App. LEXIS 25997, at *32-37 (Brown, J., dissenting from denial of
rh'g en banc) (summarizing relevant history).
---------------------------------------------------------------------------

Understandings of terms used in the CAA section 302(h) definition
of ``welfare'' also support the understanding that CAA section
111(b)(1)(A) encompasses air pollution with adverse impacts from local
or regional exposure. The statute provides that references to ``effects
on welfare'' include ``effects on soils, water, crops, vegetation,
manmade materials, animals, wildlife, weather, visibility, and
climate,'' damage to property, transportation hazards, and effects on
economic values and personal comfort and well-being. The ordinary
meaning of ``climate,'' an undefined term, was ``[t]he prevailing
weather in a particular region'' or ``[a] region manifesting particular
meteorological conditions.'' \134\ Similarly, ``weather'' meant ``[t]he
state of the atmosphere at a given time and place, described by
temperature, moisture, wind velocity, and pressure.'' \135\ Both terms
must also be read together in context, including by reference to the
other terms enumerated in the list.\136\ Each of the other terms in the
definition of ``welfare'' refers to things and mechanisms of action
that occur in a particular place or under regionally bounded
conditions.
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\134\ Climate, Am. Heritage Dictionary 136 (1970); see, e.g.,
Alameda Cons. Ass'n v. California, 437 F.2d 1087, 1096 (9th Cir.
1971) (using ``climate'' to discuss local environmental conditions
in San Francisco Bay); Levenson's Case, 194 NE2d 103, 105 (Mass.
1963) (using ``climate'' to address whether moving to another state
with a different climate is a covered medical expense).
\135\ Weather, Am. Heritage Dictionary 785 (1970).
\136\ See Fischer v. United States, 603 U.S. 480, 487 (2024)
(``[T]he canon of noscitur a sociis teaches that a word is `given
more precise content by the neighboring words with which it is
associated.' That `avoid[s] ascribing to one word a meaning so broad
that it is inconsistent with' `the company it keeps''' (citations
omitted)); Gustafson v. Alloyd Co., 513 U.S. 561, 575 (1995)
(applying canon to interpret the broad term ``communication,'' as
used in a statutory definition of ``prospectus,'' to mean only
public-facing communications that offer securities).
---------------------------------------------------------------------------

The terms Congress used speak to air pollution with adverse impacts
from local and regional exposure, not global climate change concerns
that entail a very different and much longer causal chain. The
definition is broad enough to encompass the various air pollutants and
air pollution of concern, each of which interacts differently with the
environment--e.g., smog and PM. Congress understood that air pollution
challenges varied from State to State and region to region, while, at
the same time, recognizing that the most acute challenges--e.g., smog
in highly populated urban areas--had similarities that would benefit
from national standards.\137\ But none of the many terms listed in the
definition of welfare would have been understood, absent modifying
terms, to refer to global considerations. Nor has Congress added terms
like ``global'' or ``change'' that would have expanded the scope of the
effects on welfare encompassed within the definition.\138\
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\137\ See, e.g., S. Rep. No. 91-1196, at 1-8, 24 (1970)
(discussing need for and intent of Senate bill that would eventually
form much of the 1970 CAA by reference to urban pollution problems
and areas in proximity to stationary and mobile sources and
recognizing that ``protection of the public health and welfare
requires definitive knowledge of the causal relationships between
exposure to air pollution agents . . . under varying environmental
conditions''); H.R. Rep. No. 91-1146, at 6 (1970) (similar for House
bill that informed aspects of the 1970 CAA).
\138\ Congress has used such language to specify the relevance
of global climate change concerns in more recent amendments to
different programs. CAA section 211(o)(2)(B)(ii), for example,
provides that the EPA must consider the impact of the production and
use of renewable fuels on ``climate change'' when setting renewable
fuel volumes under the RFS program. 42 U.S.C. 7545(o)(2)(B)(ii)
(emphasis added); see id. 7545(o)(1) (defining various renewable
fuels in part by reference to GHG emissions).
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The interpretation of ``air pollution'' reflected in the 2015
Findings is different in kind from contemporaneous understandings of
the term. That interpretation was, to a significant degree, rooted in
the 2009 Endangerment Finding. See 80 FR 64531. The 2009 Endangerment
Finding defined the relevant ``air pollutant'' as six ``well-mixed
GHGs'' and the relevant ``air pollution'' as total global
concentrations of ``the combined mix of'' these GHGs ``which together,
constitute the root cause of human-induced climate change and the
resulting impacts on public health and welfare.'' 74 FR 66516. The 2015
Findings likewise treated the six long-lived and directly emitted GHGs
as the relevant air pollution, 80 FR 64531 n.110, and provided that
such ``air pollution'' was reasonably anticipated to endanger public
health or welfare through the mechanism of global climate change, 80 FR
64531. The 2015 Findings further stated that the regulated ``air
pollutant'' was also GHGs, although the standards of performance for
fossil fuel-fired power plants were expressed in the form of limits on
CO<INF>2,</INF> given that CO<INF>2</INF> comprised more than 99
percent of total estimated GHG emissions from the regulated sources. 80
FR 64537.
In contrast to the air pollution that the EPA has historically
addressed under CAA section 111 and that is addressed

[[Page 59023]]

under title I of the CAA generally, GHGs do not endanger public health
or welfare through local or regional exposure. Rather, any adverse
impacts stem from GHGs becoming well mixed in the upper atmosphere,
resulting in elevated global GHG concentrations. It is then these
elevated GHG concentrations that drive phenomena that, in turn, affect
public health and welfare. To this end, the 2009 Endangerment Finding,
on which the 2015 Findings are based, asserted that GHG ``air
pollution'' would lead to increases in global temperature and change to
ocean pH that, in turn, would lead to environmental phenomena, in
combination with an open-ended universe of additional factors, which
would potentially have adverse health and welfare impacts of varying
severity in certain regions.
The Administrator admitted at the time that the circumstances were
``unique'' because ``[n]one of th[e] human health effects'' identified
in the Endangerment Finding ``are associated with direct exposure to
greenhouse gases.'' 74 FR 66527. With respect to welfare effects, the
Administrator acknowledged that the primary effects of concern could be
considered health or welfare impacts \139\ and that certain welfare
impacts were ``effects on people that do not rise to the level of
health effects'' but utilize the same causal chain. 74 FR 66527; see 74
FR 66531.\140\ In the same way that the EPA found in the Endangerment
Finding Rescission that regulating GHG emissions based on global
climate change concerns ``requires reading an additional instance of
`cause, or contribute' '' \141\ into CAA section 202(a)(1), the EPA
proposes that reading CAA section 111 to authorize the regulation of
GHG emissions based on global climate change concerns would similarly
require reading section 111(b)(1)(A) as encompassing the ``emission of
air pollutants that cause, or contribute significantly to, air
pollution that causes, or contributes to, endangerment of public health
or welfare.''
---------------------------------------------------------------------------

\139\ For example, the EPA in the 2009 Endangerment Finding
understood impacts on ``well-being'' as used in the CAA section
302(h) definition of ``welfare'' to be relevant ``whether [the
impacts] resul[t] directly or indirectly from the pollution in the
air.'' 74 FR 66528.
\140\ The Agency acknowledged that difficult questions about the
distinction between health and welfare impacts was something the
``EPA has not had to resolve'' in the past, ``as it has been clear
whether the effects relate to public health or relate to public
welfare, with no confusion over what category was at issue.'' 74 FR
66527. Rather than take this analytical difficulty as a sign that
the causal chain was different in kind from the type of ``air
pollution'' addressed by CAA section 202(a)(1), however, we
proceeded to finalize a novel invocation of authority to regulate in
response to global climate change concerns.
\141\ 91 FR 7686, 7714 (Feb. 18, 2026).
---------------------------------------------------------------------------

The EPA is proposing that background principles of causation and
proximate cause support our proposed interpretation of CAA section
111(b)(1)(A) as not extending to regulation of fossil fuel-fired power
plants based on global climate change concerns. In particular, the EPA
proposes that the terms ``cause,'' ``contribute,'' and ``reasonably be
anticipated to endanger'' must be read consistent with these
principles. In enacting and amending CAA section 111(b)(1)(A), Congress
legislated on a foundation that included ``default rules,'' including
the background principles of causation and proximate cause.\142\ These
rules are ``presumed to have [been] incorporated, absent an indication
to the contrary in the statute itself.'' \143\ Additionally, Congress
endorsed the incorporation of proximate cause principles when it added
the phrase ``may reasonably be anticipated'' to this section in the
1977 CAA Amendments. That phrase is another way of saying ``reasonably
foreseeable,'' a longstanding touchstone of proximate cause.\144\
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\142\ See, e.g., Bank of Am. Corp. v. City of Miami, 581 U.S.
189, 201 (2017); Lexmark Int'l, Inc. v. Static Control Components,
Inc., 572 U.S. 118, 132 (2014); Univ. of Tex. Sw. Med. Ctr. v.
Nassar, 570 U.S. 338, 347 (2013); City of Oakland v. Wells Fargo &
Co., 14 F.4th 1030 (9th Cir. 2021) (en banc).
\143\ Nassar, 570 U.S. at 347.
\144\ Foreseeable, 1 Webster's Third New Int'l Dictionary 890
(1966) (``being such as may reasonably be anticipated''); see, e.g.,
Hicks v. United States, 511 F.2d 407, 421 (D.C. Cir. 1975) (finding
``proximate cause'' satisfied because it was ``foreseeable'' that a
hospital's release without warning of an alcoholic patient with a
history of abusing his wife could result in harm to the patient's
wife).
---------------------------------------------------------------------------

GHG emissions from fossil fuel-fired power plants in the United
States do not have a sufficiently close connection to the harms
identified in the 2015 Findings to fit within the legal meaning of
``cause'' or ``contribute.'' This understanding is complemented by the
term ``reasonably'' in the phrase ``air pollution which may reasonably
be anticipated to endanger public health or welfare.'' Like the terms
``cause'' and ``contribute,'' the term ``reasonably'' places an outer
legal limit on the authority to anticipate dangers to public health and
welfare from air pollution. The greater the number of causal links
involved in anticipating such endangerment, the more difficult it is to
qualify the anticipation of the danger as ``reasonable.'' Global
climate change concerns involve causal relationships that are too
uncertain, conjectural, remote, and convoluted by intervening and
confounding factors to fit within the terms ``cause,'' ``contribute,''
and ``reasonably be anticipated to endanger'' as used in CAA section
111(b)(1)(A).
This reading follows from the understanding discussed above that
title I, including CAA section 111, was designed to address air
pollution with harmful impacts from local and regional exposure and
that is amenable to analysis using ordinary causation standards. In
specifying that emissions may ``cause, or contribute to'' air pollution
(emphasis added), and that air pollution need only ``be reasonably
anticipated to endanger public health or welfare,'' Congress signaled
in CAA section 111(b)(1)(A) that regulation may be appropriate when
harm is not yet occurring or is not certain to occur. But that language
bearing on the degree of certainty required does not override ordinary
background principles governing the limits of an attenuated causal
chain.
The 2015 Findings, in which the EPA first interpreted CAA section
111 as allowing it to regulate based on global climate change concerns,
represented a departure from past Agency practice. From the enactment
of CAA section 111(b)(1)(A) in 1970 until 2015, the EPA used its
authority to target air pollution that adversely impacts public health
or welfare through local or regional exposure. The EPA generally
promulgated regulations--NSPS for new sources and emission guidelines
for existing sources--in waves, starting in 1971. Once a source
category was listed pursuant to CAA section 111(b)(1)(A), the EPA
exercised judgment as to which air pollutant(s) emitted from each
source category to regulate. The earliest NSPS promulgated under CAA
sections 111(b)(1)(B) and 111(a)(1) in 1971 regulated emissions of PM
(sometimes expressed and regulated as opacity), NO<INF>X</INF>,
SO<INF>2</INF>, CO, and sulfuric acid mist.\145\ Other pollutants
addressed in the early regulatory push of the 1970s included total
fluorides,\146\ total reduced sulfur,\147\ and VOCs.\148\ In 1996, the
EPA started regulating non-methane organic compounds emitted from
landfills on the basis that they contribute to ozone formation, that
some NMOC are known or suspected carcinogens or cause other non-cancer
health effects, and that they can cause

[[Page 59024]]

an odor nuisance.\149\ The 1996 landfills rule also regulated methane
emissions based on the EPA's finding that such emissions present a fire
and explosion hazard, although we acknowledged ``ancillary'' benefits
that may arise given developing concerns about global climate
change.\150\ Overwhelmingly, the set of air pollutants and air
pollution concerns addressed in the 1970s remained the focus of
regulation under CAA section 111 for both new sources (under
111(b)(1)(B)) and existing sources (under 111(d)) through the ensuing
decades.\151\ Emissions of each of these regulated air pollutants
result in air pollution that directly affects public health or welfare
through exposure to those emissions, or to air pollution created
through the reaction of those emissions with other airborne chemicals
or conditions, at the local or regional scale.\152\ Thus, the EPA
deviated from over forty years of precedent when it expanded the reach
of CAA section 111 in the 2015 Findings.
---------------------------------------------------------------------------

\145\ 36 FR 24877 (Dec. 23, 1971).
\146\ See, e.g., 41 FR 3828 (Jan. 26, 1976) (NSPS for primary
aluminum reduction plants).
\147\ See, e.g., 43 FR 7572 (Feb. 23, 1978) (NSPS for kraft pulp
mills).
\148\ See, e.g., 39 FR 9317 (Mar. 8, 1974) (NSPS for storage
vessels for petroleum liquids).
\149\ 61 FR 9905, 9906 (Mar. 12, 1996).
\150\ Id.
\151\ The 1979 ``Priority List an Additions to the List of
Categories of Stationary Sources,'' in which the EPA promulgate a
list of major source categories for which standards of performance
were to be promulgated by 1982, considered emissions of nine
pollutants: VOC, NO<INF>X</INF>, PM, SO<INF>2</INF>, carbon
monoxide, lead, fluorides, acide mist, and hydrogen sulfide. 44 FR
49222 (Aug. 21, 1979).
\152\ The EPA addresses landfill methane emissions in section VI
of this preamble.
---------------------------------------------------------------------------

The approach taken for the 2015 Findings also required the EPA to
find endangerment and significant contribution when most emissions are
from international sources. This was similarly a departure from past
practice, and it expanded the reach of CAA section 111 by allowing the
EPA to regulate GHG emissions from U.S. fossil fuel-fired power plants
when the overwhelming bulk of the emissions underlying the finding of
endangerment were from sources outside the United States. The EPA now
proposes that interpreting ``air pollution which may reasonably be
anticipated to endanger public health or welfare'' to permit regulation
even when most of the endangerment stems from international sources is
contrary to CAA section 111. Congress has specifically provided in the
CAA when and how the EPA may consider international emissions. For
example, CAA section 115 authorizes the EPA to require controls for
domestic emissions that contribute to air pollution that endangers
public health or welfare in another country only when, among other
things, that country has adopted reciprocal protections for emissions
into the United States.\153\ CAA section 179B authorizes the EPA to
account for the impact of international emissions on NAAQS attainment
under certain conditions.\154\ Most tellingly, Congress adopted a new
regulatory regime in 1990--title VI--in response to global concerns
about depletion of the ozone layer, which contains its own findings,
policies, and regulatory authorities that required the EPA to phase out
domestic use of ozone-depleting substances.\155\ None of these
provisions encompass GHG emissions, and all support the conclusion that
Congress does not presume that general authorities in the CAA encompass
international emissions. Rather, Congress knows how to provide for the
consideration of and regulation in response to international emissions,
and has not done so for GHG emissions, either in CAA section 111 or
elsewhere.
---------------------------------------------------------------------------

\153\ 42 U.S.C. 7415.
\154\ 42 U.S.C. 7509a.
\155\ 42 U.S.C. 7671 et seq.
---------------------------------------------------------------------------

Moreover, the EPA proposes that Congress's inclusion of the
qualifier ``significantly'' in CAA section 111(b)(1)(A) is evidence of
its intent for the EPA to regulate only when a source category has a
meaningfully large contribution to air pollution that may reasonably be
anticipated to endanger public health or welfare. Congress used the
phrase ``cause(s) or contribute(s) to air pollution which may
reasonably be anticipated to endanger public health or welfare'' seven
times in the CAA.\156\ Notably, Congress used the phrase ``cause(s) or
contribute(s) significantly to air pollution which may reasonably be
anticipated to endanger public health or welfare'' four times in the
Act.\157\ Congress's intentional addition of ``significantly'' in CAA
section 111 is evidence of an intentional design, under this section in
particular, for the EPA to regulate only when a source category is
responsible for a meaningfully large portion of the anticipated adverse
public health or welfare impacts caused by the air pollution. This
interpretation is corroborated by the legislative history of CAA
section 111, which speaks to Agency regulation of source categories
under CAA section 111 that have a ``substantial'' impact on
``endangerment.'' \158\
---------------------------------------------------------------------------

\156\ 42 U.S.C. 7408(a)(1)(A), 7415(a), 7422(a), 7521(a)(1),
7521(a)(3)(D), 7521(e), 7571(a)(2)(A).
\157\ 42 U.S.C. 7411(b)(1)(A), 7411(g)(2), 7547(a)(1),
7547(a)(4) (emphasis added). Note that 42 U.S.C. 7411(g)(2) and
7547(a)(4) do not include ``cause(s).''
\158\ See, e.g., H.R. Rep. No. 91-1146, at 9-10 (explaining that
the draft legislation would authorize the EPA to ``establish
emission standards with respect to any class of new stationary
source which because of the nature of or amount of emissions may
contribute substantially to endangerment of the public health or
welfare'').
---------------------------------------------------------------------------

However, as discussed above, climate change concerns are global in
nature--in the 2009 Endangerment Finding, the EPA determined that it
was the elevated concentrations of globally well-mixed GHGs in the
atmosphere that led to climate change and adverse impacts on public
health and welfare. 74 FR 66516.\159\ These elevated GHG concentrations
are the result of emissions from myriad sources all over the world. It
is thus challenging for a single source category's contribution to the
global total to demonstrate significant adverse impacts; in 2022,
fossil fuel-fired power plants in the United States contributed 3.0
percent of global GHG emissions.\160\ Additionally, the EPA is
proposing to interpret CAA section 111(b)(1)(A) as requiring the Agency
to consider a source category's contribution to the endangerment caused
by air pollution, rather than to just the air pollution itself. Due to
the inherent nature of global climate change, GHG emissions from an
individual U.S. source category are necessarily only one small
component of a much larger and complex global emissions picture. For
global climate change concerns, the threshold for a quantity of GHGs to
comprise a ``significant'' contribution to either elevated atmospheric
GHG concentrations (the purported ``air pollution'') or the adverse
impacts thereof, is well above the likely contributions of a single
source category. Our proposed futility analysis below further supports
this conclusion. Thus, the EPA is proposing to find that it could not
have been Congress's intent for the Agency to use CAA section 111 to
regulate GHG emissions from fossil fuel-fired power plants based on
global climate change concerns.
---------------------------------------------------------------------------

\159\ The 2015 Findings adopted the same approach to
characterizing the relevant air pollution. See 80 FR 64517.
\160\ 90 FR 25768 & n.120.
---------------------------------------------------------------------------

Moreover, CAA section 111 is distinguishable from statutory
provisions or proposed legislation focused on global pollution or
climate change concerns. For instance, to address the dangers posed by
ozone depleting chemicals, title VI of the CAA, enacted in the CAA
Amendments of 1990, specifically references ``global warming
potential,'' the ``Montreal Protocol'' as governing international
treaty, and ``international cooperation.'' \161\ In contrast, CAA
section 111 includes no references to global impacts or concerns. The
CAA Amendments of 1990 were motivated in

[[Page 59025]]

part by the international negotiations leading up to the Montreal
Protocol and the need for global action on the far-reaching effects of
ozone depletion. Title VI evinces a congressional intent to address an
international problem of global concern through express language,
whereas CAA section 111 includes no such language describing global
implications or specificity on reductions.
---------------------------------------------------------------------------

\161\ See CAA sections 601, 602(e), 614, 617 et seq., 42 U.S.C.
7671 et seq.
---------------------------------------------------------------------------

CAA section 111 may also be contrasted with attempts to amend the
CAA to add authority to address global climate change. The American
Clean Energy and Security Act of 2009 would have instituted a cap-and-
trade system featuring renewable energy credits to reduce GHG
emissions, including from fossil fuel-fired power plants, and would
have directly spoken to the global concerns surrounding climate
change.\162\ Congress understood that addressing global climate change
concerns would have required a novel legislative approach, and this
legislative proposal would have added express provisions to the CAA
addressing these concerns, including through promoting CCS.\163\ Unlike
this legislative proposal, CAA section 111 includes no such reference
to global climate change or international concerns. As such, this
contrast confirms our proposed conclusion that Congress did not intend
CAA section 111 to apply to GHG emissions from fossil fuel-fired EGUs
based on global climate change concerns.
---------------------------------------------------------------------------

\162\ H.R. 2454, 111th Cong. (2009).
\163\ Id. at section 112 et seq. (proposing authorities for CCS
within the context of the CAA).
---------------------------------------------------------------------------

The EPA requests comment on its proposed interpretations of the
terms ``pollutant,'' ``pollution,'' and ``air pollution'' as focusing
on the concepts of dangerousness and contamination, consistent with
their use at the time of enactment of the 1970 CAA. The Agency is
similarly requesting comment on its proposed interpretation of
``climate'' in the definition of ``welfare'' in CAA section 302(h) as
referring to local or regional weather phenomena. We further solicit
comment on the understanding that the

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