# Reconsideration of 2009 Endangerment Finding and Greenhouse Gas Vehicle Standards

> Briefs, arguments, decisions, and more.

URL: https://www.frixlaw.com/law-library/documents/fr%3A2025-14572

## Record

- **Collection:** Federal Register
- **Document type:** Proposed Rule
- **Published:** August 1, 2025
- **Citation:** 90 FR 36288

## Text

ENVIRONMENTAL PROTECTION AGENCY
40 CFR Parts 85, 86, 600, 1036, 1037, and 1039
[EPA-HQ-OAR-2025-0194; FRL-12715-01-OAR]
RIN 2060-AW71
Reconsideration of 2009 Endangerment Finding and Greenhouse Gas Vehicle Standards

AGENCY:

Environmental Protection Agency (EPA).

ACTION:

Proposed rule.

SUMMARY:

In this action, the U.S. Environmental Protection Agency (EPA) is proposing to repeal all greenhouse gas (GHG) emission standards for light-duty, medium-duty, and heavy-duty vehicles and engines to effectuate the best reading of Clean Air Act (CAA) section 202(a). We propose that CAA section 202(a) does not authorize the EPA to prescribe emission standards to address global climate change concerns and, on that basis, propose to rescind the Administrator's prior findings in 2009 that GHG emissions from new motor vehicles and engines contribute to air pollution which may endanger public health or welfare. We further propose, in the alternative, to rescind the Administrator's prior findings in 2009 because the EPA unreasonably analyzed the scientific record and because developments cast significant doubt on the reliability of the findings. Lastly, we propose to repeal all GHG emission standards on the alternative bases that no requisite technology for vehicle and engine emission control can address the global climate change concerns identified in the findings without risking greater harms to public health and welfare.

DATES:

Comments.
Comments must be received on or before September 15, 2025. 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 September 2, 2025.

Public Hearing.
The EPA will announce information regarding the public hearing for this proposal in a supplemental
Federal Register
document. Please refer to the
SUPPLEMENTARY INFORMATION
section for additional information on the public hearing.

ADDRESSES:

Comments.
You may send comments, identified by Docket ID No. EPA-HQ-OAR-2025-0194, by any of the following methods:

•
Federal eRulemaking Portal: https://www.regulations.gov/
(our preferred method). Follow the online instructions for submitting comments.

•
Email: a-and-r-Docket@epa.gov.
Include Docket ID No. EPA-HQ-OAR-2025-0194 in the subject line of the message.

•
Mail:
U.S. Environmental Protection Agency, EPA Docket Center, OAR Docket, Mail Code 28221T, 1200 Pennsylvania Avenue NW, Washington, DC 20460.

•
Hand Delivery or Courier:
EPA Docket Center, WJC West Building, Room 3334, 1301 Constitution Avenue NW, Washington, DC 20004. The Docket Center's hours of operations are 8:30 a.m.-4:30 p.m., Monday-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
https://www.regulations.gov/,
including any personal information provided. For detailed instructions on sending comments and additional information on the rulemaking process, see the “Public Participation” heading of the
SUPPLEMENTARY INFORMATION
section of this document.

FOR FURTHER INFORMATION CONTACT:

Alan Stout, Assessment and Standards Division, Office of Transportation and Air Quality, Environmental Protection Agency, 2000 Traverwood Drive, Ann Arbor, MI 48105; telephone number: (734) 214-4805; email address:
stout.alan@epa.gov.

SUPPLEMENTARY INFORMATION:

A. Public Participation

Written Comments.
Submit your comments, identified by Docket ID No. EPA-HQ-OAR-2025-0194, at
https://www.regulations.gov
(our preferred method), or the other methods identified in the
ADDRESSES
section. Once submitted, comments cannot be edited or removed from the docket. The EPA may publish any comment received to its public docket. Do not submit to the EPA's docket at
https://www.regulations.gov
any information you consider to be Confidential Business Information (CBI), Proprietary Business Information (PBI), or other information whose disclosure is restricted by statute. If you choose to submit CBI or PBI as a comment to the EPA's docket, please send those materials to the person listed in the
FOR FURTHER INFORMATION CONTACT
section. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written comment is considered an official comment and should include discussion of all points you wish to make. The EPA will generally not consider comments or comment contents located outside of the primary submission (
i.e.,
on the web, cloud, or other file sharing system). Please visit
https://www.epa.gov/dockets/commenting-epa-dockets
for additional submission methods; the full EPA public comment policy; information about CBI, PBI, or multimedia submissions; and general guidance on making effective comments.

To facilitate comment on the portions of the rule on which the EPA is specifically soliciting comment, the EPA has indexed each comment solicitation with a unique identifier (
e.g.,
“C-1”, “C-2”) in section VII of this preamble to provide a consistent framework for effective and efficient provision of comments. Accordingly, we ask that commenters include the corresponding identifier when providing comments relevant to that comment solicitation. We ask that commenters include the identifier either in a heading or within the text of each comment, to make clear which comment solicitation is being addressed. We note that we are not limiting comment to these identified areas.

Participation in Virtual Public Hearing.
The EPA will announce information regarding the public hearing for this proposal in a supplemental document in the
Federal Register
. The hearing notice, registration information, and any updates to the hearing schedule will also be available at
https://www.epa.gov/regulations-emissions-vehicles-and-engines/proposed-rule-reconsideration-2009-endangerment-finding.
Please refer to this website for any updates regarding the hearings. The EPA does not intend to publish additional documents in the
Federal Register
announcing updates to the hearing schedule.

Docket.
All documents in the docket are listed on the
www.regulations.gov
website. Although listed in the index, some information is not publicly available,
e.g.,
CBI or other information whose disclosure is restricted by statute. Certain other material, such as copyrighted material, is not placed on the internet and will be publicly available only in hard copy form through the EPA Docket Center at the location listed in the
ADDRESSES
section of this document.

B. Action Applicability

This action relates to companies that manufacture, sell, or import into the United States light-, medium-, or heavy-duty motor vehicles and engines. Potentially affected categories and entities include the following:

NAICS code
a

NAICS title

336110
Automobile and Light-duty Motor Vehicle Manufacturing.

336120
Heavy Duty Truck Manufacturing.

336211
Motor Vehicle Body Manufacturing.

336213
Motor Home Manufacturing.

336310
Motor Vehicle Gasoline Engine and Engine Parts Manufacturing.

336390
Other Motor Vehicle Parts Manufacturing.

333618
Other Engine Equipment Manufacturing.

423110
Automobile and Other Motor Vehicle Merchant Wholesalers.

811198
All Other Automotive Repair and Maintenance.

a
NAICS Association. NAICS & SIC Identification Tools. Available online:
https://www.naics.com/search.

This table is not intended to be exhaustive but rather provides a guide for readers regarding entities potentially affected by this action. This table lists the types of entities that the EPA is presently aware could potentially be affected by this action. Other types of entities not listed in the table could also be affected. To determine whether your entity is regulated by this action, you should carefully examine the applicability criteria found in Code of Federal Regulations (CFR) title 40, parts 85, 86, 600, 1036, and 1037. If you have questions regarding the applicability of this action to a particular entity, consult the person listed in the
FOR FURTHER INFORMATION CONTACT
section.

Table of Contents

I. Executive Summary

A. Introduction

B. Need for Regulatory Action

C. Summary of the Major Provisions in This Proposed Action

II. Background

A. The EPA's Historical Approach to CAA Section 202(a)

B. Petitions for Rulemaking and
Massachusetts
v.
EPA

C. The 2009 Endangerment Finding

D. Implementation of the 2009 Endangerment Finding

E. Reconsideration of the 2009 Endangerment Finding

III. Legal Framework for Proposed Action

A. Proposed Rescission of Endangerment Finding

B. Proposed Amendments to New Motor Vehicle and Engine Regulations

IV. Proposed Rescission of the Endangerment Finding

A. Primary Rationale for Proposed Rescission

1. Best Reading of CAA Section 202(a)

2. Lack of Clear Congressional Authorization

B. Alternative Rationale for Proposed Rescission

1. Climate Science Discussion

2. Proposed Conclusions

V. Separate Bases for Proposed Repeal of GHG Emission Standards

A. There Is No Requisite Technology for Light- and Medium-Duty Vehicles That Meaningfully Addresses the Identified Dangers of the Six “Well-Mixed” GHGs

B. There Is No Requisite Technology for Heavy-Duty Vehicles That Addresses the Identified Dangers of the Six “Well-Mixed” GHGs

C. Eliminating GHG Emissions From All Motor Vehicles Would Be Futile

D. More Expensive New Vehicles Prevent Americans From Purchasing New Vehicles That Are More Efficient, Safer, and Emit Fewer GHGs

VI. Proposed Repeal of GHG Emission Standards

A. Scope and Impacts of Proposed Repeal

B. Light- and Medium-Duty Vehicle GHG Program

1. Background on the Light- and Medium-Duty Vehicle GHG Program

2. Proposed Changes to the Light- and Medium-Duty Vehicle GHG Regulations

C. Heavy-Duty Engine and Vehicle GHG Program

1. Background on the Heavy-Duty Engine and Vehicle GHG Program

2. Proposed Changes to the Heavy-Duty Engine and Vehicle GHG Regulations

VII. Requests for Comment

VIII. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review and Executive Order 14094: Modernizing Regulatory Review

B. Executive Order 14192: Unleashing Prosperity Through Deregulation

C. Paperwork Reduction Act (PRA)

1. Light- and Medium-Duty Vehicle—2024 Final Rule

2. Heavy-Duty Vehicle GHG Phase 3—2024 Final Rule

3. Nonroad Compression-Ignition Engines and On-Highway Heavy Duty Engines, Supporting Statement for Information Collection Request (March 2023 Revision)

D. Regulatory Flexibility Act (RFA)

E. Unfunded Mandates Reform Act (UMRA)

F. Executive Order 13132: Federalism

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

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

I. Executive Order 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. Executive Summary

A. Introduction

In this action, the EPA proposes to rescind all greenhouse gas (GHG) emission standards for light-duty, medium-duty, and heavy-duty vehicles and engines under CAA section 202(a). Upon review of the underlying actions and intervening legal and scientific developments, including recent decisions by the U.S. Supreme Court and the scientific information summarized in this preamble, the EPA no longer believes that we have the statutory authority and record basis required to maintain this novel and transformative regulatory program. We seek comment on all aspects of this proposal, including on the legal and scientific developments that are being subject to public comment for the first time in this rulemaking.

In 2009, the EPA took the unprecedented step of asserting authority to regulate GHG emissions in a standalone action titled “Endangerment and Cause or Contribute Finding for Greenhouse Gases Under Section 202(a) of the Clean Air Act,” 74 FR 66496 (Dec. 15, 2009) (Endangerment Finding). In that action, we interpreted CAA section 202(a) 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 also asserted that because the statute is “silent on [the] issue,” CAA section 202(a) grants “procedural discretion” to issue standalone findings that trigger a duty to regulate without considering the standards that must issue in response.

74 FR 66501-02. The Administrator exercised this newfound discretion to make separate findings that elevated global concentrations in the upper atmosphere of six “well-mixed GHGs”—carbon dioxide (CO
2
), methane, nitrous oxide (N
2
O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF
6
)—constitute “air pollution” that may reasonably be anticipated to endanger public health and welfare, 74 FR 66516-36, and that GHG emissions from all potential classes of motor vehicles and engines contribute to such elevated global concentrations of GHGs in the upper atmosphere and therefore to air pollution that endangers public health and welfare, 74 FR 66536-45.

With respect to endangerment, the Administrator found that global concentrations of GHGs from all foreign and domestic sources “constitute the largest anthropogenic driver of climate change” and attributed climate change impacts to global GHG concentrations. 74 FR 66517. Next, the Administrator summarized literature reviews finding that climate change “can increase the risk of morbidity and mortality” indirectly through increased global temperature, air quality effects, and changes in extreme weather events and can impact welfare indirectly through net impacts on food production, forestry, water resources, sea level rise, energy infrastructure, and ecosystems. 74 FR 66522-35. On that basis, the Administrator found that global concentrations of GHGs constitute “air pollution” that endangers public health and welfare. 74 FR 66516. For purposes of this preamble, we use the phrase global climate change concerns to refer to the risks the Administrator associated with climate change in 2009.

With respect to causation or contribution, the Administrator used emissions data for existing motor vehicles and engines to project that all potential classes of new motor vehicles and engines would emit four GHGs—CO
2
, methane, N
2
O, and HFCs—that would collectively amount to 4.3 percent of global GHG emissions. 74 FR 66543. The Administrator acknowledged that more would usually be required to support contribution “when addressing a more typical local or regional air pollution problem.” 74 FR 66539. Nevertheless, asserting discretion to interpret the ambiguous term “contribute,” the Administrator found that the “unique” nature of global climate change meant that “contributors must do their part even if their contributions to the global climate change problem, measured in terms of percentage, are smaller than typically encountered when tackling solely regional or local environmental issues.” 74 FR 66542-43.

The EPA subsequently relied on the Endangerment Finding to impose increasingly stringent GHG emission standards for new motor vehicles and engines and to attempt, largely without success, to extend its GHG initiative into additional CAA programs. In
Utility Air Regulatory Group
v.
EPA,
573 U.S. 302 (2014) (
UARG
), the Supreme Court rejected our attempt to extend GHG emission standards to stationary sources subject to Title I and Title V requirements, including after we admitted that applying the statutory scheme as written to GHG emissions from most covered stationary sources would be unworkable. And in
West Virginia
v.
EPA,
597 U.S. 697 (2022), the Court vacated our attempt to shift the power grid away from using fossil fuels through GHG standards for existing power plants under CAA section 111(d). The Court held in both cases that the agency actions at issue implicated the major questions doctrine, and that Congress must clearly authorize agencies to take actions that decide major questions of policy. Nevertheless, the EPA continued to retain and expand GHG emission standards for new motor vehicles and engines that impose billions of dollars in compliance costs on American businesses and consumers. Meanwhile, global GHG concentrations in the upper atmosphere have continued to rise, driven primarily by increased emissions from foreign sources,
1

all without producing the degree of adverse impacts to public health and welfare in the United States that the EPA anticipated in the 2009 Endangerment Finding.

1
Crippa, M. et al. (2023). GHG emissions of all world countries.
Publications Office of the European Union: https://doi.org/10.2760/953322.

The EPA now proposes to rescind the Endangerment Finding and all resulting GHG emission standards for new motor vehicles and engines, including the light-duty, medium-duty, and heavy-duty vehicle and engine standards for model years (MY) 2012 to 2027 and beyond. The remainder of this section describes the need for regulatory action and the scope of the proposed action, including rescission of the Endangerment Finding, repeal of related GHG emission standards, and minor conforming adjustments to unrelated emission standards for new motor vehicles and engines that we are not proposing to alter as part of this rulemaking.

Section II of this preamble sets out relevant background, including the events leading up to the Endangerment Finding, the approach taken in the Endangerment Finding to analyzing the scientific record, and the regulations issued since 2009 in reliance on the Endangerment Finding. We also summarize the premises, assumptions, and conclusions in the Endangerment Finding and the scientific information, including empirical data, peer-reviewed studies, and real-world developments since 2009 that led the Administrator to develop concerns sufficient to initiate reconsideration of the ongoing validity and reliability of the Endangerment Finding.

Section III of this preamble describes our legal authority to rescind the Endangerment Finding and repeal the resulting GHG standards issued under CAA section 202(a). Because this proposed action would not impact fuel economy standards and emission standards for criteria pollutants and hazardous air pollutants regulated under the CAA, we explain the relationship between these regulations to set the outer bounds of amendments at issue in this rulemaking.

Section IV.A of this preamble describes our proposal to rescind these prior actions because the Endangerment Finding exceeded our statutory authority under CAA section 202(a). As explained further below, we propose that the term “air pollution” as used in CAA section 202(a) is best read in context as referring to local or regional exposure to dangerous air pollution, consistent with our longstanding practice before 2009. We further propose that CAA section 202(a) does not grant the Administrator “procedural discretion” to issue standalone findings that trigger a duty to regulate, or, conversely, to prescribe standards, without making the requisite findings for the particular air pollutant emissions and class or classes of new motor vehicles or engines at issue. We also propose that CAA section 202(a) does not authorize the Administrator to make separate findings for endangerment and causation or contribution. Rather, we propose that CAA section 202(a) requires the Administrator to find that the relevant air pollutant emissions from the class or classes of new motor vehicles or engines at issue cause, or contribute to, air pollution which endangers public health or welfare, without relying on emissions from stationary or other sources regulated by distinct CAA provisions. As the Supreme Court made clear in
Loper Bright Enterprises
v.
Raimondo,
603 U.S. 369 (2024), we can no longer rely on statutory silence or ambiguity to expand our regulatory power. And

because the Nation's response to global climate change concerns is an issue of significant importance that Congress did not clearly address in CAA section 202(a), we propose that the major questions doctrine further reinforces and provides an additional basis for our proposed interpretations and actions. The Agency did not have the benefit of the Court's decisions in
Loper Bright
and
West Virginia,
among other applicable precedents, when issuing the Endangerment Finding in 2009. Finally, we explain that the EPA reached contrary conclusions in the Endangerment Finding by misconstruing the Supreme Court's decision in
Massachusetts
v.
EPA,
549 U.S. 497 (2007), which vacated our denial of a petition for rulemaking on distinct grounds. Read on its own terms,
Massachusetts
did not require the Agency to find that GHGs are subject to regulation under CAA section 202(a) and does not support our implementation of the statute since 2009.

Section IV.B of this preamble describes our alternative proposal to rescind these prior actions even if CAA section 202(a) authorizes the EPA to address GHG emissions based on global climate change concerns by concluding that the Administrator exercised that authority unreasonably in the Endangerment Finding. Specifically, we propose that the EPA misapplied the statutory standard for regulation to the scientific record by severing the analysis into separate parts without considering whether all parts of the analysis, taken as a whole, supported the findings and regulatory determinations required by the statute. We further propose that empirical data, peer-reviewed studies, and real-world developments since 2009 have cast significant doubt on many of the critical premises, assumptions, and conclusions in the Endangerment Finding such that it would be unreasonable to retain the decision and the resulting regulatory framework. In proposing this alternative, we note that the Supreme Court has continued to emphasize that agencies have significant discretion when making complex judgments within the bounds of an authorizing statute.
2

We propose that the Administrator may now exercise the discretion expressly delegated to him by Congress in the text of CAA section 202(a) by rescinding the Endangerment Finding.

2

Seven Cnty. Infrastructure Coal.
v.
Eagle Cnty.,
145 S. Ct. 1497, 1511-15 (2025);
FDA
v.
Wages & White Lion Invs., L.L.C.,
145 S. Ct. 898, 917 (2025);
Baltimore Gas & Elec. Co.
v.
NRDC, Inc.,
462 U.S. 87, 103 (1983);
see also Huntsman Petrochemical LLC
v.
EPA,
114 F.4th 727, 735 (D.C. Cir. 2024) (“In the case of EPA's evaluation of scientific data within its area of expertise, [courts] accord an extreme degree of deference.” (quotation marks omitted)).

Section V of this preamble proposes additional bases for repealing the EPA's GHG emission standards for new motor vehicles and engines under CAA section 202(a) even if the Endangerment Finding were to remain in place. We propose that there is no “requisite technology” responsive to the global climate change concerns identified in the Endangerment Finding given evidence that reducing GHG emissions from new motor vehicles and engines to zero would not have a scientifically measurable impact on global GHG concentrations and climate trends. We also propose that, on balance, and contrary to the core objectives of CAA section 202(a), GHG emission standards harm public health and welfare by increasing prices, decreasing consumer choice, and slowing the replacement of older vehicles that are less safe and emit a greater volume and variety of air pollutants than new motor vehicles and engines.

Section VI of this preamble details the scope of the proposed repeal, including its relationship to distinct regulatory programs and federal preemption, the revisions to 40 CFR parts 85, 86, 600, 1036, 1037, and 1039 required to effectuate repeal of all GHG emission standards, and conforming adjustments to regulatory provisions that we are not proposing to reopen or substantively revise. Specifically, in this NPRM we are not proposing to change at this time elements of the regulations that are necessary for programs unrelated to the Endangerment Finding, including emission standards for criteria pollutants and air hazards and the EPA's statutory role in vehicle standards administered by the National Highway Traffic Safety Administration (NHTSA).

Section VII of this preamble specifically requests comment on key aspects of this proposed action and indexes comment solicitation to promote public participation and facilitate our review of public comments. Note that we are not limiting public participation to the issues raised in this section and will respond to all comments within the scope of this proposal. Rather, we are highlighting aspects of the proposal for which public input would be particularly helpful in determining whether and in what respects to finalize this proposed action.

B. Need for Regulatory Action

Immediately upon taking office, President Trump established new Executive Branch priorities for energy, transportation, and consumer choice and committed to ensuring regulations remain within constitutional and statutory bounds. On January 20, 2025, the President issued an Executive Order titled “Unleashing American Energy” to address the burdens placed by unnecessary regulations on energy affordability, job creation, and national security.
3

As relevant here, the President directed the EPA Administrator to submit recommendations to the Director of OMB on the legality and continuing applicability of the 2009 Endangerment Finding.
4

On February 19, 2025, the President issued an Executive Order titled “Ensuring Lawful Governance and Implementing the President's `Department of Government Efficiency' Deregulatory Initiative” that further instructed agencies, including the EPA, to review existing regulations for consistency with the Constitution and the best reading of the authorizing statute.
5

3
Executive Order 14154, 90 FR 8353 (Jan. 29, 2025).

4

Id.
§ 6(f).

5
Executive Order 14219, 90 FR 10583 (Feb. 25, 2025).

Upon confirmation by the Senate, Administrator Lee Zeldin committed the EPA to prioritizing its core statutory mission 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 the “Unleashing American Energy” Executive Order, the Administrator initiated a review of the legality and applicability of the Endangerment Finding. On February 19, 2025, the Administrator submitted a memorandum to the OMB Director recommending that the EPA reconsider the Endangerment Finding to address legal and scientific developments that appear to undermine the bases for that action and subsequent regulations.
6

The Administrator noted that recent Supreme Court decisions, including
Loper Bright, West Virginia,

UARG,
and
Michigan
v.
EPA,
576 U.S. 743 (2015), provided new guidance on how we should interpret and apply the statutes Congress entrusted us to administer.
7

The Administrator further noted that the Endangerment Finding recognized significant uncertainties in its conclusions and assumptions that should be evaluated in light of more recent empirical data and scientific

evidence.
8

Accordingly, the Administrator announced on March 12, 2025, that the EPA would reconsider the Endangerment Finding and subsequent actions to determine whether our GHG regulations have an adequate statutory basis and to seek public input on developments since 2009.
9

6
Memorandum from Lee Zeldin, Administrator, Environmental Protection Agency, to Russell Vought, Director, Office of Management and Budget (Feb. 19, 2025) (Feb. 19, 2025 Memo), available in the docket for this rulemaking.

7

Id.
at 1.

8

Id.
at 8.

9
“Trump EPA Kicks Off Formal Reconsideration of Endangerment Finding with Agency Partners” (Mar. 12, 2025), available at
https://www.epa.gov/newsreleases/trump-epa-kicks-formal-reconsideration-endangerment-finding-agency-partners
.

As part of this reconsideration, the EPA closely examined applicable law, including judicial precedents and interpretive aids bearing on the meaning of CAA section 202(a) and related statutory provisions. We also reviewed actions taken to regulate GHG emissions from new motor vehicles and new motor vehicle engines since 2009, assessed the costs and non-cost adverse impacts of these GHG emission standards, and evaluated the effectiveness of these GHG emission standards in reducing the dangers identified in the Endangerment Finding, that is, in mitigating the impacts anticipated to result from elevated global GHG concentrations in the upper atmosphere.

Furthermore, the Administrator reviewed available information, including the most recently available science, bearing on the assumptions and conclusions in the Endangerment Finding, the impacts of global GHG concentrations on public health and welfare in the United States, and the relative contribution of domestic emissions from new motor vehicles and engines to global GHG concentrations. As part of that review, the Administrator received and evaluated the draft report submitted by the U.S. Department of Energy (DOE) Climate Working Group (CWG) to Secretary of Energy Christopher Wright on May 27, 2025, titled “Impacts of Carbon Dioxide Emissions on the U.S. Climate” (2025 CWG Draft Report). The 2025 CWG Draft Report analyzes empirical data, peer-reviewed studies, and available scientific information bearing on direct human influence on ecosystems and climate, climate response to CO
2
emissions, and impacts on ecosystems and society.
10

The Administrator also considered available assessments by the U.S. Government and relevant international bodies, including the Third, Fourth, and Fifth National Climate Assessments (NCAs) reported by the U.S. Global Change Research Program (USGCRP)
11

and the Fifth Assessment Report (AR5) and Sixth Assessment Report (AR6) by the United Nations Intergovernmental Panel on Climate Change (IPCC).
12

As discussed in section IV.B of this preamble, the Administrator also considered critiques of the NCAs, and the Fifth NCA in particular, and reviewed these analyses for consistency with OMB information quality guidelines
13

and the transparency and reliability requirements of Executive Order 14303, “Restoring Gold Standard Science.”
14

10
The 2025 CWG Draft Report was provided to the EPA on May 27, 2025, and was reviewed and relied upon in formulating this proposal. The EPA understands that DOE is releasing an updated version of the CWG draft report and seeking public comment on the updated report, which includes additional information and typographical corrections that the EPA did not rely upon in formulating this proposal. Interested parties may review and comment on the updated version of the CWG draft report for consideration as part of DOE's efforts through the docket available at
https://www.energy.gov/topics/climate
.

11
Created by the Global Change Research Act of 1990, Public Law 101-606, 104 Stat. 3096, the USGCRP reports an NCA at least every four years to Congress and the President that must (1) integrate, evaluate, and interpret the findings of the Program and discuss the scientific uncertainties with such findings; (2) analyze the effects of global change on the natural environment, agriculture, energy production and use, land and water resources, human health and welfare, human social systems, and biological diversity; and (3) analyze current trends in global change, both human-induced and natural, and project major trends for the subsequent 25 to 100 years.
See
15 U.S.C. 2936.

12
The IPCC invites participation by members of the United Nations and World Meteorological Organization and summarizes available literature on climate science but does not conduct its own research.
See
United Nations Intergovernmental Panel on Climate Change, About the IPCC, available online at
https://www.ipcc.ch/about/
.

13
“Guidelines for Ensuring and Maximizing the Quality, Objectivity, Utility, and Integrity of Information Disseminated by Federal Agencies; Republication,” 67 FR 8452 (Feb. 22, 2002).

14
90 FR 22601 (May 29, 2025).

The Administrator's review of the relevant information, including scientific literature, gave rise to serious concerns that our actions taken to regulate GHG emissions from new motor vehicles and engines exceed our statutory authority under CAA section 202(a) and are otherwise inappropriate. Continuing to impose billions of dollars in regulatory costs on American businesses and consumers without an adequate legal basis would threaten to undermine public confidence in our activities and commitment to fulfilling the Agency's core mission: protecting human health and the environment. The EPA has expended significant resources implementing the GHG regulatory program for mobile sources and attempting to expand its GHG regulatory program to stationary sources with limited success in the courts and no apparent real-world results, often at the expense of programs that fall squarely within our statutory authority. Prompt action is needed to address these concerns with the benefit of public participation.

Relatedly, the Administrator has serious concerns that many of the scientific underpinnings of the Endangerment Finding are materially weaker than previously believed and contradicted by empirical data, peer-reviewed studies, and scientific developments since 2009. This proposal seeks public comment on these developments for the first time. Prompt action is needed to address these concerns, and the Administrator requests stakeholder input on the continuing vitality of the assumptions, predictions, and conclusions animating the Endangerment Finding.

C. Summary of the Major Provisions in This Proposed Action

If finalized, this action would rescind the 2009 Endangerment Finding for GHGs emitted by new motor vehicles and new motor vehicle engines under CAA section 202(a) (74 FR 66496). If finalized, this action would also rescind denials of petitions for reconsideration of the Endangerment Finding in 2022 and 2010 entitled “Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Section 202(a) of the Clean Air Act; Final Action on Petitions,” 87 FR 25412 (Apr. 29, 2022), and “EPA's Denial of the Petitions to Reconsider the Endangerment and Cause or Contribute Finding for Greenhouse Gases Under Section 202(a) of the Clean Air Act,” 75 FR 49556 (Aug. 13, 2010).
15

Although the 2022 and 2010 petition denials have no prospective legal effect, we propose to rescind them for the sake of consistency and to ameliorate potential confusion regarding the EPA's proposed action. As explained later in this preamble, the denials reflect many of the same legal and scientific flaws we propose to correct by rescinding the Endangerment Finding. We seek comment on the impact of the denials, if any, and on whether the denials were legally flawed for additional reasons not explicitly explored in this proposal. In addition, as a result of these proposed changes, we would no longer have a basis for issuing or retaining GHG emission standards for new motor vehicles and new motor vehicle engines, including

for MYs that have completed manufacture but are subject to ongoing obligations. As discussed elsewhere in this preamble, the EPA is reconsidering additional endangerment findings and GHG emission standards issued under distinct provisions of the CAA in separate rulemakings and is not reopening or proposing to modify those additional findings and standards in this proceeding.

15
The 2022 petition denials included a notice of decision in the
Federal Register
(87 FR 25412), brief letters communicating the denials to the petitioners, and a decision document entitled “EPA's Denial of Petitions Relating to the Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Section 202(a) of the Clean Air Act” (Apr. 21, 2022) (2022 Denial), available online at
https://www.epa.gov/system/files/documents/2022-04/decision_document.pdf
.

In connection with the proposed rescission of the Endangerment Finding, if finalized, this action would remove all existing regulations that require new motor vehicle and new motor vehicle engine manufacturers to measure, report, or comply with GHG emission standards. Specifically, the EPA proposes to remove regulations in 40 CFR parts 85, 86, 600, 1036, and 1037 pertaining to the control of GHG emissions from light-, medium-, and heavy-duty vehicles and engines, including emission standards, test procedures, averaging, banking, and trading requirements (ABT), reporting requirements, and fleet-average emission requirements.
16

As a result of these proposed changes, motor vehicle and engine manufacturers would no longer have future or current obligations for the measurement, control, or reporting of GHG emissions for any vehicle or engine, including for previously manufactured MYs. However, we are not proposing to reopen or modify any regulations necessary for criteria pollutant and air toxic measurement and standards, Corporate Average Fuel Economy (CAFE) testing, and associated fuel economy labeling requirements. We seek comment on whether any elements of the regulations, test procedures, or GHG emission models that are proposed for removal should remain to support programs unrelated to the GHG emission standards and why the preservation of such an element is necessary to support the unrelated program or programs.

16
“Light-Duty Vehicle Greenhouse Gas Emission Standards and Corporate Average Fuel Economy Standards,” 75 FR 25324 (May 7, 2010); “Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles,” 76 FR 57106 (Sept. 15, 2011); “2017 and Later Model Year Light-Duty Vehicle Greenhouse Gas Emissions and Corporate Average Fuel Economy Standards,” 77 FR 62624 (Oct. 15, 2012); “Greenhouse Gas Emissions and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles-Phase 2,” 81 FR 73478 (Oct. 25, 2016); “The Safer Affordable Fuel-Efficient (SAFE) Vehicles Rule for Model Years 2021-2026 Passenger Cars and Light Trucks,” 85 FR 24174 (Apr. 30, 2020); “Revised 2023 and Later Model Year Light-Duty Vehicle Greenhouse Gas Emissions Standards,” 86 FR 74434 (Dec. 30, 2021); “Multi-Pollutant Emissions Standards for Model Years 2027 and Later Light-Duty and Medium-Duty Vehicles,” 89 FR 27842 (Apr. 18, 2024); “Greenhouse Gas Emissions Standards for Heavy-Duty Vehicles-Phase 3,” 89 FR 29440 (Apr. 22, 2024).

II. Background

A. The EPA's Historical Approach to CAA Section 202(a)

Congress originally enacted the language that became CAA section 202(a) as part of the Motor Vehicle Pollution Control Act of 1965, which required the Secretary of Health, Education, and Welfare to “prescribe . . . standards, applicable to the emission of any kind of substance, from any class or classes of new motor vehicles or new motor vehicle engines, which in his judgment cause or contribute to, or are likely to cause or contribute to, air pollution which endangers the health or welfare of any persons.”
17

Congress retained this language, while adding additional requirements for the content of emission standards, in the Air Quality Act of 1967,
18

and, later, incorporated it into the Clean Air Act of 1970, which transferred the Secretary's regulatory authority to the newly created EPA.
19

Separately, the 1970 CAA addressed emissions from existing vehicles and engines, stationary sources, and aircraft engines.
20

As subsequently amended, CAA section 202(a) has remained a critical part of the comprehensive national framework for regulating air pollution from mobile sources, and new motor vehicles and new motor vehicle engines in particular, under Title II of the CAA.
21

17
Public Law 89-272, 202(a), 79 Stat. 992, 992-93 (1965).

18
Public Law 90-148, 202(a), 81 Stat. 485, 499 (1967).

19
Public Law 91-604, 84 Stat. 1690 (1970).

20

Id.

21
In the Clean Air Act Amendments of 1977, Congress replaced the phrase “which endangers the public health or welfare” with “which may reasonably be anticipated to endanger public health or welfare.” Public Law 95-95, 401(d)(1), 91 Stat. 685, 791 (1977).

In its first four decades administering the statute, the EPA applied CAA section 202(a) to local and regional air pollution problems through rulemakings that prescribed standards and set forth the Administrator's findings that the relevant air pollutant emissions cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare.
22

As explained in the following subsections, the EPA maintained this approach through 2008 and never sought to invoke CAA section 202(a) to regulate in response to global climate change concerns.

22

See
74 FR 66501, 66527, 66538, 66543 (acknowledging this regulatory history).

B. Petitions for Rulemaking and Massachusetts v. EPA

In October 1999, a coalition of 19 environmental organizations petitioned the EPA to regulate the emission of four GHGs—CO
2
, methane, N
2
O, and HFCs—from new motor vehicles and engines under CAA section 202(a)(1). Petitioners claimed that these four GHGs were “air pollutant[s]” under CAA section 302(g), significantly contributed to global climate change, and met the statutory standard for regulation under CAA section 202(a)(1). Thus, petitioners claimed that the EPA had the authority and obligation to find that GHG emissions from new motor vehicles and engines cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare and to prescribe standards in response.

In September 2003, after receiving and responding to nearly 50,000 public comments on the relevant issues, the EPA denied the 1999 petitions in a final action titled “Control of Emissions from New Highway Vehicles and Engines,” 68 FR 52922 (Sept. 8, 2003) (2003 Denial). The 2003 Denial 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
2
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 recent amendments, and that “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 concluded that regulating GHG emissions from motor vehicles and engines under the CAA would interfere with NHTSA's separate authority to implement fuel economy standards. 68 FR 52929. Finally, we asserted that regulating GHG emissions from motor vehicle engines under the CAA would

undermine the President's overall policy approach of addressing global climate change through voluntary actions and incentives, the promotion of further research and technologies, and international negotiations. 68 FR 52930-31.

In
Massachusetts,
the Supreme Court narrowly reversed the D.C. Circuit's decision to uphold the EPA's denial of the 1999 petitions for rulemaking.
23

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
2
or the three other GHGs raised in the petitions for rulemaking. 549 U.S. at 528-29. The Court also addressed EPA's reliance on
Brown & Williamson,
which the majority construed as having found no congressional intent to ban the sale of tobacco products outright because such an application of the relevant statute would have been highly unlikely and because the Food and Drug Administration (FDA) had expressly refused 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 and, citing several Agency memoranda, that we had not similarly foresworn all authority to regulate GHGs as a categorical matter.
Id.
Notably, the Court expressly declined to decide whether the EPA was required to issue an affirmative endangerment finding as to GHG emissions under the standard set out in CAA section 202(a).
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 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) 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.
24

23
The D.C. Circuit majority had upheld the denial on the merits because “the EPA Administrator properly exercised his discretion under § 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 EPA's policy justifications were inadequate reasons to deny the petitions.
Id.
at 67-82 (Tatel, J., dissenting).

24
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
2
and other GHGs that naturally occur in the ambient air. 549 U.S. at 549 (Scalia, J., joined by Roberts, C.J., and Thomas and Alito, J.J., dissenting).

C. The 2009 Endangerment Finding

The EPA responded to the Supreme Court's decision in
Massachusetts
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). The Administrator began by noting it was “clear that if EPA were to regulate [GHG] emissions from motor vehicles under the Clean Air Act,” the interplay between CAA section 202(a) and similarly worded statutory provisions “could result in an unprecedented expansion of EPA authority that would have a profound effect on virtually every sector of the economy and touch every household in the land.” 73 FR 44355. The Administrator cautioned that because the CAA was “originally enacted to control regional pollutants that cause direct health effects,” invoking authority to regulate GHG emissions “would inevitably result in a very complicated, time-consuming, and, likely, convoluted set of regulations” that “would be relatively ineffective at reducing [GHG] concentrations” and have a “potentially damaging effect on jobs and the U.S. economy.”
Id.

The 2008 ANPRM echoed the Administrator's concerns by seeking public comment on invoking CAA section 202(a) to regulate new motor vehicle and engine emissions in response to global climate change concerns. We acknowledged that the CAA “was not specifically designed to address GHGs,” 73 FR 44397, and that the EPA had historically interpreted and applied its CAA regulatory authorities to address local and regional air pollution, 73 FR 44408. We further noted that Congress was considering legislation to address the Nation's response to global climate change concerns and that, since
Massachusetts,
Congress had passed and the President had signed into law the Energy Independence and Security Act (EISA), which amended provisions applicable to the EPA's Renewable Fuels Standard (RFS) program and NHTSA's CAFE standards program. 73 FR 44398. Finally, we noted that the EPA had received additional petitions to regulate stationary sources and additional GHGs, including water vapor, all of which suggested that GHG emission regulations could not readily be limited to new motor vehicles and engines. 73 FR 44399 & n.26.

As to CAA section 202(a), the 2008 ANPRM set out a framework for determining whether “GHG emissions from new motor vehicles cause or contribute to air pollution that may reasonably be anticipated to endanger public welfare” under CAA section 202(a)(1) or for “explain[ing] why scientific uncertainty is so profound that it prevents making a reasoned judgment on such a determination.” 73 FR 44398, 44421. We reviewed available information for CO
2
, methane, and N
2
O emissions and noted that HFCs, PFCs, and SF
6
are “often grouped together” and separately from the rest “because they contain fluorine, typically have large global warming potentials, and are produced only through human activities.” 73 FR 44401-02.
25

With respect to endangerment, we sought comment on whether GHGs could properly be considered dangerous air pollution because the potential health effects are indirect and the potential welfare effects may be positive on balance. 73 FR 44427. In addition, we sought comment on whether “the unique characteristics and properties of each GHG . . . as well as current and projected emissions” meant that each GHG should be analyzed individually or whether certain GHGs other than CO
2
were amenable to grouping. 73 FR 44428. With respect to causation or contribution, we presented motor vehicle and engine emissions data for each GHG separately and noted that emission trends had diverged between pollutants, with CO
2
emissions, for example, generally increasing since 1990 and N
2
O emissions, for example, increasing from 1990 to 1995 and then falling substantially from 1995 to 2006 because of fuel and technology changes. 73 FR 44430. We also presented extensive information on potential regulatory approaches that could be triggered by a positive finding under CAA section 202(a), including

approaches specific to particular GHGs. 73 FR 44438-63.

25
In the 2008 ANPRM, the EPA noted that the most recently available IPCC analysis concluded that “[t]he anthropogenic combined heating effect (referred to as forcing) of [methane], N
2
O, HFCs, PFCs and SF
6
is about 40% as large as the CO
2
cumulative heating effect since pre-industrial times.” 73 FR 44423.

Following a change in administration, however, the EPA proposed in April 2009 and finalized in December 2009 a much different approach to analyzing GHG emissions from new motor vehicles and engines under CAA section 202(a). In the Endangerment Finding, the Administrator found that “the science [was] sufficiently certain” to compel an affirmative determination and interpreted
Massachusetts
as “allow[ing] for the consideration only of science.” 74 FR 66501. Relatedly, the Administrator did not consider any of the implementation challenges or options discussed in the 2008 ANPRM, asserting instead that CAA section 202(a) confers “procedural discretion” to issue standalone findings without considering a regulatory response because the statute “is silent on this issue.”
Id.
The Administrator also defined all six “well-mixed” GHGs collectively as the relevant “air pollutants” and “air pollution” for purposes of endangerment and causation or contribution, meaning the Endangerment Finding did not need to address the different characteristics or emission trends of any particular GHG. 74 FR 66516-21, 66536-57.

With respect to endangerment, the Administrator began by excluding adaptation—human responses that reduce potential adverse impacts—and mitigation—independent measures that reduce the causes of potential adverse impacts—from the analysis of global climate change concerns. 74 FR 66513. The Administrator acknowledged that “some level of autonomous adaptation will occur” and that “this separation means this approach may not reflect the actual conditions in the real world in the future, because adaptation and/or mitigation may occur and change the risks.”
Id.
Nevertheless, the Administrator reasoned that “it would be extremely hard to make a reasoned projection of human and societal adaptation and mitigation responses” because they are “largely political” or “individual personal judgments.”
Id.
Next, the Administrator relied on IPCC Assessment Report 4 (AR4) projections to find that global temperatures would likely increase between 1.8 to 4 degrees Celsius by 2100, with an uncertainty range of 1.1 to 6.4 degrees Celsius. 74 FR 66519. Operating within this analytical framework, the Administrator found that elevated global concentrations of GHGs from all foreign and domestic sources were responsible for increased global temperatures that were responsible in turn for indirect health risks driven by (1) more frequent heat waves; (2) air quality effects, including increased formation of ozone, and (3) broader societal impacts related to increased frequency and severity of certain extreme weather events. 74 FR 66525.
26

The Administrator also found that GHG emissions could lead to welfare effects related to (1) food production and agriculture; (2) forestry; (3) water resources; (4) sea level rise; and (5) energy infrastructure and settlements, although the evidence was uncertain for several categories that may see near-term benefits. 74 FR 66531-35.
27

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, but asserted the approach was necessary given the “unique” challenge presented by global climate change. 74 FR 66527.

26
The Administrator also noted that increased global temperatures could lead to changes in certain food- and water-borne pathogens and allergens (including increases in pollen resulting from increased plant growth at higher concentrations of CO
2
) but did “not plac[e] primary weight on these factors.” 74 FR 66498, 66526.

27
The Administrator relied on welfare impacts to water resources and sea level rise as providing “the clearest and strongest support for an endangerment finding.” 74 FR 66534.

With respect to contribution, the Administrator asserted broad authority to interpret the statutory standard because “[t]he language of CAA section 202(a) is silent regarding how the Administrator is to make her contribution analysis.” 74 FR 66544. Exercising that putative interpretive authority, the Administrator concluded that “it is reasonable to consider that lower percentages contribute than one may consider when looking at a local or regional problem involving fewer sources of emissions,” 74 FR 66545, because “all contributors must do their part” to avoid “a tragedy of the commons, whereby no country or source category would be accountable for contributing to the global problem of climate change,” 74 FR 66543. Next, the Administrator relied on data showing that existing motor vehicles and engines emitted four GHGs—CO
2
, methane, and N
2
O from engines, as well as HFCs from air conditioning units—that accounted for 4.3 percent of global GHG emissions at the time. On that basis, the Administrator found that GHG emissions from new motor vehicles and engines “contribute to the air pollution” consisting of the six “well-mixed” GHGs previously identified as a danger to public health or welfare. 74 FR 66537-39.

Crucially, the Endangerment Finding made clear that the EPA was acting independently from any new congressional mandate. Rather, the Administrator interpreted CAA section 202(a) as setting out a standalone authority to issue findings that establish jurisdiction without considering implementation concerns and purported to rest the Endangerment Finding solely on a scientific judgment informed by the record as assembled by the Agency in 2009.

D. Implementation of the 2009 Endangerment Finding

In the years since issuing the Endangerment Finding, the EPA has promulgated GHG emission standards for various classes of new motor vehicles and engines in reliance on the Endangerment Finding and, as anticipated in the 2008 ANPRM, sought to expand the same analytical framework to regulatory provisions governing existing vehicles, stationary sources, aircraft, and oil and gas operations. For a full accounting of GHG emission standards adopted since 2009 under CAA section 202(a), see sections VI.B and VI.C of this preamble.

Following the Endangerment Finding, the EPA received multiple petitions for reconsideration from industry groups, States, and various organizations arguing that our approach in 2009 was legally and scientifically flawed and that external assessments by the IPCC, among others, had not adequately addressed recent criticisms of climate change science. The EPA denied these consolidated petitions in 2010 without notice and comment. Reiterating the scientific assertions from the technical support document (TSD) used in 2009, we emphasized that we had conducted an independent review of outside assessments in issuing the Endangerment Finding and asserted that the core conclusions of the Endangerment Finding remained valid notwithstanding the flaws raised by the petitioners. The EPA also issued a volume of response documents defending the methodologies and experts relied upon and concluded that no new information warranted reconsideration. 75 FR 49556.

In April 2022, the EPA denied, again without notice and comment, a new round of petitions for reconsideration and rulemaking asserting that the Endangerment Finding was legally and scientifically flawed and undermined by more recent scientific assessments. We acknowledged that several recent studies contradicted assessments by the USGCRP and IPCC but reaffirmed our earlier position that such assessment reports are entitled to greater weight

than dissenting views.
28

We also considered criticisms of the EPA's Social Cost of Carbon (SCC) methodology out of scope because “the social cost of carbon played no role in the 2009 Endangerment Finding.”
29

We further acknowledged that severing the endangerment and cause or contribute analysis from the development of subsequent regulations had impacted the EPA's approach to GHG emission standards, including because the Science Advisory Board (SAB) did not have the opportunity to review the Endangerment Finding as would otherwise have been required by the CAA.
30

Nevertheless, we reaffirmed our position that CAA section 202(a) grants “procedural discretion” to issue findings and emission standards separately and “decline[d] to exercise that discretion” differently.
31

28
2022 Denial at 15-17.

29

Id.
at 30.

30

Id.
at 36 (noting that 42 U.S.C. 4365(c)(1) requires SAB consultation for a “standard” promulgated under CAA section 202(a) but asserting that requirement does not extend to “findings” issued under the same provision).

31

Id.
at 39.

E. Reconsideration of the 2009 Endangerment Finding

Since the EPA published the 2009 Endangerment Finding, there have been developments in innovation, science, economics, and mitigation, as well as significant Supreme Court decisions that provide new guidance on how federal agencies should interpret the statutory provisions that Congress has tasked them with administering.
32

Accordingly, the Administrator has now determined that the Endangerment Finding should be reconsidered to address legal and scientific developments that present reason to question the ongoing validity and reliability of its conclusions and to subject these important issues to public comment for the first time since 2009.

32

See
Feb. 19, 2025 Memo at 1.

In initiating reconsideration, the Administrator explored all findings, support, questions, and ambiguities contained within the science relied upon by the Endangerment Finding. As acknowledged in the Endangerment Finding and recent reports, there are significant questions and ambiguities presented by both the observable realities of the past nearly two decades and the recent findings of the scientific community, including those summarized in the 2025 CWG Draft Report. There may also be as-yet-unidentified issues or discrepancies present in the underlying TSD and scientific justifications offered in the Endangerment Finding. When confronted with science offering a diverse array of conclusions, methodologies, and explanations, the Administrator strove to inform his judgment to the most impartial extent possible. A more detailed discussion of the available climate science can be found in section IV.B.

III. Legal Framework for Proposed Action

A. Proposed Rescission of Endangerment Finding

The statutory authority for this proposed action is the same as that relied upon in the prior actions at issue: CAA section 202(a)(1), which requires the Administrator to “prescribe” and “from time to time revise . . . standards” for certain air pollutants emitted by new motor vehicles and new motor vehicle engines “in accordance with the provisions of this section.”
33

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.
34

33
42 U.S.C. 7521(a)(1).

34

See Wages & White Lion,
145 S. Ct. 898;
FCC
v.
Fox Television Stations, Inc.,
556 U.S. 502 (2009);
Motor Vehicle Mfrs. Ass'n
v.
State Farm Mut. Auto. Ins. Co.,
463 U.S. 29 (1983);
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 statute prohibits or conditions our general authority to rescind prior actions. CAA section 202(a)(1) grants the Administrator discretion to “revise” standards prescribed “in accordance with the provisions of this section” and does not require retaining the same level of stringency when revising or rescinding existing standards. Moreover, the statute neither authorizes the Administrator to issue standalone findings that trigger a duty to regulate nor prohibits the Administrator from rescinding such findings. Rather, CAA section 202(a)(1) requires the Administrator to prescribe standards for emissions of any air pollutant by classes of new motor vehicles or engines when, in his judgment, emissions of such air pollutant by such classes of new motor vehicles or engines “cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare.” Notably, the EPA has consistently assumed that it has the statutory authority to rescind the Endangerment Finding in reviewing the merits of petitions for reconsideration since 2009 and did not state that we lack such reconsideration authority.
35

35

See, e.g.,
2022 Denial at 7-10 (denying mandatory reconsideration under CAA section 307(d) and reviewing the petitions on the merits as rulemaking petitions under APA section 553(e)); 75 FR 49560-63 (denying mandatory reconsideration under CAA section 307(d) without asserting that the EPA lacked statutory authority to rescind or revise the Endangerment Finding).

The EPA acknowledges that rescinding the Endangerment Finding as proposed would involve significant changes to the legal interpretations adopted in the Endangerment Finding and retained in subsequent actions. For example, if finalized, the interpretation of CAA section 202(a) proposed in this action would preclude the EPA from issuing standalone endangerment and contribution findings and would instead require the Agency to make findings for particular air pollutant emissions and classes of new motor vehicles and engines as an integral step in a rulemaking to prescribe standards for such emissions and classes, consistent with our decades-long practice prior to 2009 in regulating non-GHG air pollutants. Furthermore, if finalized, the interpretation of CAA section 202(a) proposed in this action would reverse the basis for the Endangerment Finding by concluding that global climate change concerns cannot satisfy the statutory standard for regulation under CAA section 202(a). For discussion of our proposed interpretation of CAA section 202(a) and related statutory provisions, see section IV.A of this preamble. For discussion of our alternative proposal to rescind the Endangerment Finding because the EPA exercised its authority under CAA section 202(a) unreasonably and because the Administrator no longer has confidence in the assumptions, methodology, and conclusions in the Endangerment Finding in light of the scientific record, see section IV.B of this preamble.

The EPA is also proposing additional statutory and policy rationales for repealing the GHG emission standards currently in effect for new motor vehicles and engines separate and apart from the proposed rescission of the Endangerment Finding. If finalized, these alternative rationales would change the novel position taken in rulemakings since 2009 to prescribe and revise GHG emission standards under CAA section 202(a).
36

For example, if finalized, our proposal to determine that there is no “requisite technology” for

vehicle emission control capable of having a measurable impact on the dangers identified in the Endangerment Finding would preclude any GHG emission standards from going into effect. Furthermore, if finalized, our proposal to determine that the GHG emission standards harm public health and welfare on balance would make it unreasonable and contrary to the objectives of the statute to issue and retain such standards. See section V of this preamble for further discussion of these additional rationales and the Agency's prior positions.

36
75 FR 25324 (May 7, 2010); 76 FR 57106 (Sept. 15, 2011); 77 FR 62624 (Oct. 15, 2012); 81 FR 73478 (Oct. 25, 2016); 85 FR 24174 (Apr. 30, 2020); 86 FR 74434 (Dec. 30, 2021); 89 FR 27842 (Apr. 18, 2024); 89 FR 29440 (Apr. 22, 2024).

The EPA acknowledges that repealing the GHG emission standards based on the proposed rescission of the Endangerment Finding would depart from our position in rulemakings since 2009 that prescribed and revised GHG emission standards for light- and medium-duty vehicles and heavy-duty vehicles and engines under CAA section 202(a). If finalized as proposed, the rescission would eliminate the statutory basis for those standards because we relied on the Endangerment Finding in each rulemaking to invoke our authority under CAA section 202(a) without making the required findings for GHGs emitted by the class or classes of new motor vehicles or engines at issue in each rulemaking. See section VI of this preamble for further discussion of each prior rulemaking and the regulatory changes that would be necessary to repeal all GHG emission standards currently in effect for new motor vehicles and engines on any of the bases proposed in this action.

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 202(a), respond to legal and scientific developments that undermine the conclusions and assumptions of the Endangerment Finding, and realign Agency resources to prioritize core statutory responsibilities. 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 changing legal interpretation and policy within the boundaries set by statute.
37

Democratic accountability is essential to the exercise of delegated authority by administrative agencies,
38

and retaining the Endangerment Finding without clear statutory authority would frustrate, not promote, constitutional values and the rule of law. If the EPA lacks authority to retain the Endangerment Finding under the best reading of CAA section 202(a), the statute controls regardless of policy preferences.

37

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).

38

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).

The EPA seeks comment on the nature and extent of any reliance interests that may have arisen from our assertion of regulatory authority over GHG emissions from new motor vehicles and engines and is committed to assessing any such interests, determining whether they are significant, and weighing such interests against competing rationales, as required by law.
39

39

See, e.g.,

DHS
v.
Regents of Univ. of Cal.
, 591 U.S. 1, 33 (2020).

Specifically, we seek comment on whether regulated parties have any significant reliance interests in our GHG emission standards for new motor vehicles and new motor vehicle engines. We are aware that manufacturers, importers, and sellers have already expended resources complying with GHG emission standards for MYs 2012 through 2026, and that consumer prices for vehicles in these MYs reflect the costs of such compliance. Because many compliance costs are incurred as part of research and development and during manufacturing, with the notable exception of the need to purchase compliance credits, this proposed action would have limited impacts on MYs 2012 to 2024, greater impacts for MYs 2024-2026, and would entirely relieve future regulatory obligations for MY 2027 and beyond. As discussed in sections VI.B and VI.C of this preamble, we are confident that the Agency has adequate regulatory tools to address transitional compliance concerns and note that this proposed action would not, if finalized, mandate any particular response by regulated parties. We are also aware that regulated parties may have reliance interests in national uniformity and CAA preemption with respect to emission standards for new motor vehicles and engines. As discussed in section VI.A of this preamble, CAA section 209(a) and other applicable sources of federal preemption would continue to apply, and we would retain our authority to regulate emissions, including emissions of the six “well-mixed” GHGs addressed in the Endangerment Finding, under circumstances that meet the standard for regulation under CAA section 202(a). We seek comment on each of these rationales, including on whether any reliance interests in national uniformity and preemption would support finalizing or not finalizing the proposed action, or adopting certain rationales and not finalizing other rationales. We further seek comment on the continued preemptive effect of the CAA in the event that the EPA finalizes the proposed rescission or any of the alternatives discussed herein (or in the event that the Agency determines that it lacks authority at the present time to regulate GHG emissions under one or more provisions of the CAA for any reason). As a general matter, we also seek comment on how we should repeal the Endangerment Finding and regulations if the decision is made to proceed with the proposed repeals, including under any of the options set out in this proposal or any additional grounds and means.

In addition, the EPA seeks comment on whether regulated parties and other stakeholders have significant reliance interests in GHG emission standards for new motor vehicles and engines. This proposed action would make only minor conforming adjustments to regulatory provisions for criteria pollutants and air toxics, thereby leaving most emission standards for new motor vehicles and engines in place. Nor would this proposed action impact separate economy and fuel-efficiency standards that have the effect of reducing GHG emissions per mile traveled from new motor vehicles and engines, including standards issued by NHTSA. As explained in section IV.A.1 of this preamble, we now believe that regulating GHG emissions based on global climate change concerns exceeds our statutory authority under CAA section 202(a) and, as such, propose that reliance interests alone would not justify retaining the GHG emission standards that we lacked authority to prescribe. As discussed in section IV.A.2 of this preamble, potential dangers from local or regional exposure to the six “well-mixed” GHGs covered by the Endangerment Finding are regulated separately under specific grants of statutory authority. And as discussed in section V of this preamble, we now believe that GHG emission standards for new motor vehicles and engines may harm public health and

welfare without having any measurable impact on the global climate change concerns identified in the Endangerment Finding. We seek comment on potential reliance interests in GHG emission standards for global climate change concerns under CAA section 202(a), including on whether such reliance justifies retaining standards in the absence of statutory authority and the extent to which potential dangers are addressed, or could be addressed, under more specific authorities.

The EPA recognizes that we have relied in part on the Endangerment Finding in issuing subsequent endangerment findings and GHG regulations under other CAA provisions, including for certain stationary sources and aircraft engines. The Supreme Court has since vacated several of these actions, including GHG regulations for existing sources in the fossil-fuel fired power plant source category under CAA section 111(d) and for permitted sources under CAA Title V.
40

For those actions that remain in effect, we have initiated or intend to initiate separate rulemakings that will address any overlapping issues.

40

See West Virginia,
597 U.S. 697;
UARG,
573 U.S. 302.

Among other concerns with the Endangerment Finding, we believe that severing consideration of endangerment and causation or contribution from the appropriate regulatory response under CAA section 202(a) resulted in broad statements that did not account for the statutory language in CAA section 202(a)(1) on which the Endangerment Finding purported to rely. Congress used different authorizing language to address distinct issues for stationary sources regulated under CAA section 111 and aircraft engines regulated under CAA section 231. In reconsidering actions taken under these authorities, we intend to address prior findings and standards in light of the particular statutory language, policy concerns, and scientific information relevant to each context. In this proposed action, we seek comment on reliance interests in the Endangerment Finding and GHG emission standards issued under CAA section 202(a) and reserve the right to direct out of scope comments to the appropriate rulemaking docket for the applicable regulatory action.

B. Proposed Amendments to New Motor Vehicle and Engine Regulations

As noted above, CAA section 202(a)(1) directs the Administrator to 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.” This core directive has remained substantially the same since Congress enacted the Motor Vehicle Pollution Control Act of 1965.
41

Thus, a necessary condition to regulating emissions from new motor vehicles and engines is a finding—an “endangerment finding”—that emissions of an air pollutant from a class or classes of new motor vehicles or engines cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare.

41
Public Law 89-272, 79 Stat. 992-93.

For the reasons discussed in section IV of this preamble, we are proposing to rescind the Endangerment Finding for GHG emissions from new motor vehicles and new motor vehicle engines and, on that basis, to repeal all existing GHG emission standards for passenger cars, light-duty trucks, motorcycles, buses, medium-duty vehicles, and heavy-duty vehicles and engines. The Endangerment Finding has served as the EPA's basis for regulating GHG emissions from new motor vehicles and new motor vehicle engines since 2009. Absent findings of endangerment and causation or contribution, the EPA lacks statutory authority to prescribe standards for those emissions under CAA section 202(a)(1). We propose that when the EPA rescinds an endangerment finding for an air pollutant, it must cease prescribing and enforcing standards applicable to the emission of that pollutant from new motor vehicles or new motor vehicle engines and should rescind existing standards no longer authorized by statute.

For the reasons discussed in section V of this preamble, we are also proposing additional bases to repeal GHG emission standards even if the Endangerment Finding were to remain in place. We propose that regardless of whether GHG emissions trigger the standard for regulation in CAA section 202(a)(1), our authority to prescribe and enforce emission standards for GHGs is limited by the language of CAA section 202(a)(2) and must be exercised in a reasonable manner that furthers, rather than burdens, the health and welfare of all Americans.

Accordingly, the EPA is proposing to repeal all standards and associated test procedures adopted to limit the emission of GHGs under CAA section 202(a) for highway light-, medium-, and heavy-duty vehicles and engines. The EPA notes that, for light-duty vehicles, the Energy Policy and Conservation Act of 1975 (EPCA) and the 2007 EISA authorize NHTSA to administer the CAFE program and fuel economy labeling program. These statutes also direct the EPA to determine compliance values for manufacturers subject to the CAFE program and the fuel economy labeling program. Importantly, these statutory obligations are distinct from the EPA's authority under CAA section 202(a) and from the EPA's decisions since 2009 to regulate GHG emissions under CAA section 202(a). As explained in section VI of this preamble, we are retaining and not proposing to reopen regulatory provisions related to our statutory roles in these NHTSA programs. Likewise, we are retaining and not proposing to reopen any criteria pollutant and air toxics standards for highway light-, medium-, and heavy-duty vehicles and engines under CAA section 202(a).

IV. Proposed Rescission of the Endangerment Finding

In this section, the EPA proposes to rescind the Endangerment Finding by concluding, based on multiple, independent alternative legal rationales, that the Agency's unprecedented foray into regulating GHG emissions from new motor vehicles and engines is inconsistent with the best reading of CAA section 202(a). Under any proposed alternative, the EPA would lack authority to retain existing GHG emission standards for new motor vehicles and engines and proceed to repeal the relevant provisions of Title 40 of the CFR as proposed in section VI of this preamble.

Section IV.A of this preamble describes our primary proposal to rescind the Endangerment Finding by concluding that CAA section 202(a) does not authorize the EPA to prescribe standards for GHG emissions based on global climate change concerns or to issue standalone findings that do not apply the statutory standard for regulation as a cohesive whole. If finalized, this proposal would require rescinding the Endangerment Finding and resulting regulations because we lacked statutory authority to issue them in the first instance. We begin by proposing the best reading of CAA section 202(a) and related provisions, as informed by the Supreme Court's decisions in
Loper Bright
and
UARG
. Next, we propose that the Nation's response to global climate change concerns generally, and specifically whether that response should include regulating GHG emissions from new motor vehicles and engines, is an

economically and politically significant issue that triggers the major questions doctrine under
UARG
and
West Virginia,
and that Congress did not clearly authorize the EPA to decide it by empowering the Administrator to “prescribe . . . standards” under CAA section 202(a). Throughout this section, we propose that the Endangerment Finding relied on various forms of
Chevron
deference
42

to depart from the best reading of the statute and exceeded the EPA's authority in several fundamental respects, any one of which would independently require rescission to conform to the best reading of the law.

42

Chevron U.S.A., Inc.
v.
NRDC,
Inc., 467 U.S. 837 (1984),
overruled by Loper Bright,
603 U.S. 369;
see
74 FR 66501, 66502, 66544 (asserting discretion based on statutory ambiguity, including that created by silence); 74 FR 66528, 66542, 66543 (asserting discretion based on statutory ambiguity).

Section IV.B of this preamble describes the EPA's alternative proposal that regardless of whether CAA section 202(a) authorizes regulating GHG emissions based on global climate change concerns, we would rescind the Endangerment Finding by concluding that the Administrator analyzed endangerment and contribution in an unreasonable manner. We begin by recounting the interpretation of CAA section 202(a) adopted in the Endangerment Finding, which asserted “procedural discretion” to issue standalone findings without prescribing the standards required by such findings and to sever the analysis of endangerment from the analysis of contribution. Next, we propose that the Administrator exercised that discretion unreasonably by adopting an approach that papered over substantial uncertainties in the scientific record and failed to draw the required connection between GHG emissions from a class or classes of new motor vehicles and global climate change concerns. We further propose that developments since 2009 demonstrate the uncertainties acknowledged in the Endangerment Finding are more significant than previously believed, including because many of its predictive judgments involve ranges of assumptions that largely fail to satisfy the statutory standard for regulation and because the more pessimistic assumptions have not been borne out in empirical data and peer-reviewed studies through 2025. Finally, we propose that the Administrator would exercise any discretion conferred by CAA section 202(a) differently to ensure a legally and scientifically sound approach and that, under that approach, the Endangerment Finding and resulting GHG emission standards must be rescinded.

We seek comment on every aspect of the primary and alternative proposal, including the key issues on which we specifically request comment as set out in section VII of this preamble.

A. Primary Rationale for Proposed Rescission

The Endangerment Finding announced an interpretation of CAA section 202(a) that permitted the EPA to prescribe standards in response to global climate change concerns rather than local or regional exposures, granted “procedural discretion” to issue standalone findings without considering regulatory response, and severed the finding of endangerment from the finding of contribution to that endangerment. At the time, we assumed that statutory silence granted discretion to construe the scope of our authority and asserted or implied that the Supreme Court's decision in
Massachusetts
required us to read the statute as authorizing the regulation of GHG emissions in response to global climate change concerns.

In important respects, the Endangerment Finding and the Supreme Court's decision in
Massachusetts
straddled a transitional period regarding the standards for statutory interpretation and understandings of agency authority. The breadth of agency discretion, and the question whether Congress reserves major policy questions for itself, were sharply disputed. Judicial decisions in the intervening fifteen years have significantly clarified the law in both respects. In
Loper Bright,
the Supreme Court expressly overturned the doctrine of deference to agency statutory interpretation, ruling that statutes “have a single, best meaning” that is informed, but not dictated, by Executive Branch practice. 603 U.S. at 400-01. 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 would generally reserve for itself in the first instance. 597 U.S. at 723.

In this subsection, we propose that the best reading of CAA section 202(a), as informed by
Loper Bright
and principles of statutory interpretation, does not authorize the EPA to assert jurisdiction over GHG emissions based on global climate change concerns in a standalone endangerment finding. Regardless whether GHGs are properly considered “agents of air pollution” under the general, Act-wide definition of “air pollutant” at CAA section 302(g), the EPA cannot regulate under CAA section 202(a) unless the emissions of the air pollutant by a class or classes of new motor vehicles “cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare.” Because the text, structure, and history of CAA section 202(a) and related provisions demonstrate that this language targets air pollution that threatens public health or welfare through local or regional exposure, “air pollution” defined as six “well-mixed” GHGs raising global climate change concerns that adversely impact a subset of regions globally cannot satisfy this standard. We further propose that this reading is independently confirmed and strengthened by the major questions doctrine. Specifically, we propose that the major questions doctrine applies and precludes the EPA from asserting authority to regulate in response to global climate change concerns under CAA section 202(a). At a minimum, Congress did not
clearly
authorize the EPA to decide the Nation's response to global climate change concerns by empowering the Agency to “prescribe . . . standards” for certain air pollutants emitted by new motor vehicles and engines. On these bases, and on account of the additional procedural and analytical errors set out below, we propose that the Endangerment Finding exceeded the EPA's authority and must be rescinded.

1. Best Reading of CAA Section 202(a)

Congress originally enacted the language of CAA section 202(a) in the Motor Vehicle Pollution Control Act of 1965 and retained it, with minor revisions, in the 1970 CAA and all subsequent statutory amendments. The key language in CAA section 202(a)(1) provides:

The Administrator shall by regulation prescribe (and from time to time revise) in accordance with the provisions of this section, 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.
43

43
42 U.S.C. 7521(a)(1).

Since 1977, CAA section 302(g) has defined the term “air pollutant” throughout the statute as “any air pollution agent or combination of such agents . . . which is emitted into or otherwise enters the ambient air.”

44

CAA section 302(h) also provides that any reference to “effects on welfare includes, but is not limited to, effects on” the environment, property, transportation hazards, and “on economic values and on personal comfort and well-being.”
45

44
42 U.S.C. 7602(g). Notably, the statute does not separately define “air pollution.”

45
42 U.S.C. 7602(h).

The EPA proposes that this statutory language is best read as authorizing the Agency to identify and regulate, as an integral part of a rulemaking prescribing emissions standards, air pollutants that cause or contribute to air pollution that itself endangers public health and welfare through local or regional exposures. This proposed interpretation is consistent with the text and structure of the statute, our decades-long implementation of the statute prior to 2009, and background principles of statutory interpretation, including default rules for proximate cause. This proposed interpretation is also consistent with the Supreme Court's decision in
Massachusetts,
which addressed distinct issues and must, as a matter of
stare decisis,
be read in harmony with the Supreme Court's subsequent decisions bearing on the EPA's authority and statutory interpretation in
UARG, West Virginia,
and
Loper Bright
.
46

46

See Hohn
v.
United States,
524 U.S. 236, 252-53 (1998) (Supreme Court decisions “remain binding precedent until [the Supreme Court] see[s] fit to reconsider them, regardless of whether subsequent cases have raised doubts about their continuing vitality.”);
Rodriguez de Quijas
v.
Shearson/Am. Exp., Inc.,
490 U.S. 477, 484 (1989) (similar).

Dangerous Air Pollution.
The EPA proposes that CAA section 202(a) is best read as authorizing the Agency to regulate air pollutant emissions that cause or contribute to air pollution that endangers public health or welfare through local or regional exposure. For the purposes of this proposed action, we use the phrase local or regional exposure to distinguish air pollution that impacts public health and welfare by its presence in the ambient air from “air pollution” consisting of six “well-mixed” GHGs that, as conceptualized in the Endangerment Finding, impacts public health and welfare only indirectly and not by its mere presence in the ambient air. As discussed below, this proposal would effectively return the EPA to its interpretation of CAA section 202(a) prior to 2009.

We propose that the terms “air pollutant” and “air pollution” as used in CAA section 202(a)(1) should be construed in accordance with the specific air pollutants identified for other purposes in the remainder of CAA section 202. Each of these listed air pollutants share the common quality of causing or contributing to air pollution that adversely impacts public health or welfare through local or regional exposure to the air pollution itself. CAA section 202 specifically addresses hydrocarbons (HCs), carbon monoxide (CO), oxides of nitrogen (NO
X
), and particulate matter (PM), all of which harm health and the environment through exposure (
e.g.,
inhalation and dermal contact) or by causing or contributing to air pollution that harms health and the environment through exposure (
e.g.,
smog and acid rain).
47

That pattern holds for the criteria pollutants identified in the CAA—CO, lead, ground-level ozone (O
3
), nitrogen dioxide (NO
2
), PM, and sulfur dioxide (SO
2
)—as well as the initial list of hazardous air pollutants in CAA section 112(b)(1).
48

We find it significant that in subjecting a number of air pollutants emitted by new motor vehicles and engines to regulation under CAA section 202, Congress did not include substances that are potentially indirectly harmful to public health or welfare based on elevated global concentrations in the upper atmosphere. That conspicuous omission supports the conclusion that the air pollutants subject to regulation under CAA section 202(a) are those that cause or contribute to air pollution which itself endangers public health or welfare through local or regional exposure.
49

47

See, e.g.,
42 U.S.C. 7521(a)(3)(A)(i), (b), (g), (h), (j), (k).

48
42 U.S.C. 7412(b)(1).

49
As discussed in section IV.A.2 of this preamble, the only references to GHGs in the CAA are in
non
-regulatory contexts in which Congress authorized funding for various forms of research and grant programs. The choice to limit such references to non-regulatory solutions further supports the conclusion that the CAA section 202(a) regulatory authority for responding to endangerment does not encompass GHG emissions on the basis of global climate change concerns.

Put another way, we propose that the air pollutants identified in CAA section 202 and throughout relevant provisions of the CAA are those that cause or contribute to air pollution for which the air pollution
itself,
through local or regional exposure to humans and the environment, endangers public health or welfare.
50

For certain regulated air pollutants, the air pollutants are themselves the dangerous air pollution,
i.e.,
the air pollutants are the air pollution with adverse health and welfare impacts. An example is CO, which can be harmful, and even fatal, to humans at sufficient localized concentrations.
51

For other regulated air pollutants, the air pollutants contribute to dangerous air pollution by interacting with other airborne chemicals or environmental factors such as sunlight to create the dangerous air pollution,
i.e.,
the air pollutants are ingredients that create the dangerous air pollution in combination. An example is acid rain, in which air pollutants such as SO
2
interact locally and regionally with additional airborne chemicals to form acidic precipitation.
52

50
For example, unlike other regulated air pollutants, “CO
2
is odorless, does not affect visibility and has no toxicological effects at ambient levels,” Additionally, the Permissible Exposure Limit established by the U.S. Occupational Safety and Health Administration or which diminished performance on cognitive tasks are “far larger than any plausible ambient outdoor value through the end of the 22nd century.”Add 2025 CWG Draft Report at 2.

51
U.S. Environmental Protection Agency. (Last updated Apr. 11, 2025). Carbon Monoxide's Impact on Indoor Air Quality:
https://www.epa.gov/indoor-air-quality-iaq/carbon-monoxides-impact-indoor-air-quality
.

52
U.S. Environmental Protection Agency. (Last updated Mar. 4, 2025). What is Acid Rain?:
https://www.epa.gov/acidrain/what-acid-rain
.

The definition of “air pollutant” in CAA section 302(g) and the meaning of the undefined terms pollutant, pollution, and air pollution support this reading. As a matter of ordinary language, a pollutant is “[a] poisonous or noxious substance that contaminates the environment,” and pollution is “[t]he harmful addition of a substance or thing into an environment.”
53

Definitions of air pollution similarly emphasize the emission of “[c]ontaminants into the atmosphere.”
54

The central concept is the addition of a contaminant, something, that “make[s] impure or unclean by contact or mixture.”
55

CAA section 302(g) is consistent with these definitions, adding only that an “air pollutant” is any “air pollution agent or combination of such agents” that “is emitted into or otherwise enters the ambient air.”
56

Read together with CAA section 202(a)—as the Supreme Court held we must in
UARG
—the underlying concept of dangerousness and contamination reinforces the conclusion that air pollution which endangers public health or welfare is air pollution (caused or contributed to by air pollutants) that itself endangers public health or welfare through local or regional exposures.

53
Black's Law Dictionary 1403 (11th ed. 2019).

54

Id.

55
Am. Heritage Dictionary (5th ed. 2022).

56
42 U.S.C. 7602(g).

The “air pollution” addressed in the Endangerment Finding is different in kind. In that decision, the Administrator defined the relevant “air pollutants” as six “well-mixed GHGs” and the relevant “air pollution” as “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. In contrast to the air pollution addressed expressly in CAA section 202 and elsewhere in the statute, GHGs do not endanger public health or welfare through local or regional exposure. Rather, the Endangerment Finding 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 public health and welfare impacts of varying severity in certain regions. Regulating GHG emissions based on global climate change concerns requires reading an additional instance of “cause, or contribute” into the statute, such that CAA section 202(a) encompasses the `emission of air pollutants that cause, or contribute to, dangerous air pollution that causes, or contributes to, endangerment of public health or welfare.'

This proposed interpretation is also supported by the best reading of the terms “cause” and “contribute.” In enacting and amending CAA section 202(a), Congress legislated against background legal principles, including principles of causation and proximate cause.
57

These “default rules” are “presumed to have [been] incorporated, absent an indication to the contrary in the statute itself,”
58

and nothing in the text of CAA section 202(a) indicates that Congress intended to depart from ordinary legal meaning. As a general matter, there is a point at which harm no longer has a sufficiently close connection to the relevant conduct to reasonably draw a causal link. We propose that emissions from new motor vehicles and new motor vehicle engines in the United States do not have a sufficiently close connection to the adverse impacts identified in the Endangerment Finding to fit within the legal meaning of “cause” or “contribute.” The Endangerment Finding largely avoided addressing this problem by severing the question whether GHG emissions from new motor vehicle engines contribute to GHG concentrations in the atmosphere from the question whether GHG concentrations in the atmosphere endanger public health and welfare. As discussed in further detail in section IV.A.1 of this preamble, we propose that there is no basis in the statute for severing the inquiry in that way. Nevertheless, even with respect to endangerment and contribution in isolation, we propose that global climate change concerns involve analyzing causal relationships that are too uncertain, too remote, and too confounded by intervening and confounding factors to fit within the terms “cause” and “contribute” as used in CAA section 202(a). This understanding follows from the position discussed above that CAA section 202(a) and the statute more generally were designed to regulate air pollution with harmful impacts from local and regional exposure that are analyzable by ordinary causation standards.

57

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).

58

Nassar,
570 U.S. at 347.

In proposing this interpretation, we note that a limiting construction is necessary to avoid absurd results and potential conflict with the nondelegation doctrine. Because Congress cannot delegate legislative powers to the Executive Branch, statutes granting an agency regulatory authority must provide an intelligible principle to guide its exercise.
59

Our authority under CAA section 202(a) to “prescribe . . . standards” for air pollutant emissions by a class or classes of new motor vehicles and engines is limited by the requirement that the Administrator find such air pollutants cause or contribute to air pollution that may reasonably be anticipated to endanger public health and welfare. We propose that the best reading of the statute circumscribes this authority to air pollution that itself causes or contributes to endangerment of public health or welfare. Under the interpretation adopted in the Endangerment Finding, however, our authority under CAA section 202(a) would have no readily discernible limiting principle, particularly in combination with the authority asserted to sever the analysis of endangerment and causation or contribution. Following the logic of the Endangerment Finding, any “air pollutant” emitted at more than
de minimis
volumes would trigger our authority, and the statutory obligation, to prescribe standards so long as the emission contributes to “air pollution” that, in turn, potentially contributes to phenomena with predicted adverse impacts on public health and welfare broadly defined. As discussed further below, under this logic, the release of water vapor (H
2
O) would meet the standard for regulation because water can be said to result in significant harms and because motor vehicles and engines can be said to “contribute” to that harm by emitting non-
de minimis
quantities of water vapor into the upper atmosphere. The EPA would have the authority, and statutory duty, to prescribe standards for water vapor emissions because water vapor is a recognized GHG emitted by motor vehicles and engines as well as the vast majority of other mobile and stationary sources. Because that reading effectively converts CAA section 202(a)(1) into a roaming license to “prescribe . . . standards,” we believe the reading proposed herein is more faithful to the governing principles of statutory interpretation.

59

See, e.g., Gundy
v.
United States,
588 U.S. 128 (2019).

We further emphasize that this proposed interpretation would effectively return the EPA to its longstanding practice prior to 2009 of applying CAA section 202(a) and related statutory endangerment provisions to air pollution that adversely impacts public health and welfare through local or regional exposure. As noted above, we historically utilized this authority to prescribe standards for pollutants identified in the CAA itself, including NO
X
, PM, HC, and CO. The distinction between air pollution that harms public health and welfare through local and regional exposure and global “air pollution” consisting of GHG concentrations without any such direct impacts has also played a role in our evaluation of waiver requests under CAA section 209.
60

Even in the Endangerment Finding, the Administrator recognized that we had previously applied CAA section 202(a) to “a
more typical
local or regional air pollution problem.” 74 FR 66538 (emphasis added). We propose that in adopting a novel analytical approach in the Endangerment Finding, the EPA failed adequately to address its prior practice and improperly relied on the Supreme Court's decision in
Massachusetts
for the proposition that CAA section 202(a) authorizes emission standards in response to air pollution raising global climate change concerns. As discussed below,
Massachusetts
did not construe the scope of the EPA's authority to regulate under CAA section

202(a), and the Court has since made clear in
UARG
and
West Virginia
that our authority to regulate air pollutants that fit within the Act-wide definition turns on the particular statutory provision that confers authority to regulate.

60

See, e.g.,
“California State Motor Vehicle Pollution Control Standards; Notice of Decision Denying a Waiver of Clean Air Act Preemption for California's 2009 and Subsequent Model Year Greenhouse Gas Emission Standards for New Motor Vehicles,” 73 FR 12156, 12161 (Mar. 6, 2008) (denying California's waiver request for GHG emission standards on the ground that “the different, and global, nature of the pollution at issue” requires a different conceptual approach).

In
Massachusetts,
the Supreme Court rejected the argument that GHGs are not “air pollutants” under the Act-wide definition, reasoning that CAA section 302(g)'s use of the word “any” in connection with “air pollutant agent or combination of such agents, including any physical [or] chemical . . . substance” was sufficiently broad to encapsulate the combination of GHGs at issue. 549 U.S. at 530. On this basis, the Court stated that the EPA “has the statutory authority to regulate the emission of such gases from new motor vehicles.”
Id.
at 532. The Court did not, however, decide whether including GHGs within the definition of “air pollutant” meant that we must find that GHGs meet the statutory standard for regulation under CAA section 202(a) because they cause or contribute to air pollution which endangers the public health or welfare. Rather the Court concluded its opinion by clarifying that it “need not and do[es] not reach the question whether on remand EPA must make an endangerment finding.”
Id.
at 534.

Consistent with
Massachusetts,
we propose to interpret the CAA as setting out a broad, threshold definition of “air pollutant” on an Act-wide basis that must be interpreted in the context of each applicable, particular provision granting regulatory authority in order to determine whether that provision authorizes the EPA to regulate an air pollutant under that particular authority. For purposes of CAA section 202(a), that means that even if GHGs are “air pollutant[s]” as defined on an Act-wide basis, they must meet the statutory standard for regulating emissions from new motor vehicles and engines before we may invoke our regulatory authority. Put simply, regardless whether GHGs are “air pollutants” as defined in CAA section 302(g), they must still satisfy the same standard as any other “air pollutant” by causing or contributing to air pollution which may reasonably be anticipated to endanger public health or welfare.

This understanding is confirmed by
UARG,
in which the Supreme Court distinguished between “the Act-wide definition” of air pollutant and the application of that definition to the Act's regulatory provisions. 573 U.S. at 320. The Court specifically addressed the holding in
Massachusetts,
adopting the argument that “while
Massachusetts
rejected EPA's categorical contention that [GHGs] could not be air pollutants for any purposes of the Act, it did not embrace EPA's [then] current, equally categorical position that [GHGs] must be air pollutants for all purposes regardless of the statutory context.”
Id.
(cleaned up).

In sum, we propose that CAA section 202(a) does not provide authority to regulate GHGs based on global climate change concerns because that provision authorizes regulating only air pollutants that “cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare.” The EPA must “ground its reasons for action or inaction in the statute,”
Massachusetts,
549 U.S. at 535, and “possess[es] only the authority that Congress has provided,”
NFIB
v.
DOL,
595 U.S. 109, 117 (2022). In proposing this interpretation, we note that our actions must be consistent with “the single, best meaning” of the statute and cannot expand our authority in response to pressing concerns based on statutory silence or ambiguity.
Loper Bright,
603 U.S. at 400, 411. We seek comment on this proposed interpretation, including the rationales articulated above and any further rationales that commenters believe support, or detract from, this interpretation.

Findings and Standards.
The EPA further proposes that CAA section 202(a) requires issuing emission standards together with the findings necessary to invoke our regulatory authority, rather than severing the regulatory action into separate endangerment and standards-setting proceedings. The statute begins by providing that the Administrator “shall prescribe . . . standards applicable to the emission of any air pollutant from any class or classes of new motor vehicles or new motor vehicle engines,” and follows this requirement by describing the scope of the duty to regulate air pollutant emissions “which, in his judgment cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare.” We propose that the best reading of the statute requires the Administrator, when prescribing any emission standard for new motor vehicles or engines, to find that the air pollutant or air pollutants emitted by the class or classes of new motor vehicles or engines subject to the standard cause or contribute to air pollution that may reasonably be anticipated to endanger public health or welfare.

The Endangerment Finding severed this statutory language by finding endangerment and contribution in the abstract for all potential CAA section 202(a) sources with respect to GHGs. In so doing, the Administrator vastly increased the Agency's authority by removing the restrictions Congress placed on the issuance of emission standards. As a result of this new conception of authority, the EPA may issue a single endangerment finding in the abstract with respect to emissions from all sources potentially subject to CAA section 202(a) (and their existing-source counterparts) without addressing the danger posed by any particular source category or the causal role of that particular source category in any identified danger. The EPA has since relied on the Endangerment Finding to prescribe emission standards for various classes of new motor vehicles and engines, as well as a variety of other sources under distinct statutory authorities, without making the requisite findings or assessment of factors necessary to regulate the sources in question.
61

We propose that Congress enacted CAA section 202(a) as an integrated regulatory provision for a reason, and that giving effect to the language of the statute requires the issuance of emission standards only when the Administrator has made an integrated finding of both endangerment and cause or contribution. Put another way, we propose that it is impermissible for the Administrator to make an endangerment finding without prescribing the emission standards required in response to such a finding, and conversely, that it is impermissible to prescribe emission standards without making the source- and air-pollutant specific findings required by the statute.

61

See
sections II.C, VI.B, and VI.C of this preamble for a summary of the EPA's rulemaking activities in response to the Endangerment Finding.

This proposed interpretation is consistent with the EPA's implementation of CAA section 202(a) and similar provisions of the CAA prior to 2009. In the Endangerment Finding, the Administrator acknowledged that “typically endangerment and cause or contribute findings have been proposed concurrently with proposed standards under various sections of the CAA, including CAA section 201(a).” 74 FR 66501. We propose that our historical practice under CAA section 202(a) reflects the better reading of the statute and is entitled to greater weight. As the Supreme Court recently explained, such weight is “especially warranted when an Executive Branch interpretation was issued roughly contemporaneously with enactment of the statute and remained consistent over time.”
Loper Bright,
603 U.S. at 386.

In departing from the EPA's historical practice in the Endangerment Finding, the Administrator reasoned that “[t]he text of CAA section 202(a) is silent on this issue” and “invoked the procedural discretion that is provided by CAA section 202(a)'s lack of specific direction.” 74 FR 66501. We propose that CAA section 202(a) is not silent on the issue because the statute sets out an integrated process that requires the EPA to prescribe standards when the Administrator finds certain conditions are met. When Congress intends a multi-step inquiry in the environmental context, it typically says so expressly. In the National Ambient Air Quality Standards (NAAQS) program, for example, the CAA separates our authority to establish and revise the NAAQS under CAA section 108 and 109 from our duties to implement the NAAQS by reviewing State Implementation Plans (SIPs) or promulgating Federal Implementation Plans (FIPs) under CAA section 110 and related statutory provisions.
62

A particularly relevant analogy is Clean Water Act section 303(c)(4), which pairs the Administrator's authority to “determin[e] that a revised or new [water quality standard] is necessary to meet the requirements of this chapter” with the requirement that the Administrator “shall promptly prepare and publish proposed regulations” after making such a determination and “promulgate any revised or new standard . . . not later than ninety days after he publishes such proposed standards.”
63

We further propose that even if CAA section 202(a) were ambiguous or silent in this respect, the Supreme Court recently held in no uncertain terms that “statutory ambiguity . . . is not a reliable indicator of actual delegation of discretionary authority to agencies.”
Loper Bright,
603 U.S. at 411.

62

See
42 U.S.C. 7408, 7409, 7410.

63
33 U.S.C. 1313(c)(4), (c)(4)(B). Various provisions of the Safe Drinking Water Act (SDWA) and Toxic Substances Control Act (TSCA) similarly articulate multi-step processes for determining risk and addressing risk through regulation using language that Congress did not include in CAA section 202.

Severing the EPA's standards-setting authority from the findings that trigger a duty to exercise that authority shaped the analysis in the Endangerment Finding in a manner that we propose ran counter to the statute. Recall that the Endangerment Finding first projected adverse public health and welfare impacts of global climate change and attributed those adverse impacts to all manmade sources of GHG emission around the world and then, separately, used data from existing CAA section 202(a) sources in the United States to find that new motor vehicles and engines in the United States contributed to global GHG air pollution. The Administrator treated adaptation (adjustments to the effect of climate change that lessen impacts) and mitigation (reductions in emissions and global GHG concentrations unrelated to CAA section 202(a) regulation) as outside the scope. 74 FR 66512. Moreover, the Administrator declined to consider cost, asserting that the Endangerment Finding imposed no regulatory requirements as a standalone action and relying on the Supreme Court's decision in
Whitman
v.
American Trucking Association,
531 U.S. 457 (2001), that the EPA cannot consider cost in setting and revising the NAAQS under CAA section 109. 74 FR 66515. Nor did the Administrator consider potential beneficial impacts from climate change with respect to whether and which standards would be appropriate.
See
74 FR 66524 (purporting to compare “risks and benefits” only with respect to endangerment).

Severance also shaped all subsequent standards prescribed and revised in reliance on the Endangerment Finding in a manner we propose to conclude was unlawful. The EPA asserted in subsequent rulemakings that there was no need to make particularized findings for the relevant source category because the Endangerment Finding identified public health and welfare dangers and contribution for all CAA section 202(a) source categories. Nor did we consider the impacts of adaptation or mitigation or consider when prescribing standards whether, in light of more recent empirical data, the Endangerment Finding's analysis of endangerment and contribution remained accurate with respect to the source category at issue. As a result, the decision to sever meant that the EPA has never meaningfully considered or invited public comment on the cost, effectiveness, and continued propriety of its GHG regulatory program.

We propose that these considerations should have been taken into account when the 2009 Endangerment Finding intentionally triggered a duty to regulate by invoking our CAA section 202(a) authority. CAA section 202(a)(2) expressly provides that “[a]ny regulation prescribed under paragraph (1) of this subsection . . . shall” provide adequate time for “the development and application of the requisite technology, giving appropriate consideration to the cost of compliance within such period.”
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CAA section 202(a)(1) authorizes the Administrator to “by regulation prescribe” standards “in accordance with the provisions of this section” and does not separately authorize standalone findings, meaning any action taken “under paragraph (1) of this subsection” is subject to the considerations in paragraph (2). That statutory language aside, the Supreme Court explained in
Michigan
that “agency action is lawful only if it rests `on a consideration of the relevant factors,' ” 576 U.S. at 750 (quoting
State Farm,
463 U.S. at 43), including “at least some attention to cost,”
id.
at 752. We propose that the Administrator erred in analogizing to the NAAQS program and the Supreme Court's decision in
Whitman
to avoid considering costs in the Endangerment Finding. Unlike CAA section 202(a), the language in CAA section 109(b) makes no reference to cost or implementation and focuses solely on safety and an adequate margin to protect public health. Nor does CAA section 109(b) include the lead time and technical feasibility concepts embedded in CAA section 202(a). And whereas CAA section 202(a) sets out an integrated authority to prescribe emission standards when the provision's triggering condition is satisfied, CAA section 109(b) uses mandatory language requiring the EPA to establish certain standards, the content and implementation of which are specified in various provisions throughout Title I of the Act. We further propose that the Supreme Court's decision in
Massachusetts
did not address the question whether the EPA could issue standalone findings or bar the Administrator from taking cost and implementation concerns into account when exercising CAA section 202(a) authority. Rather,
Massachusetts
must be read together with
Michigan,
and the language of CAA section 202(a)(1) must be read in context to “produc[e] a substantive effect that is compatible with the rest of the law.”
UARG,
573 U.S. at 321 (quoting
United Sav. Ass'n of Tex.
v.
Timbers of Inwood Forest Assocs.,
484 U.S. 365, 371 (1988)).

64
42 U.S.C. 7521(a)(2).

Endangerment and Cause or Contribute.
The EPA also proposes that CAA section 202(a) requires the Agency to evaluate whether source emissions cause or contribution to air pollution and whether that air pollution poses endangerment in a single causal chain, rather than considering these issues in isolation by severing the inquiries. The relevant inquiry is whether “the emission of any air pollutant from any class or classes of new motor vehicles or

new motor vehicle engines,” in the judgment of the Administrator, “cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare.” As explained in this section, the emission must cause or contribute to the danger posed by the air pollution to a sufficient extent t

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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2025-14572. Public record. Not legal advice.