Reconsideration of 2009 Endangerment Finding and Greenhouse Gas Vehicle Standards

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

ate 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

l 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

han 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

ippa, 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

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

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)

5, 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

sphere.

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

onsidered 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/

ject 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

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

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

uty 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

ch 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

t 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

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

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

s 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

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

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

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

o 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

e 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

lic 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

nce 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

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

n 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 contribu

hrough 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

e 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 . .

d 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)

d 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

tory 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

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

ent 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

hat 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

tionary 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)

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 . .

sibility 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 to satisfy the standard for regulation.

In the Endangerment Finding, the Administrator made two distinct findings based on two distinct sets of assumptions

lasses of sources that EPA intended to regulate had such an effect.

Upon review, we no longer believe that the approach taken in the Endangerment Finding was consistent with the language of CAA section 202(a) and the structure of the CAA, which requires making distinct findings for regulating distinct types of emission sources and authorizes different regulatory tools when such standards are met. For example, CAA section 111(b)(1)(A) authorizes the EPA to regulate emissions from listed categories of stationary sources if the Administrator determines those sources emit air pollutants that “significantly contribute” to dangerous air pollution. 65 When that standard is met, CAA section 111(b)(1)(B) requires the EPA to regulate such emissions from such sources by setting standards of performance that, among other things, reflect the best system of emission reduction that has been adequately demonstrated in practice. 66 The CAA similarly sets out distinct standards for regulating and distinct modes of regulation for additional major source categories, including vehicles in use, aircraft engines, and separately addresses when and how to respond to international emissions that impact the United States. The Endangerment Finding effectively attributed the total GHG emissions coming from all of these various distinct sources within the United States, as well as from all international sources, to the mobile sources regulated under CAA section 202(a) without having made the requisite determinations for any of those sources and without considering the different regulatory tools Congress authorizes for those sources as compared to CAA section 202(a) sources. The Administrator defined the relevant “air pollution” as the combination of six “well-mixed GHGs” but found that CAA section 202(a) sources emitted only four of them: CO 2 , methane, NO X , and HFCs. 74 FR 66538

e requisite determinations for any of those sources and without considering the different regulatory tools Congress authorizes for those sources as compared to CAA section 202(a) sources. The Administrator defined the relevant “air pollution” as the combination of six “well-mixed GHGs” but found that CAA section 202(a) sources emitted only four of them: CO 2 , methane, NO X , and HFCs. 74 FR 66538. As a result, the “air pollution” identified as endangering public health or welfare included PFCs and SF 6 , and the “air pollution” used to conclude that CAA section 202(a) sources satisfy the regulatory standard did not. Contrary to the EPA's conclusion at the time, 74 FR 66541, that difference is material, as PFCs and SF 6 are asserted to have many times the global warming potential of CO 2 . 67 Severing the endangerment and cause-or-contribute analysis allowed the Agency to compare apples and oranges in a manner the statute does not authorize.

65 42 U.S.C. 7411(b)(1)(A).

66 42 U.S.C. 7411(a)(1), (b)(1)(B). CAA section 111 also differentiates between new and existing stationary sources in a listed source category and limits the EPA's role with respect to existing sources by authorizing only emission guidelines implemented by the States. 42 U.S.C. 7411(d).

67 U.S. Environmental Protection Agency. (Last updated Jan. 16, 2025). Understanding Global Warming Potentials: https://www.epa.gov/ghgemissions/understanding-global-warming-potentials .

The Endangerment Finding also did not limit its analysis of contribution to “ new motor vehicles or new motor vehicle engines” in the United States, which are the only sources covered by the EPA's CAA section 202(a) authority

nmental Protection Agency. (Last updated Jan. 16, 2025). Understanding Global Warming Potentials: https://www.epa.gov/ghgemissions/understanding-global-warming-potentials .

The Endangerment Finding also did not limit its analysis of contribution to “ new motor vehicles or new motor vehicle engines” in the United States, which are the only sources covered by the EPA's CAA section 202(a) authority. 68 Because the Administrator considered all sources in analyzing the danger posed by elevated concentrations of GHGs in the upper atmosphere, the endangerment analysis necessarily included emissions from foreign and domestic vehicles that had been in use for years or decades and were not “new.” Even when analyzing contribution, the Administrator used emission estimates from “the entire fleet of motor vehicles in the United States for a certain calendar year” rather than projecting emissions from new motor vehicles and engines over time. 74 FR 66543. That decision increased the absolute contribution figure by orders of magnitude, including because newer vehicles and engines tend to be more efficient and emit less. 69 Difficulties in disaggregating emission data from emission sources, however reasonable, do not license us to read the term “new” out of the statutory text.

68 42 U.S.C. 7521(a)(1) (emphases added).

69 For additional discussion of improvements in new motor vehicles and engines relative to older vehicles and engines, see section V of this preamble.

We are also concerned that severing the endangerment and cause or contribution findings leads to untenable results and lacks any limiting principle. To illustrate the problem, the same logic would allow the EPA to issue emission standards for water vapor (H 2 O), another substance emitted by new motor vehicles and engines that is also considered a powerful GHG

es, see section V of this preamble.

We are also concerned that severing the endangerment and cause or contribution findings leads to untenable results and lacks any limiting principle. To illustrate the problem, the same logic would allow the EPA to issue emission standards for water vapor (H 2 O), another substance emitted by new motor vehicles and engines that is also considered a powerful GHG. Considered in isolation, H 2 O concentrations in the atmosphere can be said to endanger public health or welfare by resulting in rain that leads to slip-and-fall injuries, drownings, and damage to crops, livestock, and property, including through pools, rivers, and floodwater, although water vapor is not itself harmful and is necessary to sustain life. Also considered in isolation, CAA section 202(a) sources can be said to “contribute” to elevated H 2 O concentrations in the atmosphere from all anthropogenic sources, and these emissions of water vapor would thereby assertedly “contribute” to global climate effects similar to those attributed to other GHGs. CAA section 202(a) does not contemplate prescribing emission standards for such an omnipresent, naturally occurring, and essential component of the ambient air, and stakeholders have not petitioned for such regulation, because the text requires analyzing the extent to which emissions contribute to the danger. The logic of regulating water vapor would appear to be absurd, but it is the same logic required to regulate GHGs under CAA section 202(a).

We further propose that the decision to sever the analysis of endangerment from the analysis of contribution, combined with the decision to sever the Administrator's findings from any standards prescribed as a result, produced an analysis that is incompatible with the statute

ating water vapor would appear to be absurd, but it is the same logic required to regulate GHGs under CAA section 202(a).

We further propose that the decision to sever the analysis of endangerment from the analysis of contribution, combined with the decision to sever the Administrator's findings from any standards prescribed as a result, produced an analysis that is incompatible with the statute. In the Endangerment Finding, the Administrator concluded that anything more than a trivial or de minimis contribution to elevated global GHG concentrations by CAA section 202(a) sources was sufficient to trigger regulation because the “unique, global aspects of the climate change problem tend to support contribution at lower percentage levels of emissions than might otherwise be considered appropriate when addressing a more typical local or regional air pollution problem.” 74 FR 66538. Because the Endangerment Finding did not consider the standards that the statute requires when the Administrator makes such a finding, we did not consider whether emission standards for new motor vehicles would be futile as a means to address the identified dangers of GHG emissions from all anthropogenic sources. As discussed in sections IV.A and IV.B of this preamble, reducing GHG emissions from all vehicles and engines in the United States to zero would not have a scientifically measurable impact on GHG emission concentrations or global warming potential (2025 CWG Draft Report at 130). 70 It was foreseeable at the time that issuing the Endangerment Finding would trigger a duty to regulate, and that extraordinarily stringent measures would be necessary under all of the EPA's separate statutory authorities, and not just CAA section 202(a), to have any potentially measurable impact on the identified harm

ion concentrations or global warming potential (2025 CWG Draft Report at 130). 70 It was foreseeable at the time that issuing the Endangerment Finding would trigger a duty to regulate, and that extraordinarily stringent measures would be necessary under all of the EPA's separate statutory authorities, and not just CAA section 202(a), to have any potentially measurable impact on the identified harm. Additionally, the EPA did not consider “carbon leakage,” which “refers to the situation that may occur if, for reasons of costs related to climate policies, businesses were to transfer production to other countries with laxer emission constraints . . . [and] could lead to an increase in their total emissions.” 71 Foreign governments have recognized that carbon leakage can mitigate or even lead to an increase in total emissions which would significantly impact the claimed benefits of the regulatory actions. 72 Accordingly, we propose that refusing to consider these foreseeable consequences was inconsistent with the statutory scheme and, as explained further below, arbitrary and capricious and an abuse of discretion.

70 See Lomborg, B. (2016). Impact of Current Climate Proposals. Global Policy, 7(1) 109-118: https://doi.org/10.1111/1758-5899.12295 .

71 Carbon leakage. (2019). European Commission: https://climate.ec.europa.eu/eu-action/eu-emissions-trading-system-eu-ets/free-allocation/carbon-leakage_en .

72 See, e.g., id.

Finally, we propose that the Administrator did not adequately consider the meaning in context of the statutory term “endanger” and failed to identify with sufficient rigor the purported danger linked to GHG emissions from new motor vehicles and engines

or questions doctrine for the same reasons the Supreme Court applied it in UARG and West Virginia. By asserting jurisdiction to regulate in response to global climate change concerns, the EPA “ `claim[ed] to discover in a long-extant statute an unheralded power' representing a `transformative expansion in [its] regulatory authority.' ” West Virginia, 597 U.S. at 724 (quoting UARG, 573 U.S. at 324). We note that the regulatory actions reviewed in UARG and West Virginia were predicated in part on the Endangerment Finding and propose that the PSD and Title V rules in UARG and existing source emission guidelines in West Virginia are similar in scope, approach, and economic impact as the GHG emission standards for new motor vehicles and engines promulgated to fulfill the mandatory duty triggered by the Endangerment Finding. As a consequence of the novel approach taken in the Endangerment Finding to endangerment and contribution, our GHG emission standards mandate an increased and faster shift from gasoline-fueled vehicles to electric vehicles on the theory that a substantial reduction in GHG emissions is necessary to address global climate change concerns. 77 We propose that mandating a shift in the national vehicle fleet from one type of vehicle to another is indistinguishable from the emission guidelines at issue in West Virginia, which were calculated to force a shift from one means of electricity generation to another.

77 89 FR 27842, 27844.

We further propose it is “ `highly unlikely that Congress would leave' to `agency discretion' the decision” of how much gasoline should be used by vehicles and engines in the United States. West Virginia, 597 U.S. at 729 (quoting MCI Telecomms. Corp. v. AT&T Co., 512 U.S. 218, 231 (1994)). As the Supreme Court noted with respect to coal-based electricity generation, such a policy decision involves “basic and consequential tradeoffs,” and “Congress certainly has not conferred a like authority upon EPA anywhere else in the Clean Air Act.” Id

y vehicles and engines in the United States. West Virginia, 597 U.S. at 729 (quoting MCI Telecomms. Corp. v. AT&T Co., 512 U.S. 218, 231 (1994)). As the Supreme Court noted with respect to coal-based electricity generation, such a policy decision involves “basic and consequential tradeoffs,” and “Congress certainly has not conferred a like authority upon EPA anywhere else in the Clean Air Act.” Id. Until the Endangerment Finding, moreover, we had never invoked CAA section 202(a) or any other CAA authority to regulate in response to global climate change concerns, whether through a fuel-shifting strategy or any other means. That history is telling because although CAA section 202(a) has existed in substantially similar form since 1967, “the EPA had never regulated in that manner, despite having issued many prior rules governing” vehicle and engine emissions. Id.

When Congress has addressed GHGs individually or collectively, it has not granted the EPA broad regulatory authority comparable to our authority to “prescribe . . . standards” under CAA section 202(a). With respect to HFCs, Congress enacted a comprehensive phaseout scheme in the 2020 American Innovation and Manufacturing (AIM) Act, which includes detailed instructions, timelines, and requirements for implementation and allows some uses to continue under certain conditions. 78 With respect to CO 2 , Congress opted for a carrot rather than a stick by authorizing a tax credit to incentivize underground sequestration that mitigates emissions. 79 With respect to methane, Congress amended the CAA in 2021 through the Inflation Reduction Act of 2022 (IRA) to require us to establish a waste emissions charge for certain sources structured to incentivize emissions reductions over time. 80 When addressing GHGs more generally, Congress has used non-regulatory tools that incentivize, rather than mandate, changes in private ordering, including through additional funding provisions in the IRA

he CAA in 2021 through the Inflation Reduction Act of 2022 (IRA) to require us to establish a waste emissions charge for certain sources structured to incentivize emissions reductions over time. 80 When addressing GHGs more generally, Congress has used non-regulatory tools that incentivize, rather than mandate, changes in private ordering, including through additional funding provisions in the IRA. 81 We propose that multiple instances of recent legislation addressing GHGs individually and through distinct regulatory approaches suggests that Congress views such policy decisions as economically and politically significant and not adequately addressed by general statutory authorities enacted in response to different problems.

78 Public Law 116-260, Div. S, codified at 42 U.S.C. 7675 et seq.

79 26 U.S.C. 45Q. In 2020, Congress also instructed us to recommend improvements to SDWA permitting procedures for injection wells used in carbon sequestration and appropriated additional fundings for the “Class VI” permitting process. Public Law 116-260, Div. G, Title II.

80 Public Law 117-169, codified at 42 U.S.C. 7436.

81 See, e.g., Public Law 117-169, codified at 42 U.S.C. 7432-7438. We also note that CAA section 211(o)(2)(B)(ii) requires the EPA to consider “the impact of the production and use of renewable fuels on the environment, including on . . . climate change,” among many other factors, in setting volumes under the RFS program. 42 U.S.C. 7545(o)(2)(B)(ii).

The EPA notes that Congress has continued to revise these air pollutant-specific measures and nonregulatory tools as part of an ongoing national debate over the appropriate response to global climate change concerns. On July 4, 2025, President Trump signed into law significant new legislation enacted by Congress, the One Big Beautiful Bill Act (OBBB), 82 which repealed a number of relevant measures adopted in the IRA and rescinded the EPA's appropriations to carry out a number of funding programs related to GHG emissions

self to considering the impacts of GHG emissions from new motor vehicles and engines. Rather, the Endangerment Finding reviewed the totality of adverse impacts from climate change attributed to all anthropogenic sources of GHG emissions worldwide and asserted jurisdiction over CAA section 202(a) sources by finding they contributed to such impacts by emitting more than de minimis quantities of GHGs. That understanding has permeated our GHG emission rulemakings since 2009, and we have attempted to apply that framework to our distinct regulatory authorities for stationary sources and aircraft.

In Massachusetts, the Supreme Court disagreed with the EPA's argument that GHGs were not “air pollutants” because Congress had not revisited CAA section 202(a) in amending the CAA in 1990. 549 U.S. at 512-13. The Court found that our reliance on Brown & Williamson to support that argument was misplaced because unlike the ban on tobacco products at issue in that case, “EPA jurisdiction would lead to no such extreme measures.” Id. at 531. The Court also found that unlike the Food and Drug Administration's earlier statements on tobacco products, “EPA had never disavowed the authority to regulate greenhouse gases” and had issued a memorandum in 1998 suggesting that we had such authority. Id.

We propose that Massachusetts did not consider or have reason to interpret the scope of the EPA's authority under CAA section 202(a) given our position in the 2003 Denial that GHGs are not “air pollutant[s]” under any provision of the statute. Rather, we propose Massachusetts rejected our position that GHGs are “categorically” excluded from the CAA and remanded for the Administrator to determine whether four GHGs met the standard in CAA section 202(a). UARG, 573 U.S. at 320. We further propose that Massachusetts must be read together with the Supreme Court's decisions in West Virginia and UARG, which applied the major questions doctrine to statutory provisions similar to CAA section 202(a)

that GHGs are “categorically” excluded from the CAA and remanded for the Administrator to determine whether four GHGs met the standard in CAA section 202(a). UARG, 573 U.S. at 320. We further propose that Massachusetts must be read together with the Supreme Court's decisions in West Virginia and UARG, which applied the major questions doctrine to statutory provisions similar to CAA section 202(a). To that end, we seek comment on whether Massachusetts applied the major questions doctrine in the first instance, 86 and, if it did, whether that analysis informs the meaning of CAA section 202(a) on its own terms and in light of UARG and West Virginia . Finally, we propose that the EPA's course of rulemaking has not been limited to emission standards as anticipated in Massachusetts . We seek comment on whether a new major questions doctrine analysis is required because the EPA's rulemakings in response to the Endangerment Finding have included electric vehicle mandates that require shifting the national vehicle fleet from one type of vehicle and vehicle fuel to another.

86 We note that recent Supreme Court decisions have not cited Massachusetts as a precedent applying, or declining to apply, the major questions doctrine. See, e.g., Nebraska, 600 U.S. 477; West Virginia, 597 U.S. 697.

B. Alternative Rationale for Proposed Rescission

In the alternative, the EPA proposes that even if CAA section 202(a) could be read to authorize prescribing GHG emission standards for new motor vehicles and engines, the Endangerment Finding unreasonably applied the statutory standard for regulation to the scientific record and should be rescinded on that basis. This subsection proposes several reasons that the Administrator would exercise his discretionary judgment differently today in light of intervening legal and scientific developments that appear to undermine the assumptions, methodologies, and conclusions of the Endangerment Finding.

1

ly applied the statutory standard for regulation to the scientific record and should be rescinded on that basis. This subsection proposes several reasons that the Administrator would exercise his discretionary judgment differently today in light of intervening legal and scientific developments that appear to undermine the assumptions, methodologies, and conclusions of the Endangerment Finding.

1. Climate Science Discussion

The Administrator reviewed available information, including the most recently available scientific information, 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 previously explained, this review included the 2025 CWG Draft Report, which 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. 87 The Administrator also considered available assessments by the U.S. Government and relevant international bodies, including the Third, Fourth, and Fifth NCAs reported by the USGCRP and AR5 and AR6 by the United Nations IPCC. 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 88 and the transparency and reliability requirements of Executive Order 14303, “Restoring Gold Standard Science.” 89

87 As stated earlier, the 2025 CWG Draft Report was provided to the EPA on May 27, 2025, and was reviewed and relied upon in formulating this proposal

of the NCAs, and the Fifth NCA in particular, and reviewed these analyses for consistency with OMB information quality guidelines 88 and the transparency and reliability requirements of Executive Order 14303, “Restoring Gold Standard Science.” 89

87 As stated earlier, 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 at https://www.energy.gov/topics/climate .

88 67 FR 8452 (Feb. 22, 2002).

89 Executive Order 14303, 90 FR 22601 (May 29, 2025).

The Endangerment Finding itself acknowledged significant uncertainties related to climate change and its potential impacts when it stated that the “inherent uncertainty in the direction, magnitude and/or rate of certain future climate change impacts opens up the possibility that some changes could be more or less than expected, and the possibility of unanticipated outcomes.” 74 FR 66524. Specifically, the Endangerment Finding identified uncertainties including, but not limited to: the net health impacts of a temperature increase due to decreases in cold-related mortality, 74 FR 66497, 66526; increases in allergenic illnesses and pathogen borne disease vectors, 74 FR 66498; food production and crop yields, including the scope of potential beneficial impacts from climate change, 74 FR 66498, 66535; temperature at the end of the 21st Century, 74 FR 66519; records of temperature before 1600 A.D., 74 FR 66523; estimates and future projections of anthropogenic aerosols and their respective heating or cooling effects, 74 FR 66519; the extent to which human-induced climate change affects the intensity and f

arini, A. et al. (2015). Mortality risk attributable to high and low ambient temperature: a multicounty observational study. The Lancet, 386(9991), 369-375: https://doi.org/10.1016/S0140-6736(14)62114-0 .

With respect to extreme weather events, the Endangerment Finding projected adverse health impacts from increased frequency and severity of hurricanes, flooding, and wildfires. E.g., 74 FR 66498. Recent data and analyses suggest, however, that despite increased public attention and concern, such extreme weather events have not demonstrably increased relative to historical highs (2025 CWG Draft Report at 65-72, 111). 94 In reviewing the assumptions and conclusions regarding extreme weather events in the Endangerment Finding, the empirical bases asserted appear to be more generalized and unsupported than previously believed and no longer inspire the same degree of confidence. The Administrator further notes that the risks anticipated in the Endangerment Finding resulted, in part, from the Agency's decision at the time to categorically exclude consideration of adaptation and mitigation that should have been incorporated into the analysis as credible and relevant information. We propose that the data on weather events, coupled with the Agency's decision to exclude mitigation and adaptation information from the analysis, fatally undermines the Endangerment Finding's conclusions in this respect.

94 See also Masson-Delmotte, V. et al. (2021) Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press: https://doi.org/10.1017/9781009157896; Klotzbach, P.J. et al. (2018). Continental U.S. Hurricane Landfall Frequency and Associated Damage: Observations and Future Risks. Bulletin of the American Meteorological Society, 99(7), 1359-1376: https://doi.org/10.1175/BAMS-D-17-0184.1; Hodgkins, G.A. et al. (2017)

erse impacts from climate change to increased GHG concentrations, and it attributes virtually the entirety of increased GHG concentrations to anthropogenic emissions from all sources. But the causal role of anthropogenic emissions is not the exclusive source of these phenomena, and any projections and conclusions bearing on the issue should be appropriately discounted to reflect additional factors. Moreover, recent data and analyses suggest that attributing adverse impacts from climate change to anthropogenic emissions in a reliable manner is more difficult than previously believed and demand additional analysis of the role of natural factors and other anthropogenic factors such as urbanization and localized population growth (2025 CWG Draft Report at 14-22, 82-92). 97

97 McKitrick, R. (2013). Encompassing tests of socioeconomic signals in surface climate data. Climatic Change, 120(1-2), 95-107: https://doi.org/10.1007/s10584-013-0793-5; McKitrick, R. & Nierenberg, N. (2010). Socioeconomic Patterns in Climate Data. Journal of Economic and Social Measurement, 35(3-4), 149-175: https://doi.org/10.3233/JEM-2010-0336; McKitrick, R. (2021). Checking for model consistency in optimal fingerprinting: a comment. Climate Dynamics, 58(1-2), 405-411: https://doi.org/10.1007/s00382-021-05913-7; McKitrick, R. (2023). Total least squares bias in climate fingerprinting regressions with heterogeneous noise variances and correlated explanatory variables. Environmetrics, 35(2), e2835: https://doi.org/10.1002/env.2835; McKitrick, R. (2022). On the choice of TLS versus OLS in climate signal detection regression. Climate Dynamics, 60, 359-374: https://doi.org/10.1007/s00382-022-06315-z; Connolly, R. et al. (2021). How much has the sun influenced Northern Hemisphere temperature trends? An ongoing debate. Research in Astronomy and Astrophysics, 21(6), 131: https://doi.org/10.1088/1674-4527/21/6/131

10.1002/env.2835; McKitrick, R. (2022). On the choice of TLS versus OLS in climate signal detection regression. Climate Dynamics, 60, 359-374: https://doi.org/10.1007/s00382-022-06315-z; Connolly, R. et al. (2021). How much has the sun influenced Northern Hemisphere temperature trends? An ongoing debate. Research in Astronomy and Astrophysics, 21(6), 131: https://doi.org/10.1088/1674-4527/21/6/131.

In addition, and as noted in particular contexts above, the Administrator is concerned that the Endangerment Finding did not adequately balance the projected adverse impacts attributed to global climate change with the potential benefits to the United States of increased GHG concentrations, and increased CO 2 concentrations in particular. Unlike virtually every other gas regulated under the CAA, CO 2 is necessary for human, animal, and plant life, and advances public health and welfare by directly impacting plant growth and therefore the price and availability of food, the success of American agricultural and related

industries, and the traditional capacity of the United States to export significant food supplies around the world for economic and humanitarian purposes. Recent data and analysis show that even marginal increases in CO 2 concentrations have substantial beneficial impacts on plant growth and agricultural productivity, and that this benefit has been significantly greater than previously believed (2025 CWG Draft Report at 6-7, 104-09).

The Administrator also questions the decision in the Endangerment Finding to consider together all six “well-mixed” GHGs rather than analyzing the properties and impacts of each on an individual basis. 74 FR 66537. As noted in the 2008 ANPRM, new motor vehicle and engine emissions of the four GHGs they actually emit have fluctuated and diverged over time, and each has different interactions with the climate and natural environment

he decision in the Endangerment Finding to consider together all six “well-mixed” GHGs rather than analyzing the properties and impacts of each on an individual basis. 74 FR 66537. As noted in the 2008 ANPRM, new motor vehicle and engine emissions of the four GHGs they actually emit have fluctuated and diverged over time, and each has different interactions with the climate and natural environment. Nevertheless, the Endangerment Finding did not undertake individual analyses of these four GHGs and, in fact, aggregated them together along with two additional GHGs not emitted by motor vehicles or motor vehicle engines, thereby undermining the transparency, reliability, and usefulness of the findings. We propose that each of the collectively treated GHGs demonstrates different chemical properties, exhibits different interactions with the natural environment, and present different emissions profiles. The Agency did not analyze, for example, whether the three GHGs other than CO 2 emitted by new motor vehicles and engines could be addressed separately in a manner that would impact the ultimate conclusions of endangerment and contribution. Nor did the Agency analyze whether HFCs, which are emitted not by engines but by air conditioning units, could be addressed separately under CAA section 202(a) or another authority in a manner that would impact the ultimate conclusions of endangerment and contribution.

Finally, the Administrator notes that the analyses relied upon in the Endangerment Finding, including the assessment reports of the IPCC and USGCRP that were available at the time and the subsequent iterations of those reports that have been published since 2009, have been criticized on process and quality grounds. Recently, several public watchdog organizations have raised concerns related to the process and quality of the Fifth NCA, which shares the underlying assumptions and conclusions of prior NCAs and IPCC reports

of the IPCC and USGCRP that were available at the time and the subsequent iterations of those reports that have been published since 2009, have been criticized on process and quality grounds. Recently, several public watchdog organizations have raised concerns related to the process and quality of the Fifth NCA, which shares the underlying assumptions and conclusions of prior NCAs and IPCC reports. The groups state that NCA5 does not meet the requirements under Executive Order 14303 and deviated from OMB guidelines on quality, objectivity, utility, and integrity of information disseminated by Federal agencies.

The Administrator takes each of these concerns seriously and seeks public comment on the validity of these concerns and how they should be taken into account when determining whether to finalize any of the alternatives proposed in this action.

2. Proposed Conclusions

Based on this review of the Endangerment Finding and the most recently available scientific information, data, and studies, the Administrator proposes to find, in an exercise in discretionary judgment, that there is insufficient reliable information to retain the conclusion that GHG emissions from new motor vehicles and engines in the United States cause or contribute to endangerment to public health and welfare in the form of global climate change. This proposed conclusion is animated both by the Administrator's commitment to analyzing the statutory standard as a cohesive whole and by the scientific record, which includes too many analytical gaps, uncertainties, and speculative predictions to reach an affirmative endangerment finding and promulgate corresponding emission standards based on such a finding.

As explained above, the Administrator previously asserted in the Endangerment Finding that CAA section 202(a) grants “procedural discretion” to sever the findings that trigger regulation from consideration of the resulting regulations and to sever the endangerment analysis from the causation or contribution analysis

r the first time since the 2009 Endangerment Finding was proposed, on whether, due to new scientific information and developments since the 2009 Endangerment Finding, there is a strong enough scientific record to support an affirmative finding that GHG emissions from section 202(a) sources cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare. Prompt action is needed to address these concerns, and the Administrator looks forward to stakeholder input on the continuing vitality of the assumptions, predictions, and conclusions animating the 2009 Endangerment Finding.

Additionally, the EPA seeks comment on, if the EPA were to make such a

finding, whether a new comment period would be required and what information would be necessary to provide such a finding. To aid in the EPA's decision making, we also seek comment on the breadth of the Administrator's discretion to exercise judgment by rejecting the approach taken in the Endangerment Finding and the results of adopting a different approach. We also seek comment on any additional aspects of the Endangerment Finding that may have fallen short of the administrative law requirement that agency action be reasonable and reasonably explained. Conversely, we seek comment on why the approach taken in the Endangerment Finding remains reasonable given the legal and scientific developments discussed in this proposal, and the impact, if any, of the EPA's denial of rulemaking petitions in 2022 and 2010 on this alternative proposal. As previously noted, we are also seeking comment on whether the denials in 2022 and 2010 were unlawful for any additional reasons not explored explicitly in this proposal.

V. Separate Bases for Proposed Repeal of GHG Emission Standards

In this section, the EPA proposes repealing existing GHG emission standards for reasons unrelated to the decision to rescind or retain the Endangerment Finding

control” the air pollution that endangers public health or welfare. 100 CAA section 202(a)(2) further provides that emission standards cannot go into effect until “after such period as the Administrator finds necessary to permit the development and application of the requisite technology, giving appropriate consideration to the cost of compliance within such period.” 101

100 42 U.S.C. 7521(a)(1).

101 42 U.S.C. 7521(a)(2).

As noted elsewhere in this preamble, GHG emissions from the United States were 11 percent of global GHG emissions in 2022, 102 down from 23.5 percent in 2005. 103 The U.S. transportation sector accounted for 28 percent of domestic GHG emissions in 2022, and light- and medium-duty vehicles accounted for 57 percent of U.S. transportation sector GHG emissions. 104 Taken together, the best available data indicate that GHG emissions from light- and medium-duty vehicles in the United States amounted to approximately 1.8 percent of global GHG emissions in 2022. Reducing GHG emissions from light- and medium-duty vehicles in the United States to zero would result in a 1.8 percent decrease in global GHG emissions, which corresponds to an approximate 3 percent reduction in predicted warming trends (2025 CWG Draft Report at 130). 105 To note, these percentages do not account for trends demonstrating that the United States has been decreasing absolute GHG emissions while other countries like China are significantly increasing their GHG emissions. 106

102 U.S. Environmental Protection Agency. (Last updated Mar. 31, 2025). Global Greenhouse Gas Overview: https://www.epa.gov/ghgemissions/global-greenhouse-gas-overview.

103 74 FR 66539.

104 U.S. Environmental Protection Agency. (Last updated July 1, 2025). Inventory of U.S. Greenhouse Gas Emissions and Sinks: https://www.epa.gov/ghgemissions/inventory-us-greenhouse-gas-emissions-and-sinks.

105 See also U.S. Transportation Sector Greenhouse Gas Emissions 1990-2022. (2024). United States Environmental Protection Agency 89 FR 11275 (Feb

gy costs which will likely lead to large increases in purchase prices, and the impact battery electric and fuel cell vehicle technologies will have on purchasing decisions of consumers (for light-, medium-, and heavy-duty vehicle buyers). Increased prices and some consumers rejecting battery electric and fuel cell vehicle technologies may lead consumers to hold on to their existing vehicles longer. Vehicles are more likely to emit less air pollution with each subsequent model year because of improvements in technology, ordinary wear and tear that decreases the effectiveness of installed technology, and greater stringency in more recent regulations for criteria pollutants and hazardous air pollutants.

111 A discussion of the impact of higher vehicle prices on slowing fleet turnover and thus increasing emissions can be found at 85 FR 24186 and 25039 (Apr. 30, 2020).

For these reasons, the EPA has serious concerns that its GHG standards may be harming air quality by raising prices and reducing fleet turnover. We seek comment on this proposed basis for repeal, including on the economics of fleet turnover, the relative efficiency and emission reductions achieved by newer vehicles, modeling of the changes vehicle criteria pollutant and air toxic emissions as well as changes in upstream emissions, modeling of potential changes in air quality (including ozone and particulate matter) and the potential costs to air quality of retaining standards that may slow fleet turnover as compared to the potential benefits of retaining GHG emission standards in response to global climate change concerns.

In addition, the EPA notes that greater availability of new vehicles at lower prices furthers public welfare by promoting vehicle safety and consumer choice. New vehicles must meet all Federal Motor Vehicle Safety Standards (FMVSS), which NHTSA continually updates over time to respond to new concerns and to incorporate improvements in safety technology

response to global climate change concerns.

In addition, the EPA notes that greater availability of new vehicles at lower prices furthers public welfare by promoting vehicle safety and consumer choice. New vehicles must meet all Federal Motor Vehicle Safety Standards (FMVSS), which NHTSA continually updates over time to respond to new concerns and to incorporate improvements in safety technology. Manufacturers install technologies to meet these safety requirements and may also include newer safety features not required by regulation. NHTSA has found that newer vehicles offer improved safety features and designs, leading to reduced fatalities and injuries in crashes relative to older vehicles. 112 A delay in the turnover of the fleet also could lead to a higher risk to drivers and passengers and delay the safety benefits provided by new vehicles, thereby harming the public welfare in a more direct way than the global climate change impacts animating the EPA's GHG standards.

112 U.S. Department of Transportation, National Highway Traffic Safety Administration. How Vehicle Safety Has Improved Over the Decades: https://www.nhtsa.gov/how-vehicle-safety-has-improved-over-decades.

Moreover, the EPA notes that the ability to own a vehicle is an important means to unlock economic freedom and participate in society as an employee, consumer, and community member. Transportation mobility is essential to economic and social mobility, and there are no readily available substitutes for passenger vehicles in many urban and virtually all non-urban communities throughout the United States. By increasing the price of new vehicles and existing vehicles subject to the standards at manufacture, our GHG emission standards may prevent some people from accessing the benefits of vehicle ownership. For example, in EPA's 2024 vehicle GHG rules, the EPA projected significant increases in vehicle technology costs which we estimated would be passed on to consumers as price increases

ited States. By increasing the price of new vehicles and existing vehicles subject to the standards at manufacture, our GHG emission standards may prevent some people from accessing the benefits of vehicle ownership. For example, in EPA's 2024 vehicle GHG rules, the EPA projected significant increases in vehicle technology costs which we estimated would be passed on to consumers as price increases. 113 In addition, the 2025 OBBB ended the IRA's 30D new clean vehicle tax credit before the end of 2025 (while the IRA allowed for this tax credit through 2032). This significant change will increase the effective price of many new battery electric, plug-in hybrid electric, and fuel cell vehicles, including leased vehicles.

113 For a discussion of this topic, see chapter 4.2 of the Multi-Pollutant Emissions Standards for Model Years 2027 and Later Light-Buty and Medium-Duty Vehicles final rule RIA, https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P1019VPM.pdf, and Chapter 3 of the Greenhouse Gas Emissions Standards for Heavy-Duty Vehicles: Phase 3 final rule RIA, https://nepis.epa.gov/Exe/ZyPDF.cgi/P101ABVT.PDF?Dockey=P101ABVT.PDF.

The EPA seeks comment on these additional rationales, including on whether such public welfare considerations can and should be considered when prescribing and revising emission standards under CAA section 202(a). As noted earlier in this preamble, Congress defined “effects on welfare” broadly in CAA section 302(h) to include, but not be limited to, “hazards to transportation, as well as effects on economic values and on personal comfort and well-being.” 42 U.S.C. 7602(h)

uch public welfare considerations can and should be considered when prescribing and revising emission standards under CAA section 202(a). As noted earlier in this preamble, Congress defined “effects on welfare” broadly in CAA section 302(h) to include, but not be limited to, “hazards to transportation, as well as effects on economic values and on personal comfort and well-being.” 42 U.S.C. 7602(h). We seek comment on how to give effect to this statutory language as incorporated into the reference in CAA section 202(a) to effects on “public health or welfare.” We further seek comment as a general matter on whether the Endangerment Finding and resulting regulations have resulted in disbenefits, that is, on any public health and welfare harms that may flow from the Endangerment Finding and resulting regulations themselves.

VI. Proposed Repeal of GHG Emission Standards

Consistent with the proposed rescission of the Endangerment Finding in section IV.A and IV.B of this preamble, the additional considerations in section V of this preamble, and the discussion of legal authority in section III of this preamble, the EPA is proposing to repeal all GHG emission standards for light-duty vehicles, medium-duty vehicles, heavy-duty vehicles, and heavy-duty engines. This includes emission standards for the subset of four of the six “well-mixed GHGs” whose elevated concentrations in the upper atmosphere the 2009 endangerment finding identified as the “air pollution” in question that are actually emitted by such vehicles and engines—CO 2 , N 2 O, methane, and HFCs—as well as the compliance provisions for the GHG standards. These proposed changes would apply to all MYs of vehicles and engines, including MYs that have completed manufacture prior to the effective date of any final rule.

Under the proposed revisions, manufacturers may in some cases already be changing their production processes to apply updated emission control information labels for vehicles and engines

gulatory scheme for parties currently subject to the standards. As explained in this section and elsewhere in this preamble, we are not proposing to reopen or substantively revise any emission standards for criteria pollutants or hazardous air pollutants or to reopen or substantively revise any regulatory provisions related to NHTSA's CAFE standards or the EPA's role in administering EPCA and EISA. Moreover, this proposed action would not impact Federal preemption for motor vehicle and engine emission standards under CAA section 209(a) or under EPCA and EISA, including with respect to GHGs.

In section VI.B of this preamble, we describe the light-duty (LD) and medium-duty (MD) vehicle program and the proposed changes to the GHG regulations for that program. In section VI.C of this preamble, we describe the heavy-duty (HD) engine and vehicle program and proposed regulatory changes. We request comment on all proposed changes described in this section, including on any additional regulatory provisions for engines and vehicles that should be removed as part of repealing the GHG standards or should be retained to effectuate unrelated standards that we are not proposing to repeal or revise. To aid in public participation, we have submitted a memorandum to the docket that includes redline text highlighting all proposed changes to the regulations. 114

114 Memorandum to Docket EPA-HQ-OAR-2025-0194, “Redline Version of EPA's Proposed Regulations for the Reconsideration of 2009 Endangerment Finding and Greenhouse Gas Vehicle Standards.” August 2025.

The EPA's engine and vehicle programs are codified in Title 40 of the CFR. Specifically, the standard-setting parts for light- and medium-duty vehicles are located in 40 CFR part 85 and 86. The standard-setting part for heavy-duty engines is located in 40 CFR part 1036 and the standard-setting part for heavy-duty vehicles is 40 CFR part 1037

carbon monoxide (CO)), air toxic emissions, or evaporative and refueling emissions. 115 We may consider those issues, as appropriate, in future rulemakings.

115 In this proposed rulemaking, NO X , HC, PM, and CO are sometimes described collectively as “criteria pollutants” because they are either criteria pollutants under the CAA or precursors to the criteria pollutants ozone (O 3 ) and PM.

A. Scope and Impacts of Proposed Repeal

The EPA is proposing to repeal all regulatory provisions relating to our GHG emission programs for light- and medium-duty vehicles and heavy-duty vehicles and engines on the bases set forth in sections III.A, III.B, and IV of this preamble. If finalized, any one of these alternative proposals would provide a sufficient basis for repealing our existing GHG regulations for new motor vehicles and new motor vehicle engines. Finalizing the proposed rescission of the Endangerment Finding as set out in section IV.A would provide sufficient basis for repeal because the EPA would lack statutory authority to regulate emissions based on global climate change concerns under CAA section 202(a). Finalizing the proposed rescission of the Endangerment Finding as set out in section IV.B would provide sufficient basis for repeal because the Administrator would conclude that the scientific evidence of endangerment and contribution is too uncertain to satisfy the standard for regulation under CAA section 202(a). And finalizing the proposed rationales set out in section V would provide sufficient basis for repeal, separately or in combination, because the EPA would conclude that our GHG emission standards do not further public health and welfare and cannot go into effect.

The repeal proposed in this NPRM is limited to the regulatory provisions for GHG emission standards found in 40 CFR parts 85, 86, 1036, and 1037, with minor conforming adjustments to unrelated emission standards for new motor vehicles and engines in 40 CFR parts 600 and 1039

ubdivision. 117 If finalized, this action would not reopen or revise any fuel economy standards or alter the EPA's statutory role in co-administering

any such standards, including NHTSA's CAFE standards.

116 49 U.S.C. 32919(a).

117 49 U.S.C. 32919(b)-(c).

The proposed repeal also would not impact Federal preemption of emission standards for new motor vehicle and engine emission standards. CAA section 209(a) provides that “[n]o State or any political subdivision thereof shall adopt or attempt to enforce any standard relating to the control of emissions from new motor vehicles or new motor vehicle engines subject to this part,” including “certification,” “inspection” or “approval” requirements “relating to the control of emissions from” such vehicles or engines. 118 Because new motor vehicles and engines currently subject to GHG emission standards would remain subject to Title II of the CAA, the statute would continue to preempt “any” State or local “standard relating to the control of emissions.” Relatedly, the CAA would continue to preempt Federal common-law claims for GHG emissions because “Congress delegated to EPA the decision whether and how to regulate” such emissions. Am. Elec. Power Co. v. Connecticut, 564 U.S. 410, 426 (2011). We would retain our authority to prescribe emission standards for any air pollutant that, in the Administrator's judgment, causes or contributes to air pollution that may reasonably be anticipated to endanger public health or welfare. The bases for repeal proposed in this action would not foreclose us from regulating CO 2 , methane, NO X , HFCs, PFCs, or SF 6 emissions from new motor vehicles or engines if the Administrator determines that one or more of those gases meet the requirements for regulation under CAA section 202(a), as discussed herein

ar the CO 2 standard. Section VI.A.2 of this preamble describes the proposed changes to the light-duty and medium-duty vehicle GHG regulations.

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

In 2010, the EPA relied on the Endangerment Finding to adopt the first GHG emission standards for passenger cars and light trucks for MYs 2012 through 2016 in a joint rulemaking with NHTSA. 119 In 2012, the EPA and NHTSA adopted another set of GHG standards (issued by EPA) and fuel economy standards (issued by NHTSA) for passenger cars and light trucks for MYs 2017 and later in a joint rulemaking. 120 In 2020, the EPA and NHTSA revised the standards that had previously been adopted and extended them for MYs 2021 through 2026. 121 In 2021, we further revised GHG standards for passenger cars and light trucks for MYs 2023 through 2026. 122 For medium-duty vehicles, we initially adopted GHG standards as part of the Phase 1 and Phase 2 heavy-duty GHG standards, as described in section VI.B.1 of this preamble. In 2024, we adopted new standards for passenger cars, light trucks, and medium-duty vehicles starting in MY 2027, effectively combining standards that had previously been maintained separately. 123

119 75 FR 25324 (May 7, 2010).

120 77 FR 62624 (Oct. 15, 2012).

121 85 FR 24174 (Apr. 30, 2020).

122 86 FR 74434 (Dec. 30, 2021).

123 89 FR 27842 (Apr. 18, 2024).

The EPA has also taken various actions to comply with statutory obligations under EPCA and EISA. Enacted in 1975, EPCA requires NHTSA to establish a regulatory program for motor vehicle fuel economy (now known as CAFE standards) and requires the EPA to establish measurement procedures, data collection procedures, and rules for calculating average fuel economy values in support of NHTSA's CAFE standards. In 2007, Congress amended EPCA by enacting EISA, which required continuing increases in the stringency of CAFE standards for passenger cars and light trucks through MY 2020

motorcycles. 40 CFR part 86 includes emission standards and certification provisions for both criteria pollutant and GHG emissions. 40 CFR part 600 includes measurement and reporting procedures related to fuel economy and GHG standards and to fuel economy labeling.

In the following subsections, we describe our proposed removal and amendment of specific portions of each of these regulatory parts. In general, the approach taken in this proposal is to remove the MY 2012 and later GHG emission standards for passenger cars and light trucks and the MY 2014 and later GHG emission standards for medium-duty vehicles. We also propose to remove the testing and reporting requirements associated with the GHG emission standards. In keeping with our obligations under EPCA, as noted in section VI.A.1 of this preamble, we are not proposing to remove the testing and reporting requirements related to CAFE standards for passenger cars and light trucks and are not reopening those requirements. We request comment on the proposed regulatory changes and whether additional changes should be considered.

a. 40 CFR Part 85—Compliance Provisions for Light- and Medium-Duty Vehicles

In general, we propose to amend 40 CFR part 85 to remove all references to GHG emission standards and related provisions while retaining provisions that support our criteria pollutant emission program. In this subsection, we describe several proposed amendments that are necessary to remove GHG-related provisions from 40 CFR part 85 while ensuring that criteria pollutant emission standards are not substantively impacted. Table 1 provides a summary of the proposed amendments to 40 CFR part 85.

Table 1—Summary of Proposed Changes to Light-Duty and Medium-Duty Highway Engine Regulations Under 40 CFR Part 85 40 CFR part 85 Sections proposed to amend Subpart F—Exemption of Clean Alternative Fuel Conversions From Tampering Prohibition 85.525. Subpart P—Importation of Motor Vehicles and Motor Vehicle Engines 85.1515. Subpart S—Recall Regulations 85.1803, 85.1805

mendments to 40 CFR part 85.

Table 1—Summary of Proposed Changes to Light-Duty and Medium-Duty Highway Engine Regulations Under 40 CFR Part 85 40 CFR part 85 Sections proposed to amend Subpart F—Exemption of Clean Alternative Fuel Conversions From Tampering Prohibition 85.525. Subpart P—Importation of Motor Vehicles and Motor Vehicle Engines 85.1515. Subpart S—Recall Regulations 85.1803, 85.1805. Subpart T—Emission Defect Reporting Requirements 85.1902. Subpart V—Warranty Regulations and Voluntary Aftermarket Part Certification Program 85.2103. The regulations at 40 CFR part 85, subpart F, provide an exemption from the general tampering prohibition for clean alternative fuel conversions. Specifically, the regulations describe how anyone modifying an in-use vehicle to run a different fuel can demonstrate that the fuel conversion maintains a level of emission control that qualifies them for an exemption from the tampering prohibition. This exemption generally allows for the modifying of vehicles already certified to emission standards in a way that does not cause the modified vehicle to exceed the emission standards that apply for the certified vehicle. The demonstration applies for both criteria and GHG emissions. We are proposing to revise 40 CFR 85.525 by removing the requirement to demonstrate compliance with GHG emissions. Program requirements related to criteria exhaust, evaporative, and refueling emissions and onboard diagnostics would remain unchanged.

The regulation at 40 CFR 85.1515 describes the standards that apply for Independent Commercial Importers in their practice of importing used vehicles. We are proposing only to remove text disallowing generation and use of GHG emission credits. We note further that the regulation requires Independent Commercial Importers to meet all the standards that apply under 40 CFR part 86. With the proposed changes described in this action, the removal of GHG standards from 40 CFR part 86, subpart S, would apply equally to imported vehicles

is provision to heavy-duty vehicles with a maximum value of 19,500 pounds GVWR. We believe this limitation is the best way to maintain a consistent approach for certifying affected vehicles.

125 81 FR 73478 (Oct. 25, 2016).

We are proposing to amend the definitions in 40 CFR 86.1803-01 by removing several defined terms that are used only in regulatory provisions that we are proposing to remove. This includes proposing to remove the definition of “configuration”; while this definition is no longer needed, we are proposing to retain the slightly different definition of “vehicle configuration,” since that definition is needed to support standards related to criteria pollutants. We are accordingly proposing to amend several references across 40 CFR part 86, subpart S, to change from a generic reference to “configuration” and replace it with the specific reference to “vehicle configuration.” We are also proposing to amend 40 CFR 86.1803-01 by adding a definition for “work factor” that is consistent with the definition that is embedded in 40 CFR 86.1819-14. We adopted the definition of “work factor” in 40 CFR 86.1819-14 primarily as a means of accounting for specific vehicle characteristics in establishing GHG emission standards for medium-duty vehicles. We are proposing to remove all of 40 CFR 86.1819-14 as described below. However, we are keeping the definition of work factor to support the definition of “medium-duty passenger vehicle,” which relies on the work factor concept to categorize vehicles for applying criteria pollutant emission standards.

We are proposing to amend 40 CFR 86.1803-01 and 86.1809-12 by removing references to the air conditioning efficiency test as part of the consideration for determining what is a defeat device. We are proposing to eliminate the air conditioning efficiency test from the EPA certification program because it was only used to generate GHG credits

ing provisions for MY 2010 and later light-duty vehicles and for MY 2014 and later medium-duty vehicles. We propose to discontinue the requirement to demonstrate compliance with these GHG standards and further propose that this discontinuation would apply as of the effective date of the final rule. Manufacturers need not amend existing certificates for ongoing production for the current model year. Manufacturers would in any case not need to submit credit reports at the end of the current model year to demonstrate compliance with the fleet average CO 2 standards.

We are proposing to amend test group specifications in 40 CFR 86.1823-08 by removing durability demonstration requirements related to GHG emission standards.

We are proposing to amend the provisions for establishing test groups in 40 CFR 86.1827-01 by removing the reference to CO 2 emission standards.

We are proposing to amend testing specifications in 40 CFR 86.1829-15 by removing references to GHG emission standards, except where needed to account for emission measurements related to fuel economy labeling. We are also proposing to change the nomenclature for the reference brake-specific CO 2 emission rate needed to perform calculations related to in-use testing for engines certified under 40 CFR 1036.635 for use in vehicles with high towing capacity.

We are proposing to amend the compliance provisions 40 CFR 86.1835-01, 86.1838-01, 86.1841-01, 86.1848-10, and 86.1854-12 by removing references to GHG emission standards.

We are proposing to amend carryover testing provisions in 40 CFR 86.1839-01 by removing references to accuracy requirements for battery monitoring for

electric vehicles and plug-in hybrid electric vehicles.

We are proposing to amend instructions for the application for certification in 40 CFR 86.1844-01 by removing references to refrigerant leakage rates and GHG emission standards

andards.

We are proposing to amend carryover testing provisions in 40 CFR 86.1839-01 by removing references to accuracy requirements for battery monitoring for

electric vehicles and plug-in hybrid electric vehicles.

We are proposing to amend instructions for the application for certification in 40 CFR 86.1844-01 by removing references to refrigerant leakage rates and GHG emission standards.

We are proposing to amend in-use testing requirements in 40 CFR 86.1845-04 and 86.1846-01 by removing references to testing GHG emissions and testing related to battery monitor accuracy and battery durability for electric vehicles and plug-in hybrid electric vehicles. We are also proposing to amend 40 CFR 86.1845-04 by changing the nomenclature for the reference brake-specific CO 2 emission rate needed to perform calculations related to in-use testing for engines certified under 40 CFR 1036.635 for use in vehicles with high towing capacity.

We are proposing to amend the credit provisions for criteria exhaust and evaporative emissions in 40 CFR 86.1861-17 by referencing the credit provisions in 40 CFR part 1036, subpart H, instead of 40 CFR part 1037, subpart H. We are proposing to remove the credit provisions in 40 CFR part 1037, subpart H, in this rule because they are needed only in relation to the GHG standards in 40 CFR part 1037, which we are proposing to remove in this rule. The referenced credit provisions in 40 CFR part 1037, subpart H, are equivalent to the analogous credit provisions in 40 CFR part 1036, subpart H. We are also proposing to amend 40 CFR 86.1861-17 by removing a reference to 40 CFR 86.1865(j)(3), which we are proposing to remove in this action.

We are proposing to remove 40 CFR 86.1865-12. This section describes the emission credit provisions related to the fleet average GHG standards. See the discussion related to 40 CFR 86.1818-12 and 86.1819-14 for the transition to discontinued GHG standards for the model year currently in production for the year when the final rule is effective

(3), which we are proposing to remove in this action.

We are proposing to remove 40 CFR 86.1865-12. This section describes the emission credit provisions related to the fleet average GHG standards. See the discussion related to 40 CFR 86.1818-12 and 86.1819-14 for the transition to discontinued GHG standards for the model year currently in production for the year when the final rule is effective. More specifically, we are proposing no longer to recognize manufacturers' positive or negative GHG credit balances as of the effective date of the final rule. Note also that we are proposing to remove 40 CFR 86.1865-12(j)(3), which describes recall provisions for vehicles that do not comply with GHG standards. We recognize that a credit-based approach to recall is no longer appropriate without a GHG credit program. Accordingly, we are proposing to remove the provisions describing a credit-based remedy for noncompliance that does not involve a vehicle defect that can be repaired to bring vehicles into compliance with standards.

We are proposing to remove 40 CFR 86.1866-12, 86.1867-12, and 86.1867-31. These sections describe GHG credit programs for advanced technology and air conditioning leakage that serve only in relation to the GHG standards that we are proposing to remove in this rule.

We are proposing to amend the credit provisions for air conditioning efficiency and for off-cycle technologies in 40 CFR 86.1868-12 and 86.1869-12 by removing references to the fleet average GHG standards and adjusting the description to clarify that these credit provisions continue to serve as inputs for calculating fuel consumption improvement values and average fuel economy for light-duty program vehicles under 40 CFR 600.510. The 2024 final rule included new standards for light-duty program vehicles and several changes related to these credit programs, and we are not reopening those decisions

s and adjusting the description to clarify that these credit provisions continue to serve as inputs for calculating fuel consumption improvement values and average fuel economy for light-duty program vehicles under 40 CFR 600.510. The 2024 final rule included new standards for light-duty program vehicles and several changes related to these credit programs, and we are not reopening those decisions. 126 First, we adopted a change for both air conditioning efficiency credits and off-cycle credits to not allow vehicles without engines to generate those credits starting in model year 2027. Second, we created a schedule to phase down off-cycle credits for vehicles with engines by establishing a declining value of the cap on off-cycle credits through model year 2032, with off-cycle credits fully discontinued for all vehicles starting in model year 2033. Third, we removed the option for manufacturers to generate off-cycle credits according to the provisions of 40 CFR 86.1869-12(c) and (d) starting in model year 2027.

126 89 FR 27842 (Apr. 18, 2024).

We are proposing to remove 40 CFR 86.1870-12. This section describes a GHG credit program for full-size pickup trucks with hybrid technology. Those GHG credits were also used for calculating fuel consumption improvement values and average fuel economy for light-duty program vehicles under 40 CFR 600.510. However, we amended those credit provisions in the 2021 final rule to establish model year 2024 as the last year that manufacturers could generate those credits. 127 Because those credits are already discontinued for purposes of demonstrating compliance with EPA emission standards, manufacturers can no longer use those provisions to create fuel consumption improvement values under 40 CFR part 600.

127 86 FR 74434 (Dec. 30, 2021).

c

ions in the 2021 final rule to establish model year 2024 as the last year that manufacturers could generate those credits. 127 Because those credits are already discontinued for purposes of demonstrating compliance with EPA emission standards, manufacturers can no longer use those provisions to create fuel consumption improvement values under 40 CFR part 600.

127 86 FR 74434 (Dec. 30, 2021).

c. 40 CFR Part 600—Requirements Related to Fuel Economy for Light- and Medium-Duty Vehicles

In general, we propose to amend 40 CFR part 600 to remove all references to GHG emission standards and related provisions while retaining provisions that support compliance with CAFE standards and fuel economy labeling for passenger cars and light trucks. In the remainder of this subsection, we describe several proposed amendments that are needed to remove GHG-related provisions from 40 CFR part 600 without affecting provisions related to CAFE standards and fuel economy labeling. Table 3 provides a summary of the regulations we propose either to remove or to amend in 40 CFR part 600.

Table 3—Summary of Proposed Changes to Light-Duty and Medium-Duty Highway Engine Regulations Under 40 CFR Part 600 40 CFR part 600 Sections proposed to remove Sections proposed to amend Subpart A—General Provisions 600.001, 600.002, 600.006, 600.007, 600.008, 600.010. Subpart B—Fuel Economy and Exhaust Emission Test Procedures 600.101, 600.111-08, 600.113-12, 600.114-12, 600.116-12, 600.117. Subpart C—Procedures for Calculating Fuel Economy and Carbon-related Exhaust Emission Values 600.206-12, 600.207-12, 600.210-12. Subpart F—Procedures for Determining Manufacturer's Average Fuel Economy 600.514-12 600.507-12, 600.509-12, 600.510-12, 600.512-12. We are proposing to amend the applicability statements in 40 CFR 600.001 by removing references to carbon-related exhaust emissions and fleet average CO 2 standards

g to amend several references across 40 CFR part 600 to change from a generic reference to “configuration” and replace it with the specific reference to “vehicle configuration.”

We are proposing to amend the information requirements in 40 CFR 600.006 through 600.010 by removing references to carbon-related exhaust emissions, GHG emission standards, and reporting GHG-related information generally.

We are proposing to amend the testing overview in 40 CFR 600.101 and 600.111-08 by removing references to carbon-related exhaust emissions and fleet average CO 2 emissions.

We are proposing to amend the emission calculations in 40 CFR 600.113-12 by removing references to carbon-related exhaust emissions and other GHG emissions.

We are proposing to amend the interim testing provisions in 40 CFR 600.117 by removing paragraph (a)(5) since we are proposing to discontinue GHG testing with in-use vehicles under 40 CFR 86.1845-04. We are also proposing to revise paragraphs (a)(6) and (b) to clarify that manufacturers do not adjust measured fuel economy values to account for fuel effects, whether they test with E0 or E10 gasoline.

We are proposing to amend the testing, calculation, and reporting specifications in 40 CFR 600.116-12, 600.507-12, 600.509-12, and 600.510-12 by removing references to carbon-related exhaust emissions. We note that calculations related to off-cycle credits in 40 CFR 600.510(c)(3)(ii) continue to rely on carbon-related exhaust emissions as specified in 40 CFR 86.1869-12.

We are proposing to amend the reporting requirements in 40 CFR 600.512-12 by removing references to carbon-related exhaust emissions. This includes amending 40 CFR 600.512-12(c)(5)(i) to explain that the purpose for performing the calculations in 40 CFR 600.510-12(c)(3) is to support credit calculations for fuel economy improvement factors, rather than demonstrating compliance with the fleet average standard for carbon-related exhaust emissions

ents in 40 CFR 600.512-12 by removing references to carbon-related exhaust emissions. This includes amending 40 CFR 600.512-12(c)(5)(i) to explain that the purpose for performing the calculations in 40 CFR 600.510-12(c)(3) is to support credit calculations for fuel economy improvement factors, rather than demonstrating compliance with the fleet average standard for carbon-related exhaust emissions. We are proposing to move the existing reporting requirement for emission credits related to fuel consumption improvement values from 40 CFR 86.1865-12(l)(2)(iii), which we are proposing to remove, to 40 CFR 600.512-12(c)(3) to preserve the existing provisions needed for fuel economy reporting. We are also proposing to remove the reporting requirements in 40 CFR 600.514-12, which are solely related to GHG emissions.

C. Heavy-Duty Engine and Vehicle GHG Program

This subpart includes background on EPA's heavy-duty GHG emission program and describes our proposed changes to the engine-based GHG regulations and our proposed changes to the vehicle-based GHG regulations.

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

The EPA promulgated new GHG emission standards for heavy-duty engines and vehicles in three separate rulemakings. In 2011, the EPA established the first GHG standards for model year 2014 and later heavy-duty engines and vehicles in an action titled “Greenhouse Gas Emissions and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles” (HD GHG Phase 1). 128 In 2016, the EPA set new GHG standards for model year 2021 and later heavy-duty engines and vehicles in an action titled “Greenhouse Gas Emissions and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles—Phase 2” (HD GHG Phase 2)

es in an action titled “Greenhouse Gas Emissions and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles” (HD GHG Phase 1). 128 In 2016, the EPA set new GHG standards for model year 2021 and later heavy-duty engines and vehicles in an action titled “Greenhouse Gas Emissions and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles—Phase 2” (HD GHG Phase 2). 129 Most recently, in 2024, the EPA finalized an action titled “Greenhouse Gas Emissions Standards for Heavy-Duty Vehicles—Phase 3” (HD GHG Phase 3), which set new CO 2 emission standards for model year 2032 and later heavy-duty vehicles that phase in starting as early MY 2027 for certain vehicle categories. 130 The phase-in revises MY 2027 GHG standards that were established previously under the EPA's HD GHG Phase 2 rulemaking. 131

128 76 FR 57106 (Sept. 15, 2011).

129 81 FR 73478 (Oct. 25, 2016).

130 See 89 FR 29559-29561 (Apr. 22, 2024).

131 89 FR 29440 (Apr. 22, 2024).

The EPA and NHTSA jointly issued the HD GHG Phase 1 and HD GHG Phase 2 rulemakings covering heavy-duty GHG emission and fuel efficiency standards. The EPA set GHG emission standards under CAA section 202(a), and NHTSA set fuel consumption standards under EISA. 132 The EPA and NHTSA programs are harmonized through MY 2026; however, NHTSA has not adopted changes in fuel consumption standards corresponding to the EPA's HD GHG Phase 3 standards. As a result, the CO 2 emission and fuel consumption standards currently diverge in MY 2027 and later.

132 49 U.S.C. 32902(k).

The EPA's regulations include the test procedures along with a certification and compliance program, which is led by the EPA. As noted previously, this regulatory structure was designed to maximize efficiency within the Federal government and minimize the burden on the engine and vehicle manufacturers by centralizing data submission

ral, the approach taken in this proposal is to remove the MY 2014 and later heavy-duty GHG emission standards promulgated in HD GHG Phase 1, Phase 2, and Phase 3, collectively, along with the testing and reporting requirements associated with the GHG emission standards. We request comment on the proposed regulatory changes and whether additional changes are necessary to remove GHG regulations.

a. 40 CFR Part 1036—Emission Standards and Compliance Provisions for Heavy-Duty Engines

40 CFR part 1036 contains regulations related to the final rule titled “Control of Emissions from New and In-Use Heavy-Duty Highway Engines,” including emission standards and compliance provisions for criteria pollutant emissions, evaporative and refueling emissions, and GHG exhaust emissions ( i.e., CO 2 , N 2 O, and methane). 40 CFR part 1036 is divided into nine subparts with three appendices. Subpart A defines the applicability of part 1036 and gives an overview of regulatory requirements. Subpart B describes the emission standards and other requirements that must be met to certify engines under this part. Subpart C describes how to apply for a certificate of conformity for heavy-duty engines. Subpart D addresses testing of production engines and hybrid powertrains. Subpart E addresses in-use testing, while Subpart F describes how to test engines to demonstrate compliance with the criteria pollutant and GHG emission standards. Subpart G describes requirements, prohibitions, and other provisions that apply to engine manufacturers, vehicle manufacturers, owners, operators, rebuilders, and all others. Subpart H describes how manufacturers can optionally generate, bank, trade, and use emission credits to certify heavy-duty engines. Subpart I includes definitions and other reference material. Appendix A includes a summary of previous emissions standards. Appendix B includes the transient duty cycles

ply to engine manufacturers, vehicle manufacturers, owners, operators, rebuilders, and all others. Subpart H describes how manufacturers can optionally generate, bank, trade, and use emission credits to certify heavy-duty engines. Subpart I includes definitions and other reference material. Appendix A includes a summary of previous emissions standards. Appendix B includes the transient duty cycles. Appendix C includes engine fuel maps used in the certification of specific vehicles to meet the heavy-duty vehicle CO 2 emission standards.

This subsection includes an overview of the regulations related to the heavy-duty engine program we propose to remove or revise. In general, we propose to amend 40 CFR part 1036 to remove all GHG emission standards, references to such standards, and related provisions; however, most of 40 CFR part 1036 is retained for EPA's heavy-duty engine criteria pollutant emission program. In this subsection, we describe the proposed amendments to remove GHG-related provisions from 40 CFR part 1036, which include some amendments needed to retain, without reopening, the efficacy of the criteria pollutant emission standards. Table 4 provides a summary of the regulations we propose either to remove or to amend in 40 CFR part 1036.

Table 4—Summary of Proposed Changes to Heavy-Duty Highway Engine Regulations Under 40 CFR Part 1036 40 CFR part 1036 Sections proposed to remove Sections proposed to amend Subpart A—Overview and Applicability 1036.1, 1036.5, 1036.15. Subpart B—Emission Standards and Related Requirements 1036.108 1036.101, 1036.115, 1036.130, 1036.135, 1036.150. Subpart C—Certifying Engine Families 1036.241 1036.205, 1036.225, 1036.230, 1036.231, a 1036.235, 1036.245. Subpart D—Testing Production Engines and Hybrid Powertrains 1036.301. Subpart E—In-Use Testing 1036.415. Subpart F—Test Procedures 1036.505, 1036.535, 1036.540, 1036.543, 1036.550 1036.501, 1036.510, 1036.512, 1036.514, 1036.520, 1036.530, 1036.545, 1036.580

15, 1036.130, 1036.135, 1036.150. Subpart C—Certifying Engine Families 1036.241 1036.205, 1036.225, 1036.230, 1036.231, a 1036.235, 1036.245. Subpart D—Testing Production Engines and Hybrid Powertrains 1036.301. Subpart E—In-Use Testing 1036.415. Subpart F—Test Procedures 1036.505, 1036.535, 1036.540, 1036.543, 1036.550 1036.501, 1036.510, 1036.512, 1036.514, 1036.520, 1036.530, 1036.545, 1036.580. Subpart G—Special Compliance Provisions 1036.610, 1036.615, 1036.620, 1036.625, 1036.630, 1036.635 1036.605. b Subpart H—Averaging, Banking, and Trading for Certification 1036.745, 1036.755 1036.701, 1036.705, 1036.710, 1036.720, 1036.725, 1036.730, 1036.740, 1036.750. Subpart I—Definitions and Other Reference Information 1036.801, 1036.805, 1036.810, 1036.815. Appendices Appendix C a We are proposing to move 40 CFR 1037.231 to a new 40 CFR 1036.231. b We are proposing similar revisions in 40 CFR 86.007-11(g) and 86.008-10(g) for model year 2026 and earlier engines for specialty vehicles. Within 40 CFR part 1036, subpart B, we propose to remove 40 CFR 1036.108, which includes the GHG emission standards for CO 2 , N 2 O, and methane. We also propose to remove several paragraphs from 40 CFR 1036.150 that describe interim provisions related to the heavy-duty engine or vehicle GHG programs. We propose to remove and reserve 40 CFR 1036.150(b), (d), (e), (g)-(j), (l)-(n), (p)-(s), and (w) and otherwise to retain the existing section numbering. We propose to remove 40 CFR 1036.150(aa) at the end of the section.

In 40 CFR part 1036, subpart C, we propose to remove 40 CFR 1036.230(f) and (g), which describe how manufacturers divide their product lines into engine families for certifying to the GHG emission standards. We propose several revisions in 40 CFR 1036.235 to remove GHG emission testing requirements. In 40 CFR 1036.235(a), we propose to migrate text from 40 CFR 1037.235(a) that provides direction on how manufacturers select the test powertrain to replace GHG-related testing requirements in 40 CFR 1036.235(a)(2)

ivide their product lines into engine families for certifying to the GHG emission standards. We propose several revisions in 40 CFR 1036.235 to remove GHG emission testing requirements. In 40 CFR 1036.235(a), we propose to migrate text from 40 CFR 1037.235(a) that provides direction on how manufacturers select the test powertrain to replace GHG-related testing requirements in 40 CFR 1036.235(a)(2). We propose to remove in its entirety 40 CFR 1036.241, which describes how to demonstrate compliance with the heavy-duty engine GHG emission standards. In 40 CFR 1036.245, existing provisions allow manufacturers to use vehicle-based duty cycles for engine service accumulation in the laboratory to determine deterioration factors. As described in section VI.C.2.b of this preamble, we are proposing to remove the referenced vehicle-based duty cycles from 40 CFR part 1037, so we are proposing to revise 40 CFR 1036.245(c)(3)(ii) to allow manufacturers to request approval of a

different test sequence, without requiring specific duty cycles.

Also in 40 CFR part 1036, subpart C, we propose to migrate the provisions that relate to powertrain families from the vehicle standard-setting part in 40 CFR 1037.231 to the engine standard-setting part as a new 40 CFR 1036.231 with proposed revisions described in this section. In a previous rule (89 FR 29616), we migrated the powertrain test procedure from the heavy-duty vehicle procedures (formerly 40 CFR 1037.550) to the heavy-duty engine procedures in 40 CFR 1036.545 because we expected powertrain testing to be primarily used by engine manufacturers in certifying engines to criteria pollutant standards or in place of engine-based procedures for GHG standards. Similarly, we are proposing to migrate the related provisions manufacturers would use to divide their product line into powertrain families. In general, we propose to migrate the text from the vehicle program in 40 CFR 1037.231 to a newly created section in the engine program under 40 CFR 1036.231

ing engines to criteria pollutant standards or in place of engine-based procedures for GHG standards. Similarly, we are proposing to migrate the related provisions manufacturers would use to divide their product line into powertrain families. In general, we propose to migrate the text from the vehicle program in 40 CFR 1037.231 to a newly created section in the engine program under 40 CFR 1036.231. We propose to modify the text previously under 40 CFR 1037.231(b)(1), such that the new 40 CFR 1036.231(b)(1) would no longer require powertrains to share the same engine families described in 40 CFR 1036.230 but would require the engine share the same design aspects specified in 40 CFR 1036.230. Since a manufacturer may choose to certify the whole powertrain to the standards in 40 CFR part 1036, there would only be a powertrain family, not a certified engine family that contains just the engine. Similarly, and consistent with our approach for defining engine families in 40 CFR 1036.230, we see no need to limit the powertrain family based on the vehicle service class the powertrain goes into and propose not to migrate the existing 40 CFR 1037.231(b)(2) that requires powertrain families to share vehicle service class groupings. We are also proposing not to migrate “energy capacity” as an example attribute in the proposed new 40 CFR 1036.231(b)(10), since it is not needed for the criteria pollutant standards. Similarly, we are proposing not to migrate existing 40 CFR 1037.231(b)(11) since rated output of hybrid mechanical power technology is also not needed for a criteria pollutant family definition.

In 40 CFR part 1036, subpart D, we propose to revise 40 CFR 1036.301 to remove paragraphs (a) through (d) describing how the EPA would conduct selective enforcement audits related to heavy-duty CO 2 engine emissions

e are proposing not to migrate existing 40 CFR 1037.231(b)(11) since rated output of hybrid mechanical power technology is also not needed for a criteria pollutant family definition.

In 40 CFR part 1036, subpart D, we propose to revise 40 CFR 1036.301 to remove paragraphs (a) through (d) describing how the EPA would conduct selective enforcement audits related to heavy-duty CO 2 engine emissions. We propose to revise the existing statement that selective enforcement audits apply for engines as specified in 40 CFR part 1068, subpart E, by adding that they apply for powertrains, consistent with 40 CFR 1036.301(c) which we are proposing to remove.

As previously noted, we are retaining and not reopening the in-use testing procedures in 40 CFR part 1036, subpart E, which apply for the criteria pollutant emission standards. More specifically, within the in-use test procedures, we are retaining references to measuring CO 2 for use in required chemical balance test procedures and to calculate the criteria pollutant emissions values for in-use testing. Also, in 40 CFR 1036.415(g), we continue to require that manufacturers override any adjustable idle-reduction features on vehicles used for in-use testing; however, we propose to revise the text to include a more general statement describing what it means to be adjustable.

In 40 CFR part 1036, subpart F

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