Up In The Air: EPA Opens Comment On Repealing Endangerment Finding, Motor Vehicle GHG Rules

Highlights

• The U.S. Environmental Protection Agency (EPA) proposes to rescind the 2009 Endangerment Finding and repeal all greenhouse gas (GHG) emission standards for light-duty, medium-duty, and heavy-duty vehicles and engines established under Clean Air Act (CAA) Section 202(a) since 2010.
• EPA's primary rationale is that CAA Section 202(a) does not authorize the agency to regulate GHG emissions based on global climate change concerns, asserting that the CAA was designed to address air pollutants that contribute to dangerous air pollution "through local or regional exposures" rather than global atmospheric effects.
• EPA proposes several other rationales, including that the scientific evidence is too uncertain, Congress did not clearly authorize EPA to regulate motor vehicle emissions as a response to climate change, the statute forbids stand-alone endangerment findings separate from a regulatory response and there is no technology capable of having a measurable impact on climate-based harms.
• If finalized and upheld by courts, this would create a regulatory vacuum for mobile sources of GHGs and could undermine stationary-source GHG regulation as well, with significant implications for efforts to reduce domestic emissions.

The U.S. Environmental Protection Agency (EPA) on Aug. 1, 2025, published a proposal to repeal all greenhouse gas (GHG) emission standards for light-duty, medium-duty, and heavy-duty vehicles and engines from model year 2012 and beyond. As part of that effort, EPA proposed to rescind the 2009 Endangerment Finding, which provides the regulatory predicate for the agency to issue those regulations.

This proposal is among the most significant steps announced so far as part of EPA Administrator Lee Zeldin's deregulation agenda being undertaken to advance executive orders issued by President Donald Trump. (See Holland & Knight's previous alert, EPA Announces Deregulatory Initiative to "Power the Great American Comeback", March 17, 2025.)

On the same day that Zeldin announced the reconsideration, U.S. Department of Energy (DOE) Secretary Chris Wright released a report titled "A Critical Review of Impacts of Greenhouse Gas Emissions on the U.S. Climate," questioning the science behind GHG's contribution to climate change and capacity of U.S. policy decisions to shape the global climate trajectory. The DOE report is open for public comment for 30 days.

Background on the Endangerment Finding

The term "Endangerment Finding" is often used as a shorthand for a set of predicate findings the EPA administrator makes under the Clean Air Act (CAA), authorizing EPA to establish emission standards for new motor vehicles and engines. Specifically, CAA section 202(a)(1) requires EPA to regulate:

"...the emission of any air pollutant from any class or classes of new motor vehicles or new motor vehicle engines, which in his judgment cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare."

This statutory language became the cornerstone of EPA's regulatory approach to greenhouse gases, shaping nearly two decades of climate policy debate and litigation. Central to these efforts was the landmark U.S. Supreme Court case Massachusetts v. EPA, 549 U.S. 497 (2007), in which the Court held that the term "air pollutant" is broad enough to encompass GHGs. Massachusetts v. EPA arose in the context of a 1999 rulemaking petition to EPA requesting federal regulation of GHG emissions from new motor vehicles under the CAA. EPA denied the petition four years later on the basis that "the CAA notably does not authorize regulation to address global climate change," especially from cars and trucks and, in any event, regulation of motor vehicle GHG emissions would not be appropriate for international policy reasons. (68 Fed. Reg. 52922, 52925 (Sept. 8, 2003))

The Supreme Court rejected those rationales in Massachusetts v. EPA, marking a pivotal moment in federal climate regulation. The Court held that "greenhouse gases fit well within the Clean Air Act's capacious definition of 'air pollutant,'" which includes any physical or chemical substance that is "emitted into or otherwise enters the ambient air." On this point, the CAA was "unambiguous." Accordingly, EPA had statutory authority to regulate GHG emissions from new motor vehicles, provided the administrator makes a "judgment" under CAA Section 202(a)(1) that those emissions contribute to climate change. Notably, not a single justice who sided with the 5-4 majority in Massachusetts v. EPA remains on the court, while three of four justices who dissented remain.

Following the decision, the Bush Administration initiated the process of making an endangerment finding in response but did not move forward with a proposal.¹

The Obama Administration took up the issue and, in December 2009, EPA concluded that concentrations of six key "well-mixed" GHGs "endanger both the public health and the public welfare of current and future generations" via climate change and, furthermore, that the emissions of these GHGs from new motor vehicles "cause or contribute" to that dangerous air pollution. (See Holland & Knight's previous alert, "EPA Finds That Greenhouse Gases Endanger Public Health and Welfare," Dec. 14, 2009.) These GHGs are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulfur hexafluoride (SF6).

The Endangerment Finding withstood all legal challenges in Coalition for Responsible Regulation v. EPA, 684 F.3d 102 (D.C. Cir. 2012). The U.S. Court of Appeals for the District of Columbia Circuit affirmed EPA's scientific judgment as both "supported by substantial evidence" and not the product of "arbitrary or capricious decision-making" (Id. at 119-123). The court also rejected arguments that an endangerment finding under CAA Section 202(a)(1) should include policy judgments or cost-benefit analyses, rather than scientific judgments.

On Jan. 19, 2021, the last full day of the first Trump Administration, EPA Administrator Andrew Wheeler denied four petitions seeking reconsideration of the Endangerment Finding. In a three-sentence letter, Wheeler stated that the petitioners had provided insufficient information to justify revisiting the 2009 finding.

A few months later during the Biden Administration, EPA Administrator Michael Regan withdrew the Wheeler denials for lacking "an adequate justification for the denial," then issued a more detailed denials in April 2021.² Over 40 pages of point-by-point analysis, the Regan denials concluded that the petitions presented "inadequate, erroneous, and deficient arguments and evidence" and that none of the information provided undermined the "robust, voluminous, and compelling" scientific basis for the 2009 Endangerment Finding.

Rationale for Rescinding the Endangerment Finding

EPA now proposes to change course. On Aug. 1, 2025, the agency published a proposal to eliminate all GHG emission standards for light-duty, medium-duty, and heavy-duty vehicles and engines based on what it describes as the "best reading" of CAA Section 202(a). The proposal advances three main arguments:

1. CAA Section 202(a) does not provide EPA authority to set emission standards addressing global climate change and that accordingly, the 2009 Endangerment Finding should be rescinded.
2. Alternatively, the 2009 Endangerment Finding should be rescinded because it contained an unreasonable analysis of scientific evidence, with subsequent developments casting significant doubt on its reliability.
3. Even if the Endangerment Finding stays in place, all GHG emission standards should be repealed because no available vehicle emission control technology can meaningfully address global climate change concerns without potentially causing greater harm to public health and welfare.

EPA advances a number of more specific legal, scientific and policy arguments, including:

1. The CAA Section 202(a) reference to "air pollution" – not just "air pollutant" – is best read as extending only to harms caused by "local or regional exposure," not from climate change.
2. CAA Section 202(a) does not allow EPA to make separate findings for "endangerment" and "cause or contribute."
3. CAA Section 202(a) does not allow EPA to issue "standalone findings" at all, such as the 2009 Endangerment Finding, without simultaneously issuing vehicle standards.
4. Recent Supreme Court precedents have undermined prior agency and judicial applications of CAA section 202(a), including the elimination of Chevron deference in Loper Bright Enterprises v. Raimondo, 603 U.S. 369 (2024), and recent "major question doctrine" cases such as Utility Air Regulatory Group v. EPA, 573 U.S. 302 (2014), and West Virginia v. EPA, 597 U.S. 697 (2022).
5. The Massachusetts v. EPA decision did not require the EPA administrator to actually find that GHGs are subject to regulation under CAA Section 202(a) and "does not support our implementation of the statute since 2009."
6. New "empirical data, peer-reviewed studies, and real-world developments" have "cast significant doubt on many of the critical premises, assumptions, and conclusions" of the Endangerment Finding.
7. There is no "requisite technology" for new motor vehicles and engines that would be responsive to global climate change concerns because "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."
8. Public health and welfare are harmed by vehicle GHG standards because they increase the price of vehicles, decrease consumer choice in what vehicles to purchase and, thus, slow the replacement of older, more GHG-polluting and less-safe vehicles.

Motor Vehicle and Motor Vehicle Engine Standards Targeted for Repeal

As discussed above, the 2009 Endangerment Finding most directly led to multiple rounds of tailpipe GHG emission standards for light-duty, medium-duty, and heavy-duty vehicles and engines.³ Regardless of the rationales adopted, EPA's proposal would repeal several prior EPA actions, including numerous vehicle and engine standards:

1. EPA's previous denials of 2010 and 2022 petitions for reconsideration of the Endangerment Finding⁴
2. "Light-Duty Vehicle Greenhouse Gas Emission Standards and Corporate Average Fuel Economy Standards," 75 FR 25324 (May 7, 2010)
3. "Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles," 76 FR 57106 (Sept. 15, 2011)
4. "2017 and Later Model Year Light-Duty Vehicle Greenhouse Gas Emissions and Corporate Average Fuel Economy Standards," 77 FR 62624 (Oct. 15, 2012)
5. "Greenhouse Gas Emissions and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles-Phase 2," 81 FR 73478 (Oct. 25, 2016)
6. "The Safer Affordable Fuel-Efficient (SAFE) Vehicles Rule for Model Years 2021-2026 Passenger Cars and Light Trucks," 85 FR 24174 (April 30, 2020)
7. "Revised 2023 and Later Model Year Light-Duty Vehicle Greenhouse Gas Emissions Standards," 86 FR 74434 (Dec. 30, 2021)
8. "Multi-Pollutant Emissions Standards for Model Years 2027 and Later Light-Duty and Medium-Duty Vehicles," 89 FR 27842 (April 18, 2024)
9. "Greenhouse Gas Emissions Standards for Heavy-Duty Vehicles-Phase 3," 89 FR 29440 (April 22, 2024)

Implications for Other CAA Programs

Although the 2009 Endangerment Finding led most directly to GHG emission standards for new motor vehicles and engines, it also set off a cascade of broader regulatory activity under the CAA. As EPA's proposal notes, the agency applied the Endangerment Finding's analytical framework to a range of other areas, including stationary source permitting,⁵ emission standards for power plants and other stationary sources,⁶ aircraft,⁷ and oil and gas operations.⁸

For example, preconstruction permits for major stationary sources under the Prevention of Significant Deterioration (PSD) program must include the "best available control technology" (BACT) for "each pollutant subject to regulation under [the Clean Air Act]."⁹ The treatment of GHG emissions in PSD permits and in Title V operating permits reached the Supreme Court in Utility Air Regulatory Group v. EPA, 573 U.S. 302 (2014), with the Court clarifying the extent to which greenhouse gases could be regulated through these permitting regimes.

EPA's current proposal recognizes that EPA has "relied in part on the Endangerment Finding" for other EPA actions and states that where such rules are still on the books, the agency has "initiated or intend[s] to initiate separate rulemakings that will address any overlapping issues." Depending on the rationale EPA adopts in a final rule, the logic or legal ramifications of its action on the Endangerment Finding and vehicle emission standards could extend much more broadly.

For example, EPA has separately proposed repealing all GHG limits for coal- and gas-fired power plants under CAA Section 111, though based on reasoning largely distinct from the Endangerment Finding proposal. However, EPA specifically notes that the existing power sector GHG rules "relied on [the] conclusion in the 2009 Endangerment Finding" regarding the causes and impacts of GHG emissions.¹⁰ (For more information on the power sector proposal, see Holland & Knight's previous alert, "EPA Launches Comment Period on Power Plant Climate and Air Toxics Rules," June 20, 2025.)

Implications for California and Preemption

Earlier this year, Congress moved to rescind three Biden Administration waivers granted to California under the Congressional Review Act (CRA). This marked the most significant challenge to California's long-standing authority to set its own vehicle emission standards – an authority rooted in the Air Quality Act of 1967, which predates the modern CAA:

1. J.Res. 87 disapproved EPA's waiver for multiple California heavy-duty vehicle programs, including Advanced Clean Trucks (requiring increasing percentages of zero-emission truck sales), Zero Emission Airport Shuttles and Zero-Emission Power Train Certification.
2. J.Res. 88 disapproved EPA's waiver for Advanced Clean Cars II, which required all new passenger cars, trucks and SUVs sold in California to be zero-emission by 2035.
3. J.Res. 89 disapproved EPA's waiver for the "Omnibus" Low NOx regulation, which establishes more stringent emissions standards for heavy-duty vehicles.

Whether the waiver decisions constitute "rules" subject to CRA review remains a matter of legal debate. (For more information on these Resolutions, see Holland & Knight's previous alert, "Up in the Air: Congress Nullifies Clean Air Act Waivers for California," May 23, 2025.)

If the federal government were to dismantle the 2009 Endangerment Finding, it could have wide-ranging consequences and uncertainty in terms of state authority. For example, the State of California has previously asserted that if GHGs are not regulated under the CAA then it does not need to seek EPA approval to regulate GHG tailpipe emissions.

EPA's regulation of GHGs under the CAA has been used as a legal defense to state tort actions alleging damages from GHG emissions and as a defense to recent "climate superfund laws" seeking to hold similar compensation. (For more information on these matters, see Holland & Knight's previous alert, "An Update on Climate Superfund Laws and Climate Change Lawsuits," May 14, 2025.) Those legal defenses rely to varying degrees on the Supreme Court case, American Electric Power Co. v. Connecticut, 564 U.S. 410 (2011), which unanimously held that "the Clean Air Act and the EPA actions it authorizes displace any federal common law right to seek abatement of carbon-dioxide emissions from fossil-fuel fired power plants.

In short, because of these interconnected legal and regulatory dynamics, there would be significant near-term uncertainty depending on the rationale EPA relies on for a final rule.

Future Legal Challenges

Lawsuits are inevitable if EPA finalizes its proposal. The litigation timelines will hinge on EPA's speed in reviewing public comments and issuing a final action. Some of the rationales EPA has proposed would take longer to finalize than others. The Obama Administration took roughly nine months from proposal to finalization of the Endangerment Finding in 2009. In a fast-track scenario, if EPA undoes the Endangerment Finding in early 2026, followed by expedited D.C. Circuit briefing and a late 2026 decision by that court, the Supreme Court could potentially hear and decide an appeal by mid-2027. However, that would be a very accelerated course, and any delays in EPA's process or court proceedings could push this timeline substantially farther into the future.

What Comes Next

EPA's proposal, taken together with other policies and congressional actions, creates considerable uncertainty within the automotive sector and beyond. During what is expected to be years of litigation and regulatory uncertainty associated with federal climate policy, companies should remain engaged through monitoring of and participation in public comment and hearing opportunities and also monitor California's (and other states') responses to federal actions and other initiatives they take to continue to advance their climate objectives.

Public comments on the EPA proposal must be received by Sept. 15, 2025. A virtual public hearing will be held Aug. 19-20, 2025. Requests to speak may be directed to EPA-MobileSource-Hearings@epa.gov. It is advisable for those seeking to testify to pre-register by Aug. 12, 2025.

The proposed rescission of the Endangerment Finding represents a fundamental shift in federal climate policy, with potentially far-reaching implications for automotive manufacturers, suppliers and many other industries. Holland & Knight has extensive experience navigating complex regulatory transitions and can assist clients in developing effective strategies to protect their interests during this period of regulatory uncertainty.

Footnotes

1 EPA's Endangerment Finding: "On December 5, 2007, EPA sent a draft proposal to the White House Office of Management and Budget, finding that concentrations of six key greenhouse gases in the atmosphere endanger the public welfare and that emissions from new motor vehicles contribute to this problem. After the Bush Administration refused to consider the proposal, EPA later withdrew the rulemaking." (Dec. 7, 2009).

2 87 Fed. Reg. 25412 (Apr. 29, 2022).

3 See, e.g., 40 C.F.R. § 86.1818-12.

4 Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Section 202(a) of the Clean Air Act; "Final Action on Petitions," 87 Fed. Reg. 25412 (April 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 Fed. Reg. 49556 (Aug. 13, 2010).

5 See, generally, Utility Air Regulatory Group v. EPA, 573 U.S. 302 (2014).

6 See West Virginia v. EPA, 597 US 697 (2022) (discussing the Clean Power Plan and Affordable Clean Energy Rule).

7 81 Fed. Reg. 54,422 (Aug. 15, 2016).

8 See 40 C.F.R. Part 60, Subparts OOOO, OOOOa, OOOOb and OOOOc.

9 42 U.S.C. § 7475(a)(4).

10 90 Fed. Reg. 25752, 25767 (June 17, 2025).

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