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Over the course of the last 15 years, the U.S. Environmental Protection Agency (EPA) developed a suite of regulations under the Clean Air Act (CAA) built upon EPA's finding – originally made in 2009 – that greenhouse gas (GHG) emissions in the atmosphere endanger public health and welfare. At President Trump's direction, EPA initiated a process in March 2025 for "formal reconsideration of the 2009 Endangerment Finding in collaboration with the Office of Management and Budget (OMB) and other relevant agencies." As part of this review, EPA stated that it "also intends to reconsider all of its prior regulations and actions that rely on the Endangerment Finding." On July 29th, EPA released a 302-page proposed rule for reconsideration of the 2009 Endangerment Finding, which was published in the Federal Register, at 90 Fed. Reg. 36,288, on August 1st. The proposal broadly reevaluated EPA's authority to regulate GHG emissions while also opening the door to reconsideration of EPA's prior scientific assessment of climate change risks, among other things. EPA received over 570,000 comments.
On February 12, 2026, EPA announced that it was finalizing rescission of the 2009 Endangerment Finding and also repealing all subsequent federal GHG emissions standards for all vehicles and engines (for model year 2012 onward) promulgated pursuant to the Endangerment Finding. A day later, EPA released the text of the 436-page pre-publication version of the final rule (Rescission Rule).
- The Rescission Rule rests, first and foremost, on a legal rationale for repeal based on the text of the CAA and subsequent legal developments and court rulings that have occurred since 2009. EPA takes the view that the 2009 Endangerment Finding rested on a "profound misreading" of the Supreme Court's decision in Massachusetts v. EPA, and that, fundamentally, the question of whether federal law extends to GHG emissions from motor vehicles is something that Congress must, in the first instance, resolve.
- Though EPA does not rely on any "new findings" related to climate change, the Rescission Rule includes a rationale for repeal based on the lack of "any material impact" that the GHG tailpipe emission standards could have on "global climate change concerns." In other words, EPA takes the view that regulations in this context are "futile." EPA further discusses several other possible "bases" for the Rescission Rule – such as a "Climate Science Alternative Basis" - but EPA is careful not to premise the Rescission Rule on those concerns.
- While the Rescission Rule repeals the GHG tailpipe standards, EPA has deferred – at least for now – action on other regulatory rollbacks of power plant GHG standards and the GHG Reporting Program. EPA expressly states that this rule does not impact criteria pollutant standards, air toxics programs, Corporate Average Fuel Economy ("CAFE") Standards, and fuel economy labeling requirements.
To help shed light on what this controversial new action means for industry, our team of experienced environmental attorneys prepared a list of nine questions regarding rescission of the 2009 Endangerment Finding, with updated information reflecting EPA's final Rescission Rule. A new bonus question and answer addresses what's to come next.
Q: When does the Clean Air Act require EPA to make "endangerment" findings?
A: Several provisions of the CAA require EPA to make a finding that a source category contributes or significantly contributes to air pollution "which may reasonably be anticipated to endanger public health or welfare" prior to regulating emissions from that source category. Section 202(a) requires EPA to regulate air pollutants from new motor vehicles if the Agency finds that they "cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare." Similarly, Section 111(b) requires EPA to establish new source performance standards for stationary source categories that "cause[], or contribute[] significantly to, air pollution which may reasonably be anticipated to endanger public health or welfare." EPA must make an endangerment finding pursuant to these provisions before EPA can adopt pollutant-specific standards for these sources.
Q: What did the U.S. Supreme Court decide in Massachusetts v. EPA?
In 2007, the Supreme Court addressed EPA's failure to make an endangerment finding decision for GHGs emissions pursuant to Section 202(a) in response to a petition filed by Massachusetts and other states. See Massachusetts v. EPA, 549 U.S. 497 (2007). EPA argued that it did not have the power to regulate GHGs under the CAA because they do not meet the CAA's definition of air pollutant. In response, the Court held that the CAA's definition of "air pollutant" in Section 302(g) unambiguously permits EPA to regulate GHGs, emphasizing that the CAA's broad language confers flexibility for EPA to address harms that Congress may not have specifically anticipated when it enacted the provision, and further found that EPA could not defer making an endangerment finding based on potential uncertainties in scientific evidence related to climate change and its effects. Notably, as emphasized in EPA's Rescission Rule, the majority opinion in Massachusetts v. EPA acknowledged that the Court "need not and [did] not reach the question whether ... EPA must make an endangerment finding, or whether policy concerns can inform EPA's actions in the event that it makes such a finding." 549 U.S. at 534-35.
However, Chief Justice Roberts along with Justices Thomas, Scalia, and Alito, vigorously dissented in Massachusetts v. EPA, calling into question the petitioners' standing to challenge EPA's failure to act on climate change-related issues. These justices also argued that EPA could reasonably find that the CAA excludes GHGs from regulation as air pollutants or that scientific uncertainty prevented the Agency from making an endangerment finding. The Trump Administration spotlighted these dissents in its Rescission Rule.
Q: What is the 2009 Endangerment Finding?
A: In December 2009, following the Massachusetts v. EPA decision, EPA published a final rule finding that the mix of six directly-emitted, long-lived GHGs in the atmosphere—carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride—threaten public health and welfare. This 2009 finding was made pursuant to the motor vehicle emissions provision found at CAA Section 202(a). EPA pointed to current observations and projected risks of climate-related impacts associated with these emissions, including changes in air quality, increases in temperatures, changes in extreme weather events, and increases in food- and water-borne pathogens. While EPA acknowledged that new motor vehicles do not emit all six of these GHGs, the Agency took the position that an endangerment finding requires only that air pollution associated with any well-mixed GHGs be reasonably anticipated to endanger public health and welfare, and that a domestic source category—in this case, new motor vehicles—causes or contributes to this air pollution.
Q: Has EPA issued other climate-specific endangerment findings since 2009?
A: EPA has made at least three additional endangerment findings for well-mixed GHGs since 2009:
- In October 2015, EPA made an endangerment finding pursuant to Section 111(b) for new, modified, and reconstructed electric utility generating units. In that rulemaking, EPA took the position that Section 111(b) does not require a pollutant-specific endangerment finding, but rather allows EPA to regulate all pollutants emitted by a listed source category. EPA nevertheless made a pollutant-specific finding for well-mixed GHGs, referring to the 2009 Endangerment Finding and scientific developments since. In making that finding, EPA emphasized that "fossil fuel-fired [units] are by far the largest emitters of GHGs among stationary sources in the U.S., primarily in the form of CO2."
- In June 2016, EPA made an endangerment finding for GHGs (in particular, methane), volatile organic compounds, and sulfur dioxide, pursuant to Section 111(b) for new, modified, and reconstructed facilities in the oil and gas sector. EPA cited to the 2009 Endangerment Finding and more recent scientific developments for public health and welfare impacts associated with GHG emissions, while also pointing to non-climate related impacts from methane emissions as a precursor to ground-level ozone formation.
- In August 2016, EPA made an endangerment finding pursuant to Section 231(a)(2)(A) for certain classes of aircraft engines. EPA placed "considerable weight" on the 2009 Endangerment Finding and concluded that more recent scientific assessments "strengthen and further support the judgment that GHGs in the atmosphere may reasonably be anticipated to endanger the public health and welfare of current and future generations."
In the Rescission Rule, EPA repudiates the legal interpretation of "air pollution" that served as the foundation for the 2015 and 2016 findings, but stops short of also rescinding those findings. Instead, EPA acknowledges that each of these findings from 2015 and 2016 were predicated on the 2009 finding, and notes that EPA would address those actions as appropriate in separate rulemakings.
Q: How did the Trump Administration address this issue in its first term?
A: During the first Trump Administration, EPA did not reconsider or alter the 2009 Endangerment Finding. Notably, in January 2021 during the final weeks of the first Trump Administration, EPA relied on the 2009 Endangerment Finding to finalize a "Significant Contribution Finding" (SCF) pursuant to Section 111(b) for new, modified, and reconstructed electric utility generating units, which applied a threshold of 3% of total U.S. GHG emissions to assess significance, while also considering secondary factors such as emission trends and relative contribution of domestic sources. However, the D.C. Circuit vacated and remanded this rule in accordance with a request by the Biden Administration. See California v. EPA, No. 21-1035 (D.C. Cir. Apr. 5, 2021).
Q: What did EPA propose in 2025?
A: On January 20, 2025, President Trump signed Executive Order 14154, "Unleashing American Energy," which directed agencies to review agency actions that may "impose an undue burden" on domestic energy resources. In particular, President Trump directed EPA to make a recommendation to the OMB Director within 30 days regarding the legality and continuing applicability of the 2009 Endangerment Finding.
On March 12, 2025, Administrator Zeldin announced that the Agency will reconsider the 2009 Endangerment Finding, as well as "regulations and actions that rely on that Finding." On June 17th, EPA subsequently proposed to repeal the 2024 GHG performance standards for the electric utility sector, based in part on the Agency's finding that the causal connection between GHG emissions from domestic fossil fuel-fired EGUs and dangerous air pollution is too attenuated to constitute a significant contribution within the meaning of Section 111(b).
EPA proposed to rescind the 2009 Endangerment Finding based on the Agency's interpretation that EPA lacks authority to "prescribe emission standards to address global climate change concerns," or, in the alternative, that the 2009 Endangerment Finding was not based on reliable evidence. As part of this action, EPA proposed to repeal all GHG emissions standards for light-, medium- and heavy-duty vehicles and heavy-duty engines, which would impact model years 2012 and later.
Q: Did the Inflation Reduction Act address the 2009 Endangerment Finding?
A: The Inflation Reduction Act (IRA), which was enacted in 2021, added several new sections of the Clean Air Act defining GHGs as "air pollutants." These definitions are section-specific, and it will be debated whether the IRA definition is controlling for purposes of Section 202(a) or Section 111(b). The Supreme Court has held that "air pollutant" may have different meanings in different sections of the CAA. See Utility Air Regulatory Group v. EPA, 573 U.S. 302, 320 (2014). In the Rescission Rule, EPA points to the IRA as evidence that, "[w]hen addressing GHGs and global climate change concerns more generally, Congress has used non-regulatory tools that incentivize, rather than mandate, changes in manufacturing and consumer choice," such as through the IRA's funding mechanisms.
Q: What are some of the other potential implications of repeal of the 2009 finding?
A: Some commentators have suggested, though others disagree, that withdrawing the 2009 Endangerment Finding in its entirety might result in greater GHG regulation at the state level, due in part to the potential impact on arguments that federal law currently displaces state law on GHG emissions. Some also observe that regulation of GHG emissions under the CAA has supported one line of preemption defenses to state-based GHG regulations, as well as a host of climate tort suits based in state common law brought against fossil fuel producers, utilities, and power plants. Several state courts have dismissed the tort suits, citing to preemption or displacement arguments.
In the Rescission Rule, EPA explains why this final action "does not impact [f]ederal preemption for motor vehicle and engine emission standards ... or under EPCA and EISA, including with respect to GHGs." This was a significant concern for many commenters, who had urged EPA to articulate a clear basis for continued federal preemption of state laws (including state common law causes of action). EPA's view is that "regardless" of whether EPA actually "prescribe[s] standards for GHG emissions from new motor vehicles or engines," federal preemption under CAA section 209(a) "continues to apply by its own force." EPA also explains that "the CAA continues to preempt [f]ederal common-law claims for vehicle and engine emissions because Congress adopted a standard for when such emissions rise to the level of regulatory concern" and that Congress has given EPA the authority to decide "whether and how to regulate" these emissions. Going a step further, EPA also explains that the CAA "continues to preempt state common-law claims and statutes that seek to regulate out-of-state emissions, independently of CAA section 209(a)[]..."
Various sectors could encounter greater short-term uncertainty as to GHG emission standards. For example, EPA is still reconsidering the 2024 Power Plant GHG Rules, but it remains unclear whether EPA will ultimately issue a replacement Power Plant Rule or withdraw all GHG-related requirements for the source category—or pursue both outcomes through different actions. On the other hand, EPA has regulated methane emissions from the oil and gas sector based on non-climate related impacts as well as climate impacts. Thus, even in the absence of the 2009 Finding, EPA might continue to assert authority to regulate methane emissions from the refining sector separate and apart from the 2009 Endangerment Finding.
As to mobile sources (vehicles), under Section 209(a) of the CAA, states are prohibited from "adopt[ing] or attempt[ing] to enforce any standard relating to the control of emissions from new motor vehicles or new motor vehicle engines subject to this part . . ." California, however, has specific authority under Section 209(b) to obtain a waiver of this preemption under certain circumstances. (There is corollary language in Section 209(e) applicable to nonroad engines and nonroad vehicles). The Rescission Rule states that Section 209(a) "continues to apply by its own force to preempt State laws, regulations, and causes of action that adopt or attempt to enforce any standard relating to the control of emissions from new motor vehicles or engines." The Rescission Rule also highlights that, in June 2025, the President signed three Congressional Review Act resolutions (H.J. Res. 87, 88, and 89) to rescind three 209(b) waivers previously granted to California that had allowed the state to enforce their own zero-emission vehicle mandates. Those CRA resolutions are subject to ongoing litigation.
Q: What are some of the issues that EPA's Rescission Rule revisits as part of the 2009 Endangerment Finding rescission?
A: EPA's proposed reconsideration raised several key issues and questions. EPA addressed each of these in the Rescission Rule as follows:
- Regulation of Air Pollutants: The 2009 Endangerment Finding defined "air pollutant" as the mix of six directly-emitted, long-lived, and well-mixed GHGs and based EPA's authority to regulate GHGs on indirect, climate-related public health and welfare impacts. EPA's proposed rule took a narrower view of EPA's authority to set emissions standards, focusing on air pollution that directly harms public health or welfare through local or regional exposure. In the Rescission Rule, EPA builds on the reasoning in its proposal, emphasizing that the definition of "air pollution" in CAA Section 202(a) "must be construed in context with the specific air pollutants and air pollution concerns" identified in that provision, which does not include air pollutants that "may endanger public health or welfare only on a global scale and through an attenuated and indirect causal chain." EPA further explains that "Congress knows how to provide for the consideration of and regulation in response to international emissions," but did not do so in Section 202(a).
- Level of Contribution: The 2009 Endangerment Finding evaluated climate-related impacts in the United States associated with worldwide emissions of GHGs. EPA's Rescission Rule takes a more particularized approach, focusing on the contribution and resulting impacts from new motor vehicles alone. In accordance with this approach, EPA finds that these impacts are too uncertain and attenuated to support a finding of contribution. EPA explains: "Put another way, the inability of new motor vehicle and engine GHG emission standards to have any material impact on the global climate change concerns relied upon by the Agency in the 2009 Endangerment Finding suggests that it is unreasonable to conclude that GHG emissions from [such sources] cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare."
- Supreme Court Precedent: Consistent with the proposal, EPA's Rescission Rule argues that regulation of GHG emissions implicates the major questions doctrine as articulated in West Virginia v. EPA and therefore requires clear congressional authorization. According to EPA, this narrower interpretation of the Agency's authority to regulate GHGs within the context of Section 202(a) is consistent with Massachusetts v. EPA, since the Court did not hold that GHGs must be air pollutants for all purposes under the Clean Air Act. Indeed, EPA explains that its updated interpretation corrects a longstanding misreading of Massachusetts v. EPA and better accounts for the Supreme Court's decision in Utility Air Regulatory Group v. EPA, 573 U.S. 302 (2014), which "distinguished between 'the Act-wide definition' of air pollutant and the application of that definition to the Act's regulatory provisions." According to EPA, a "limiting construction" of the definition of air pollutant is necessary "to avoid absurd results and potential conflict with the nondelegation doctrine."
- Scientific Evidence: As an alternative basis for its proposal, EPA's proposed reconsideration rule pointed to "significant uncertainties" in projected climate-related impacts underlying the 2009 Endangerment Finding, noting that these projections now appear "unduly pessimistic" based on observed trends. EPA's proposal further suggested that the 2009 Endangerment Finding did not appropriately account for potential benefits associated with climate change. As noted above, the Rescission Rule does not rely on any "new findings" related to climate change, though EPA does identify and discuss other possible "climate science" grounds for the Rescission Rule. However, EPA is careful not to premise the Rescission Rule on those reasons.
Bonus Question: What comes next?
EPA's repeal of its longstanding 2009 Endangerment Finding is likely to draw significant responses from states and environmental groups. State governors and environmental groups have already announced their intent to pursue judicial review of the Rescission Rule, citing to the Supreme Court's decision in Massachusetts v. EPA. These litigants may seek an immediate stay of the Rescission Rule and rescission of related motor vehicle emissions standards, with the primary venue likely being in the D.C. Circuit.
In the interim, states with strong climate policies also could be motivated by the rescission to establish or strengthen their own GHG emission standards and other GHG-related requirements. Environmental groups and state or local governments may also be motivated to bring additional state-level climate litigation against larger sources of GHG emissions based on the uncertain preemptive effect of the CAA in the absence of the 2009 Endangerment Finding or related regulations. In addition, State and local entities may also enact their own climate-focused requirements in an attempt to fill any perceived regulatory gaps as a result of rescission. Such an approach could result in a patchwork of competing and conflicting state and local rules.
Many commentators also expect the Rescission Rule to have broader policy and regulatory impacts beyond the scope of mobile sources, and could affect other, pending, or existing regulations on methane, oil and gas, and power plants, potentially increasing compliance and transactional uncertainty across a wide range of sectors.
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