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On July 29, 2025, the Environmental Protection Agency (EPA) proposed rescinding its 2009 Greenhouse Gas Endangerment Finding (Endangerment Finding).1 Issued by EPA in response to the Supreme Court's 2007 holding in Massachusetts v. EPA (Massachusetts) affirming EPA's authority to regulate greenhouse gas (GHG) emissions under the Clean Air Act (CAA),2 the Endangerment Finding supported a wide variety of regulatory programs intended to reduce GHGs from automobiles, power plants, and oil and gas production.3 In light of this federal regulation, the Supreme Court determined in a 2011 landmark decision (AEP v. Connecticut) that the CAA and GHG regulatory programs adopted pursuant to it displaced federal public nuisance claims by plaintiffs seeking damages from and injunctive relief against large GHG emitters.4
EPA now proposes to rescind the Endangerment Finding, arguing that the Supreme Court's ruling in Massachusetts was incorrect and that the EPA in fact never had the authority under the CAA to regulate GHG emissions.5 When finalized later this year, EPA's rescission may undermine judicial rationales like the one in AEP v. Connecticut for dismissing federal or state common law claims, like public nuisance, as being displaced or pre-empted by federal regulatory policies. This in turn could embolden plaintiffs to continue to pursue claims seeking monetary damages and injunctive relief requiring emissions reductions from energy companies, manufacturers and other large GHG emitters.
As further background, Section 202(a) of the CAA directs the EPA administrator to prescribe emission standards for new motor vehicles and new motor vehicle engines for “air pollution which may reasonably be anticipated to endanger public health or welfare.”6 In Massachusetts, the Supreme Court held that EPA (1) has authority to regulate GHG emissions under Section 202(a) of the CAA and (2) must regulate GHG emissions if the EPA administrator concludes that GHG emissions endanger public health and welfare.7 In the Endangerment Finding, EPA concluded for the first time that GHG emissions cause or contribute to GHG pollution, contributing to climate change and endangering public health and welfare.8 In the following years, EPA enacted GHG emission control regulations for new motor vehicles and new motor vehicle engines. EPA also used the substance of the Endangerment Finding to support GHG emission standards for electric power plants and other energy sources.
Massachusetts and resulting GHG emissions limits promulgated by EPA marked a major shift in the legal landscape targeting GHG emissions. For years prior to Massachusetts, states, municipalities, private land trusts and others had brought nuisance claims in federal court against large emitters, seeking both significant damages to pay for the costs of adapting to climate shifts allegedly caused by such emissions and injunctions seeking to limit GHG emissions from these sources. In the 2011 case, AEP v. Connecticut, the Supreme Court concluded that EPA's authority to regulate GHG emissions under the CAA displaced federal common law claims, often brought under a theory of public nuisance, targeting carbon emissions from power plants.9 The Supreme Court did not address, and has not addressed, whether the CAA pre-empts state law claims targeting GHG emissions.10
With federal common law public nuisance claims displaced, plaintiffs have moved to bring state law nuisance claims and other types of claims, such as greenwashing and false advertising claims, in both state and federal courts. While the number of cases has increased, the Supreme Court is now considering whether to hear a case in which it would address the question of the CAA's pre-emptive effect on state nuisance law claims, potentially closing off those causes of action to plaintiffs.11 A Supreme Court decision that the CAA and related regulations pre-empt state law nuisance claims would further limit plaintiffs' options to use litigation as a mechanism for seeking to reduce GHG emissions.
Now, EPA seeks to rescind the Endangerment Finding and proposes to repeal all GHG regulations for new motor vehicles and new motor vehicle engines.12 EPA's primary justification for rescinding the Endangerment Finding and repealing GHG regulations is that such actions exceed EPA's authority under the CAA. EPA argues that the “text, structure, and history” of Section 202(a) suggest that GHGs are not air pollutants that endanger public health or welfare under the statute and there is no separate statutory basis to regulate GHG emissions based on climate change concerns.13 Rather, EPA argues, GHG emissions impact air quality “only indirectly.”14
EPA also relies on Supreme Court decisions issued since Massachusetts. First, EPA cites the 2022 decision in West Virginia v. EPA, which held that agency actions with major social, economic and political impacts cannot be performed in the absence of “clear congressional authorization.”15 According to EPA, there is a lack of clear statutory authority under Section 202(a) to regulate GHG emissions, supported by the fact that for decades before Massachusetts, EPA did not interpret the CAA to permit GHG regulations.16 EPA also bases its reasoning on the Supreme Court's 2024 decision in Loper Bright Enterprises v. Raimondo (Loper Bright), which instructed that the “best” reading of a statute must be used to determine the permissibility of agency actions.17 EPA now claims that under the “best” reading of CAA Section 202(a), it does not have authority to regulate GHG emissions.18
These arguments squarely reject EPA's authority under Massachusetts to regulate GHG emissions under CAA Section 202(a) and thus, plaintiffs may argue, undermine the Court's finding in AEP v. Connecticut that the CAA and GHG emissions regulations promulgated pursuant to it displace federal common law nuisance claims.
It is worth noting, however, that even if EPA rejects its authority to regulate GHGs under CAA Section 202(a), plaintiffs will still have significant hurdles to overcome in successfully pursuing federal public nuisance claims, as EPA claims its authority under the act will continue to displace federal common law claims targeting GHG emissions.19 To fully overturn AEP v. Connecticut and allow federal public nuisance claims to proceed against GHG emitters, the Supreme Court would need to not only reject its original rationale that such claims are displaced by the CAA but also determine that potential other alternative theories that could justify dismissal of such cases — including standing to bring claims, the political questions doctrine, the presumption against extraterritoriality, and a court's ability to provide viable remedies to address the harm — do not themselves warrant keeping public nuisance cases out of federal court. And even if these initial hurdles to bringing claims were cleared, plaintiffs would have significant additional hurdles to reaching favorable judgments, such as proving that defendants' GHG emissions (or more precisely, alleged emissions caused by wrongful conduct of defendants) caused harm to plaintiffs.
Furthermore, once finalized, the Endangerment Finding rescission will face its own formidable legal challenges. The Supreme Court's ruling in Loper Bright means that EPA will have to prove that its interpretation of the CAA in the Endangerment Finding rescission is the “best” reading of the statute, more difficult than showing it was entitled to the Chevron20deference Loper Bright eliminated.
Because nuisance claims can support requests for injunctions ordering emissions reductions along with requests for monetary relief (e.g., abatement funds) and can obtain these forms of potential remedial relief at a time when the federal government is itself rescinding GHG emissions reduction regulations, energy companies, manufacturers and other large emitters should anticipate the continued filing of lawsuits in state and federal courts under state and federal common law theories of liability, including public nuisance. And once the EPA's rule rescinding its prior Endangerment Finding is final, the contours of critical defenses to such claims based on pre-emption and displacement may shift and defendants will need to adjust such defenses and others to the implications of a new regulatory regime, including to an EPA that is now rescinding its own Endangerment Finding and prior GHG regulations.
Footnotes
1. Proposed Rule: Reconsideration of 2009 Endangerment Finding and Greenhouse Gas Vehicle Standards | US EPA.
2. 549 U.S. 497, 528-29 (2007) (citing 42 U.S.C. § 7602(g)).
3. 74 Fed. Reg. 66496, 66502 (2009).
4. Am. Elec. Power Co. v. Connecticut, 564 U.S. 410, 424-25 (2011).
5. 90 Fed. Reg. 36288, 36289 (proposed July 29, 2025).
6. 42 U.S.C. § 7521(a)(1).
7. Massachusetts, 549 U.S. at 528-29 (citing 42 U.S.C. § 7602(g)).
8. 74 Fed. Reg. 66496, 66499 (2009).
9. 564 U.S. 410, 424 (2011).
10. Id. at 429.
11. See Suncor Energy (U.S.A.) Inc., et al. v. County Commissioners of Boulder County, et al., No. 25-170.
12. 90 Fed. Reg. 36288, 36293 (proposed July 29, 2025).
13. Id. at 36299.
14. Id. at 36300.
15. West Virginia v. EPA, 597 U.S. 697, 723 (2022) (citation omitted).
16. 90 Fed. Reg. 36288, 36307 (proposed July 29, 2025).
17. 603 U.S. 369, 400 (2024).
18. 90 Fed. Reg. 36288, 36298 (proposed July 29, 2025).
19. Id. at 36315.
20. See Chevron U.S.A. Inc. v. Natural Resources Defense Council, Inc.,467 U.S. 837 (1984).
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