EPA’s Proposed Reversal of the Greenhouse Gas Endangerment Finding—How Politics Drives Legal Reinterpretation of the Clean Air Act

On August 20, 2025, Massachusetts Attorney General Andrea Campbell, among several other state attorneys general, testified in opposition to the Environmental Protection Agency’s (EPA) proposal to reverse its 2009 finding that greenhouse gas emissions pose a threat to public health and welfare. Reversal of the endangerment finding would enable EPA Administrator Zeldin to carry out the Trump Administration’s plan to deregulate greenhouse gas emissions from vehicles and other sectors of the economy.

Relying on the Supreme Court’s 2007 decision in Massachusetts v. EPA [1] that the EPA has the “authority under the Clean Air Act to regulate greenhouse gases that threaten public health and welfare,” AG Campbell claims such a reversal would be unlawful.[2] Massachusetts v. EPA involved the state’s appeal of EPA’s denial of a petition to regulate greenhouse gas emissions from motor vehicles under Section 202 of the Clean Air Act. That section requires the EPA to establish emissions standards for any air pollutant from motor vehicles which, in the Administrator’s judgment, “cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare.” [3] In 2003, the agency declined to make such a finding. Critically, the “EPA [did] not dispute the existence of a causal connection between man-made greenhouse gas emissions and global warming.”[4] Nevertheless, it denied the petition in part because it concluded that it lacked authority to regulate greenhouse gases, as they are not “air pollutants” within the meaning of the Clean Air Act. Alternatively, EPA concluded that even if it possessed the authority, it would decline to do so because the regulation would conflict with other administrative priorities.

The Court rejected EPA’s argument that it lacked legal authority to regulate greenhouse gases based on straightforward statutory interpretation. Nevertheless, the current EPA has again taken the position that it lacks such authority in support of its proposed reversal of the endangerment finding. Moreover, the Agency reiterates the argument, previously rejected by the Court, that the endangerment finding and regulation of greenhouse gases conflict with other administration priorities. The Court dismissed EPA’s prior policy-based argument as follows:

Under the clear terms of the Clean Air Act, EPA can avoid taking further action only if it determines that greenhouse gases do not contribute to climate change or if it provides some reasonable explanation as to why it cannot or will not exercise its discretion to determine whether they do. To the extent that this constrains agency discretion to pursue other priorities of the Administrator or the President, this is the congressional design.[5]

EPA’s proposal to reverse the endangerment finding relies on “underlying actions and intervening legal and scientific developments, including recent decisions by the U.S. Supreme Court and the scientific information summarized in [the Federal Register Notice to conclude that] the EPA no longer believes that we have the statutory authority and record basis required to maintain this novel and transformative regulatory program.”[6] In its Notice of Proposed Rulemaking, EPA criticized the endangerment finding as having “interpreted CAA Section 202(a) for the first time to authorize regulation of domestic emissions from new motor vehicles and engines based upon global climate change concerns rather than air pollution that endangers public health and welfare through local or regional exposure.”[7] The Agency also relies upon two more recent U.S. Supreme Court decisions applying the “major questions doctrine” to vacate two later attempts by EPA to regulate greenhouse gas emissions from stationary sources in reliance on the endangerment finding.[8]

While it is beyond the scope here to describe all the legal arguments and claims of scientific uncertainty advanced by EPA to support reversal of the endangerment finding and rescind the resultant greenhouse gas emission standards for vehicles, suffice it to say that the Agency has woven together a web of legal arguments based on recent conservative Supreme Court precedent, including Loper Bright and related cases, to challenge the legal foundation for the original endangerment finding. For example, it asserts that “the endangerment finding relied upon various forms of Chevron deference to depart from the best reading of the statute and exceeded EPA’s authority in several fundamental respects, any one of which would independently require rescission to conform to the best reading of the law.”[9]

This proposed action reflects the evolving changes in the power dynamics among the three coequal branches of the federal government. The invocation of the major questions doctrine challenges the ability of state governments and civil society to use the judicial process to shape national priorities when the federal government fails to act. Frustrated with the federal government’s inaction on climate change, private organizations and state governments sought judicial affirmation of the EPA’s authority (and resultant obligation) to regulate greenhouse gases. Empowered by that judicial declaration and unable to secure congressional legislation addressing climate change, the executive branch, under democratic administrations, advanced greenhouse gas emissions limitations on motor vehicles that promised to fundamentally change a major economic sector. Later Republican appointments of conservative Supreme Court justices shifted the Court’s composition, resulting in decisions such as Loper Bright, which significantly altered the balance of power between the executive and legislative branches. The Trump administration now cites this divestiture of executive power to eschew any responsibility for regulating greenhouse gases. The Agency emphasizes that it has an electoral mandate to change legal interpretations critical to national climate policy:

Importantly, the Nation’s policy response to global climate change concerns was a major issue in the 2024 presidential election, in which voters were presented with distinct legal and policy approaches and elected a candidate promising a change in policy. Under these circumstances, the election of a new Administration is an independent and sufficient basis for changing legal interpretation and policy within the boundaries set by statute.[10]

As discussed in a June 2025 blog post on Executive Order 14215[11], ultimately, it will be the Supreme Court that decides whether such significant politically motivated changes in statutory interpretations are lawful.

[1] 549 U.S. 497 (2007).
[2] AG Campbell Testifies Before EPA to Oppose Proposed Rescission of Landmark Finding that Greenhouse Gas Emissions Endanger Public Health and Welfare | Mass.gov
[3] 42 U.S.C. 7521 U.S.C. Title 42 – THE PUBLIC HEALTH AND WELFARE
[4] Massachusetts v. EPA, 549 U.S. at 523.
[5] Id. at 533.
[6] 90 F.R. 36288 at 36289 (August 1, 2025) Federal Register :: Reconsideration of 2009 Endangerment Finding and Greenhouse Gas Vehicle Standards
[7][7] Id.
[8] Citing Utility Air Regulatory Group v. EPA, 573 U.S. 302 (2014) and West Virginia v. EPA, 597 U.S. 697 (2022)
[9] 90 F.R. at 36299.
[10] Id. at 36297.
[11] Ensuring Accountability for All Agencies – The White House