In August 2025, the Environmental Protection Agency (EPA) proposed to rescind its longstanding finding that greenhouse gas emissions from motor vehicles cause or contribute to air pollution that endangers public health (Proposed Endangerment Rescission). EPA made its first endangerment finding concerning greenhouse gas emissions in 2009 (commonly known as the 2009 Endangerment Finding). The finding fulfills an obligation under Section 202(a)(1) of the Clean Air Act, which requires EPA to promulgate standards for emissions “of any air pollutant from any class or classes of new motor vehicles . . . which in [its] judgment cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare.”
EPA made the 2009 Endangerment Finding following the Supreme Court’s determination in Massachusetts v. EPA that greenhouse gases are air pollutants under Section 202, and accordingly EPA must regulate greenhouse gas emissions from new motor vehicles if the agency finds they contribute to air pollution that endangers public health or welfare. On this basis, EPA established standards for greenhouse gas emissions from light-duty vehicles in 2010 and for medium- and heavy-duty vehicles in 2011. EPA has revised and strengthened these emission standards several times over the last 15 years.
EPA now seeks to rescind the 2009 Endangerment Finding alongside all greenhouse gas emission standards for motor vehicles. Among the agency’s myriad arguments for repealing the finding, EPA claims that regulating greenhouse gas emissions under Section 202 violates the major questions doctrine. Under the doctrine, “clear congressional authorization” is required when the “history and the breadth of the authority that the agency has asserted, and the economic and political significance of that assertion, provide a reason to hesitate before concluding that Congress meant to confer such authority.”10 In practice, the Supreme Court applies the doctrine in “extraordinary” cases where the government’s action is unheralded, transforms the government actor’s role, and has great economic and political significance. According to EPA in the Proposed Endangerment Rescission, the major questions doctrine precludes EPA from using Section 202 to regulate pollutants which endanger human health or welfare through means other than “local or regional exposure”—such as greenhouse gases. In addition, EPA claims that the holding of Massachusetts must be interpreted “together” with more recent Supreme Court decisions applying the major questions doctrine and that regulating in response to climate change is the type of “major question[] of policy” to which the doctrine applies.
EPA’s invocation of the major questions doctrine demonstrates a broader effort by the Trump Administration to achieve its deregulatory goals by relying on overly broad readings of recent Supreme Court decisions—including West Virginia v. EPA, which announced the major questions doctrine. The Administration has already cited major questions concerns in its proposed repeals of greenhouse gas emission standards for power plants15 and the Public Lands Rule. Accordingly, understanding how the Supreme Court has articulated the major questions doctrine, and how EPA’s argument errs, is critical not only for understanding the legality of the 2009 Endangerment Finding, but for identifying how the Administration’s broader deregulatory attempts misapply the doctrine.
As this issue brief explains, EPA’s major questions argument in the Proposed Endangerment Rescission fails for several reasons. First, the major questions doctrine is not implicated because regulating greenhouse gas emissions under Section 202 is neither unheralded nor transformative, both of which are needed for the doctrine to apply. Second, even if the doctrine were triggered, the Clean Air Act supplies the clear authority the doctrine requires. Third, although the Supreme Court did not use the label “major questions doctrine” until its 2022 decision in West Virginia, its analysis in Massachusetts effectively rejected the argument that the major questions doctrine applies to EPA’s regulation of greenhouse gas emissions under Section 202. And fourth, regardless of the status of the major questions doctrine in 2007, Massachusetts’s holding that Section 202 permits EPA to regulate greenhouse gases is entitled to stare decisis.