Endangerment and Cause or Contribute Findings under the Clean Air Act
GHG Emissions from Motor Vehicles
Before regulating a new pollutant under certain Clean Air Act programs, EPA must make a finding that the pollutant endangers public health or welfare, and that emissions targeted by the regulations cause or contribute to such pollution. In Massachusetts v. EPA, 549 U.S. 497 (2007), the Supreme Court concluded that greenhouse gases (GHGs) are air pollutants under the Clean Air Act, and that EPA must determine under section 202(a) of the Clean Air Act whether or not GHG emissions from new motor vehicles cause or contribute to air pollution that would endanger public health or welfare.
On July 2029, 2025, EPA announced its intent to rescind its 2009 Endangerment Finding on greenhouse gases. The Endangerment Finding is the legal prerequisite used by the Obama and Biden Administrations to regulate emissions from new motor vehicles and new motor vehicle engines. More broadly, absent this finding, EPA would lack statutory authority under Section 202(a) of the Clean Air Act (CAA) to prescribe standards for greenhouse gas emissions. (See Environmental Defense Fund v. Wright in Litigation below.)
Second Trump Administration (2021-2025)
On July 2029, 2025, EPA announced its intent to rescind its 2009 Endangerment Finding on greenhouse gases. The Endangerment Finding is the legal prerequisite used by the Obama and Biden Administrations to regulate emissions from new motor vehicles and new motor vehicle engines. More broadly, absent this finding, EPA would lack statutory authority under Section 202(a) of the Clean Air Act (CAA) to prescribe standards for greenhouse gas emissions. (See Environmental Defense Fund v. Wright in Litigation below.)
Biden Administration (2021-2024)
In April 2022, EPA denied four petitions for reconsideration of the 2009 endangerment finding and cause and contribute finding for GHG emissions from new motor vehicles. 87 Fed. Reg. 25,412 (Apr. 29, 2022).
First Trump Administration (2017-2020)
N/A
Obama Administration (2009-2016)
On December 7, 2009, EPA promulgated an “endangerment finding” for six GHGs, finding them to threaten public health and welfare: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). 74 Fed. Reg. 66,496 (Dec. 15, 2009). At the same time, EPA promulgated a “cause or contribute finding” for new motor vehicles, concluding that vehicular emissions of greenhouse gases contribute to the endangerment created by greenhouse gas pollution.
EPA used the December 2009 endangerment and contribution findings as a basis for subsequent motor vehicle emission standards. EPA also extensively referenced the endangerment finding in proposing and finalizing subsequent emission standards for new and existing power plants and the oil and gas sector.
- Final Rule, 74 Fed. Reg. 66,496 (Dec. 15, 2009)
- Proposed Rule, 74 Fed. Reg. 18,886 (Apr. 24, 2009)
- Supporting Documents
Litigation
Environmental Defense Fund v. Wright
On August 12, 2025, non-profit organizations filed a complaint against EPA, DOE, and the Climate Working Group for unlawfully relying on a report created by the Climate Working Group to justify rescinding the Endangerment Finding.
Utility Air Regulatory Group v. EPA
Twenty-seven cases challenging the Endangerment Finding were consolidated in Utility Air Regulatory Group v. Environmental Protection Agency (D.C. Cir. 2012). In June 2012 the Court of Appeals for the DC Circuit Court upheld the Endangerment Finding, in addition to the Tailpipe Rule (discussed below), holding that EPA’s interpretation of the governing Clean Air Act provisions is unambiguously correct.