Endangerment and Cause or Contribute Findings under the Clean Air Act

GHG Emissions from Electric Generating Units (EGUs)

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.

Second Trump Administration (2021-2025)

On June 11, 2025, EPA proposed to repeal the 2015 emissions standards for new fossil fuel-fired power plants issued during the Obama Administration, and the 2024 rule for new and existing fossil fuel-fired power plants issued during the Biden Administration. EPA asserted that the Clean Air Act requires the agency to make a finding that the targeted emissions from fossil fuel-fired power plants “significantly contribute” to dangerous air pollution before regulating these emissions from this source category. In addition, EPA claimed that greenhouse gas emissions from fossil fuel-fired power plants do not contribute significantly to dangerous air pollution within the meaning of the statute.

First Trump Administration (2017-2020)

On January 13, 2021, EPA promulgated a final rule with a “significant contribution finding” for GHG emissions from electric generating units (EGUs). 86 Fed. Reg. 2,542 (Jan. 13, 2021). The rule was issued in connection with the regulation of emissions from EGUs under section 111(b) of the Clean Air Act. In the rule, EPA concluded that “GHG emissions from the EGU source category would contribute significantly to dangerous air pollution.”