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Proposed Endangerment and Cause or Contribute Findings for Greenhouse Gases under the Clean Air Act - Archived Page

Please note that the Final Endangerment and Cause or Contribute Findings for Greenhouse Gases under the Clean Air Act is located at https://www.epa.gov/climatechange/endangerment/index.html and was signed by the Administrator (date).

EPA is maintaining this archived Proposed Endangerment and Cause or Contribute Findings for GHGs under the Clean Air Act page for historical purposes.


On April 2, 2007, in Massachusetts v. EPA, 549 U.S. 497 (2007), the Supreme Court found that greenhouse gases are air pollutants covered by the Clean Air Act. The Court held that the Administrator must determine whether or not emissions of greenhouse gases from new motor vehicles cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare, or whether the science is too uncertain to make a reasoned decision. In making these decisions, the Administrator is required to follow the language of section 202(a) of the Clean Air Act. The Supreme Court decision resulted from a petition for rulemaking under section 202(a) filed by more than a dozen environmental, renewable energy, and other organizations.


You will need Adobe Acrobat Reader, available as a free download, to view some of the files on this page.  See EPA's PDF page to learn more about PDF, and for a link to the free Acrobat Reader.

The Administrator signed a proposal with two distinct findings regarding greenhouse gases under section 202(a) of the Clean Air Act:

  • The Administrator is proposing to find that the current and projected concentrations of the mix of six key greenhouse gases-carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6)-in the atmosphere threaten the public health and welfare of current and future generations. This is referred to as the endangerment finding.
  • The Administrator is further proposing to find that the combined emissions of CO2, CH4, N2O, and HFCs from new motor vehicles and motor vehicle engines contribute to the atmospheric concentrations of these key greenhouse gases and hence to the threat of climate change. This is referred to as the cause or contribute finding.

This proposed action, as well as any final action in the future, would not itself impose any requirements on industry or other entities. An endangerment finding under one provision of the Clean Air Act would not by itself automatically trigger regulation under the entire Act.

The Proposed Endangerment and Cause or Contribute Findings for Greenhouse Gases under the Clean Air Act was signed on April 17, 2009. On April 24, 2009, the proposed rule was published in the Federal Register (www.regulations.gov) under Docket ID No. EPA-HQ-OAR-2009-0171:

The public comment period ended June 23, 2009.  The comment period was open for 60 days, following publication of the proposed rule in the Federal Register, April 24, 2009.  Late comments were submitted on the proposed rule and were considered to the extent practicable; however, the Clean Air Act does not require that the Environmental Protection Agency consider comments submitted past the end of the official comment period, when developing the final rule.

Public Hearings

Two public hearings were held for this proposal—on May 18, 2009 in Arlington, VA, and on May 21, 2009 in Seattle, WA.  The transcript of each hearing can be found at www.regulations.gov under Docket ID No. EPA-HQ-OAR-2009-0171.  The document numbers for the transcripts are EPA-HQ-OAR-2009-0171-2818 (Arlington) and EPA-HQ-OAR-2009-0171-2895 (Seattle).


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