EPA's Endangerment Finding
Legal Background
Today's Action
On December 7, 2009, EPA finalized its finding under Clean Air Act section 202(a) that greenhouse
gases in the atmosphere endanger both the public health and the environment for current and future
generations. The agency also found that the combined emissions of greenhouse gases from new
motor vehicles and new motor vehicle engines are contributing to the buildup of greenhouse gases in
the atmosphere, and thus to the climate change problem. The specific findings are:
•	EPA finds that the elevated concentrations of the six greenhouse gases in the atmosphere—
carbon dioxide (C02), methane (CH4), nitrous oxide (N20), hydrofluorocarbons (MFCs),
perfiuorocarbons (PFCs), and sulfur hexafluoride (SF6)—endanger both the public health and
the public welfare of current and future generations.
•	EPA finds that the combined emissions of greenhouse gases from new motor vehicles and new
motor vehicle engines contribute to the greenhouse gas air pollution which endangers both
public health and welfare.
Key Milestones
•	On October 20, 1999, the International Center for Technology Assessment and 18 other
environmental and renewable energy industry organizations filed a petition seeking the
regulation of greenhouse gas emissions from on-road vehicles under the Clean Air Act.
•	On April 2, 2007, after years of litigation related to the petition, the Supreme Court ruled in
Massachusetts v. EPA, that greenhouse gases are air pollutants covered by the Clean Air Act
and that EPA 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.
•	On December 5, 2007, EPA sent a draft proposal to the White House Office of Management and
Budget (OMB), finding that concentrations of six key greenhouse gases in the atmosphere
endanger the public welfare and that emissions from new motor vehicles contribute to this
problem. The previous administration, however, did not consider the proposal, and EPA later
withdrew the rulemaking.
•	On July 11, 2008, EPA issued a broad Advance Notice of Proposed Rulemaking (ANPR)
regarding regulating greenhouse gases under the Clean Air Act. The ANPR, among other things,
summarized the key issues from the 2007 endangerment and contribution proposal, and
included a "technical support document" that summarized the findings of the major science
assessment reports on climate science and impacts.
•	On April 17, 2009, EPA issued the proposed findings for greenhouse gases under Section
202(a) of the Clean Air Act and released a revised technical support document, updated to
reflect more recent science and input received through public comment on the ANPR.
•	During the 60-day public comment period on the Proposed Findings, which ended June 23,
2009, EPA received more than 380,000 public comments, including both written comments and
oral testimony at two public hearings in Arlington, Virginia and Seattle, Washington.
•	EPA carefully reviewed and considered the public comments, as indicated in EPA's Final
Findings, the final Technical Support Document, the 11-volume Response to Comments
document, and other supporting materials released along with the Findings.
•	On December 7, 2009, under the Obama Administration, the final finding cleared OMB's
interagency review process, and EPA Administrator Lisa P. Jackson signed it.