Today the U.S. EPA issued its much-anticipated proposal to find that greenhouse gases in the atmosphere endanger the public health and welfare. The so-called positive "endangerment finding," when issued in form of a final rule, would mark the agency's response to the U.S. Supreme Court's 2007 decision in Massachusetts v. EPA, in which the court ordered the agency to make an endangerment determination in response to a petition to regulate GHG emissions from new motor vehicles under the Clean Air Act. A positive endangerment finding, according to the court, would obligate the agency to regulate GHG emissions from new motor vehicles. In addition, and significantly, such a finding would also empower the agency to regulate GHG emissions under the CAA more broadly.

The proposed finding is based upon EPA's conclusion that unprecedented levels of GHGs in the atmosphere are "very likely the cause of the observed increase in average temperatures and other climatic changes," posing risks including more frequent and intense heat waves, wildfires, degraded air quality, flooding, drought, sea level rise, more intense storms, and harm to water resources, agriculture, wildlife, and ecosystems.

The agency's decision displays a marked departure from EPA's actions in the latter days of the previous administration, when former Administrator Johnson described the Clean Air Act as "ill-suited for the task of regulating" GHG emissions, and the agency merely outlined the potential regulatory impacts of a positive endangerment determination in an Advance Notice of Proposed Rulemaking.

As noted above, the likely initial result of a final rule will be regulation of GHGs from new motor vehicles. While the proposed rule states that the agency is not proposing any action under any other provision of the CAA, because the CAA also empowers the agency to regulate emissions of air pollutants from other sources in the presence of a positive endangerment finding, the potential implications of the proposed rule are wide-ranging. Whether EPA acts voluntarily or in response to petitions from interested parties, many of which have already been working their way through the agency and the courts, the agency is likely to begin taking action related to GHG emissions from non-road engines and vehicles as well as stationary sources.

The proposed rule will next enter the 60-day public comment period. Public hearings are scheduled for May 18 and 21, 2009. To view the proposed rule in its entirety, click here: http://epa.gov/climatechange/endangerment.html