On November 6, the U.S. Environmental Protection Agency sent its proposed finding that six greenhouse gases–carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride–endanger the public health and welfare to the Office of Management and Budget for final review prior to publication. In the landmark decision of Massachusetts v. EPA, the U.S. Supreme Court held that greenhouse gases are “pollutants” within the meaning of the Clean Air Act, requiring EPA to make a finding as to whether they endanger the public health and welfare. EPA proposed its endangerment finding in April 2009, seeking public comment. Although the Massachusetts v. EPA case was limited to the section of the Clean Air Act dealing with automobile pollution, some of the greenhouse gases that are the subject of the proposed endangerment finding are not produced by automobiles, signaling that finalization of the endangerment finding will foretell broad greenhouse gas regulation under the Clean Air Act unless Congress enacts legislation, such as the American Climate and Energy Security Act passed by the House earlier this year, that changes the method of regulation of greenhouse gases.