Regulation of greenhouse gases under the Clean Air Act

The United States Environmental Protection Agency (EPA) began regulating greenhouse gases (GHGs) under the Clean Air Act ("CAA" or "Act") from mobile and stationary sources of air pollution for the first time on January 2, 2011. Standards for mobile sources have been established pursuant to Section 202 of the CAA, and GHGs from stationary sources are currently controlled under the authority of Part C of Title I of the Act. The basis for regulations was upheld in the United States Court of Appeals for the District of Columbia in June 2012.

Section 202(a)(1) of the CAA requires the Administrator of the EPA to establish standards "applicable to the emission of any air pollutant from…new motor vehicles or new motor vehicle engines, which in [her] judgment cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare" (emphasis added). On October 20, 1999, the International Center for Technology Assessment (ICTA) and several other parties (petitioners) petitioned the EPA to regulate greenhouse gases from new motor vehicles under the Act. The petitioners argued that carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and hydrofluorocarbons meet the definition of an air pollutant under section 302(g) of the Act, and that statements made by the EPA, other federal agencies, and the United Nations Intergovernmental Panel on Climate Change (IPCC) amounted to a finding that these pollutants are reasonably anticipated to endanger public health and welfare. Based on these factors, the petitioners asserted that EPA had a mandatory duty to regulate greenhouse gases under section 202 of the Act, and asked the agency to carry out that duty.

On September 8, 2003, EPA denied the ICTA petition on the ground that it did not have authority under the CAA to promulgate regulations to address global climate change and that CO₂ and other GHGs therefore could not be considered air pollutants under the provisions of the CAA, including section 202. The agency further stated that even if it had the authority to regulate GHGs from motor vehicles, it would decline to do so as a matter of policy. The agency maintained that regulating motor vehicle GHG emissions would neither address the global problem effectively, nor be consistent with President Bush's policies for addressing climate change, which centered on non-regulatory efforts such as voluntary reductions in GHGs, public-private partnerships aimed at reducing the economy's reliance on fossil fuels, and research to probe into scientific uncertainties regarding climate change. The agency's action on the ICTA petition set the stage for a prolonged legal battle, which was eventually argued before the Supreme Court on November 29, 2006.

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