Petitioners: states of California, Connecticut, Illinois, Maine, Massachusetts, New Jersey, New York, Oregon, Rhode Island, Vermont, and Washington. The cities of New York, Baltimore, and Washington DC, the territory of American Samoa, and the Centre for Biological Diversity, Friends of the Earth, Center for Food Safety, Conservation Law Foundation, Environmental Advocates, Environmental Defense, Greenpeace, International Center for Technology Assessment, National Environmental Trust, Natural Resources Defense Council, Sierra Club, Union of Concerned Scientists, and US Public Interest Research Group.Respondents: the Environmental Protection Agency, the Alliance of Automobile Manufacturers, National Automobile Dealers Association, Engine Manufacturer’s Association, Truck Manufacturers Association, CO2 Litigation Group, Utility Air Regulatory Group and the states of Michigan, Alaska, Idaho, Kansas, Nebraska, North Dakota, Ohio, South Dakota, Texas and Utah. In 2003, the Environment Protection Agency determined that it did not have the authority to regulate carbon dioxide emissions under the Clean Air Act. This action was opposed by the petitioners who argued that carbon dioxide was an air pollutant under the Clean Air Act. The U. S. Court of Appeals for the District Columbia Circuit upheld the Environment Protection Agency’s decision, however similar to the lower courts the rationale for the decision was divided. In 2006, the US Supreme Court granted a writ of certiorari to grant an appeal.