The plaintiffs represented 12 states, 3 cities, and 3 environmental groups in the unprecedented effort. The suit began working its way up from the lower courts after the EPA rejected a 1999 petition by the International Center for Technology Assessment and other environmental groups to regulate carbon dioxide emissions from motor vehicles. The plaintiffs drew upon the broad language of the Environmental Protection Act, which gives the federal government authority to regulated "any air pollutant" emitted from an internal combustion engine.

The plaintiff's intention was to impose the standards of the Kyoto Protocol, rejected by the U.S. Senate in 1999. Even though President Bush, significant congressional majorities, and most voters oppose the Kyoto treaty, a precedent-setting decision in this case would establish a national energy-rationing program almost identical to Kyoto in all sectors of energy production.

Carbon dioxide is the byproduct of carbon-based fuels, which supply 85 percent of the energy Americans use. It is also the byproduct of human respiration. EPA will have the power to require automakers to restrict production of SUVs and large passenger cars, leading to the potential demise of the auto industry itself. This ruling could put the brakes on the fastest-growing industrialized economy and 3rd most populous nation in the world.