Since 2003, 12 US states, several cities and a dozen environmental groups have waged a legal battle against the federal Environmental Protection Agency (EPA), which has chosen not to curb greenhouse emissions on new cars.

The EPA maintains that the federal Clean Air Act does not address global climate change and that carbon dioxide is not defined as a pollutant under the law. The administration of President George W. Bush has advocated voluntary controls instead of mandatory limits on emissions.

The plaintiffs in the suit, which include the states of California, Massachusetts and New York, argue that the Clean Air Act obliges the EPA to regulate emissions from cars and power plants such as carbon dioxide and three other gases linked to global warming.

Carbon dioxide and similar emissions are believed to trap heat in the earth's atmosphere, causing global temperatures to rise.

A federal appeals court in Washington ruled in July 2005 that the EPA's policy was justified, saying the agency was not legally required to regulate causes of global warming and that scientific evidence was lacking to support such measures.

In papers filed with the Supreme Court, the US government called the lawsuit "speculative" as it remained unclear if global warming could be traced to emissions from new cars and even if the link was proven, it was not clear that requiring more fuel efficient cars would have a major impact on climate change.

The issue of global warming could be better addressed through international efforts supported by the United States, the government said.

The case will have a "far-reaching" effect on the US approach to global warming, according to the environmental group Sierra Club.

"The Bush administration has continually tried to say that it's not their job to fight global warming. In fact, they have both the legal and moral responsibility to tackle global warming pollution," David Bookbinder, senior attorney for the Sierra Club, said in a statement.

Related Links
-