BOSTON - Massachusetts Attorney General Martha Coakley is one of 12 attorneys general celebrating a U.S. Supreme Court ruling that will require the Bush administration re-examine regulation of carbon dioxide emission from cars.

The Court ruled Monday in a 5-4 decision that the Bush administration's policy on global warming presents a risk to states.

Twelve states, three cities and 13 environmental groups filed the suit in 2003 against the U.S. Environmental Protection Agency, with Massachusetts being the lead plaintiff.

"Given EPA's failure to dispute the existence of a causal connection between man-made greenhouse gas emissions and global warming, its refusal to regulate such emissions, at a minimum, contributes to Massachusetts' injuries," Justice Paul Stevens wrote in the majority opinion.

Chief Justice John Roberts and justices Samuel Alito, Antonin Scalia and Clarence Thomas dissented.

Rhode Island Attorney General Patrick Lynch, one of the attorneys general involved, called the decision landmark.

"They might be inconvenient truths for the Bush Administration, but the Clean Air Act is the law of the land, carbon dioxide is a pollutant, and the Environmental Protection Agency can't continue to flout the law," he said.

"On the most important environmental-protection case in at least a generation, the Supreme Court has delivered a ringing victory for everybody who genuinely cares about the fate of our nation and our planet."

The EPA argued that carbon dioxide, the primary greenhouse gas alleged to be causing global warming, is not an air pollutant and could not regulate it. Even if it could regulate it, the EPA said it would not because of certain policy considerations, Lynch said, since any global warming would be a global problem.

Other plaintiffs included the states of California, Connecticut, Illinois, Maine, New Jersey, New Mexico, New York, Oregon, Vermont, and Washington. They were joined by the District of Columbia, and cities Baltimore and New York, by the Pacific Island of American Samoa, and by organizations that include the Sierra Club, Greenpeace, the Union of Concerned Scientists, and Friends of the Earth.

Chief Justice Roberts, in his dissent, said that dealing with the issues expressed in the suit should be the job of Congress.

In Aug. 2003, the EPA denied a four-year-old petition from various environmental groups that asked the EPA to set motor vehicle emission standards for greenhouse gases. The EPA said it had no statutory authority to do that and would not even if it could.

In Oct. 2003, Massachusetts challenged the decision in the U.S. Court of Appeals for the District of Columbia Circuit.

On July 15, 2005, a three-judge panel of the D.C. Circuit upheld EPA's ruling with a 2-1 vote.

Five months later, the full D.C. Circuit denied en banc review with a 4-3 vote.

On June 26, 2006, the U.S. Supreme Court granted certiorari, and oral arguments were heard five months later.