I don't usually post breaking news but this is a big ruling for climate change policy. Here's the AP report:

The Supreme Court ordered the federal government on Monday to take a fresh look at regulating carbon dioxide emissions from cars, a rebuke to Bush administration policy on global warming.

In a 5-4 decision, the court said the Clean Air Act gives the Environmental Protection Agency the authority to regulate the emissions of carbon dioxide and other greenhouse gases from cars.

Update: here's the text of the decision (pdf) and an explanation from the Supreme Court blog:

Ruling 5-4, the Supreme Court on Monday found that the federal government had the authority to regulate greenhouse gases that may contribute to global warming, and must examine anew the scientific evidence of a link between those gases contained in the exhausts of new cars and trucks and climate change. In the most important environmental ruling in years, the Court rebuffed the Environmental Protection Agency's claim that regulating those gases was beyond its authority, and the agency's claim that it need not take action even if it did have the power to do so. Justice John Paul Stevens wrote for the majority.

That decision came in Massachusetts v. EPA (05-1120). The Court also concluded that the state of Massachusetts had a right to sue to challenge EPA on the climate change issue because it had shown it would be affected directly by global warming. Relying primarily on a 1907 ruling (Georgia v. Tennnessee Copper Co.), the Court said it was noteworthy that the key party challenging EPA on the issue was a sovereign state. The Court quoted froom that opinion by Justice Oliver Wendell Holmes, Jr.: "The state...has the last word as to whether its mountains shall be stripped of their forests and its inhabitants shall breathe pure air." Congress, the Court said, has ordered EPA to protect Massachusetts and others by laying down standards to regulate air pollutants.