The United States Supreme Court ruled Monday the Environmental Protection Agency cannot use the 1970 Clean Air Act as an excuse for refusing to regulate automobile emissions that produce greenhouse gases.

The 5-4 ruling was a setback for the Bush administration, which has long opposed mandatory limits on emissions linked to global warming, saying such restrictions would cost jobs, drive industry overseas and increase energy costs for consumers.

Writing for the majority, Justice John Paul Stevens said the EPA “offered no reasoned explanation” for its refusal to regulate emissions of four greenhouse gases, including carbon dioxide.

Massachusetts and 11 other states sued the EPA, claiming it had abdicated its responsibility under the Clean Air Act by refusing to regulate greenhouse gas emissions from new automobiles.

The EPA refused to issue new emission rules in 2003, interpreting language in the Clean Air Act narrowly to claim the law does not regard greenhouse gases as “air pollutants.” Even if the agency had the authority, it said it would refuse to exercise that authority, because a causal link between rising levels of greenhouse gases and global warming “cannot be unequivocally established.”

Reversing a ruling by an appeals court that sided with the EPA, the Supreme Court said the Clean Air Act is “unambiguous” that it embraces all airborne compounds, including carbon dioxide, methane, nitrous oxide and hydrofluorocarbons in regulation of “physical and chemical substances” emitted into ambient air.

Chief Justice John Roberts Jr. and Justice Antonin Scalia wrote dissenting opinions. Justices Clarence Thomas and Samuel Alito joined in dissent.

Justice Anthony Kennedy cast the deciding vote. Justices David Souter, Ruth Bader Ginsburg and Stephen Breyer joined the majority.

“If EPA makes a finding of endangerment, the Clean Air Act requires the agency to regulate emissions of the deleterious pollutant from new motor vehicles,” the opinion said. Under clear terms of the Clean Air Act, the majority said, the EPA can “avoid taking further action only if it determines that greenhouse gases do not contribute to climate change or if it provides some reasonable explanation as to why it cannot or will not exercise its discretion to determine whether they do.”

The court found the EPA “has refused to comply with this clear statutory command,” instead offering “a laundry list of reasons not to regulate.”

“In short, EPA has offered no reasoned explanation for its refusal to decide whether greenhouse gases cause or contribute to climate change,” the court decided, calling its inaction “arbitrary, capricious” and “not in accordance with law.”

While the ruling does not require the EPA to issue vehicle standards for greenhouse gas emissions, Massachusetts Attorney General Martha Coakley said in a statement, it makes it more difficult for the EPA to refuse such regulation in the future.

“Despite acknowledging that global warming poses serious dangers to our environment and health, the Bush administration has done little or nothing to regulate greenhouse gas emissions,” Coakley said. “As a result of today’s landmark ruling, EPA can no longer hide behind the fiction that it lacks any regulatory authority to address the problem of global warming.”

White House spokesperson Dana Perrino said the administration had not yet had time to review the Supreme Court ruling in detail, but that the EPA would look at it and consider what it means for future policy decisions.

“The wise majority on the Supreme Court deserves our gratitude,” said Robert Parham of the Baptist Center for Ethics. “Thankfully the court has not yet been completely stacked with conservative ideologues who favor global warming and science fiction over science and earth keeping. It is, however, regrettable that the highest court in the land was needed to stop the Bush administration’s evasiveness, irresponsibility and inaction on global warming. Hopefully this decision will contribute to constructive action on the part of the American government to address global warming and to end its deception about earth care.”

The nation’s automakers, who had sided with the EPA in the case, called for a broad approach to global warming by industries across the economy in the wake of the Supreme Court’s ruling.

The Alliance of Automobile Manufacturers issued a statement saying that “there needs to be a national, federal, economy-wide approach to addressing greenhouse gases.” The alliance which includes the U.S. “Big Three” automakers–General Motors, Ford and DaimlerChrysler–as well as Toyota Motor Corp. and five other manufacturers, said it “looks forward to working constructively with both Congress and the administration, including EPA and the National Highway Traffic Safety Administration, in developing a national approach.”

In another Monday ruling related to the environment, the Supreme Court ruled unanimously to vacate a lower-court ruling that favored a power company with plants in North and South Carolina.

Duke Energy Corporation upgraded 29 coal-fired electric generating units to allow them to run longer each day, increasing daily emissions. The company claimed the modifications were legal, because they were not “major” and didn’t increase the hourly rate of emissions.

The two cases are Environmental Defense v. Duke Energy Corporation and Massachusetts v. Environmental Protection Agency.

Bob Allen is managing editor of

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