WASHINGTON - In a defeat for the Bush administration, the Supreme Court ruled on Monday that a U.S. government agency has the power to regulate greenhouse gas emissions that spur global warming.By a 5-4 vote, the nation's highest court said the U.S. Environmental Protection Agency "has offered no reasoned explanation" for its refusal to regulate carbon dioxide and other emissions from new cars and trucks that contribute to climate change.
The ruling in one of the most important environmental cases to reach the Supreme Court marked the first high court decision in a case involving global warming.
President George W. Bush has opposed mandatory controls on greenhouse gases as harmful to the U.S. economy, and the administration has called for voluntary programs instead of regulation. The states and environmental groups that brought the lawsuit hailed the ruling.
"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," Massachusetts Attorney General Martha Coakley said.
"Today the nation's highest court has set the White House straight. Carbon dioxide is an air pollutant, and the Clean Air Act gives EPA the power to start cutting the pollution from new vehicles that is wreaking havoc with our climate," said David Doniger of the Natural Resources Defense Council.
Greenhouse gases occur naturally and also are emitted by cars, trucks and factories into the atmosphere. They can trap heat close to Earth's surface like the glass walls of a greenhouse.
Such emissions have risen steeply in the past century and many scientists see a connection between the rise, an increase in global average temperatures and a related increase in extreme weather, wildfires, melting glaciers and other damage to the environment.
Democrats in Congress predicted the ruling could add pressure on lawmakers to push forward with first-ever caps on carbon dioxide emissions. The United States is the world's biggest emitter of such gases.
Writing for the court majority, Justice John Paul Stevens, rejected the administration's argument that it lacked the power under the federal clean air law to regulate such emissions.
He said nothing suggested that Congress in adopting the law meant to curtail the EPA's power to treat greenhouse gases as air pollutants.
Stevens wrote that the EPA's decision was "arbitrary, capricious or otherwise not in accordance with law."
In sending the case back for further proceedings, Stevens said the EPA can avoid regulation only if it determined that the gases do not contribute to climate change or if it provided a reasonable explanation.
"If the scientific uncertainty is so profound that it precludes EPA from making a reasoned judgment as to whether greenhouse cases contribute to global warming, EPA must say so," he said.
The EPA said the administration was committed to reducing greenhouse gases and it was "reviewing the court's decision to determine the appropriate course of action."
The court's four most conservative members -- Chief Justice John Roberts and Justice Samuel Alito, both Bush appointees, and Justices Antonin Scalia and Clarence Thomas -- dissented.
They said the environmental groups and the states lacked the legal right to bring the lawsuit in the first place.
"No matter how important the underlying policy issues at stake, this court has no business substituting its own desired outcome for the reasoned judgment of the responsible agency," Scalia wrote.
Additional reporting by Chris Baltimore
© Reuters 2007.