WASHINGTON -- In a major victory for the Obama administration, the Supreme Court on Tuesday upheld the authority of the Environmental Protection Agency to regulate the smog from coal plants that drifts across state lines from 27 Midwestern and Appalachian states to the East Coast.
The 6-2 ruling bolsters the centerpiece of President Barack Obama's environmental agenda: a series of new regulations aimed at cutting pollution from coal-fired power plants. Republicans and the coal industry have criticized the regulations, which use the Clean Air Act as their legal authority, as a "war on coal." The industry has waged an aggressive legal battle to undo the rules.
Legal experts said the decision, written by Justice Ruth Bader Ginsburg, signaled that the Obama administration's efforts to use the Clean Air Act to fight global warming could withstand legal challenges.
In June, the EPA is expected to propose a sweeping new Clean Air Act regulation to cut emissions of carbon dioxide, the heat-trapping greenhouse gas that scientists say is the chief cause of climate change. Coal plants are the biggest source of greenhouse gas emissions in the United States.
"It's a big win for the EPA, and not just because it has to do with this rule," said Jody Freeman, director of Harvard University's environmental law program. "It's the fact that it's setting the stage and creating momentum for what's to come."
If the Supreme Court had decided against the Obama administration in Tuesday's decision, Ms. Freeman said, "It would have been a shot across the bow to the EPA as it takes the next steps" toward issuing the climate change regulations.
The Supreme Court decision is only the latest blow to coal. Also on Tuesday, a U.S. District Court ordered the EPA to propose by Dec. 1 a new nationwide regulation to rein in smog pollution from coal-fired power plants and other major polluters.
This rule would come on top of the regulation covering cross-state air pollution. The EPA had been preparing to issue that regulation in 2011, but Mr. Obama told the agency to delay it after his advisers warned that it could hurt his re-election chances in coal-reliant swing states such as Ohio.
Two weeks ago, the U.S. Court of Appeals for the District of Columbia Circuit upheld another major EPA Clean Air Act rule that would cut coal-plant pollution from mercury.
"Today's Supreme Court decision is a resounding victory for public health and a key component of EPA's efforts to make sure all Americans have clean air to breathe," EPA Administrator Gina McCarthy said in a statement. She added that "the court's finding also underscores the importance of basing the agency's efforts on strong legal foundations and sound science."
The interstate air pollution regulation, also known as the "good neighbor" rule, has pitted Rust Belt and Appalachian states such as Ohio, Michigan and Kentucky against East Coast states such as New York and Connecticut. In its arguments before the court, the EPA said the rules were necessary to protect the health and the environment of downwind states.
East Coast states in particular are vulnerable to pollution blown by the prevailing west-to-east winds of the United States. The soot and smog produced by coal plants are linked to asthma, lung disease and premature death.
The EPA says Pennsylvanians will gain health benefits from air-quality improvements in 15 other states. The agency said improved air quality in Pennsylvania will benefit residents of 30 other states.
In her decision, Justice Ginsburg noted that in reining in interstate pollution, regulators must account for the vagaries of the wind. "Some pollutants stay within upwind states' borders, the wind carries others to downwind states, and some subset of that group drifts to states without air quality problems," she wrote, adding a biblical quotation from the Book of John: "The wind bloweth where it listeth, and thou hearest the sound thereof, but canst not tell whence it cometh, and whither it goeth."
In a dissent, Justice Antonin Scalia, joined by Justice Clarence Thomas, said the regulation was unwieldy and suggested that it was Marxist. As written, the regulation will require upwind polluting states to cut pollution in relation to the amounts of pollution each state produces, but also as a proportion of how affordably a state can make the cuts. In other words, states that are able to more cost-effectively reduce pollution will be required to cut more of it.
Justice Samuel A. Alito Jr. recused himself from the case.
The utilities and 15 states opposed to the regulations argued that the rules, as written by the Obama administration, gave the EPA too much authority and placed an unfair economic burden on the polluting states.
The decision will force coal plant owners to install costly "scrubber" technology to curb smokestack pollution of smog-forming chemicals. Many owners have said the regulation would be so expensive to carry out that they expected to shut down their oldest and dirtiest coal plants.
Republicans in Congress denounced the decision. "This is just the latest blow to jobs and affordable energy," Fred Upton, R-Mich., House Energy and Commerce Committee chairman, and Rep. Edward Whitfield, R-Ky., said in a statement. Both are from states that rely heavily on cheap coal-fired electricity.
They added: "The administration's overreaching regulation will drive up energy costs and threaten jobs and electric reliability. We cannot allow EPA's aggressive regulatory expansion to go unchecked. We will continue our oversight of the agency and our efforts to protect American families and workers from EPA's onslaught of costly rules."
In 2011, the Obama administration issued the "good neighbor" rule, which was to apply to 27 states east of Nebraska -- half of the country -- but the U.S. Court of Appeals for the District of Columbia struck it down, ruling that the EPA had not followed the Clean Air Act when it calculated how to assign responsibility for cross-state air pollution. The Supreme Court's ruling overturned that decision.
East Coast states' governors for more than 15 years have been subject to tougher air pollution requirements than other parts of the nation.
The East Coast governors have long criticized the Appalachian and Rust Belt states for their more lenient rules on pollution from coal plants, factories and tailpipes -- allowing those state economies to profit from cheap energy while their smog and soot has been carried eastward by prevailing winds.