In a major ruling on Tuesday, the U.S. Supreme Court upheld the Environmental Protection Agency’s (EPA’s) authority to regulate power plant emissions across state lines under the Cross-State Air Pollution Rule (CSAPR).

The U.S. Court of Appeals for the D.C. Circuit had struck down the CSAPR in 2012, finding that the EPA had exceeded its authority under the Clean Air Act (CAA). The court then denied a petition for rehearing from the EPA in early 2013. The Supreme Court today overturned that decision in a 6-2 ruling.

Justice Ruth Bader Ginsberg, writing for the Court, found that the D.C. Circuit had failed to give proper deference to the EPA’s interpretations in crafting the CSAPR, and in doing so had read into the Act elements not present in the statutory language. Though the provisions at issue are ambiguous and problematic in some respects, “the practical difficulties cited by the Court of Appeals do not justify departure from the Act’s plain text,” the Court held.

Though the states and utilities challenging the rule had argued it would result in uneven and potentially excessive emissions reductions, the Court was unconvinced, finding that despite a “voluminous record” they were unable to point to more than a few instances of unnecessary reductions. Further, given the “inevitable” imprecision in managing downwind emissions over large areas, a few examples of over-control were not surprising. “Required to balance the possibilities of under-control and over-control, EPA must have leeway in fulfilling its statutory mandate,” the Court said.

The D.C. Circuit had found the CSAPR invalid because it felt the EPA could not force states to reduce their emissions by more than an amount determined to be their “significant contribution” to nonattainment in other states. The Supreme Court, however, rejected that interpretation.

The CAA, it said, “does not require EPA to disregard costs and consider exclusively each upwind State’s physically proportionate responsibility for each downwind air quality problem. EPA’s cost-effective allocation of emission reductions among upwind States, we hold, is a permissible, workable, and equitable interpretation.”

A typically caustic dissent by Justice Antonin Scalia, joined by Justice Clarence Thomas, argued that the EPA had departed from the intent of Congress in drafting the CAA. “Too many important decisions of the Federal Government are made nowadays by unelected agency officials exercising broad lawmaking authority, rather than by the people’s representatives in Congress,” he wrote.

The CSAPR has been deeply controversial since it was proposed by the EPA in 2008. The rule, finalized in July 2011, required more than 3,000 electric generating units at more than 1,000 coal-, gas-, and oil-fired facilities in 28 states to reduce nitrogen oxide (NOx), sulfur dioxide (SO2), and particulate emissions that cross state lines and contribute to ground-level ozone and fine particle pollution. According to EPA projections, the rule would cost about $800 million annually, but the nation would see $120 billion to $280 billion in annual benefits.

Reactions to the ruling fell along predictable lines.

Laura Sheehan, senior vice president of communications for the American Coalition for Clean Coal Electricity, said in a statement, “We are profoundly concerned about the costs and reliability impacts of rules like CSAPR and the absence of oversight in identifying and addressing” them.

Meanwhile, Fred Krupp, president of the Environmental Defense Fund, said, “Today’s Supreme Court decision means that millions of Americans can breathe easier. Power plant pollution creates serious health risks for millions of Americans, especially children and the elderly. The Supreme Court’s decision means that our nation can take the necessary steps to ensure healthier and longer lives for the 240 million Americans at risk from power plant smokestack pollution near and far.”

Today’s ruling is expected to add momentum to the Obama Administration’s efforts to control climate change under the CAA. Still to come is the EPA’s final decision on carbon emissions limits for new plants. The latest version of the proposed rule was published in January.

—Thomas W. Overton, JD, associate editor (@thomas_overton, @POWERmagazine)