In a setback for environmentalists, the Supreme Court justices signaled that they will throw out a huge global-warming lawsuit brought by six states, including New York, that seeks limits on carbon pollution from coal-fired power plants in the South and Midwest.
Encouraged by the Obama administration's top courtroom lawyer, the justices said the problem of regulating greenhouse gases should be left to the Environmental Protection Agency. It is too complex and unwieldy to be handled by a single federal judge acting on a "public nuisance" lawsuit, some of them said.
A defeat for the lawsuit would put more pressure on the Obama administration and the EPA to enforce limits on carbon pollution in the face of strong opposition from congressional Republicans, environmental advocates said.
"The stakes will be very high. The question is whether they can deliver," said David D. Doniger, a climate-change expert for the Natural Resources Defense Council.
The issue debated before the high court Tuesday was not whether greenhouse gases are causing global climate change, but who should regulate these gases. The decision involves politics, economics and science, the lawyers said.
"It's a question of trade-offs," said Peter D. Keisler, a lawyer representing the power producers. "There is no legal principle here to guide the decision" if it were made by a judge.
Keisler, a former Bush administration official, was joined by acting Solicitor General Neal K. Katyal in urging the justices to throw out the lawsuit against the power plants as too sprawling.
"In the 222 years that this court has been sitting, it has never heard a case with so many potential perpetrators and so many potential victims," Katyal began. Everyone on the planet is an emitter of carbon dioxide, he said, and everyone is a potential victim of global warming. Judges and courts are not suited to handling "global" problems through a lawsuit, he said.
In their comments and questions, it became clear that the justices -- liberals and conservatives alike -- were also dubious of allowing a single judge to decide on the regulation of greenhouse gases.
This "sounds to me a lot like what the EPA does," Justice Ruth Bader Ginsburg told a New York State lawyer who was defending the lawsuit. A judge cannot be "a super EPA" who sets and enforces detailed regulations, she said.
Four years ago, the justices cleared the way for the EPA to regulate greenhouse gases under the Clean Air Act. Since then, the government has adopted stricter standards for new motor vehicles, which take effect next year. But regulation of power plants has stalled. The agency says it will propose new rules in July.
All the while, however, the states have pressed ahead with their "nuisance" lawsuit against the five large power producers.