The plaintiffs contended that by contributing to global warming, the defendants' emissions substantially and unreasonably interfered with public rights, in violation of the federal common law of interstate nuisance, or, in the alternative, of state tort law.

The plaintiffs ask for a decree setting carbon-dioxide emissions for each defendant at an initial cap, to be further reduced annually.

The utilities and the Obama administration want the Environmental Protection Agency (EPA) to enforce laws against global warming. But the states contended that the EPA is not acting to limit carbon-dioxide emissions that lead to global warming.

In the majority decision, Justice Ruth Bader Ginsburg held that “the Clean Air Act and the Environmental Protection Agency actions it authorizes displace any federal common law right to seek abatement of carbon-dioxide emissions from fossil-fuel fired power plants”

She said prior precedent, Massachusetts v. EPA, “made plain that emissions of carbon dioxide qualify as air pollution subject to regulation under the Act.”

And, Ginsburg added, “We think it equally plain that the Act speaks directly' to emissions of carbon dioxide from the defendants' plants.

In the decision, Ginsburg took great pains to distance the court from “setting emissions standards by judicial decree under federal tort law.”

Lawyers at Nelson Levine de Luca & Horst, Blue Bell, Pa. say that while the decision “dealt a substantial setback to global warming nuisance claimants,” it was not the “death knell” that the power industry had hoped for.

“To the contrary, the court decision's curious final sentences suggest the possibility that aggrieved parties might pursue climate nuisance claims under the law of the particular states where the emissions occurred,” say William Stewart and Danielle Sivert, of Nelson Levine.

“If, and how, those state law claims might proceed are issues for another day,” Stewart and Sivert add.

The final sentences referenced by Stewart and Sivert state, “In light of our holding that the Clean Air Act displaces federal common law, the availability [or not] of a state lawsuit depends, [among other things], on the preemptive effect of the federal act…. None of the parties have briefed preemption or otherwise addressed the availability of a claim under state nuisance law. We therefore leave the matter open fo consideration on remand.”

Five justices joined in supporting Justice Ruth Bader Ginsburg's decision. Judge Samuel Alito filed an opinion concurring in part, in which Justice Clarence Thomas joined. Justice Sonia Sotomayor did not participate in the case.

Paul Blume, senior vice president state government affairs and acting general counsel for the Property Casualty Insurers Association of America (PCI), says PCI supported the majority decision, which held that other branches of government, not the courts, should determine environmental issues such as the regulation of greenhouse gas emission levels.

“These issues are political in nature and are best addressed by Congress and the Environmental Protection Agency rather than the courts,” Blume says.

He adds that the ruling is a “positive step toward curbing the use and abuse of public nuisance law.”