The U.S. Supreme Court justices on Tuesday questioned whether a common law public nuisance suit against major greenhouse gas emitters was treading on territory usually, and perhaps more fittingly, handled by the U.S. Environmental Protection Agency (EPA).

During oral arguments in American Electric Power Co. v. Connecticut, case number 10-174, Justice Ruth Bader Ginsburg told New York Solicitor General Barbara D. Underwood — who argued for the states and conservation groups that brought the global warming case — that the emissions standards sought in the litigation “sounds like the kind of thing that EPA does,” reported Law360.

At issue is a 2009 Second Circuit ruling that revived the climate change public nuisance lawsuit against four power companies and the Tennessee Valley Authority over carbon emissions.

There has yet to be a ruling on the merits of the case, and the Supreme Court is weighing whether the states and conservation groups have standing to bring the action, whether the cause of action can be implied under federal common law and whether the claims can be resolved through court.

After the Supreme Court granted the utilities' request for certiorari, the EPA said it would complete a rulemaking by 2012 on whether to impose carbon dioxide emissions limits on existing power plants. Underwood on Tuesday said that when the agency sets such limitations, the plaintiffs' federal common law claims would be displaced.

According to Law360, Chief Justice John Roberts said addressing global warming raised cost and benefit issues in regard to the world economy, adding “and I think that's a pretty big burden ... to impose on a district court judge.”

Underwood argued that the plaintiffs weren't asking the court to solve global warming in its entirety and then assign some of that responsibility to the utilities, but instead to decide whether those defendants “can take reasonable cost-effective measures that would help to slow the pace of global warming.”

Counsel for the four power companies argued that plaintiffs lack Article III standing, that federal common law shouldn't be expanded to include the present claims and that the case presents nonjusticiable political questions.

“To classify climate change as a tort would trigger a massive shift of institutional authority away from the politically accountable branches and to the courts, which we think would be inconsistent with separation of powers,” defense counsel presented in its rebuttal.

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The American Electric Power Co. v. Connecticut suit goes back to 2004, when California, Connecticut, Iowa, New Jersey, New York, Rhode Island, Vermont and Wisconsin, along with New York City, sued AEP, the Tennessee Valley Authority, Xcel Energy Inc., Southern Co. and Cinergy Corp., which is now part of Duke Energy Corp., demanding that they first cap their emissions and then reduce them over a period of time.

Three land trusts — Open Space Institute Inc., Open Space Conservancy Inc. and the Audubon Society of New Hampshire — filed a similar suit, and the two were consolidated.

The suits, brought under a federal common-law claim of nuisance, alleged that by contributing to global warming, the power company defendants were harming the environment, the states' economies and public health.

In 2005 a federal judge dismissed the complaint, saying it presented political questions that should be handled by the legislative or executive branches and not by the courts. But the suit it was revived in September 2009 by a two-judge panel of the Second Circuit, which said the district court had wrongly read the plaintiffs' claims as seeking a change in national policy rather than protection from immediate harm.