The U.S. Supreme Court has ruled that it is the role of the Environmental Protection Agency, not the court system, to regulate greenhouse gas emissions from powerplants under the Clean Air Act.

In a June 20 decision in AEP v. Connecticut, the high court said that states and conservation groups could not challenge powerplants' greenhouse gas emissions in federal court through “public nuisance” lawsuits.

In the 8-0 ruling, the justices said that Congress clearly intended that the EPA develop a policy to deal with greenhouse gases. EPA is expected to announce by May 2012 whether it will regulate such emissions under the Clean Air Act.

David Doniger, policy director of the Natural Resources Defense Council's Climate Center, says the ruling “reaffirms EPA's duty under the Clean Air Act to regulate air pollution.” Pat Hemlepp, spokesman for AEP, Columbus, Ohio, says the company is pleased with the court decision. One result, he adds, is that AEP will avoid having to incur the costs of defending against public nuisance lawsuits.