States can't invoke federal law to force utilities to cutgreenhouse-gas emissions, the U.S. Supreme Court ruled, shuttingoff one avenue for groups that advocate bolder steps againstclimate change.

The unanimous ruling is a victory for five companies — AmericanElectric Power Co., Duke Energy Corp., Southern Co. and thegovernment-owned Tennessee Valley Authority, based in Knoxville —that had been sued by six U.S. states, including California, andthe city of New York.

The states, which sought a cap on emissions, argued that carbondioxide spewed by the utilities is a public nuisance because itcauses climate change. The justices said the EnvironmentalProtection Agency was better equipped than federal judges to assessthe costs and benefits of reducing greenhouse gases.