Some of the nation's largest power companies on Thursday defended efforts to reduce carbon dioxide emissions (search), saying a lawsuit accusing them of neglecting the threat of global warming (searchseeks a "piecemeal response" to a worldwide problem.

In court papers filed in federal court in Manhattan, the companies said the July lawsuit brought by eight states wants the court to usurp the policy-setting role that Congress and the president have in dealing with global warming.

"The Constitution does not entrust such policy decisions to the unelected judiciary," the power companies said.

Connecticut Attorney General Richard Blumenthal, who announced the lawsuit in July, said the plaintiffs were not surprised by the response.

"It's entirely unmerited because our lawsuit makes clear and compelling claims under well-established federal law," he said. "We intend to pursue our case."

In court papers, the states noted that Congress has repeatedly studied the issue and chosen not to regulate carbon dioxide emissions to address global climate change.

The lawsuit seeks to force a reduction of carbon dioxide emissions by American Electric Power Co.; Cinergy Corp.; Southern Co.; Xcel Energy Inc.; and the Tennessee Valley Authority.

The plaintiffs want a federal judge to force the power producers to reduce emissions 3 percent annually for 10 years.

Carbon dioxide is believed to be one of the main culprits of global warming (search). The greenhouse gas is produced when coal, gasoline and other fossil fuels burn. Climatologists forecast continued temperature increases that will cause rising tides, droughts and other climate disruptions if nothing is done.

The plaintiffs said in a statement this summer that CO2 emissions can be reduced by increasing efficiency at coal-burning plants, switching from coal to cleaner burning fuels, investing in energy conservation and using clean energy sources such as wind and solar power.

The states that filed the lawsuit include California, Connecticut, Iowa, New Jersey, New York, Rhode Island, Vermont and Wisconsin. New York City and three nonprofit land trusts also are part of the lawsuit.