In a landmark decision, a federal appeals court ruled this week that states trying to curb global warming can sue five electric utilities to force them to cut greenhouse gas pollution.

The heavily-polluting companies named in the suit, which together serve 20 states, are all either headquartered in or do business in the South. They are American Electric Power, an Ohio-based company with customers in seven Southern states; the Southern Co. of Atlanta; the federal Tennessee Valley Authority headquartered in Knoxville, Tenn.; Xcel Energy, which is based in Minneapolis but also serves Texas; and Cinergy, an Ohio company that was acquired by North Carolina-based Duke Energy in 2005.

The ruling was released Monday -- the same day world leaders met in New York for the U.N. Climate Summit.

"Today's decision opens the way for citizens to protect themselves from the polluters responsible for global warming," said Matt Pawa, lead attorney for plaintiffs the Open Space Institute and the Audubon Society of New Hampshire. "Power companies that release millions of tons of dangerous carbon pollution are not above the law."

Besides those two land trusts, the other plaintiffs in the suit are the states of Connecticut, New York, California, Iowa, New Jersey, Rhode Island, Vermont and Wisconsin; the City of New York; and the Open Space Conservancy. The plaintiffs argued that the greenhouse gas pollution from the companies' plants was a public nuisance and would cause irreparable harm to property, citing studies from the United Nations and the National Academy of Sciences.

The 2nd Circuit Court of Appeals in Manhattan handed down its decision in the case, Connecticut v. American Electric Power, on Monday. Crafting the ruling were Joseph McLaughlin, who was appointed to the court by President George H.W. Bush, and Peter W. Hall, appointed by President George W. Bush. They made their decision without the input of the panel's former third member -- Sonia Sotomayor, who was elevated last month to the U.S. Supreme Court.

Originally brought in 2004 by the states and New York City and later joined by the land trusts, the lawsuit had been appealed from the U.S. District Court for the Southern District of New York, where Judge Loretta Preska ruled in 2005 that dealing with greenhouse gas emissions was a matter for Congress or the President, not the courts -- a legal theory known as the "political question doctrine." The federal appeals court disagreed, writing that Preska had "erred."

TVA had also argued that the complaints against it should be dismissed on the basis of the discretionary exception function, which holds that the federal government is not subject to lawsuits under the Federal Tort Claims Act -- even for something that a private company could be held liable for. The appeals court ruled that TVA's arguments for dismissal "are without merit."

The plaintiffs said they were pleased with the court's ruling. "Today's decision allows us to press this crucial case forward and address the dangers posed by these coal-burning power plants," New York Attorney General Andrew Cuomo told Reuters.

But a spokesperson for AEP said that "[l]itigation is not the best way to address climate issues." Company President Michael G. Morris recently wrote an op-ed for the Charleston (W.V.) Gazette arguing that federal climate legislation was needed.

Duke Energy has also been lobbying for passage of a climate change bill. The company recently dropped out of the American Coalition for Clean Coal Electricity as well as the National Association of Manufacturers over other coalition members' opposition to climate legislation. And it recently hired the Podesta Group, a high-powered D.C. lobbying firm, to press for climate legislation on its behalf.