The case, which comes before the Supreme Court on Tuesday, is important because it could open the way for an array of states and citizen groups to battle the threat of global warming and other environmental causes.
Corporations and business groups are concerned that the case could subject them to open-ended litigation over emissions of greenhouse gases outside any national framework established by Congress and enforced by the EPA.
One of the lawsuits was filed on behalf of six states and the City of New York. The states are New York, Connecticut, California, Iowa, Rhode Island, and Vermont. The other was filed by the Open Space Institute, the Open Space Conservancy, and the Audubon Society of New Hampshire.
Both suits accuse the five power companies of causing a public nuisance by operating fossil-fuel power plants in 20 states that emit 650 million tons of carbon dioxide a year. That amounts to roughly 10 percent of annual carbon-dioxide emissions in the US, according to the suits.
The power companies are American Electric Power Co., American Electric Power Service Corp., Southern Company, Excel Energy, and Cinergy Corp. The Tennessee Valley Authority is also a defendant in the suits.