U.S. power plants dumped 2.56 billion tons of carbon dioxide into the environment in 2007 -- and much of that came from the nation's older coal-fired plants.

That's among the findings of "America's Biggest Polluters," a new report from Environment America. Based on an analysis of Environmental Protection Agency data, the study finds that the nation's power plants are dirty as well as old -- and that those two characteristics tend to go hand in hand.

"Coal-fired giants have dominated our electricity for decades and have been allowed to pollute without license," says Environment America's Courtney Abrams. "In order to stop global warming and reap all the benefits of clean energy, we must require old coal-fired clunkers to meet modern standards for global warming pollution."

Two-thirds of the nation's fossil-fuel-generated electricity comes from plants built before 1980. At the same time, those older facilities produced 73% of U.S. carbon dioxide emissions from power plants, the report found:

For each year older a coal generator is on average, it created 0.001 more tons of CO2 for each Megawatt-hour of electricity it produced in 2007.

Of the nation's 25 dirtiest power plants, 10 are in the South -- and all but one of those was built before 1980. The nation's dirtiest power plant -- the Southern Co.'s Plant Scherer in Georgia, which emitted more than 27.2 million tons of carbon dioxide in 2007 -- was built in 1982.

The South's nine other dirtiest power plants in terms of carbon emissions are Southern Co.'s Miller plant in Alabama (releasing 23.7 million tons of CO2 in 2007, it was built in 1978) and its Bowen plant in Georgia (23.2 million tons, 1971), Luminant's Martin Lake plant in Texas (21.8 million tons, 1977), NRG's W.A. Parish plant in Texas (20.9 million tons, 1958), Luminant's Monticello plant in Texas (18.3 million tons, 1974), the Tennessee Valley Authority's Cumberland plant in Tennessee (17.9 million tons, 1972), AEP's John E. Amos plant in West Virginia (17.4 million tons, 1971), Progress Energy's Crystal River plant in Florida (16 million tons, 1966) and Duke Energy's Marshall plant in North Carolina (14.5 million tons, 1965).

The report calls on the EPA to finalize its proposal to require coal plants and other big smokestack industries to meet up-to-date standards for global warming pollution when new plants are built or existing plants are upgraded. It also urges Congress to pass strong climate legislation that caps global warming pollution at science-based levels and to eliminate subsidies for fossil fuel power generation.

Environment America supports the Senate climate legislation approved by the Senate Environment and Public Works Committee last month, calling it an improvement over the House bill because it makes deeper cuts in greenhouse gas pollution. The group is critical of the House version of the bill for striking EPA's authority to regulate carbon dioxide emissions from existing coal-fired generators, which it sees as a hindrance to cleaning up aging plants.

The report's release comes as Progress Energy announced plans to begin
closing 11 of its aging coal-fired generating units at four sites across North
Carolina and replacing them with facilities that burn natural gas. Company officials told the Raleigh News & Observer that they were taking the action because they anticipated new federal restrictions on air pollution, mercury emissions and coal ash storage ponds, and retrofitting the old facilities would have cost $2 billion -- $500 million more than building new plants.

"Progress Energy's announcement is important for North Carolina's air
quality," said N.C. Gov. Bev Perdue. "The transition toward cleaner
sources of energy is good for the environment and the economy."