The Pleasants Power Station operated by Allegheny Energy is one of several coal-fired power plants that operate along the Ohio River. Many of the coal fire plants are facing tougher environmental regulations that will be taking effect in the next couple of years.The Natural Resources Defense Council kicked off an effort Tuesday to press the Obama administration for carbon dioxide emission limits from existing power plants. (Michael S. Williamson/WASHINGTON POST)

The Natural Resources Defense Council kicked off an effort Tuesday to press the Obama administration to set limits on carbon dioxide emissions for existing power plants, a goal that environmentalists say is their top priority for the president’s second term.

The proposal would offer ways to limit the regulation’s economic impact by letting states use different routes to meeting federal standards, including credits for utilities that implement wide-ranging energy efficiency programs. It would also let utilities average their emissions from old plants with the zero emissions from new renewable energy projects to meet guidelines.

The old coal plants emit 40 percent of the nation’s total emissions, and while the Environmental Protection Agency has proposed limits on new power plants, it has yet to address CO2 emissions from existing ones. The NRDC said that by 2020 its plan would help slash carbon dioxide emissions from existing power plants by 26 percent, compared to 2005 levels, and by 17 percent from 2011 levels.

“We break the conventional wisdom that great savings can only be achieved at great expense,” said David Doniger, policy director of the climate and clean air program at the NRDC. He said the environmental group’s proposal could generate $25 billion to $60 billion worth of benefits from reductions in sulfur, nitrogen oxide and carbon emissions for as little as $4 billion. He said it would “expand the options of how to comply and reduce the cost of reaching the limit.”

Carbon dioxide is a common greenhouse gas that scientists say contributes to climate change.

The electric power generating industry is already in upheaval. Many utilities are closing down old coal plants and replacing them with new natural gas-fired power plants, taking advantage of cheap, plentiful gas supplies. The new gas plants also have climate benefits because burning natural gas generates only half the emissions as coal, though some experts say that gas leakage offsets some or all of those benefits.

Doniger said that the NRDC proposal would still accelerate the closure of old coal plants.

Individuals in and close to the Obama administration have said that the EPA is considering ways to use the Clean Air Act to promote greater energy efficiency. The NRDC proposal would be one way to achieve that.

Doniger said the proposal would have the EPA set state-specific emissions rates depending on the current profile of each state’s electricity sector. Power plant owners and state regulators would have flexibility to meet the standards in the most cost-effective way. A state could choose to build new natural gas plants or renewable energy plants or create energy efficiency programs to meet standards limiting the amount of CO2 emissions per megawatt hour.

Owners of multiple power plants could average the emissions rates of their plants and meet standards by running the worst polluting coal plants less often, rather than by buying costly scrubbers and other emission control devices. The plan would allow the trading of credits between companies within a state or across state lines if states allow it, further lowering compliance costs.