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“The administration has multiple ways to move forward with smart policies to reduce U.S. emissions,” said Nicholas Bianco, author of a World Resources Institute study released last week that concludes the U.S. could attain Mr. Obama’s 17 percent emissions cut through regulatory measures. “The best opportunity is to enact new standards for existing power plants, which represent one-third of all U.S. emissions.”

Without any action by Congress, Mr. Obama could meet his international commitment not only by moving to limit carbon emissions from existing and new power plants, but by limiting methane emissions from natural-gas production, increasing energy-efficiency mandates for appliances and businesses, and curbing such non-energy gases as hydrofluorocarbon, a refrigerant, Mr. Bianco said.

Better than legislation

A study by Resources for the Future, an environmental think tank, in October also found that by sticking with the current regulatory course, the administration could achieve its commitments, and actually might accomplish more than a bill to cap greenhouse emissions that failed in the Senate in 2010.

The group’s study credited the drop in emissions since 2005 not only to EPA’s aggressive use of its regulatory authority, but to the existing trend toward fuel conservation by consumers, the switch to natural gas by utilities, and a push toward greater use of wind power and other renewable fuels in 29 U.S. states.

“To the surprise of many, the United States appears able to meet its mitigation obligations under the Copenhagen agreement,” and is doing even better today than it would have under the climate-change bill passed by the House in 2010, said Dallas Burtraw, co-author of the Resources for the Future study.

While the White House has not publicly committed to following the course urged by environmental groups, the president was not shy about using regulatory powers during his first term and has shown signs of stepping up executive actions this year despite continuing opposition in Congress.

“We know what releases carbon into the atmosphere, and we have tools right now that would start scaling that back,” Mr. Obama told The New Republic in a recent interview, although he added that more technological breakthroughs are needed to achieve the most ambitious goals laid down by scientists and environmentalists to eliminate the threat of climate change. Activists want to cut emissions by as much as 80 percent by 2050.

But Theda Skocpol, a Harvard University political scientist, said imposing a strict regulatory regime that raises the intense opposition of business and Republicans in Congress may backfire on Mr. Obama.

“Most professional environmentalists have an overriding faith in regulatory solutions and do not understand that regulation alone will soon falter unless it is sustained by congressional majorities,” she said. “If EPA regulations go too far, too fast, backlashes across the country could contribute to what may happen anyway: Democratic loss of control of the Senate in 2014. Many Democratic voters tend to stay home in midterm elections, and many key seats currently held by Democrats are up for grabs.”