The biggest step, major legislation that would have capped emissions and set up markets to trade pollution credits, failed in 2010 and is unlikely to be resurrected.

But there’s plenty more the administration could do without legislation, said the Clean Air Task Force, a nonprofit that’s dedicated to reducing air pollution. The task force wrote a letter to the president earlier this month saying the administration could work to curb methane emissions from the pipeline and production system, even as domestic oil and gas production booms.

They’d also like to see more attention to coal. Given recent projections that show the use of coal surging worldwide, even as older, inefficient plants close in the United States, the Clean Air Task Force would like some attention paid to developing the technology to capture carbon emissions from coal-fired plants.

Such technology also could be applied to natural gas, which in the United States is rapidly replacing coal. Although natural gas-fired power plants still produce greenhouse gas emissions, it’s at about half the rate of coal plants.

"To get serious about climate means getting serious about solving coal emissions, because they won’t disappear or be replaced," said John Thompson, the head of the Clean Air Task Force’s fossil transition team. "We need carbon capture in the United States, not just for coal, but for gas as well. When it comes to pathways for climate change, all paths have to lead to addressing coal and gas through carbon capture technology."

The most likely path in coming months, though, may be through the EPA’s regulatory authority. The administration is finalizing emission rules for new power plants; environmental groups such as the Natural Resources Defense Council are calling for rules that would target existing plants.

White House Press Secretary Jay Carney wouldn’t say this week whether the administration would move to regulate existing plants. The EPA administrator, Lisa Jackson, is stepping down, and the president hasn’t yet named a new leader for an agency that Republicans often target as overbearing.

"I can certainly confirm that the president intends to continue progress on the new national standard for harmful carbon pollution from new power plants, and to implement that standard," Carney said. "I can’t comment on any specific future actions that he might take, except that he has demonstrated in his record during his first term that we can, together, take action that is not only helpful to our environment, in that it addresses the issue of climate change."

Obama himself warned in his inaugural address that the path toward sustainable energy sources would be "long and sometimes difficult." His administration hasn’t tipped its hand when it comes to the Keystone pipeline, which, if approved, environmentalists would consider a failure to rein in future greenhouse gas emissions.

The pipeline’s rejection is one of the key goals of the Sierra Club, which said this week that for the first time in its 120-year history it would pursue a strategy of civil disobedience to oppose the pipeline. Obama’s mention of acts of civil disobedience in Selma, Ala., Seneca Falls, N.Y., and Manhattan’s Stonewall inspired their action, said the club’s executive director, Michael Brune.

"We want him to follow up that speech by exercising his full authority as an executive," Brune said, "but also his full abilities as chief persuader."