Elisabeth Rosenthal is a reporter and blogger on environmental issues for The New York Times.

IN 2008, both the Democratic and Republican candidates for president, Barack Obama and John McCain, warned about man-made global warming and supported legislation to curb emissions. After he was elected, President Obama promised “a new chapter in America’s leadership on climate change,” and arrived cavalry-like at the 2009 United Nations Climate Conference in Copenhagen to broker a global pact.

But two years later, now that nearly every other nation accepts climate change as a pressing problem, America has turned agnostic on the issue.

In the crowded Republican presidential field, most seem to agree with Gov. Rick Perry of Texas that “the science is not settled” on man-made global warming, as he said in a debate last month. Alone among Republicans onstage that night, Jon M. Huntsman Jr. said that he trusted scientists’ view that the problem was real. At the moment, he has the backing of about 2 percent of likely Republican voters.

Though the evidence of climate change has, if anything, solidified, Mr. Obama now talks about “green jobs” mostly as a strategy for improving the economy, not the planet. He did not mention climate in his last State of the Union address. Meanwhile, the administration is fighting to exempt United States airlines from Europe’s new plan to charge them for CO2 emissions when they land on the continent. It also seems poised to approve a nearly 2,000-mile-long pipeline, from Canada down through the United States, that will carry a kind of oil. Extracting it will put relatively high levels of emissions into the atmosphere.