The world leaders at the U.N. climate conference in Copenhagen are trying to prove wrong an adage widely attributed to Mark Twain: "Everybody talks about the weather, but nobody does anything about it." Twain might win that argument, though.

Sarah Palin certainly seems to think so. She wrote in The Washington Post, "The agenda-driven policies being pushed in Copenhagen won't change the weather, but they would change our economy for the worse."

The problem is that global warming has been losing urgency as an issue in the United States. That decline puts this country out of step with the rest of the world -- or almost all of the rest of it. The BBC World Service/GlobeScan poll has been tracking global opinion on climate change since 1998. The poll found that concern has been falling in only two of the 23 countries it surveyed, the United States and China.

That finding is no small problem. The U.S. and China together are responsible for 40 percent of the world's greenhouse-gas emissions. By 2020, China's emissions are expected to top those of the United States. But the two countries have been fundamentally at odds over who should bear the greater burden of curbing emissions -- developed countries that have been polluting the atmosphere for decades, or developing countries, which will account for 97 percent of the growth in emissions during the next decade (with half of that increase coming from China).

The Environmental Protection Agency has declared that greenhouse gases are a threat to human health, thus making them liable to regulation under the Clean Air Act. Businesses are fearful of regulation; they feel more comfortable with legislation, which they can influence as it goes through Congress. The Obama administration agrees. "We need legislation," EPA Administrator Lisa Jackson said.

A cap-and-trade bill to control emissions passed the House in June by a narrow margin, 219-212. That's just over 50 percent. In the Senate, such legislation could be blocked by a filibuster unless it attracts 60 percent support. Moreover, sparsely populated rural states and energy-producing states all have two senators apiece who are likely to be skeptical of cap-and-trade legislation and nervous about the fact that 2010 is a congressional election year. Many House Democrats are worried about paying a political price for having supported the legislation.

The belief that global warming is caused by humans has been declining for months.

Most Americans continue to see global warming as real. But the numbers have been going down, from 80 percent to 72 percent over the past year in the ABC News/Washington Post poll. The more striking decline is in the number of respondents who believe that global warming is caused by human activity. In 2007, according to a Harris poll, 71 percent of Americans said they thought that increased greenhouse-gas emissions would lead to global warming. That number is now just 51 percent.

In CNN polls conducted in 2007 and 2008 by Opinion Research, majorities of Americans believed that global warming is mostly caused by emissions from cars and industrial facilities. That view has since dropped to 45 percent. There has been a sharp increase in the number who believe that "global warming is a theory that has not yet been proven" (23 percent in 2008; 31 percent now).

Is it because of Climategate, e-mails written by scientists at a British university that were hacked last month? Those e-mails suggest that climate scientists were manipulating data to discredit global-warming skeptics. In a Pew Research Center poll, only 56 percent of Americans said they thought that scientists generally agree that humans are responsible for global warming. Among scientists polled by Pew, the figure actually was 84 percent. The Pew poll was taken in July, months before Climate-gate broke. The belief that global warming is caused by humans has been declining for months.

The real reason for the drop? Politics. CNN found that the falloff has been almost entirely among Republicans. The Post reports that "the increase in climate skepticism is driven largely by a shift within the GOP." The issue of climate change has been embraced by a Democratic president whom Republicans are determined to oppose. Moreover, Palin and other conservatives have linked the issue to "politicized science." Her assertion, which appears to be gaining traction within the GOP, is, "We can't say with assurance that man's activities cause weather changes."

Sarah Palin, meet Mark Twain.

This article appeared in the Saturday, December 19, 2009 edition of National Journal.

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