WASHINGTON — The number of Americans who believe there is solid evidence that the Earth is warming because of pollution is at its lowest point in three years, according to a survey released Thursday.
The poll of 1,500 adults by the Pew Research Center for the People & the Press found that only 57 percent believe there is strong scientific evidence that the Earth has gotten warmer over the past few decades, and as a result, people are viewing the problem as less serious. That's down from 77 percent in 2006.
The steepest drop occurred during the last year, as Congress and the Obama administration have taken steps to control heat-trapping emissions for the first time. The drop also was seen during a time of mounting scientific evidence of climate change — from melting ice caps to the world's oceans hitting the highest monthly recorded temperatures this summer.
The poll was released a day after 18 scientific organizations wrote Congress to reaffirm the consensus behind global warming.
"The priority that people give to pollution and environmental concerns and a whole host of other issues is down because of the economy and because of the focus on other things," said Andrew Kohut, the director of the research center, which conducted the poll from Sept. 30 to Oct. 4. "When the focus is on other things, people forget and see these issues as less grave."
Despite misgivings about the science, half the respondents still said they supported limits on greenhouse gases, even if it could lead to higher energy prices. But many of those supporters have heard little to nothing about cap-and-trade, the main mechanism for reducing greenhouse gases favored by the White House and central to legislation passed by the House and a bill the Senate will take up next week.
Under cap-and-trade, a price is put on each ton of pollution and businesses can buy and sell permits to meet emissions limits.
Other results of the survey also suggest that it will be tough politically to enact a law limiting emissions of global warming pollution. While three-quarters of Democrats believe the evidence of a warming planet is solid, and nearly half believe the problem is serious, far fewer conservative and moderate Democrats see the problem as grave as they did last year.
Earlier polls, from different organizations, have not detected a growing skepticism about the science behind global warming.
Since 1997, the percentage of Americans that believe the Earth is heating up has remained constant — at around 80 percent — in polling done by Jon Krosnick of Stanford University. Krosnick, who has been conducting surveys on attitudes about global warming since 1993 was surprised by the Pew results.
He described the decline in the Pew results as "implausible," saying there is nothing that could have caused it.