The number of Americans who are worried about global warming has fallen to nearly the historic low reached in 1998, a poll released Monday showed.
Just 51 percent of Americans -- or one percentage point more than in 1998 -- said they worry a great deal or fair amount about climate change, Gallup's annual environment poll says.
In 2008, a year after former US vice president Al Gore and the UN Intergovernmental Panel on Climate Change won the Nobel Peace Prize, two-thirds of Americans were concerned about climate change.
The rate of concern among Americans has fallen steadily since then to 60 percent in 2009 and 52 percent last year.
The poll also found that for the first time since the late 1990s, a minority of Americans -- 49 percent -- believe global warming has already begun to impact the planet, down sharply from more than six in 10 Americans who three years ago said climate change was already impacting the globe.
"The reasons for the decline in concern are not obvious, though the economic downturn could be a factor," Gallup analysts say, citing a poll from two years ago that shows that in the minds of Americans, economy takes precedence over environment.
The pollsters also found that a plurality of Americans -- 43 percent -- think the media exaggerates the seriousness of global warming, and that how Americans view climate change and its impacts varies widely depending on their political beliefs.
Just over a quarter of Americans believe reports in the press about climate change are generally correct, while nearly three in 10 believe the US media understates the effects of global warming.
Conservative Republicans are three times as likely as liberal Democrats to think the media is exaggerating the severity of global warming, while Democrats are roughly twice as likely as Republicans to be concerned about climate change and to think it is already impacting the planet.
The year that Americans' concern about the effects of climate change hit its lowest point, 1998, was the year that the Kyoto Protocol, the UN treaty to reduce greenhouse gas emissions worldwide, was open for ratification.
Eighty-four countries ratified the treaty. The United States was not among them.
Gallup's poll was based on telephone interviews conducted March 3 and 6 with 1,021 US adults.
Explore further: Montana oil spill estimate lowered to 30,000 gallons