The upcoming UN report on climate change is not likely to rattle US deniers of global warming who hold sway in the halls of power, experts say.
A hefty analysis of the latest science on global climate change, the report is packed with recommendations for policymakers.
It will be released at the Intergovernmental Panel on Climate Change (IPCC) next week, though most Republicans in the US government are expected to dismiss it outright.
"The IPCC report will help for the observers and the public to understand where the majority of the scientists' opinion stands," said Alden Meyer of the Union of Concerned Scientists.
"But I don't think it will change the mind of the hard core deniers."
Meyer added: "We don't call them skeptics, because they are not putting forward alternatives ideas and having them tested in a peer review journals. They basically deny this problem."
Climate skeptics and deniers dominate the House of Representatives, but Meyer said some legislators admit privately that the science is correct and that global warming is being exacerbated by fossil fuel use.
"But they cannot say it because they will be challenged in the primary (elections in 2014) by the Tea Party," the ultraconservative wing of the Republican party.
They "say what they have to say to get reelected," Meyer told AFP.
Public opinion polls have shown that an increasing number of Americans believe climate change is real.
According to a Pew research poll this spring, 69 percent of Americans, a 12 point hike over 2009, believe there are strong indications the planet is getting warmer.
However, these surveys have also shown that a just a third of the US public thinks climate change is a serious problem..
Surveys also show a stark partisan divide, with 50-58 percent of Republicans saying they do not believe that climate change is happening.
Americans' views on climate change are closely linked to their political orientations; those who doubt the theory of evolution and believe in creationism are often climate skeptics or deniers, according to Joe Casola, an expert at the Center for Climate and Energy Solutions in Washington.
"With the IPCC report, the older arguments—that climate change does not exist or CO2 is not responsible for warming or the humans are not responsible—are harder and harder to make," he said.
"I think there was a subtle shift in the last few months to focusing more on this kind of future tense that warming will not be that bad," he added.
"It will be interesting to see if the old arguments come back, or if they shift to the new ones."
According to Meyer, the Republican thinking on climate science has made it harder for the US political system to enact alternative policies to slow the pollution from cheap fossil fuels.
The movement to deny climate change is bolstered by influence groups that oppose regulations that would limit CO2 emissions, the main greenhouse gas, which the United States emits more of than any other country but China.
According to Greenpeace, these lobbies have funnelled nearly $150 million to more than 80 conservative groups from 2002 to 2011. Among the largest donors are billionaires Charles and David Koch of Koch Industries, as well as oil giant ExxonMobil.
"Their intent is to intimidate scientists and, indeed, to get them to second guess themselves," said Michael Mann, professor at Penn State University and author of "The Hockey Stick and the Climate War."
"In that sense, the hundreds of millions of dollars spent by industry front groups and individuals like the Koch Brothers to attack and intimidate the scientists have partly achieved their goal," Mann told AFP.
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