Scientists and economists have been offered $10,000 each by a lobby group funded by one of the world's largest oil companies to undermine a major climate change report due to be published today.

Letters sent by the American Enterprise Institute (AEI), an ExxonMobil-funded thinktank with close links to the Bush administration, offered the payments for articles that emphasise the shortcomings of a report from the UN's Intergovernmental Panel on Climate Change (IPCC).

Travel expenses and additional payments were also offered.

The UN report was written by international experts and is widely regarded as the most comprehensive review yet of climate change science. It will underpin international negotiations on new emissions targets to succeed the Kyoto agreement, the first phase of which expires in 2012. World governments were given a draft last year and invited to comment.

The AEI has received more than $1.6m from ExxonMobil and more than 20 of its staff have worked as consultants to the Bush administration. Lee Raymond, a former head of ExxonMobil, is the vice-chairman of AEI's board of trustees.

The letters, sent to scientists in Britain, the US and elsewhere, attack the UN's panel as "resistant to reasonable criticism and dissent and prone to summary conclusions that are poorly supported by the analytical work" and ask for essays that "thoughtfully explore the limitations of climate model outputs".

Climate scientists described the move yesterday as an attempt to cast doubt over the "overwhelming scientific evidence" on global warming. "It's a desperate attempt by an organisation who wants to distort science for their own political aims," said David Viner of the Climatic Research Unit at the University of East Anglia.

"The IPCC process is probably the most thorough and open review undertaken in any discipline. This undermines the confidence of the public in the scientific community and the ability of governments to take on sound scientific advice," he said.

The letters were sent by Kenneth Green, a visiting scholar at AEI, who confirmed that the organisation had approached scientists, economists and policy analysts to write articles for an independent review that would highlight the strengths and weaknesses of the IPCC report.

"Right now, the whole debate is polarised," he said. "One group says that anyone with any doubts whatsoever are deniers and the other group is saying that anyone who wants to take action is alarmist. We don't think that approach has a lot of utility for intelligent policy."

One American scientist turned down the offer, citing fears that the report could easily be misused for political gain. "You wouldn't know if some of the other authors might say nothing's going to happen, that we should ignore it, or that it's not our fault," said Steve Schroeder, a professor at Texas A&M university.

The contents of the IPCC report have been an open secret since the Bush administration posted its draft copy on the internet in April. It says there is a 90% chance that human activity is warming the planet, and that global average temperatures will rise by another 1.5 to 5.8C this century, depending on emissions.

Lord Rees of Ludlow, the president of the Royal Society, Britain's most prestigious scientific institute, said: "The IPCC is the world's leading authority on climate change and its latest report will provide a comprehensive picture of the latest scientific understanding on the issue. It is expected to stress, more convincingly than ever before, that our planet is already warming due to human actions, and that 'business as usual' would lead to unacceptable risks, underscoring the urgent need for concerted international action to reduce the worst impacts of climate change. However, yet again, there will be a vocal minority with their own agendas who will try to suggest otherwise."

Ben Stewart of Greenpeace said: "The AEI is more than just a thinktank, it functions as the Bush administration's intellectual Cosa Nostra. They are White House surrogates in the last throes of their campaign of climate change denial. They lost on the science; they lost on the moral case for action. All they've got left is a suitcase full of cash."

On Monday, another Exxon-funded organisation based in Canada will launch a review in London which casts doubt on the IPCC report. Among its authors are Tad Murty, a former scientist who believes human activity makes no contribution to global warming. Confirmed VIPs attending include Nigel Lawson and David Bellamy, who believes there is no link between burning fossil fuels and global warming.