One of the 70 authors of a draft UN report on climate change said he had pulled out of the writing team because it was "alarmist" about the threat.
Richard Tol, a regularly collaborator with well known ‘sceptical’ environmentalist Bjorn Lomborg, told Reuters he disagreed with some findings of the summary to be issued in Japan on March 31.
"The drafts became too alarmist," the Dutch professor of economics at Sussex University in England said by telephone from Yokohama, Japan, where governments and scientists are meeting to edit and approve the report.
But he acknowledged some other authors "strongly disagree with me".
The final draft says warming will disrupt food supplies, slow economic growth, and may already be causing irreversible damage to coral reefs and the Arctic.
"The report is a product of the scientific community and not of any individual author," the UN's Intergovernmental Panel on Climate Change said in a statement. "The report does not comprehensively represent the views of any individual."
It said Tol notified it in September that he was withdrawing from the team writing the summary. He had been invited to Japan to help the drafting and is also the coordinating lead author of a sub-chapter about economics.
Tol, who has sometimes been at odds with other scientists in the past by pointing to possible benefits from global warming, had not made his pullout widely known until now.
The report will help governments prepare a deal to cut rising greenhouse gas emissions, mainly by shifting from fossil fuels to renewable energies, at a summit in Paris in late 2015.
Risk and opportunity
Tol said the IPCC emphasised the risks of climate change far more than the opportunities to adapt. A Reuters count shows the final draft has 139 mentions of "risk" and 8 of "opportunity".
Tol said farmers, for instance, could grow new crops if the climate in their region became hotter, wetter or drier. "They will adapt. Farmers are not stupid," he said.
He said the report played down possible economic benefits of low levels of warming. Less cold winters may mean fewer deaths among the elderly, and crops may grow better in some regions.
"It is pretty damn obvious that there are positive impacts of climate change, even though we are not always allowed to talk about them," he said. But he said temperatures were set to rise to levels this century that would be damaging overall.
Another expert criticised Tol, saying his IPCC chapter exaggerated possible benefits.
"Of the 19 studies he surveyed only one shows net positive benefits from warming. And it's the one he wrote," said Bob Ward, policy and communications director of the Grantham Research Unit on Climate Change and the Environment at the London School of Economics.
The IPCC summary says warming of 2.5 degrees above pre-industrial times will reduce world economic income by between 0.2 and 2.0 per cent a year.
Among rare examples of past dissent within the IPCC, Richard Landsea, a US meteorologist, pulled out of the last report published in 2007, accusing the IPCC of overstating evidence that global warming was aggravating Atlantic hurricanes.