An upcoming United Nations report on climate change has been altered after the expert review stage, with changes added that downplay the economic impacts of a warming planet, according to one of the reviewers.
Bob Ward, an expert reviewer for the Intergovernmental Panel on Climate Change, also said alterations to the economics chapter of the draft report sent to governments included an assessment of a paper by the chapter's own convening lead author Richard Tol that contained at least one error.
An added section also included a line likely to be hotly contested if it survives a final review by IPCC delegates gathered this week in Yokohama, Japan, to approve the Working Group II report: "Estimates agree on the size of the impact (small relative to economic growth) but disagree on the sign."
Mr Ward said disagreement over whether the sign of climate change's economic impact is positive or negative "is patently not supported by the evidence presented".
Of the data assessed, only one study out of about 18 suggests there would be a significant positive impact on gross domestic product from global warming, Mr Ward told the IPCC in an email seen by Fairfax Media.
Earlier analysis of economic costs by one of the assessed papers - by Professor Tol - also "excluded a long list of important impacts, including those relating to recreation, tourism, extreme weather, fisheries, construction, transport, energy supply and morbidity," said Mr Ward, who is also a policy director at the London School of Economics.
Professor Tol, who is a professor at University of Sussex in the UK, said Mr Ward's complaints were reviewed "and found that most of them were unfounded". One typo was identified and a dropped minus sign was re-instated. "Both errors have been corrected," Professor Tol said.
In a paper published last year, Professor Tol stated that "the impact of a century of climate change is roughly equivalent to a year's growth in the global economy," and that "carbon dioxide emissions are probably a negative externality".
Professor Tol is a member of the academic advisory council for The Global Warming Policy Foundation, a climate change sceptic think tank founded by the UK's Lord Lawson. The council also includes prominent Australian sceptics Bob Carter and Ian Plimer, according to its website.
Unless resolved in the final week, a row over the contents of UN report may cast a cloud over some of its major findings, which include the prospect of widespread social dislocation of climate change and big impacts for eco-systems such as Australia's Great Barrier Reef.
Mr Ward said the IPCC had been widely criticised after an early report in 2007 was later found to assert more rapid melting of the Himalayan glaciers than supported by the cited peer-reviewed report.
"The IPCC is supposed to be an assessment," Mr Ward said. "It's not supposed to just regurgitate the information but be a critical review of it."
Mr Ward has also sought corrections from Professor Tol and the publisher of the original paper, Elsevier.
Professor Tol on his blog has described Mr Ward as "Nick Stern's attack dog" in reference to Lord Nicholas Stern who wrote the Stern Review on the Economics of Climate Change in 2006, and accused him of reaching "a new level of trolling".
Delegates in Japan will get to vote on each chapter of the report before approval.
Stanford's Professor Chris Field, co-chair of the Working Group II report, said the authors "did carefully review the issues" raised by Mr Ward. He said the additional material had been transferred from another chapter.
Mr Ward's comments "arrived outside the normal review process, but everyone in the IPCC is glad for the chance to triple-check all of the contents of the report," he told Fairfax, adding the authors "agreed that at least one of the items [Mr Ward] identified was a small error".