The UN climate panel should only make predictions when it has solid evidence and should avoid policy advocacy, scientists said in a report Monday that called for thorough reform of the body.
The UN Intergovernmental Panel on Climate Change (IPCC) was hit with a wave of criticism after acknowledging in January that its 2007 global warming report had exaggerated the pace of Himalayan glaciers melting. It had previously said the report overstated how much of the Netherlands is below sea level.
"Qualitative probabilities should be used to describe the probability of well-defined outcomes only when there is sufficient evidence," said a review group supported by the academies of science from the United States, Netherlands, Britain and other countries.
The report said the IPCC's mandate calls for it to be "policy relevant" without advocating specific policies. But some IPCC leaders have been criticized for remarks that appeared to support specific policy approaches.
"Straying into advocacy can only hurt IPCC's credibility," the report said.
The review said the limit of two six-year terms for the chair of the IPCC, currently Rajendra Pachauri of India, was too long and should be shortened to one term, as should the terms of other senior officials at the UN climate panel.
The report did not call for replacing Mr. Pachauri, IPCC chairman since 2002. Asked if he would consider resigning if requested to, Mr. Pachauri told reporters he would abide by any decision the IPCC made.
The report also called for an overhaul of the panel's management, including the creation of an executive committee that would include people from outside the IPCC.
Regarding the errors in IPCC reports, the review group called for stronger enforcement of the panel's scientific review procedures to minimize future mistakes.
Harold Shapiro, a Princeton University professor and chair of the committee that reviewed the IPCC's work, told reporters one report by an IPCC working group "contains many statements that were assigned high confidence but for which there is little evidence."
Mr. Shapiro said the IPCC's response to errors when they were subsequently revealed was "slow and inadequate."
The errors, he said, "did dent the credibility of the process."
Asked about the Himalayan glaciers error, Mr. Shapiro said, "At least in our judgment, it came from just not paying close enough attention to what (peer) reviewers said about that example."
He added that there was concern about the UN climate panel's lack of a conflict of interest policy. The report called for development of a "rigorous conflict of interest policy" that applies to all top IPCC officials.
Achim Steiner, Head of the U.N. Environmental Program said the review of the IPCC "re-affirms the integrity, the importance and validity of the IPCC's work while recognizing areas for improvement in a rapidly evolving field."
UN Secretary-General Bank Ki-moon has acknowledged there were a small number of mistakes in what is known as the Fourth Assessment Report published in 2007, a document of more than 3,000 pages that cited more than 10,000 scientific papers. But he has insisted its fundamental conclusions were correct.
Critics of the idea of mandatory limits on so-called greenhouse gas emissions have said the IPCC errors show the science behind global warming is questionable.
The United Nations has been concerned that focusing only on IPCC errors could undermine the broader U.N. message that climate change is a real phenomenon requiring urgent action.
The next IPCC report on climate change will be published in 2013 and 2014.