A major report on climate change being compiled by the United Nation's climate science panel was on Friday leaked online in what appeared to be an attempt by a climate sceptic to discredit the panel.
The Intergovernmental Panel on Climate Change (IPCC) said the full draft of its Fifth Assessment Report, which is not set for official publication until next September, had been published online by one of 800 experts contributing to the report.
The climate body did not identify the culprit, but a climate sceptic named Alec Rawls announced in a blog posting that he had posted the report in what appeared to be a bid to discredit it.
The IPCC is a favoured target for sceptics, who stirred a scandal in the run up to a UN climate summit in Copenhagen in 2009 by pointing out flaws in the panel's landmark Fourth Assessment Report.
Perhaps anticipating a similar attack, the IPCC warned Friday that "the unauthorised and premature posting of the drafts (of the Fifth Assessment Report), which are works in progress, may lead to confusion because the text will necessarily change."
The body pointed out that the report had been reviewed in October and November by the 800 experts and 26 governments, who together had submitted 31,422 comments that needed to be considered.
It also stressed that the authors would still be accepting peer-reviewed published literature contributions until mid-March.
"The text that has been posted is thus not the final report," it said.
The Fourth Assessment Report, which was published in 2007, marked a turning point in the history of climate change.
It declared there was scientific consensus that Earth was warming as a result of carbon from fossil fuels and that signs of climate change were already visible.
It built momentum for global action against emissions from burning coal, gas and oil, and helped earn the IPCC a share in the 2007 Nobel Peace Prize along with US climate campaigner and ex-US vice president Al Gore.
The Fifth Assessment Report will meanwhile be issued in three volumes starting from next September, but it is the first volume on the physics of climate change that will be most closely scutinised.
Scientists associated with the drafting of the report said Friday the leaking of the draft was an abuse of confidentiality and an assault on peer review, a process whereby scientific evidence is weighed and discussed without external pressure.
They said that the document was in any case only at a preliminary stage and would be vetted several times, including by policymakers, before it is approved.
"It's a pity, but it's not the end of the world," said French expert Jean Jouzel, who is vice president of the IPCC group drafting the first volume.
"It won't stop the way that we work. These are only provisional documents and far from being the final version. We have more than 31,000 comments to take into account" before publication, Jouzel told AFP.
Some scientists also attacked what they said was deliberate selection of data in a long and complex document in order to serve the sceptics' view.
Bob Ward, policy director at the Grantham Research Institute on Climate Change and the Environment at London School of Economics (LSE), said the leak was "cherry-picking quotes out of context."
In his posting, Rawls for instance charged that the draft report proved the importance of solar influence on climate change but that the authors were trying to downplay that fact -- something he said resulted in "an un-scientific absurdity."
"In fact, the draft report concludes that there are strong arguments against the cosmic ray theory, while there is compelling evidence that greenhouse gas emissions are driving the unequivocal rise in global average temperature," he said.