Delegates at UN climate change talks are close to agreeing a document that could shape environmental policies for decades, sources close to the talks said this evening.
The document, which gives a summary of the latest scientific knowledge on the causes and effects of climate change, will be put before environment ministers at a meeting next month in Bali, Indonesia, which is likely to agree a two-year strategy to negotiate a successor to the Kyoto Protocol.
"I think the final agreement will be reached this afternoon and after this, no politician will be able to argue that they don't know what is happening," said Han Verolme, director of the World Wildlife Fund conservation group's Climate Change Programme, after a negotiating session that lasted all night.
"This meeting is a landmark that will influence policymakers for decades," he told reporters at a news briefing. The report says climate change is "unequivocal" and that human activities, led by burning fossil fuels, are "very likely" to blame.
"Very strong language from the IPCC will require governments to take strong action," Mr Verolme said. "The ball is in the politicians' court."
Scientists and government officials from the 130-state Intergovernmental Panel on Climate Change (IPCC) have been meeting all week in Valencia to boil down the findings of three reports they have issued this year about the risks of warming. The report will be presented tomorrow.
Running to over 3,000 pages, the reports on the causes, consequences and possible remedies for climate change are being turned into a summary for policy-makers to make progress on the issue at the Bali meeting, which is expected to lay down the climate change agenda after Kyoto's first period ends in 2012.
The summary is set to say that human activity is causing rising temperatures and says deep cuts in greenhouse gas emissions, mainly from burning fossil fuels, are needed to avert ever more heat waves, melting glaciers and rising sea levels.
The Kyoto treaty obliges 36 industrial nations to cut emissions by at least five per cent below 1990 levels by the time the treaty expires in 2012.
A new deal would aim to involve outsiders led by the US and China, the world's top two emitters which have no Kyoto goals.
The IPCC has drawn much more attention since it became the joint winner of the 2007 Nobel Peace Prize along with former US vice president Al Gore and this has meant that governments are watching and shaping its conclusions with even more care.
With the summary agreed, delegates will turn to other issues, including what to consider in a next report likely around 2013. "That would be the start of a discussion that will last into next year," a delegate said.
This year's IPCC reports are good at describing global warming but are far less precise in pinpointing which regions are most at risk from droughts, floods or storms. And there are still uncertainties about climate science, such as whether there will be more or less clouds in a warmer world. The white tops of clouds can bounce heat back into space and slow warming.