A United Nations panel of experts is meeting to review the final draft of a scientific report to be released on Friday that will lay the responsibility for global warming fairly squarely on humans.
The long-awaited report raises the probability that climate change is 95 per cent the responsibility of humans and warns of ever more extreme weather unless governments take strong action.
Reuters Newsagency reports scientists and officials from more than 110 governments began a four-day meeting in the Swedish capital, Stockholm, to edit and approve the 31-page draft.
The document will also try to explain a “hiatus” in the pace of global warming this century despite rising greenhouse gas emissions.
The Intergovernmental Panel on Climate Change (IPCC) will go through the document line by line and present it on Friday as a main guide for governments, which have agreed to work out a UN deal by the end of 2015 to fight global warming.
“I expect the world will understand the simplicity and the gravity of the message that we provide,” Dr Rajendra Pachauri, chairman of the IPCC, said after the opening session.
Climate change “will transform our lives, our economies and indeed the way our planet will function in the future,” Achim Steiner, head of the UN Environment Program, told delegates.
A shift towards a greener economy, based on renewable energies, would hold multiple benefits for society, he said.
IPCC drafts seen by Reuters say human activities, primarily burning fossil fuels, are “extremely likely”, at least a 95 per cent probability, to be the main cause of global warming since the 1950s.
That is up from “very likely”, or at least a 90 per cent probability, in the last report in 2007 and 66 per cent in 2001, draining hopes that natural variations in the climate might be the cause.
“There is high confidence that this has warmed the ocean, melted snow and ice, raised global mean sea level, and changed some climate extremes,” the draft says of man-made warming.
Most impacts are projected to get worse unless governments cut greenhouse gas emissions sharply, it says.
The report, by 259 authors in 39 countries, is the first of four due in the next year about climate change by the IPCC.
One of the hardest issues for the IPCC may be accounting for why temperatures have not risen much this century.
“Fifteen-year-long hiatus periods are common,” in historical climate records, an accompanying 127-page technical summary says.
Reuters reports a combination of natural variations, including a cyclical dip in energy emitted by the sun, and factors such as volcanic eruptions, which send ash into the atmosphere and help block sunlight, have caused the hiatus, it says, predicting a resumption of warming in coming years.
The report also finds that the atmosphere may be slightly less sensitive to a build-up of carbon dioxide than expected.
Thomas Stocker, a scientist from the University of Bern who is co-chair of the UN panel, urged delegates to produce a clear document “with no compromises to scientific accuracy.”
The draft says temperatures could rise by up to 4.8 degrees Celsius this century, but could be held to a rise of 0.3 degrees Celsius with deep cuts in greenhouse gas emissions.
Governments have promised to limit a rise in temperatures to two degrees Celsius above pre-industrial times.
The draft also says sea levels, which rose 19 centimetres in the 20th century, could rise by an extra 26cm to 81cm towards the end of this century, threatening coasts.
That rise is more than was projected in 2007, although that report did not take full account of melting ice in Greenland and Antarctica.
The report is the main guide for governments planning action against global warming and steps to mitigate its effects.
Environmentalists have already called for quick action, with Greenpeace urging governments to heed the report and shift to clean energies.
The WWF’s Samantha Smith said: “The natural world is sending a distress signal and we’re ignoring it at our own peril.”
