The UN's climate panel warns evidence is mounting each year of changes to Earth's weather system as it begins talks on a new global warming report.
The world's paramount authority on the greenhouse effect, the Intergovernmental Panel on Climate Change (IPCC), will on Friday release the first volume of a comprehensive report on climate change, its impacts and ways to cope with the challenge.
The IPCC, co-winner of Nobel Peace Prize in 2007, gathers an army of specialists in physical science, agronomics, biology, economies and sociology. They have written four previous overviews in the panel's 25-year history.
"The scientific evidence of... climate change has strengthened year after year, leaving few uncertainties apart from the serious consequences," the panel's chairman Rajendra Pachauri said at the start of a gathering on Monday leading up to the report's release.
The panel on Friday will issue a main text on the physical science for climate change, plus a far smaller summary for policymakers, which is vetted by governments.
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"I'm looking forward to working with you in the next four days to deliberate and approve (this summary) line by line," said Pachauri.
The volume is expected to paint a bleak picture of climate change in the coming decades.
The worst-case scenario, based on relentless emissions of heat-trapping fossil-fuel gases, predicts warming of more than triple the target set by vulnerable small-island states.
"Climate change is one of the greatest challenges of our time," said Thomas Stocker, co-chairman of the working group that has written the volume.
"Because this change threatens our primary resources, land and water - in short, because it threatens our only home - we must face this challenge."
He said the report was based on millions of measurements in the atmosphere, in the ocean, on land, in ice, and from space.
"I know of no document that has undergone this scrutiny and that has involved so many critical people who offered their insight and advice. This is what makes this report so unique," he said.
