The UN climate panel agreed its starkest warning yet today that human activities are causing global warming that may bring more droughts, heatwaves and rising seas, delegates said.
The report, due for release tomorrow and bolstering conclusions from a 2001 study, may put pressure on governments and companies to do more to curb greenhouse gases mainly from burning fossil fuels in power plants, factories and cars.
Scientists and government officials in the Intergovernmental Panel on Climate Change (IPCC), the most authoritative group on global warming, agreed it was "very likely" that human activities were the main cause of warming in the past 50 years, delegates said.
In IPCC language, "very likely" means at least 90 percent probability and is the strongest link to human activities since the IPCC was set up in 1988. The previous study in 2001 said a link was "likely", or 66 per cent probable.
IPCC officials declined comment, saying that the report would be issued at 8.30am.
The IPCC, grouping 2,500 scientists from 130 countries, is also set to say that oceans will keep rising for more than 1,000 years even if governments stabilise greenhouse gas emissions.
The report is the first of four this year by the panel that will outline threats of warming.
Delegates said the Paris meeting, looking at the science of global warming, later agreed a "best estimate" that temperatures will rise by 3 degrees Celsius by 2100 over pre-industrial levels, the biggest change in a century for thousands of years.
It says bigger gains, of up to 6.3C in one model, cannot be ruled out but do not fit well with other data. The world is now about 5C warmer than during the last Ice Age.
The draft accord projects that Arctic ice will shrink, and perhaps disappear in summers by 2100, while heatwaves and downpours would get more frequent. The numbers of tropical hurricanes might decrease but the storms would become stronger.
The Gulf Stream bringing warm waters to the North Atlantic could slow, although a shutdown is highly unlikely, it says.
And sea levels are likely to rise by between 28 and 43 cm (11-17 inches) this century, a lower range than forecast in 2001. Rising seas threaten low-lying Pacific islands and low-lying coastal nations from Bangladesh to the Netherlands.
"Governments planning coastal defences have to live with large uncertainties for now, and quite some time in future," said Stefan Rahmstorf of Germany's Potsdam Institute for Climate Impact Research.
Mr Rahmstorf wrote a report last year saying that observations of past changes indicated a bigger rise by 2100, of 50-140 cm.