GLOBAL warming is made worse by man-made pollution and even optimistic projections suggest that the Earth will warm by a dangerous 3 degrees by 2050, according to a draft report by the world's leading climate scientists.
The increase will be the biggest in 20,000 years and is likely to cause drought, famine and mass extinction, scientists said.
The report by the Intergovernmental Panel on Climate Change (IPCC) has confirmed that humans are the main force behind warming and that further temperature increases are in store even if emissions are curtailed.
The report will mark the first time the IPCC has placed a figure on the progress of warming, an assurance of scientific certainty that it avoided in its last report in 2001.
The figure is also significant as it follows a report by Sir David King, Britain's chief scientific adviser, that laid out the effects of such an increase - drought, devastated wildlife and 400 million people at risk of starvation.
The IPCC also concludes that temperatures could rise by as much as 6C as the result of "positive feedbacks" in the climate resulting from melting sea ice, thawing permafrost and the acidification of the oceans.
It also finds that climate change will continue for decades and perhaps centuries, even if man-made emissions can be curbed.
It says: "2005 and 1998 were the warmest two years on record. Five of the six warmest years have occurred in the past five years (2001-2005).
"There is widespread evidence of anthropogenic warming of the climate system in temperature observations taken at the surface, in the free atmosphere and the oceans.
"It is very likely that greenhouse gas forcing has been the dominant cause of the observed global warming over the past 50 years."
The move has prompted some scientists and environmental groups to question whether the Bush administration is seeking to defuse its bold conclusions.
Previous IPCC reports have been instrumental in establishing national and international strategies to reduce heat- trapping "greenhouse" gases.
All industrial powers except Australia and the United States have accepted mandatory restrictions on greenhouse gases under the Kyoto Protocol.
The draft document is the report of the IPCC's Working Group 1, which examines scientific findings related to the physical cause of climate change. The analyses of Working Groups II and III, which lay out consequences from the first group's findings and suggest mitigation strategies, have not been released.
The report's strong language should refute climate change sceptics who say rising temperatures are the result of natural variation rather than human activity, environmentalists said.
Stuart Hay, the head of policy and research for Friends of the Earth Scotland said: "This is the most definitive scientific evidence yet that climate change is happening and humans are to blame.
"The IPPC report clearly shows we must end our addiction to fossil fuels or face serious and irreversible consequences for society."
Elliot Morley the minister with responsibility, for climate change said :
"The UK made climate change one of the prime objectives of both the G8 and the EU presidencies in 2005, and we continue to raise the profile of climate change to heads of government.
"This report gives weight to the government's view of the need to tackle climate change at local, national, European and international levels."