Blair may be saying that a deal on climate could be in the pipeline, but every day our politicians dither, the science gets stronger. No more so than the latest report from 2000 of the world’s leading climate scientists, who argue that the effects of man-made emissions of carbon dioxide are being felt now on every continent.

A draft copy of the fourth report of the Intergovernmental Panel on Climate Change (IPCC) says that global temperature rises this century of between 2C and 4.5C are almost inevitable. It also says that much higher increases of 6C “or more” cannot be ruled out.

In addition to rising surface temperatures around the world, scientists have now linked man-made emissions of greenhouse gases to significant increases in ocean temperatures, rises in sea levels and the dramatic melting of Arctic sea ice over the past 35 years.

The final version of the IPCC’s latest report will be published on Friday but a draft copy, seen by The Independent newspaper, makes it clear that climate change could be far worse than previously thought because of potentially disastrous “positive” feedbacks which could accelerate rising temperatures.

All the climate models used by the IPCC also found that rising global temperatures will erode the planet’s natural ability to absorb man-made CO2. This could lead to CO2 concentrations in the atmosphere rising by a further 44 per cent, causing global average temperatures to increase by an additional 1.2C by 2100.

The IPCC’s Fourth Assessment Report will go further than any of its three previous reports in linking the clear signs of global climate change with increases in man-made emissions of CO2 and other greenhouse gases since the start of the Industrial Revolution.The IPCC says that over the coming century we are likely to see big changes to the Earth’s climate system. These include:

* Heat waves, such as the one that affected southern Europe in summer 2003, are expected to be more intense, longer-lasting and more frequent.

* Tropical storms and hurricanes are likely to be stronger, with increased rainfall and higher storm surges flooding coastlines.

* The Arctic is likely to become ice free in the summer, and there will be continued melting of mountain glaciers, ice caps and ice sheets.

* Sea levels will rise significantly even if levels of CO2 are stabilised. By 2100 sea levels could be 0.43 metres higher on average than present, and by 2300 they could be up to 0.8 metres higher.

Other key findings:

* Global temperatures continue to rise with 11 of the 12 warmest years since 1850 occurring since 1995. Computer models suggest a further rise of about 3C by 2100, with a 6C rise a distant possibility

* It is virtually certain that carbon dioxide levels and global warming is far above the range of natural variability over the past 650,000 years

* It is virtually certain that human activity has played the dominant role in causing the increase of greenhouse gases over the past 250 years

* Man-made emissions of atmospheric aerosol pollutants have tended to counteract global warming, which otherwise would have been significantly worse

* The net effect of human activities over the past 250 years has very likely exerted a warming influence on the climate

* It is likely that human activity is also responsible for other observed changes to the Earth’s climate system, such as ocean warming and the melting of the Arctic sea ice

* Sea levels will continue to rise in the 21st Century because of the thermal expansion of the oceans and loss of land ice

* The projected warming of the climate due to increases in carbon dioxide during the 21st Century is likely to cause the total melting of the Greenland ice sheet during the next 1,000 years, according to some computer forecasting models

* The warm Gulf Stream of the North Atlantic is likely to slow down during the 21st Century because of global warming and the melting of the freshwater locked up in the Greenland ice sheet. But no models predict the collapse of that warm current by 2100.