The group, the most authoritative on climate change with 2,500 scientists from 130 countries, is also due to say that oceans will keep rising for more than 1,000 years even if governments stabilise greenhouse gas emissions this century.

Scientists and government officials in the Intergovernmental Panel on Climate Change (IPCC) have been meeting in Paris since Monday to review the report, including a 15-page summary for policymakers.

“The talks are moving forward,” one IPCC official said. The IPCC says it will publish the results on Friday.

The report, increasing certainty that humans are to blame for warming, may put pressure on governments and companies to do more to curb a build-up of greenhouse gases mainly from burning fossil fuels in power plants, factories and cars.

“It is very likely that (human) greenhouse gases caused most of the observed increase in globally averaged temperatures since the mid-20th century,” according to a final draft.

“Very likely” means a probability of at least 90 per cent — up from a judgment of “likely”, or a 66 per cent probability, in the previous 2001 report. The report is the first of four this year by the panel that will outline threats of warming.

The Paris study, looking at the science of global warming, will also project a “best estimate” that temperatures will rise by 3 C by 2100 over pre-industrial levels, the biggest change in a century for thousands of years. It says bigger gains, of up to 6.3 C in one model, cannot be ruled out but do not fit well with other data. The world is now about 5 C warmer than during the last Ice Age.

The draft projects that Arctic ice will shrink, and perhaps disappear in summers by 2100, while heat waves and downpours would get more frequent. The numbers of tropical hurricanes and typhoons 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 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.

UN officials hope the IPCC report will spur stalled talks on expanding the fight against global warming. Thirty-five industrial nations aim to cut emissions of greenhouse gases to five percent below 1990 levels by 2008-12 under the UN’s Kyoto Protocol and want outsiders such as the United States, China and India to do more. Last week US President George W. Bush said climate change was a “serious challenge”. But he has stopped short of capping emissions despite pressure from Democrats who control both houses of Congress — arguing Kyoto would damage the economy.

Heat’s on

Human factor

• Human greenhouse gas increase may be behind rise in temperatures in last 50 years

• Warming of the climate system is unequivocal, evident in rising average air and ocean temperatures, melting of snow and ice, rising sea levels

• Greenhouse gases would have caused more warming in recent times, partly offset by volcano dust and pollution

Projections

• Temperatures are likely to rise by 2-4.5 degree Celsius above pre-industrial levels. The “best estimate” for the rise is about 3C

• It is “very likely” that extremes such as heat waves and heavy rains will become more frequent.

• Antarctica is likely to stay too cold for widesurface melting and is expected to gain in mass due to more snow

What happens if temperature rises by...

1 degree C

• Shrinking glaciers threaten water for 50 million people

• Modest increases in cereal yields in temperate regions

• At least 300,000 people each year die from malaria, malnutrition and other climate-related diseases

• Reduction in winter mortality in higher latitudes

• 80 per cent bleaching of coral reefs, e.g. Great Barrier Reef

2 degrees C

• 5 - 10% decline in crop yield in tropical Africa

• 40 - 60 million more people exposed to malaria in Africa

• Up to 10 million more people affected by coastal flooding

• 15 - 40% of species face extinction (one estimate)

• High risk of extinction of Arctic species, e.g. polar bear

• Potential for Greenland ice sheet to start to melt irreversibly, committing world to 7- metre sea-level rise

3 degrees C

• In Southern Europe, serious droughts once every 10 years

• 1 - 4 billion more people suffer water shortages

• Some 150 - 550 additional millions at risk of hunger

• 1 - 3 million more people die from malnutrition

• Onset of Amazon forest collapse

• Rising risk of collapse of West Antarctic ice sheet

• Atlantic Conveyor of warm water

• Rising risk of abrupt changes to the monsoon

4 degrees C

• Agricultural yields decline by 15 - 35 per cent in Africa

• Up to 80 million more people exposed to malaria in Africa

• Loss of around half Arctic tundra

5 degrees C

• Possible disappearance of large glaciers in Himalayas, affecting one quarter of China’s population, many in India

• Continued increase in ocean acidity seriously disrupting marine ecosystems and possibly fish stocks

• Sea level rise threatens small islands, coastal areas such as Florida and major cities such as New York, London, and Tokyo