Even if dramatic measures are taken to reduce the carbon dioxide (CO2) emissions that drive warming, temperatures will continue to climb for decades to come, the experts are set to conclude.

By 2080, according to the report, it is likely that 1.1 to 3.2 billion people worldwide will experience water scarcity, 200 to 600 million will be threatened by hunger and each year an additional two to seven million will be victims of coastal flooding.

The report by the UN's Intergovernmental Panel on Climate Change (IPCC) will be unveiled on Friday after 400 experts, meeting behind closed doors, approve a roughly 50-page summary for policymakers.

A final draft of the 1,400-page main document obtained by AFP assesses the past and future impact of rising temperatures on the planet's physical and ecological systems and inhabitants, and evaluates the ability to cope with the predicted changes.

It warns that the brunt of the problems will fall squarely on to the world's poorest inhabitants, who are least to blame for the fossil-fuel pollution that drives global warming.

Hundreds of millions of people living in more than three dozen deltas -- including the Nile in Egypt, the Red River in Vietnam and the Ganges-Brahmaputra in Bangladesh -- are likely to find themselves wedged between rising sea levels and more frequent flooding. Tropical diseases are likely to spread as well.

Green groups urged industrialised countries, especially the United States, which accounts for a quarter of global carbon emissions, to step up action.

"The scientific findings are stronger than ever," said Friends of the Earth International's Catherine Pearce.

"This report is likely to confirm that not only are we seeing the impacts of climate change around us already, but worse is yet to come and the world's poorest people are being hardest hit."

"The devastating impacts of climate change are beginning to affect us today," said Lara Hansen, chief scientist with WWF's Global Climate Change Programme.

"Forest fires, coral bleaching, failed crops and species disappearing are all signs of worst things to come. While cutting emissions, governments must address these impacts and protect people and nature."

In February, the IPCC issued a first volume of its latest review with an assessment of the scientific evidence for global warming. It predicted temperatures would probably rise between 1.8 to 4.0 C (3.2-7.2 F) by century's end.

But a rise of as much as 6.4 C (11.5 F) could not be ruled out if carbon emissions and low-efficiency energy use rise unabated and the world's population continues to surge, it said.

A final volume, due to be released in early May, will discuss how warming can be mitigated.

Besides the impact on human society, climate change will also have far-reaching consequences for the planet's biodiversity, the Brussels report will say.

It predicts that 20 to 30 percent of species will be threatened with extinction if temperatures rise 1.5 to 2.5 C (2.7-4.5 F), on the lower side of end-of-century warming forecasts.

If temperatures rise by 4 C (7.2 F), "few ecosystems will be able to adapt," says the report.

Compiled to help governments make policy choices, the report will probably sharpen debate on global warming.

The big issues include demands for funds to help poor countries cope with the stress of climate change -- and how such spending should be balanced against financial demands for slashing the fossil-fuel emissions that stoke the warming.

Set up in 1988, the IPCC, gathering 190 countries, is charged with giving impartial and accurate information about climate change.

This is its fourth so-called assessment report since its inception; the last was in 2001, but the evidence for man-made global warming, and the scientific techniques for monitoring it, have grown hugely since then.

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