Today, experts say such refugees may already number in the millions and could reach 200 million by century's end, stoking tensions and potential for conflict.

They point to Inuit communities literally undercut by melting ice in North America and Greenland, to the thirsty peoples around central Africa's fast-shrinking Lake Chad and the tens of thousands displaced from New Orleans by Hurricane Katrina.

In the future, these ranks could be swollen by refugees fleeing flooded homes, parched farmland or wrecked economies, from small island states in the Pacific to tropical Africa and the Mediterranean rim.

"The issue of environmental refugees promises to rank as one of the foremost human crises or our time," Norman Myers, an Oxford University professor.

What constitutes a refugee can stoke emotive debate.

Critics of the term say it is a politically-charged misnomer, liable to hype or inaccuracy.

Climate refugees, they argue, should not be confused with people who flee their homes because of ecological stress caused by over-population, pollution, abuse of freshwater or other acts of greed, ill judgement or bad planning.

In the case of Katrina, scientists acknowledge a single extreme weather event cannot by itself be pinned to a long-term phenomenon, although they also point out that warmer seas provide raw fuel to make hurricanes more vicious.

But they also say that global warming is already amplifying environmental problems in many countries -- and in the future, it will almost certainly help to push vulnerable communities over the edge.

"There is going to be a lot of population movement linked to climate," said Thomas Downing, director of the Stockholm Environment Institute in Oxford.

"Not all will be permanent refugees, but when you add climate to other forces that push people beyond the capacity to cope, the numbers will increase."

A Red Cross and Red Crescent study in 2000 said 25 million people had left their homes because of environmental stress, roughly as many as the refugees from armed conflict.

Myers, one of the leading experts on the link between climate change and forced migration, says the number could double by 2010 and reach as high as 200 million "once global warming kicks in."

For fragile island nations such as Tuvalu in the South Pacific and Maldives in the Indian Ocean, global warming poses a triple threat.

Warmer seas spell a threat to the coral upon which islanders depend to attract both fish and tourists; decreasing rainfall threatens drinking water supplies; and higher sea levels pose a threat by storm flooding or even inundation.

In the densely populated flood-plains of Bangladesh, rising seas will not only ruin fertile flood plains but stoke the storm surges that periodically ravage the low-lying nation.

Drought or water stress is another problem. According to one study, the crippling heatwave that struck Western Europe in 2003 and left tens of thousands dead is likely to be commonplace by 2100, a scenario that is especially bleak for people on the Mediterranean coast and its hinterland.

But even in cases where global warming is clearly to blame, there exists no clear mechanism to help its victims or provide legal redress against the polluters who caused the problem.

"There is no legal recognition of people displaced by environmental causes" and no international treaty protecting them, explained Stephanie Long of Friends of the Earth International.

On Friday, the UN's top expert forum on global warming, the Intergovernmental Panel on Climate Change (IPCC) was to issue an update of the scientific knowledge for global warming.

A draft IPCC document seen by AFP said Earth's surface temperature could rise by up to 4.5 C (8.1 F) or even higher if carbon dioxide (CO2) levels double over pre-industrial levels.

On current trends, this pollution level could be reached early in the next half of this century.

Sea levels would rise by between 28 and 43 centimetres (11.2-17.2 inches).

Downing says the refugee issue is getting short shrift among both scientists and policymakers. Tens of millions of people without homes or jobs provides fuel for friction.

"The IPCC should be assessing the big risks -- and refugees should be one of those issues, in so far as it has the capacity to affect world stability."

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