Mass movements of people across the world are likely to be one of the most dramatic effects of climate change in the coming century, a study suggests.
The report, from the aid agency Tearfund, raises the spectre of hundreds of millions of environmental refugees and says the main reason will be the effects of climate - from droughts and water shortages, from flooding and storm surges and from sea-level rise.
The study, "Feeling the Heat", says there are already an estimated 25 million environmental refugees, and this figure is likely to soar as rain patterns continue to change, floods and storms become more frequent and rising tides start to inundate low-lying countries such as Bangladesh or some of the Pacific islands.
Tearfund says that without urgent action, world governments will lose the fight to tackle the world water crisis and the growing threat of climate-change refugees in catastrophic numbers.
The report calls for governments at the UN Climate Change conference, beginning in Nairobi in a fortnight, to move towards a global framework for cutting climate-changing greenhouse gases such as carbon dioxide that goes beyond the existing climate treaty, the Kyoto protocol, and to commit billions more to help poor countries adapt to the coming changes.
"There will be millions more thirsty, hungry and ill poor people living in high-risk areas of the world by the end of the century," the report says. "It makes sense politically, economically and morally, for governments to act with urgency now."
Andy Atkins, advocacy director of Tearfund, said one of the most devastating impacts of climate change was on water supply. "In some parts of the world, floods, storms and poor rainfall are beginning to have catastrophic effects, threatening the lives and livelihoods of millions of people," he said.
This process will be steadily exacerbated, the report says, by the differing yet equally serious changes predicted to be part of a warming world. While some parts of the globe may experience much less rainfall and thus drought, others regions will have much more intense rain likely to bring about flooding. Sea-level rise , which a recent report suggested could be up to 50cm by 2050, would at that rate breach 100,000 kms (62,000 miles) of coastline around the world.
The report says: "As floods, drought and storms increase climate change will have a potentially catastrophic impact on water supply, threatening the lives and livelihoods of millions of people. Poor people - like the 80 per cent of Malawi's population who farm small plots - are reliant on rain for their harvests, and are least able to adapt to climate change. By exacerbating existing water stresses, climate change impacts many other areas of human development such as health and even industry."
It goes on: "Already, there are an estimated 25 million environmental refugees - more than half the number of political refugees. Experts such as the ecologist Norman Myers suggest this figure could soar to 200 million in less than 50 years. Unseen and uncounted, millions are already on the move in search of greater water security. In some countries, the exodus began years ago."
In the report's foreword, Sir John Houghton, former chairman of the Scientific Assessment Working Group of the Intergovernmental Panel on Climate Change, says politicians' strong words on climate change must now be matched by sufficient investment and strong action to cut global emissions, and help for the poorest nations adapt to climate change on their doorstep. A key to this will be helping poorer nations manage existing water supplies more efficiently.
"If your house is on fire, do you urgently try to save it, or throw your hands up in despair and walk away?" Sir John saysd. "Well, the house is on fire and it requires much more determined efforts to bring it under control and put it out. The UN climate change conference in Nairobi is an opportunity for failings to be addressed. Time is running out on us and world governments need to act much more responsibly, effectively and quickly."
The devastating impact
The report cites examples of where water problems are already causing a mass exodus or movement of people. They include:
* Poor crop yields are forcing more and more Mexicans to risk death by illegally fleeing to the US.
* One in five Brazilians born in the arid north-east of the country are moving to avoid drought.
* The spread of the Gobi desert, at a rate of 4,000 square miles a year, is forcing the populations of three provinces in China to abandon their homes.
* In Nigeria, 1,350 sq miles of land is turning to desert each year. Farmers and herdsmen are being forced to move to the cities.
* The population of Tuvalu, a group of eight Pacific islands north-east of Australia, is already being evacuated; nearly 3,000 Tuvalans have left so far.