LONDON - Across the world, they are coming: the water wars.
From Israel to India, from Turkey to Botswana, arguments are going on over disputed water supplies that may soon burst into open conflict.
Yesterday, Britain's Defence Secretary, John Reid, pointed to the factor hastening the violent collision between a rising world population and a shrinking world water resource: global warming.
In a grim first intervention in the climate-change debate, the Defence Secretary issued a bleak forecast that violence and political conflict would become more likely in the next 20 to 30 years as climate change turned land into desert, melted ice fields and poisoned water supplies.
Climate campaigners echoed Mr Reid's warning, and demanded that ministers redouble their efforts to curb carbon emissions.
Tony Blair will today host a crisis Downing Street summit to address what he called "the major long-term threat facing our planet", signalling alarm within Government at the political consequences of failing to deal with the spectre of global warming.
Activists are modelling their campaign on last year's Make Poverty History movement in the hope of creating immense popular pressure for action on climate change.
Mr Reid used a speech at Chatham House last night to deliver a stark assessment of the potential impact of rising temperatures on the political and human make-up of the world.
He listed climate change alongside the major threats facing the world in future decades, including international terrorism, demographic changes and global energy demand.
Mr Reid signalled Britain's armed forces would have to be prepared to tackle conflicts over dwindling resources.
Military planners have already started considering the potential impact of global warming for Britain's armed forces over the next 20 to 30 years.
They accept some climate change is inevitable, and warn Britain must be prepared for humanitarian disaster relief, peacekeeping and warfare to deal with the dramatic social and political consequences of climate change.
Mr Reid warned of increasing uncertainty about the future of the countries least well equipped to deal with flooding, water shortages and valuable agricultural land turning to desert.
He said climate change was already a contributory factor in conflicts in Africa.
Mr Reid said: "As we look beyond the next decade, we see uncertainty growing; uncertainty about the geopolitical and human consequences of climate change.
"Impacts such as flooding, melting permafrost and desertification could lead to loss of agricultural land, poisoning of water supplies and destruction of economic infrastructure.
"More than 300 million people in Africa currently lack access to safe water; climate change will worsen this dire situation."
He added: "These changes are not just of interest to the geographer or the demographer; they will make scarce resources, clean water, viable agricultural land even scarcer.
"Such changes make the emergence of violent conflict more rather than less likely... The blunt truth is that the lack of water and agricultural land is a significant contributory factor to the tragic conflict we see unfolding in Darfur. We should see this as a warning sign."
Tony Juniper, the executive director of Friends of the Earth, said: "The science of global warming is becoming ever more certain about the scale of the problem we have, and now the implications of that for security and politics is beginning to emerge."
He said the problems could be most acute in the Middle East and North Africa.
Charlie Kornick, head of climate campaigning at the pressure group Greenpeace, said billions of people faced pressure on water supplies due to climate change across Africa, Asia and South America.
He said: "If politicians realise how serious the problems could be, why are British CO2 emissions still going up?"
Tony Blair will be joined by the Chancellor Gordon Brown, the Environment Secretary, Margaret Beckett, and the International Development Secretary, Hilary Benn, at today's talks in Downing Street.
They will be meeting representatives of the recently created Stop Climate Chaos, an alliance of environmental groups including Greenpeace, Friends of the Earth and Oxfam.
It will also meet opposition parties.
The alliance will call for the Government to commit itself to achieving a 3 per cent annual fall in carbon dioxide emissions.