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(CNN) -- Climate change could create a refugee crisis worse than that faced at the end of World War Two with up to one billion people displaced from their homes by the middle of the century, a new report has warned.
The figure would represent around one in nine people on earth, according to current population projections, but would mainly affect the world's poorest people in Africa, Asia and Latin America, according to the authors of "Human Tide: The Real Migration Crisis," produced buy the charity Christian Aid.
"We believe that forced migration is now the most urgent threat facing poor people in the developing world," says John Davison, the report's lead author.
There are already around 155 million people displaced by conflicts and disasters, notably in civil war-ravaged countries such as Sudan, Colombia and Sri Lanka.
"To add many more millions of uprooted people to this mix makes an already apocalyptic picture potentially even more devastating," the report says.
Incidents such as the 2004 tsunami in the Indian Ocean and Hurricane Katrina, which devastated New Orleans in 2005, have provided deadly evidence of the power of nature to wreak destruction and throw human communities into chaos.
But while rising sea levels, flooding, drought and famine caused by global warming are all likely to contribute to the refugee crisis, the report also warns of the indirect consequences such as the prospect of more widespread conflicts as rival communities battle for control of scarce resources.
Christian Aid warns that the current conflict in the Darfur region of Sudan -- a crisis summed up by some as the world's first "climate change war" as spreading desertification and water shortages contributed to clashes between the region's African farmers and nomadic Arabs -- could be a taste of a "nightmare scenario" set to be repeated elsewhere across Africa and the world.
"Let Darfur stand as the starkest of warnings about what the future could bring," the report says.
One country on the opposite side of Africa where that scenario may already have started to play out is Mali, the third poorest nation in the world, where rainfall levels have been in decline for the past 30 years across the semi-arid Sahel region. In consequence traditional farming lifestyles have become untenable for growing numbers, triggering mass migration to the country's capital, Bamako.
"All this makes life much more difficult," said Ibrahim Togola of the Mali Folke Center, set up to help Malians adapt to their changing conditions. "There were 600,000 people living in Bamako 20 years ago. Now there are about two million. This causes insecurity, the spread of HIV and eventually emigration to Europe."
Despite Western fears over rising levels of immigration to Europe and North America, the report suggests that internal migration within countries poses a more serious humanitarian threat, with migrants struggling to survive in desperate conditions with no rights under international law.
"We hear a lot about people trying to come to Europe and other rich countries but the real crisis is developing a long way away and remains largely unreported."
Dennis McNamara, a United Nations special adviser on emergency relief and forced migration said the situation needed to be addressed "both for humanitarian as well political and security reasons."
"Tens of millions of the poorest people in the poorest parts of the world are uprooted and lack basic assistance and protection. They are the world's voiceless and often inaccessible refugees," he said.
Sudanese refugees are treated in a hospital in Chad.