GENEVA - Climate change stands to drive as many as one billion people from their homes over the next four decades, the International Organization for Migration said in a study Tuesday.
The IOM report, launched on the second day of international climate talks in Copenhagen, estimated 20 million people were made homeless last year by sudden-onset environmental disasters that are set to amplify as global warming increases.
But it found that few of the climate refugees are able to leave their countries, lacking the means and the ability to travel to wealthier places.
Instead, the report found the displaced people were moving in droves to already-crowded cities -- putting extra pressure on the poorer countries at highest risk from environmental stress and degradation associated with climatic shifts.
Aside from the immediate flight in the face of disaster, migration may not be an option for the poorest and most vulnerable groups, it said.
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In general, countries expect to manage environmental migration internally, with the exception of small island states that in some cases have already led to islands disappearing under water, forcing international migration.
The IOM cited a wide range of projections for numbers of people likely to be displaced. Estimates have suggested that between 25 million to 1 billion people could be displaced by climate change over the next 40 years, the report said. However, it noted that the lowest projection was dated.
The number of natural disasters has more than doubled in the past 20 years, and the IOM said desertification, water pollution and other strains would make even more of the planet uninhabitable as greenhouse gases keep building up.
Further climate change, with global temperatures expected to rise between 2 and 5 degrees centigrade by the end of this century, could have a major impact on the movement of people, the report supported by the Rockefeller Foundation said.
It also identified future hotspots where large numbers of people are expected to flee as a result of environmental and climate pressures. These include Afghanistan, Bangladesh, most of central America, and parts of west Africa and southeast Asia.
The IOM conclusions compound concerns expressed this week by U.N. High Commissioner for Refugees Antonio Guterres, who said half of the world's refugees are now living in cities where xenophobic tensions are on the rise.
Guterres warned that cities such as Kabul, Bogota, Abidjan and Damascus were struggling to absorb the new arrivals who have driven up costs of food and accommodation and made it harder for local people to scrape by.
The resultant pressure can create tensions between local and refugee populations, and in worst cases, can fuel xenophobia with catastrophic results, he said.