Rising sea levels, desertification and shrinking freshwater supplies will create up to 50 million environmental refugees by the end of the decade, experts warn today. Janos Bogardi, director of the Institute for Environment and Human Security at the United Nations University in Bonn, said creeping environmental deterioration already displaced up to 10 million people a year, and the situation would get worse.

"There are well-founded fears that the number of people fleeing untenable environmental conditions may grow exponentially as the world experiences the effects of climate change," Dr Bogardi said. "This new category of refugee needs to find a place in international agreements. We need to better anticipate support requirements, similar to those of people fleeing other unviable situations."

The Red Cross says environmental disasters already displace more people than war. Such people are currently not recognised under international agreements as refugees, Dr Bogardi said, so are denied access to assistance received by victims of violence or political persecution.

Hans van Ginkel, UN under-secretary-general and rector of the university, said: "This is a highly complex issue, with global organisations already overwhelmed by the demands of conventionally recognised refugees. However, we should prepare now to define, accept and accommodate this new breed of refugee."

Environment-related migration has been most acute in sub-Saharan Africa, but also affects millions of people in Asia and India. Europe and the US face increased pressure from people driven from north Africa and Latin America by deteriorating soil and water conditions.

New Zealand has already agreed to accept the 11, 600 inhabitants of the low-lying Pacific island state Tuvalu if rising sea levels swamp the country. Elsewhere, as many as 100 million people live in areas that are below sea level or liable to storm surge. A total of 213 communities in Alaska are threatened by tides that creep three metres further inland each year.

Tony Oliver-Smith, a natural hazards expert at the University of Florida, said: "Around the world vulnerability is on the increase, due to the rapid development of megacities in coastal areas. Combine this trend with rising sea levels and the growing number and intensity of storms and it is a recipe for a disaster, with enormous potential to create waves of environment-driven migration."

Dr Bogardi called for an intergovernmental panel on environmental degradation to be established to assess the situation, feed advice to politicians and distinguish genuine environmental refugees from economic migrants. "If you see a group of young men trying to climb over a fence, it's very difficult to say those are environmental refugees, because, if you are an environmental refugee you bring your whole family with you. The whole population would be on the move."

There was also a need for international agreements on how individual states support people who move within a country because of environmental pressures, such as those who fled the New Orleans region after Hurricane Katrina, he added. The statement was timed to coincide with the UN day for disaster reduction.