There will be as many as 50 million environmental refugees in the world in five years' time.
That is the conclusion of experts at the United Nations University, who say that a new definition of "environmental refugee" is urgently needed.
They believe that already environmental degradation forces as many people away from their homes as political and social unrest.
The UNU issued its statement to mark UN Day for Disaster Reduction.
"There are many different environmental issues involved and there can be interactions between them," said Janos Bogardi, director of the United Nations University's Institute for Environment and Human Security (UNU-EHS) in Bonn, Germany.
"In poorer rural areas especially, one of the biggest sources of refugees is land degradation and desertification, which may be caused by unsustainable land use interacting with climate change, amplified by population growth," he told the BBC News website.
"A second issue is flooding, caused I would say by increasing levels of carbon dioxide in the atmosphere super-imposed with probably some natural fluctuations."
Worse than wars
The projected figure of 50 million is derived from a number of previous reports, including the 1999 World Disasters Report from the International Red Cross.
This calculated that natural disasters in the previous year had created more refugees than wars or other armed conflicts.
It said that falling soil fertility, drought, flooding and deforestation drove 25 million people from their homes, with many of these environmental refugees joining already fragile urban squatter communities.
The UNU believes that environmental refugees need better protection than they have now, and in order for that to happen, there needs to be an accepted definition of their situation.
Environmental refugees need better protection, says the UNU
The 1951 Convention relating to the State of Refugees defines refugees as people having a "...well-founded fear of being persecuted for reasons of race, religion, nationality, membership of a particular social group or political opinion..."
"We need to define what we mean by political, economic and environmental refugees," said the UNU's Rector Hans van Ginkel.
"If we define the problem better, we can prepare for the level of need to be catered for," he told the BBC News website.
Another issue is that historically, people are considered refugees only when they go to another country, whereas as Hurricane Katrina has graphically shown, those displaced by environmental damage often remain within their native country.