Over a billion people could be forced to leave their homes over the next 50 years as climate change worsens an already serious migration crisis, argues the development agency, Christian Aid, in a new report.

The analysis, which is based on latest UN population and climate change figures, says conflict, large-scale development projects and widespread environmental deterioration will combine to make life unsupportable for hundreds of millions of people, mostly in the Sahara belt, south Asia and the Middle East.

According to the development charity, the world faces its largest movement of people forced from their homes. “Forced migration is now the most urgent threat facing poor nations,” said John Davison, the report’s lead author. “Climate change is the great, frightening unknown in this equation.”

The authors admit that the figures are uncertain “because there are no recent, authoritative global figures on the number of people who could be displaced by climate change”. But they argue that “the growing number of disasters and conflicts linked to future climate change will push the numbers far higher unless urgent action is taken. We estimate that between now and 2050 a total of 1 billion people will be displaced from their homes.”