Desertification represents one of the “greatest environmental challenges of our times” and, coupled with global warming, could set off mass migrations of people fleeing degraded homelands, a United Nations report warned Thursday.

The report called on governments in arid regions to revise rules on land use to halt overgrazing and unsustainable irrigation practices. It also urged better coordinated policies to address the problem of desertification.

The report said about 2 billion people, a third of the Earth’s population, are potential victims of desertification, which is defined as land degraded by human activities like farming and grazing.

If the problem is left unchecked, some 50 million people could be forced from their homes over the next decade.

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