Desertification is a growing menace that puts at risk global efforts to tackle poverty and hunger, a new report from a coalition of scientists states.
Regions around the Sahara are among those at greatest risk
The group says bad crop management and the misuse of irrigation in a number of regions is putting unsustainable pressure on dryland areas.
The UN-led team estimates that 10-20% of drylands are already degraded.
They warn that unless practices change these areas will become unproductive, blighting the lives of millions.
Their report is called Ecosystems and Human Well-Being: Desertification Synthesis. It is the latest document produced by the Millennium Ecosystem Assessment (MA) project.
This $22m, four-year study by 1,300 experts from 95 countries has been described as the most detailed "green healthcheck" yet on the state of the planet.
In the case of drylands, preventing their degradation into deserts is an immense global problem, say the authors.
"Given the size of population in drylands, the number of people affected by desertification is likely larger than any other contemporary environmental problem," they write.
Drylands cover 41% of the planet's land surface, and are growing. They are home to over two billion people, including the world's most impoverished, in areas such as central Asia and northern Africa.
One of the biggest problems is that as land dries up, it becomes unsuitable for farming. This exacerbates poverty and creates environmental refugees.
Sand from the Sahara Desert blows over the Mediterranean Sea
The authors estimate that hundreds of thousands of people will be in need of new homes and lifestyles over the next 30 years as the Earth dries up.
The effects are also felt far beyond the desert areas themselves. Dust storms from the Gobi Desert in Asia and the African Sahara are responsible for respiratory problems as far away as North America, says the report.
Co-author Professor Uriel Safriel, of Hebrew University of Jerusalem, says population pressure and bad land management practices are the cause of degradation.
"The process of desertification starts from direct impact of people by transforming range lands to cultivated lands that cannot be covered by protective vegetation cover during the whole year," he told BBC News.
"In the dry season, they become bare, their soil then is not protected from the wind or from floods and erodes or becomes dust."
Better management of crops, more careful irrigation and strategies to provide non-farming jobs for people living in drylands could help address the problem. But it is easier to prevent desertification than to reverse it, says the report.