M.V.K. Sivakumar of the U.N.'s World Meteorological Organisation (WMO) said the crunch could come in just over a decade as all continents see more weather-related disasters like heat waves, floods, landslides and wildfires.

"Should we worry about land being degraded? Yes," Sivakumar, who leads the WMO's agricultural meteorology division, told a news conference in Geneva.

"Today we feed the present world population of 6.3 billion from the 11 per cent of the land surface that can be used for serious food production. The question is: Will we be able to feed the 8.2 billion that we expect to populate the globe in 2020 if even less land is available for farming?," he said.

Africa, Latin America and parts of Asia -- where the climate is already more extreme and arid regions are common -- will be most affected as rainfall declines and its timing becomes less predictable, making water more scarce, he said.

But Europe, particularly around the Mediterranean, would also suffer from heat waves like those that this summer have led to devastating fires in Greece.

Declining rainfall and evaporation of water supplies could also mean less was available for irrigation and for generating electricity for farm machinery, causing lower crop productivity.