Mikesh Ram would watch his rice crops begin to rot during the dry season in Guyana, because salt water from the nearby Atlantic Ocean was displacing freshwater from the Mahaica River he and other farmers used to flood their rice paddies.

Eighteen national science prize-winners in Chile have called for a halt to the over-extraction of water in the four regions over which the Atacama Desert spreads in the north of the country, a problem that threatens the future of 1.5 million people.