Nearly 40 percent of the global land surface is at risk of desertification, a new study says. The areas at risk represent eight of the 15 natural 'eco-regions,' coded according to their degree of aridity. "Unsustainable land use may lead to the soil becoming degraded. If this happens in arid, semi-arid and dry sub-humid regions, such as Spain, this degradation is known as desertification, and the effects can be irreversible, because they lead to areas becoming totally unproductive," says Montserrat N