This week in Bonn, Germany, the United Nations is observing the 10th anniversary of its international campaign to fight desertification

This week in Bonn, Germany, the United Nations is observing the 10th anniversary of its international campaign to fight desertification. Desertification is the degradation of once useful land that the U.N. says is threatening food security and triggering humanitarian and economic crises. One fifth of the world's population is threatened by the impact of desertification. Defined as the degradation of formally productive land, the effects of desertification can be seen all over the world. Thursday, experts say one third of the earth's surface is threatened by desertification, which adds up to an area of over 4 billion hectares of the planet. On the tenth anniversary of the U.N. convention to combat desertification, the United Nations and its agencies are highlighting the issues involved. Mary Seely is director of the desert research foundation of Namibia.