Desertification is the persistent degradation of dryland ecosystems, in which the land becomes increasingly arid and results in a loss of biological productivity. Drylands, which occupy about forty percent of the earth's land area, are home to about a third of the human population.
Desertification occurs on all continents except Antarctica. It can be caused by natural processes, including natural climatic changes and changes in rainfall patterns. However, it has recently been increasingly a result of human activity. In particular, it is being accelerated by human-induced climate change, by excessive grazing of livestock, and by excessive agriculture. As with so many other environmental problems, these human causes are largely the result of rapid human population growth.