Desertification is not the advance of deserts, though it can include the encroachment of sand dunes on land. Rather, it is the persistent degradation of dryland ecosystems by human activities and climatic variations. Because of its toll on human well-being and on the environment, desertification ranks among the greatest development challenges of our time.

Desertification occurs when the tree and plant cover that binds the soil is removed. It occurs when trees and bushes are stripped away for fuelwood and timber, or to clear land for cultivation. It occurs when animals eat away grasses and erode topsoil with their hooves. It occurs when intensive farming depletes the nutrients in the soil. Wind and water erosion aggravate the damage, carrying away topsoil and leaving behind a highly infertile mix of dust and sand. It is the combination of these factors that transforms degraded land into desert.

There are many factors that contribute to desertification. Prolonged periods of drought can take a severe toll on the land. Conflict can force people to move into environmentally fragile areas, putting undue pressure on the land. Mining can cause damage. In the coming years, climate change will accelerate the rate of desertification in some areas, such as the drier areas of Latin America.