- A common definition distinguishes between true deserts, which receive less than 250 millimetres of average annual precipitation, and semideserts or steppes, which receive between 250 millimetres (10 in) and 400 to 500 millimetres (16 to 20 in).
- Desertification is the degradation of land in drylands.
- Caused by a variety of factors, such as climate change and human activities, desertification is one of the most significant global environmental problems.
- The world's great deserts were formed by natural processes interacting over long intervals of time. During most of these times, deserts have grown and shrunk independent of human activities.
- Dryland ecosystems are already very fragile, and can rarely sustain the increased pressures that result from intense population growth. Many of these areas are inappropriately opened to development, when they cannot sustain human settlements.
- The most common cause of desertification is the over cultivation of desert lands.
