Climate change occurs in geologic time; but cultural desertification can occur relatively fast, usually in decades rather than millennia.

Humans prefer the relative health of deserts to the muggy rain forests.

Humans have a tendency to make deserts through their economic activities on the land.

[The conversion of forests to grazing lands, grazing lands to agricultural lands, agricultural lands to urban lands, is an example of ecosystem climate change from wetter to drier].

There are many examples of this throughout the world (the Sahel, in subtropical Africa, is one).

The semiarid ecosystems (400-800 mm of annual precipitation) are particularly at risk.