The Sahara Desert, an expanse comparable in size to the U.S., is one of the hottest and most arid regions of the planet. Up until the 1990s, global warming seemed to be causing more frequent and severe Sahara droughts. But in the last three decades, a surprising transformation has been occurring: increased rainfall, more plant growth, and an overall greening of the desert.
Eleven thousand years ago, the Sahara was green and alive, pocked with lakes, rivers, grasslands, and even forests. Scientists think that over time, humans and their goats tipped the balance, turning the area into an immense desert. With temperatures rising everywhere, how is it that the Sahara, unfriendly to plants, is re-vegetating?
Warmer ocean temperatures are leading to increased evaporation off the Atlantic coast of Africa. This moisture is carried inland by high-altitude winds, causing increased precipitation. As more plants grow, evaporation from their leaves increases precipitation even more. Moreover, plants stabilize the sands, furthering an anti-wind-erosion tendency and reducing the number of sand-dust storms and their desiccating effect.