Blame the Plants for Speed of Sahara Expansion
It is important to note that even after taking into account the effects of the Earth's wobble and the shift in summer temperatures, climate experts cannot account for the speed with which the grasses withered and the Sahara expanded.
Blame the plants, concluded a team of German scientists led by Martin Claussen, which published its results recently in Geophysical Research Letters. The researchers concluded that the atmosphere, oceans, clouds, and plants all respond to changes in climate in ways that can greatly magnify the effects. The scientists used a supercomputer to calculate those effects. For instance, as grassland turns to desert the plants work many changes. Plants hold water, stabilize soils, absorb solar energy, take in carbon dioxide, release oxygen, increase humidity, and affect how much water goes into streams. They also hold down topsoil, which has a big impact on how much dust rises in great billows from the surface of the desert. That dust, in turn, affects rainfall patterns. So as the climate heats, the plants falter, which makes the land more prone to erosion during the increasingly infrequent heavy rains. The increased erosion and lack of plant cover stir up more dust, which can further decrease rainfall.
Some scientists who studied the startling expansion of the Sahara to roughly its present size some 6,000 years ago concluded that the changes were abrupt, taking place in a span of decades rather than centuries. So clearly, the evolution of the Sahara Desert represents a disturbing, cautionary tale for scientists and policy makers worried about the current effects of global warming caused by the release of pollutants and deforestation.