Saturday, April 24, 2010

The problem of Desertification Part.II

Professor Marcel Boodt, director of the World center for the study of Deserts, argues that we must look far back into the history of the earth’s deserts if we are to understand their current phase of expansion. Twenty thousand years ago, during the coldest period of the ice ages, the Sahara extended in the some places up to five hundred kilometer further south that its present boundary. At that time, these zones would have been too hot and dry for human occupation. Then, around 9,500 years ago towards the end of the last ice age the climate in this southern zone became wetter. This meant that the limit of the tropical summer rainfall region pushed northwards, and with it, the belt of savanna vegetation. Hollows became lakes and their shores supported crocodile, hippos and rhinoceros. About 4,500 years ago, the warm period following the ice age came to an end and the earth cooled significantly. The land dried out and the deserts took over.

 The alternation of wet and dry climatic periods may be tired to long tern variations in temperature. When the temperatures are cooler, there is less evaporation and therefore also less rainfall. During the ice ages, for example, rainfall would have been only about half what it is to day.

While the main reason for the advance and retreat of the world’s deserts may lie with long tern climatic cycles, humans have certainly interfered with natures balance. The Sahel is particularly vulnerable, and endured four droughts in the 20th century. The last major drought in 1968-1985 led to the widespread misery and starvation. After the drought, there was a partial recovery and greening along the southern edge of the Sahara, but no one can predict if another drought is on its way or not. And it will take many decades before scientists can unravel the complex causes of desertification.

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