The Greening of The Deserts
Photo courtesy cdogstar.
By Ayisha Yahya
BBC, World Service
It has been assumed that global warming would cause an expansion of the world’s deserts, but now some scientists are predicting a contrary scenario in which water and life slowly reclaim these arid places.
They think vast, dry regions like the Sahara might soon begin shrinking.
The evidence is limited and definitive conclusions are impossible to reach but recent satellite pictures of North Africa seem to show areas of the Sahara in retreat.
It could be that an increase in rainfall has caused this effect.
Farouk el-Baz, director of the Centre for Remote Sensing at Boston University, believes the Sahara is experiencing a shift from dryer to wetter conditions.
“It’s not greening yet. But the desert expands and shrinks in relation to the amount of energy that is received by the Earth from the Sun, and this over many thousands of years,” Mr el-Baz told the BBC World Service.
“The heating of the Earth would result in more evaporation of the oceans, in turn resulting in more rainfall.”
But it might be hard to reconcile the view from satellites with the view from the ground.
While experts debate how global warming will affect the poorest continent, people are reacting in their own ways.
Droughts over the preceding decades have had the effect of driving nomadic people and rural farmers into the towns and cities. Such movement of people suggests weather patterns are becoming dryer and harsher.
The Intergovernmental Panel on Climate Change warned recently that rising global temperatures could cut West African agricultural production by up to 50% by the year 2020.
But satellite images from the last 15 years do seem to show a recovery of vegetation in the Southern Sahara, although the Sahel Belt, the semi-arid tropical savannah to the south of the desert, remains fragile.
The fragility of the Sahel may have been exacerbated by the cutting of trees, poor land management and subsequent erosion of soil.
The broader picture is reinforced by studies carried out in the Namib Desert in Namibia.
This is a region with an average rainfall of just 12 millimetres per year – what scientists call “hyper-arid”. Scientists have been measuring rainfall here for the last 60 years.
Last year the local research centre, called Gobabeb, measured 80mm of rain.
In the last decade they have seen the local river, a dry bed for most of the year, experience record-high floods. All this has coincided with record-high temperatures.
“Whether this is due to global change or is a trend anyway, it’s hard to distil actually out of the [data] but certainly we’ve had record highs of temperature,” said Joh Henschel, director of Gobabeb.
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