Passage 5
Desertification,drought,and despair-that is what global warming has in store for much of Africa.Or so we hear.
Emerging evidence is painting a very different scenario,one in which rising temperatures could benefit millions of Africans in the driest parts of the continent.Scientists are now seeing signals that the Sahara desert and surrounding regions are greening due to increasing rainfall.If sustained,these rains could revitalize drought-ravaged regions,reclaiming them for farming communities.This desert-shrinking trend is supported by climate models,which predict are turn to conditions that turned the Sahara into a lush plain some 12,000 years ago.
The green shoots of recovery are showing up on satellite images of regions including the Sahel,a semi-desert zone bordering the Sahara to the south that stretches some 2,400 miles.
Images taken between 1982 and 2002 revealed extensive re-greening throughout the Sahel,according to a new study in the journal Biogeo sciences.The study suggests huge increases in vegetation in areas including central Chad and western Sudan.The transition may be occurring because hotter air has more capacity to hold moisture,which in turn creates more rain,said Martin Claussen of the Max Planck Institute for Meteorology in Hamburg,Germany.“The water-holding capacity of the air is the main driving force.”Claussen said.
While satellite images can’t distinguish temporary plants like grasses that come and go with the rains,ground surveys suggest recent vegetation change is firmly rooted.In the eastern Sahara area of southwestern Egypt and northern Sudan,new trees are flourishing,according to Stefan Kropelin,a climate scientist at the University of Cologne’s Africa Research Unit in Germany.
“Before,there was not a single scorpion,not a single blade of grass,”said Kropelin,who has studied the region for two decades.“Now you have people grazing their camels in areas which may not have been used for hundreds or even thousands of years.You see birds,ostriches,coming back,even sorts of amphibians coming back,”he said.“The trend has continued for more than 20 years.It is indisputable.”
An explosion in plant growth has been predicted by some climate models.For instance,in 2005 a team led by Reindert Haarsma of the Royal Netherlands Meteorological Institute in De Bilt,the Netherlands,forecast significantly more future rainfall in the Sahel.The study in Geophysical Research Letters predicted that rainfall in the July to September wet season would rise by up to two millimeters a day,by2080.
Satellite data shows“that indeed during the last decade,the Sahel is becoming greener,”Haarsma said.Even so,climate scientists do not agree on how future climate change will affect the Sahel—some studies simulate a decrease in rainfall.“This issue is still rather uncertain,”Haarsma said.
Max Planck’s Claussen said North Africa is the area of greatest disagreement among climate change modelers.Forecasting how global warming will affect the region is complicated by its vast size and the unpredictable influence of high-altitude winds that disperse monsoon rains,Claussen added.“Half the models follow a wetter trend,and half a drier trend.”
According to Martin Claussen,what is the main cause of the increased vegetation in deserted areas （ ）
根据题干关键词Claussen定位至第四段，The transition may be occurring because hotter air has more capacity to hold moisture,which in turn creates more rain,...根据发表在《生物地球科学》杂志上的一项新研究，1982年至2002年间拍摄的照片显示，萨赫勒地区出现了大面积的重新绿化。这项研究表明，包括乍得中部和苏丹西部在内的地区植被大幅增加。Martin Claussen说，这种转变之所以会发生，可能是因为更热的空气有更大的容纳水分的能力，这反过来又会产生更多的雨水。空气的持水能力是主要的动力。故本题正确答案选B。
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