卫生类A级：概括大意Soot and Snow
New research from NASA scientists suggests emissions of black soot alter the way sunlight reflects off snow.According to a computer simulation，black soot may be responsible for 25 percent of observed global warming over the past century.
2 Soot in the higher latitudes of the Earth.where ice is more common，absorbs more of the sun’s energy and warmth than an icy， white background.Dark-colored black carbon，or soot，absorbs sunlight，while lighter colored ice reflects sunlight.
3 Soot in areas with snow and ice may play all important role in climate change.Als0，if snow and ice covered areas begin melting.the warming effect increases，as the soot becomes more concentrated on the snow surface.“This provides a positive feedback，as glaciers and ice sheet smelt，they tend to get even dirtier，” said Dr.James Hansen，a researcher at NASAs Goddard Institute for Space Studies，NewYork.
4 Hansen found soot’s effect on snow albedo(solar energy reflected back to space)，which may be contributing to trends toward early springs in the Northern Hemisphere，such as thinning Arctic sea ice，melting glaciers and permafrost.Soot also is believed to play a role in changes in the atmosphere above the oceans and land.
5 “Black carbon reduces the amount of energy reflected by snow back into space，thus heating the snow surface more than if there were no black carbon~，”Hansen said.Soot’s increased absorption of solar energy is especially effective in warming the world’s climate. “This forcing is unusually effective，causing twice as much global warming as a carbon.dioxide forcing of the same magnitude，”Hansen noted.
6 Hansen cautioned.although the role of soot in altering global climate is substantial，it does not alter the fact that greenhouse gases are the primary cause of climate warming during the past century.Such gases are expected to be the largest climate forcing f10r也e rest of this century.
7 The researchers found that observed warming in the Northern Hemisphere was 1arge in the winter and spring at middle and high latitudes.These observations were consistent with the researchers’ climate model simulations，which showed some of the largest warming effects occurred when there were heavy snow cover and sufficient sunlight.
词汇：
soot n.煤烟，煤灰
emission n.释放，散发，排放
simulation v.模拟
latitude n.纬度
glacier n.冰川，冰河
albedo n.反照率
permafrost n.永冻层
forcing n.温室作用
dioxide n.二氧化物
magnitude n.量，大小
练习：
1.Paragraph 3____________
2.Paragraph 4____________
3.Paragraph 6____________
4.Paragraph 7____________
5.In the twentieth century，soot____________
6.Hansen cautioned that greenhouse gases____________
7. Black soot covered snow and ice____________
8.A soot forcing is unusually effective，which____________
参考答案:
1.C 第三段解释了为什么soot会增加地球升温效应。
2.A 第四段介绍了soot在两方面起的作用：(1)soot增加了雪吸收太阳能量和热量的能力；(2)soot导致海洋和陆地上空的大气层发生变化。
3.F第六段的关键句子是：“…greenhouse gases are the primary cause of climate warming during the past century.” .
4.B第七段介绍了在研究北半球的纬度、雪覆盖面和日照诸因素与气温升高之间的关系方面取得的成果。
5.B 选择B的依据是第一段。有关的句子是：。“…black soot may be responsible for 25 percent of observed global warming over the past century.”选项B中用了过去式contributed，也是选B的一个线索，因为第五题的题干中有in me twentieth century，这个时间状语要求谓语动词用过去式，而4个选项中只有B项的动词用的是过去式。
6.E Hansen cautioned和greenhouse gases仅出现在第六段。该段的大意是：虽然煤烟在改变全球气候方面所起的作用相当显着，但是上个世纪气温上升的主要因素还是温室气体。选项E概括了第六段的意思。
7.D 本题答案的依据是第二段第一句。
8.A本题答案的依据是第五段的下列句子： Soot’s increased absorption of solar energy is especially effective in warming the world’s climate.“This forcing is unusually effective， causing twice as much global warming as a carbon-dioxide forcing of the same magnitude，”Harisen noted.