英语六级阅读理解练习带答案：气候环境

　　According to a weather expert's prediction. theatmosphere will be 3C warmer m the year 2050 than it is today, if man continues to bum fuelsat the present rate. If this warming up took place, the ice caps in the poles would begin to melt.thus raising sea level several meters and severely flooding coastal cities. Also, the increase inatmospheric temperature would lead to great changes in the climate of the northernhemisphere, possibly re9ulting in an alteration of the earth's chief food-growing zones.

　　In the past, concern about a man-made warming of the earth has concentrated on the Arcticbecause the Antarctic is much colder and has a much thicker ice sheet. But the weather expertsare now paying more attention to West Antarctic, which may be affected by only a few degreesof warming: in other words, by a warming on the scale that will possibly take place in the nextfifty years from the burning of fuels.

　　Satellite pictures show that large areas of Antarctic ice are already disappearing. The evidenceavailable suggests that a warming has taken place. This fits the theory that carbon dioxidewarms the earth.

　　However. most of the fuel is burnt in the northern Hemisphere, where temperatures seem to befalling. Scientists conclude. therefore. that up to now natural influences on the weather haveexceeded those caused by man. The question is: Which natural cause has most effect on theweather?

　　One possibility is the variable behavior of the sun. Astronomers at one research station havestudied the hot spots and "cold” spots (that is, the relatively less hot spots) on the sun. As thesun rotates, every 27.5 days. it presents hotter or "colder" faces to the earth, and differentaspects to different parts of the earth. This seems to have a considerable effect on chedistribution of the earth's atmospheric pressure, and consequently on wind circulation.The sun is also variable over a long term: its heat output goes up and down in cycles. chelatest trend being, downward.

　　Scientists are now finding mutual relations between models of solar-weather interactions andthe actual climate over many thousands of years, including the last Ice Age. The problem is thatche models are predicting that the world should be entering a new Ice Age and it is not. Oneway of solving this theoretical difficulty is to assume a delay of thousands of years while thesolar effects overcome the inertia (惯性) of the earth's climate. If this is right. the warmingeffect of carbon dioxide might thus be serving as a useful counterbalance to the sun’sdiminishing heat.

　　[1]大气中二氧化碳的作用很像单向的镜子——即镶在温室屋顶的玻璃，它允许阳光进入，却阻止热量散失。

　　据气象专家预测，如果人类继续以目前的速度消耗燃料，到2050年时大气温度将比现在高3C。如果真的发生升温，两极的冰冠会开始融化，从而使海平面上升几米，违成海滨城市洪水泛滥。而且，大气温度升高也将引起北半球气候剧变，可能会导致地球上主要的粮食生产带发生变化。

　　过去，人们关注人为造成的地球升温时，注意力集中在北极地区，因为南极寒冷得多，冰层也厚得多。但现在气象专家更关注南极西部。因为即使温度只上升几度，这个地区也会受到影响，也就是说，在未来50年内因为消耗燃料而可能引起的那种幅度的升温，南极西部也会受到影响。

　　卫星图片显示，南极大面积的冰块正在消融。已有的证据表明，温度已经升高了。这种情况符合二氧化碳使地球变暖的理论。

　　然而，大部分燃料是在北半球消耗的，这里的温度却似乎在下降。科学家因此得出结论：到目前为止，自然因素对大气的影响超过人类因素的影响。问题是：哪一种自然因素对天气影响最大?

　　[3]一种可能性是变化无常的太阳活动。一个研究站的天文学家们研究进太阳表面的热点和“冷”点(即相对而言不太热的区域)。太阳旋转时，每隔27.5天，其较热或较“冷”的一面就朝向地球，给地球上的不同地区带来不同的特点。这似乎对地球上的气压分布影响很大，并因此影响大气循环。从长期来看，太阳也是多变的：它的热量输出周期性地上升或下降，最近的趋势是下降。

　　科学家现在发现了太阳-天气互动模式与包括上一个冰川期在内的几千年间的实际气候之间的相互关系。[4]问题是，互动模式预示世界应该正进入新的冰川期，但事实上并没有出现这样的情况。解决这个理论难题的一个方法是做这样的假设：太阳虽然对地球有影响，但要克服地球气候的惯性，因此冰川期要推迟几千年到来。[5]如果这个假设成立，二氧化碳的温室效应可以对太阳正在下降的热量起到有益的抵消平衡作用。