In the atmosphere， carbon dioxide acts rather like a one-way mirror the glass in the roof of a greenhouse which allows the sun's rays to enter but prevents the heat from escaping.
According to a weather expert's prediction， the atmosphere wilbe3C warmer in the year 2050thanitis today， if man continues to burn fuels at the present rate.If this warming up took place， the icecaps in the poles would begin to melt thus raising sea level several meters and severely flooding coastal cities.Also， the increase in atmospheric temperature would lead to great changes in the climate of the northern hemisphere(半球) ， possibly resulting 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 Arctic because the Antarctic is much colder and has a much thicker ice sheet.But the weather experts are now paying more attention to West Antarctic， which maybe affected by only a few degrees of warming：in other words， by a warming on the scale that will possibly take place in the next fifty years from the burning of fuels.
Satellite pictures show that large areas of Antarctic ice are already disappearing.The evidence available suggests that a warming has taken place.This fits the theory that carbon dioxide warms the earth.
However， most of the fuel is burnt in the northern hemisphere， where temperatures seem to be falling Scientists conclude，therefore，that up to now natural influences on the weather have exceeded those caused by man.The question is：Which natural cause has most effect on the weather?
One possibility is the variable behavior of the sun.Astronomers at one research station have studied the hot spots and“cold”spots(that is， the relatively less hot spots) on the sun.As the sun rotates(旋转) ， every 27.5 days it presents hotter or“colder”faces to the earth， and different aspects to different parts of the earth.This seems to have a considerable effect on the distribution of the earth's atmospheric pressure， and consequently on wind circulation.The sun is also variable over along term：its heat output goes up and down in cycles， the latest trend being downward.
Scientists are now finding mutual relations between models of solar-weather interactions and the actual climate over many thousands of years， including the last Ice Age.The problem is that the models are predicting that the world should be entering a new Ice Age and it is not.One way of solving this theoretical difficulty is to assume a delay of thousands of years while the solar effects overcome the inertia(惯性) of the earth's climate.If this is right，the warming effect of carbon dioxide might thus be serving as a useful counter-balance to the sun's diminishing(减少) heat.
1．Why is the fuel consumption greater in then or them hemisphere， but temperatures there seem to be falling?
A．Mainly because the levels of carbon dioxide are rising.
B．Possibly because the output of solar energy varies.
C．Because the inertia of the earth's climate take effect.
D．Possibly because the icecaps in the poles are melting
2．On the basis of their models， scientists are of the opinion that
A．the climate of the world should be becoming cooler
B．the new Ice Age will be delayed by the greenhouse effect
C．the man-made warming effect helps to increase the solar effects
D．it will take thousands of years for the inertia of the earth's climate to take effect
3．If the assumption about the delay of a new Ice Age is correct， .
A．the best way to overcome the cooling effect would be to burn more fuels
B．ice would soon cover the northern hemisphere
C．the increased levels of carbon dioxide would warm up the earth quickly
D．the greenhouse effect could work to the advantage of the earth
4．The purpose of the article is to explain .
A．the greenhouse effect
B．the solar effects on the earth
C．the models of solar-weather interactions
D．the causes affecting weather
1．B
2．A
3．D
4．D
【分析】
本文是一篇说明文。文章主要分析了全球变暖的真正原因。
1．细节理解题。根据第五段的Scientists conclude，therefore，that up to now natural influences on the weather have exceeded those caused by man.（因此，科学家得出结论，到目前为止，自然对天气的影响已经超过了人为的影响）可知，自然对天气的影响超过了人类对天气的影响；再根据第六段的One possibility is the variable behavior of the sun.（一种可能性是太阳的变化行为），表明一种自然因素的可能性是太阳的可变行为，即太阳能量释放的不同。综上可知北半球的燃料消耗更大，但那里的温度似乎在下降的原因是太阳能的输出是变化的。故选B。
2．推理判断题。定位到最后一段第二句The problem is that the models are predicting that the world should be entering a new Ice Age and it is not（问题是，这些模型预测世界将进入一个新的冰河世纪，而事实并非如此）可以推测科学家认为地球气候应变冷，而进入新的冰河时期。也就是说根据他们的模型，科学家们认为世界的气候应该变得更冷，故选A。
3．推理判断题。定位到最后一段最后一句If this is right，the warming effect of carbon dioxide might thus be serving as a useful counter-balance to the sun's diminishing(减少) heat.（如果这是正确的，那么二氧化碳的变暖效应可能会对太阳热量的减少起到有效的平衡作用）可知，如果新的冰河时期推迟的假设正确，那么二氧化碳的变暖效应可能会作为一种有用的平衡来对抗太阳的热量衰减，也就是温室效应会对地球有利，故选D。
4．推理判断题。通读全文以及第五段的Which natural cause has most effect on the weather?（哪一种自然因素对天气影响最大?）这句关键句可知，本文介绍了二氧化碳对全球气候的影响和太阳能量的输出活动对气候的影响，分析全球变暖的真正原因，故全文的写作主旨一直在探讨全球变暖的原因， 故选D。