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 may be affected by only a few degress 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 dispappearing. The evi-
dence 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, every 27. 5 days, it presents hotter or "colder" faces to the earth, and different as-
pects 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 a long 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 ef-
fects overcome the inenia (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 heat .
36. It can be concluded that a concentration of carbon dioxide in the atmosphere would
A. prevent the sun's rays from leeching the earth's surface
B. mean a warming up in the Arctic
C. account for great changes in the climate in the noHhem hemisphere
D. raise the temperature of the earth' s surface
37. The article was written 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
38. Although the fuel consumption is greater in the northem hemisphere, temperatures there
seem to be faILing. This is
A. mainly because the levels of carbon dioxide are rising
B. possibly because the ice caps in the poles are melting
C. exclusively due to the effect of the inenia of the earth' s climate
D. partly due to variations in
[责任编辑:bulesky]
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