考博考试

【单选题】Climatic conditions are delicately adjusted to the composition of theEarth’s atmosphere. If there were a change in the atmosphere--for example, in the relative proportions of atmosphere gases--the climate would probably change also.
A、slight increase in water vapor, for instance, would increase the hem-retaining capacity of the atmosphere and would lead to a rise in global temperatures. In contrast, a large increase in water vapor would increase the thickness and extent of the cloud layer, reducing the mount of solar energy reaching theEarth’ surface.
The level of carbon dioxide,CO₂ in the atmosphere has important effect on climatic change. Most of theEarth’s incoming energy is short-wavelength radiation, which tends to pass through atmosphericCO₂ easily. TheEarth, however, reradiates much of the received energy as a long-wavelength radiation, WhichCO₂ absorbs and then remits toward theEarth. This phenomenon, known as the greenhouse effect, can result in an increase in the surface temperature of a planet.An extreme example of the effect is shown by the Venus, a planet covered by heavy clouds composed mostly ofCO₂, whose surface temperatures have been measured at 430℃. If theCO₂ content of the atmosphere is reduced, the temperature falls.According to one respectable theory, if the atmosphericCO₂ concentration were halved, theEarth would become completely covered with ice.Another equally respectable theory, however, states that a halving of theCO₂ concentration would lead only to a reduction in global temperatures of 3℃.
If, because of an increase in forest fires or volcanic activity, theCO₂ content of the atmosphere increased, a warmer climate would be produceD、Plant growth, which relies on both the warmth and the availability ofCO₂, would probably increase.As a consequence, plants would use more and moreCO₂.EventuallyCO₂ levels would diminish and the climate, in turn, would become cooler. With reduced temperatures many plants would die;CO₂ would thereby be returned to the atmosphere and gradually the temperatures would rise again. Thus, if this process occurred, there might be a long-term oscillation in the amount ofCO₂ present in the atmosphere, with regular temperature increase and decrease of a set magnitude.
Some climatologists argue that the burning of fossil fuels has raised the level ofCO₂ in the atmosphere and has caused a global temperature rise of at least 1℃.But a supposed global temperature rise of 1℃ may in reality be only several regional temperature increase, restricted to areas where there are many meteorological stations and caused simply by shifts in the pattern of atmospheric circulation. Other areas, for example the Southern Hemisphere oceanic zone, may be experiencing an equivalent temperature decrease that is unrecognized because of the shortage of meteorological recording stations.
The passage supplies information for answering which of the following questions
A、Why are projections of the effects of changes in water vapor levels on the climate so inaccurate
B、What are the steps in the process that takes place asCO₂ absorbs long-wavelength radiation
C、How might our understanding of the greenhouse effect be improved if the burning of fossil fuels were decreased
D、What might cause a series of regular increases and decreases in the amount ofCO₂ in the atmosphere
网考网参考答案：D
网考网解析：
[解析] 本题的四个选项中，只有D项为正确答案。这可从文中第三段和第四段的第一句话推知。 document.getElementById("warp").style.display="none"; document.getElementById("content").style.display="block"; 查看试题解析出处>>