Question

Climatic conditions are delicately adjusted to composition of the Earth's atmosphere. If there were a change in the atmosphere ― for example, in the relative amounts of atmospheric gases ― the climate would probably change also. A slight increase in water vapor (蒸汽) , for example, would increase the heat-keeping capacity of the atmosphere and would lead to a rise in global temperatures.

The level of carbon dioxide, CO₂, in the atmosphere has an important effect on climatic change. Most of the Earth's incoming energy is short-wavelength radiation (短波辐射) , which tends to pass through atmospheric CO₂ easily. The Earth, however, reradiates much of the received energy as long-wavelength radiation (长波辐射), which CO₂ absorbs and then goes toward the Earth. 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 Venus, a planet covered by heavy clouds composed mostly of CO₂, whose surface temperatures have been measured at 430~C.If the CO₂ content of the atmosphere is reduced, the temperature falls. According to one respectable theory, if the atmospheric CO₂ concentration were halved, the Earth would become completely covered with ice.  Another equally respectable theory, however, states that a halving of the CO₂ concentration would lead only to a reduction in global temperatures of 3℃.

If, because of an increase in forest fires or volcanic activity, the CO₂ content of the atmosphere increased, a warmer climate would be produced. Plant growth, which relied on both the warmth and the availability of CO₂, would probably increase. As a consequence, plant would use more and more CO₂.  Eventually CO₂ levels would decrease and the climate, in turn, would become cooler. With reduced temperatures many plants would die; CO₂ would thus be returned to the atmosphere and gradually the temperature would rise again. Thus, if this process occurred, there might be a long-term oscillation (波动) in the amount of CO₂ present in the atmosphere, with regular temperature increase and decrease.

Some climatologists argue that the burning of fossil fuels has raised the level of CO₂ in the atmosphere and has caused a global temperature increase of at least 1℃. But a supposed global temperature rise of 1 ℃ may in reality be only several regional temperature increases, restricted to areas where there are many meteorological (气象的) stations. Other areas, for example, the Southern Hemisphere oceanic zone, may be experiencing an equal temperature decrease that is unrecognized because of the shortage of meteorological recording stations.

 

51. Which of the following questions does the information supplied in this passage try to answer?

A. What are the steps in the process that takes place as CO₂ absorbs long-wavelength radiation?

B. How might our understanding of the greenhouse effect be improved if the burning of fossil  were decreased?

C. What might cause a series of regular increases and decreases in the amount of CO₂ in the atmosphere?

D. Why are there fewer meteorological recording stations in the Southern Hemisphere oceanic zone than atmosphere?

52. The author is primarily concerned with ________.

A. explaining the effects that the burning of fossil fuels might have on climate

B. explaining the effects of CO₂ on atmospheric radiation

C. discussing effects that changes in the CO₂ level in the atmosphere might have on climate

D. challenging hypotheses (假说)  about the effects of water vapor and CO₂ on climate

53. The passage suggests that a large decrease in the amount of CO₂ in the atmosphere would result in _________.

A. at least a slight decrease in global temperatures

B. at the most a slight increase in short-wavelength radiation reaching the Earth

C. a slight long-term increase in global temperatures

D. a slight short-term increase in atmosphere water vapor content

54. The author refers to Venus primarily in order to _______.

A. show that the greenhouse effect works on other planets but not on Earth

B. show the degree to which Earth's atmosphere differs from that of Venus

C. support the opinion that as water vapor increases, the amount of CO₂ increases

D. support the argument that the CO₂ level in the atmosphere has a significant effect on climate

55. The discussion of climate in the passage suggests that _________.

A. climate is perfectly stable

B. we are unable at present to measure global temperature changes precisely.

C. the only cause of regional climatic fluctuations (波动) is the change in CO₂ 1evel in the atmosphere

D. slight regional temperature changes can be considered an abnormal feature (特征) of the environment

Answer 1

51.C  52. C  53. A  54. D  55. B