問題詳情

C.Conservation reduces petroleum imports, saves money, and reduces air pollution. In short, conservation is responsiblestewardship of the environment and it makes practical sense. But its effect on global warming is less certain. Although agrowing number of scientists believe the increasing amount of CO2 in the atmosphere is the major impetus behind globalwarming, the issue is not yet settled. For example, recent findings published in Nature conclude that the sun is more active nowthan at any time in the past 8,000 years. Other natural cycles may also be playing a role. Deforestation and other land usechanges contribute to warming. Towns and cities and the roads that connect them form heat islands that cause significant localand even regional warming.Scientists are especially uncertain about the global warming roles of water vapor, clouds and particles in the atmosphere.Water vapor is a much more potent greenhouse gas than carbon dioxide. If the atmosphere were devoid of the warm air trappedby water vapor, the Earth would be so cold that the oceans would be frozen. Warm air can hold more water vapor than cool air.Increasing the water vapor in the atmosphere can trap more heat, thus increasing temperature. On the other hand, increasing thewater vapor can also increase cloud cover, which reduces the solar irradiance that increases the temperature. The interactions of第 6 頁，共 6 頁these poorly understood mechanisms contribute to the uncertainty of global warming models. So does the presence of particlesin the atmosphere, which can either reflect sunlight (a cooling effect) or absorb it (a warming effect).The melting of glaciers is powerful evidence that the Earth is indeed warming. Or is it? Consider Alaska’s Bering Glacier,the largest in North America. According to NASA’s Earth Observatory website, warmer temperatures and changes inprecipitation over the past century have thinned the Bering Glacier by several hundred meters. Since 1900 the glacier hasretreated some 7.5 miles. It seems only logical to blame the retreat of a massive glacier on global warming, but checking thetemperature record suggests something else must be at work. The temperature has been measured on either side of the BeringGlacier since 1909, and the temperature record at both sites does not show obvious warming or cooling trends that are foundelsewhere around the Earth. So why is the giant glacier receding?James Hansen, NASA’s primary global warming advocate, has shown that soot may be causing significant melting ofglobal ice and snow. Major sources of soot include agricultural fires around the world, coal-burning power plants in China,cooking fires in India, and massive forest fires in Alaska, Canada, and Russia. The smoke from these fires is clearly visible inNASA satellite images. The possible role of soot in melting glaciers might someday be viewed as a major discovery,particularly if it explains the melting of glaciers, such as Bering Glacier, in the absence of any warming trends. Meanwhile,global warming advocates continue to claim that warming alone is melting glaciers.This brings us to the issue of the magnitude of global warming, for there is great controversy over the accuracy ofmeasurements used to determine temperature trends. The central issue is that many stations that measure temperature aroundthe world have become surrounded by development that causes an artificial warming effect. Climate modelers have attemptedto remove this heat island effect, but there is controversy over their success.
46. What is the main purpose of this passage?
(A) To prove that conservation is still contributive to lessening the extent of global warming.
(B) To elaborate on potential factors, other than carbon dioxide emissions, of global warming.
(C) To explain possible reasons for clouds and particles to affect the range of global warming.
(D) To persuade readers that the receding of glaciers does supply a strong proof of global warming.

參考答案

答案：B
難度：適中0.586957
統計：A(4),B(27),C(11),D(3),E(0)

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