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  3. Aided by the recent ability to analyze samples of air trapped in glaciers, scientists now have a clearer idea of the relationshi

Aided by the recent ability to analyze samples of air trapped in glaciers, scientists now have a clearer idea of the relationshi

admin2014-12-26  39
问题     Aided by the recent ability to analyze samples of air trapped in glaciers, scientists now have a clearer idea of the relationship between atmospheric composition and global temperature changing over the past 160,000 years. In particular, determination of atmospheric composition during periods of glacial expansion and retreat(cooling and warming)is possible using data from the 2,000 meter Vostok ice core drilled in Antarctica. The technique involved is similar to that used in analyzing cores of marine sediments, where the ratio of the two common isotopes of oxygen, 180 and 160, accurately reflects past temperature changes. Isotopic analysis of oxygen in the Vostok core suggests mean global temperature fluctuations of up to 10 degrees centigrade over the past 160,000 years.
    Data from the Vostok core also indicate that the amount of carbon dioxide has fluctuated with temperature over the same period: the higher the temperature, the higher the concentration of carbon dioxide and the lower the temperature, the lower the concentration. Although change in carbon dioxide content closely follows change in temperature during periods of deglaciation, it apparently lags behind temperature during periods of cooling. The correlation of carbon dioxide with temperature, of course, does not establish whether changes in atmospheric composition causing the warming and cooling trends or were caused by them.
    The correlation between carbon dioxide and temperature throughout the Vostok record is consistent and predictable. The absolute temperature changes, however, are from 5 to 14 times greater than would be expected on the basis of carbon dioxide’s own ability to absorb infrared radiation, or radiant heat. This reaction suggests that, quite aside from changes in heat-trapping gases, commonly known as greenhouse gases, certain positive feedbacks are also amplifying the temperature change. Such feedbacks might involve ice on land and sea, clouds, or water vapor, which also absorb radiant heat.
    Other data from the Vostok core show that methane gas also correlates closely with temperature and carbon dioxide. The methane concentration nearly doubled, for example, between the peak of the penultimate glacial period and the following interglacial period. Within the present interglacial period it has more than doubled in just the past 300 years and is rising rapidly. Although the concentration of atmospheric methane is more than two orders of magnitude lower than that of carbon dioxide, it cannot be ignored: the radiative properties of methane make it 20 times more effective, molecule for molecule, than carbon dioxide in absorbing radiant heat. On the basis of a simulation model that climatological researchers have developed, methane appears to have been about 25 percent as important as carbon dioxide in the warming that took place during the most recent glacial retreat 8,000 to 10,000 years ago.
According to the passage, which of the following statements about methane is true?
选项 A、Methane is found in marine sediments.
B、Methane is more effective than carbon dioxide in absorbing radiant heat.
C、The Earth’ s atmosphere now contains more than twice as much methane as it does carbon dioxide.
D、The higher the concentration of carbon dioxide in the Earth’ s atmosphere, the lower the concentration of methane.
答案B
解析 细节题。根据“methane”定位到第四段。根据Although the concentration ofatmospheric methane is more than two orders of magnitude lower than that of carbondioxide，it cannot be ignored：the radiative properties of methane make it 20 times moreeffective，molecule for molecule，than carbon dioxide in absorbing radiant heat．“尽管大气甲烷的含量要比二氧化碳的含量低两个多数量级，但它仍不能被忽视：就分子与分子相对比，甲烷的辐射特性使其在吸收辐射热这方面，要比二氧化碳强出20倍。”说明甲烷在吸收辐射热这方面比二氧化碳有效。和选项B的表述一致，所以答案是B。A“甲烷是在海洋沉积物中发现的”原文没有提及．C是对原文“甲烷的含量几乎翻了一倍。在目前的间冰期范围内，它在过去短短的300年就已经增加了两倍多，并正在迅速增长”的误解，D“二氧化碳含量越高，甲烷含量越低”也没有提及。
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