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GRE阅读模拟在线练习附答案一百六十三

2018-11-21 16:44:00来源：网络

　　对于GRE阅读部分，最好的练习资料就是模拟资料。通过模拟练习，可以让大家更好地发现自己在备考中的不足，重点攻克自己的短板内容，有效的提升阅读分数。下面新东方在线GRE频道为大家整理了详细的内容，供大家参考。

点击查看》》》【GRE阅读真题在线练习附答案汇总】

　　The molecules of carbon dioxide in the Earth's atmosphere affect the heat balance of the Earth by acting as a oneway screen. Although these molecules allow radiation at visible wavelengths, where most of the energy of sunlight is concentrated, to pass through, they absorb some of the longer-wavelength, infrared emissions radiated from the Earth's surface, radiation that would otherwise be transmitted back into space. For the Earth to maintain a constant average temperature, such emissions from the planet must balance incoming solar radiation. If there were no carbon dioxide in the atmosphere, heat would escape from the Earth much more easily. The surface temperature would be so much lower that the oceans might be a solid mass of ice.

　　Today, however, the potential problem is too much carbon dioxide. The burning of fossil fuels and the clearing of forests have increased atmospheric carbon dioxide by about 15 percent in the last hundred years, and we continue to add carbon dioxide to the atmosphere. Could the increase in carbon dioxide cause a global rise in average temperature, and could such a rise have serious consequences for human society? Mathematical models that allow us to calculate the rise in temperature as a function of the increase indicate that the answer is probably yes.

　　Under present conditions a temperature of -18°C can be observed at an altitude of 5 to 6 kilometers above the Earth. Below this altitude (called the radiating level), the temperature increases by about 6°C per kilometer approaching the Earth's surface, where the average temperature is about 15°C. An increase in the amount of carbon dioxide means that there are more molecules of carbon dioxide to absorb infrared radiation. As the capacity of the atmosphere to absorb infrared radiation increases, the radiating level and the temperature of the surface must rise.

　　One mathematical model predicts that doubling the atmospheric carbon dioxide would raise the global mean surface temperature by 2.5°C. This model assumes that the atmosphere's relative humidity remains constant and the temperature decreases with altitude at a rate of 6.5°C per kilometer. The assumption of constant relative humidity is important, because water vapor in the atmosphere is another efficient absorber of radiation at infrared wavelengths. Because warm air can hold more moisture than cool air, the relative humidity will be constant only if the mount of water vapor in the atmosphere increases as the temperature rises. Therefore, more 　　infrared radiation would be absorbed and radiated back to the Earth's surface. The resultant warming at the surface could be expected to melt snow and ice, reducing the Earth's reflectivity. More solar radiation would then be absorbed, leading to a further increase in temperature.

本文关键字: GRE阅读练习 GRE阅读 GRE

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