GRE考试

【单选题】Scientists studying the effect of large volcanic eruptions on global climate have long focused on the major quantities of carbon dioxideC02), a gas known to contribute to the greenhouse effect, produced by these eruptions. It is well observed that such greenhouse gases trap heat radiated from the surface of the earth, thereby forming a type of insulation around the planet. The greenhouse effect is essential for ecological equipoise because it maintains the temperature of the planet within habitable parameters, but there is growing concern that man-made production of gases such asCO[,2] from the burning of fossil fuels may be threatening the system’’s tolerance, and have resulted in excessive warming on a global scale. While volcanic eruptions indubitably metabolize and accumulateC0[,2] in the atmosphere, it has been recently discovered that their impact is virtually trivial compared to the quantity produced by human activities, especially heavy industry. In reality, the more substantive climatic effect from volcanoes results from the production of atmospheric haze, whereby large eruption columns inject ash particles and sulfur-rich gases into the troposphere and stratosphere, clouds that circumscribe the globe within weeks of the volcanic activity.Ash and aerosol clouds from large volcanic eruptions disseminate quickly through the atmosphere, and the small ash particles decrease the amount of sunlight reaching the surface of the earth and lower average global temperatures, while the sulfurous gases combine with water in the atmosphere to form acidic aerosols that also absorb incoming solar radiation and scatter it back out into space.　　There is evidence that volcanoes’’ stratospheric ash clouds has a lesser effect on global temperatures than aerosol clouds, given that the major Mt. St. Helens eruption had lowered global temperatures by about 0.1 degreeC, while two years later the much smaller eruption ofElChico had, by contrast, three to five times the global cooling effect worldwide.Despite its smaller ash cloud,ElChico emitted more than 40 times the volume of sulfur-rich gases produced by Mt. St. Helens, revealing that the formation of atmospheric sulfur aerosols has a more substantial effect on global temperatures than simply the volume of ash produced during an eruption. Sulfate aerosols appear to necessitate several years to settle out of the atmosphere, one of the reasons their effects are so widespread and enduring. This corroborates the opinion of those scientists who argue that without the cooling effect of major volcanic eruptions such asElChico, global warming effects caused by human activities would be far more substantial. It should be noted that major volcanic eruptions have additional climatic effects beyond global temperature decreases and acid rain, for ash and aerosol particles suspended in the atmosphere scatter light of red wavelengths, often resulting in brilliantly colored sunsets and sunrises around the worl
D、The passage suggests that the effects of volcanic carbon dioxide on the environment differ from those of sulfurous gases in that________.
A、carbon dioxide tends to alleviate environmental haze, while sulfurous gases usually increase it
B．carbon dioxide tends to increase temperatures by trapping sunlight, while sulfurous gases tend to decrease temperatures by blocking it
C．carbon dioxide tends to have an effect on the environment, while sulfurous gases for the most part do not

D、sulfurous gases have played an even more significant role than carbon dioxide in pushing environmental temperatures outside the habitable range
E．sulfurous gases tend to decrease the level of solar radiation outside the earth’’s atmosphere, while carbon dioxide plays only a negligible role

网考网参考答案：B
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