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  3. Scientists studying the effect of large volcanic eruptions on global climate have long focused on the major quantities of c

Scientists studying the effect of large volcanic eruptions on global climate have long focused on the major quantities of c

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问题          Scientists studying the effect of large volcanic eruptions on global climate
     have long focused on the major quantities of carbon dioxide (C02), 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
(5)   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 as CO[,2] from the burning of fossil fuels may
     be threatening the system’s tolerance, and have resulted in excessive warming
(10)  on a global scale.
          While volcanic eruptions indubitably metabolize and accumulate C0[,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
(15)  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
(20)  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
(25)  effect on global temperatures than aerosol clouds, given that the major Mt. St.
     Helens eruption had lowered global temperatures by about 0.1 degree C, while
     two years later the much smaller eruption of El Chico had, by contrast, three to
     five times the global cooling effect worldwide. Despite its smaller ash cloud, El
     Chico emitted more than 40 times the volume of sulfur-rich gases produced by
(30)  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 I
     widespread and enduring. This corroborates the opinion of those scientists who
(35)  argue that without the cooling effect of major volcanic eruptions such as El
     Chico, 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,
(40)  often resulting in brilliantly colored sunsets and sunrises around the world.
选项 A、the greenhouse gas effect produced by human activities tends to have a much greater environmental effect than that of volcanic explosions
B、clouds of sulfur-rich gases tend to achieve greater heights in the stratosphere than do ash clouds
C、a particular explosion producing high sulfur and little ash had a greater environmental effect than the converse
D、the burning of fossil fuels tends to exacerbate the effects of sulfurous aerosols, but not those of ash clouds
E、global warming effects tend to minimize the impact of ash clouds, but not those of sulfurous aerosols
答案C
解析
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