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狗主考古求确认
第一篇
V3
1P说甲烷和二氧化碳一样是一种温室气体;也会造成global warming。列举了造成大气中M物质增加的原因，如燃烧石化燃料等。fuel fossil burn, fire and other.(有题考这段的作用，我认为是提供背景资料)
2P “Surprisingly”(转折)科学家发现植物plant也会释放M，提出如卫星空照的证据，说热带地区因为有较密集的丛林tropical forest，所以大气中的M特别集中。The article listed two studys to demonstrate that the plants really emit the methane.
3P (有些地方没读通) 继续说这一发现可以用于解释ice age前后甲烷的变化;似乎是说植物释放M也可以解释古老的冰块中的气泡浬为何也有M…植物排放M的事实也解释了另一个科学谜题，即为什么古老的冰层取样中有小气泡含有S(又一个不认识的单词)。。。。可能是说随着冰河入到海洋，海底也沉积了很多M，上一个冰河时期的结束可能就是这些储存在海底的M被释放的结果。但是证据显示海底大概四万年都没有剧烈变动，所以这个应该不是导致冰河期结束的原因。推测应该是植物大量的繁衍，释放出M,导致平均气温越来越高才使得冰河期结束。
4P 虽然植物会释放M，但是希望藉由减少植物来阻止溫室效应仍然是不对的，但是全球变暖是不可逆的，还得有植物。因为植物可以吸收其它更多的温室气体。想要缓和温室效应还是应该从减少石化原料fuel.的使用下手。(这段无考点)
V5.疑似原文（待确认）
Most people know methane (often written as the chemical formula CH4) as natural gas. Approximately 600 million metric tons of it—both anthropogenic (from human activities) and natural—rise into the atmosphere every year. Wetlands such as swamps, marshes and rice paddies provide the greatest share. Cattle, sheep and termites also make methane, as a by-product of anaerobic microbial digestion in their gut. Forest and savanna fires release methane, as does the combustion of fossil fuels. Over the years, researchers have gained considerable knowledge about the global methane cycle, and the consensus of the Intergovernmental Panel on Climate Change (IPCC) in 2001 was that the major sources had probably been identified (although the proportion each source contributes was still uncertain).
In 2005 the scientists’ satellite measurements revealed “clouds” of methane over tropical forests. In light of our findings, however, their work made sense: green vegetation was the source of the methane clouds. Our findings would explain a trend that has puzzled climate scientists for years: fluctuations in methane levels in parallel with changes in global temperatures. Ice cores serve as natural archives that store information about atmospheric composition and climate variability going back almost a million years. Tiny bubbles of air trapped in the ice reveal the relative concentrations of atmospheric gases in the past. We see in the ice cores, for example, that variations of past carbon dioxide levels are closely linked to changes in global temperatures. During ice ages, carbon dioxide concentrations are low; during warm spells, levels increase. Another explanation that has been suggested involves the gas in a form known as methane hydrates. These develop at high pressure, such as that found on the ocean floor. An unknown but possibly very large quantity of methane is trapped in this form in ocean sediments. The sudden release of large volumes of methane from these sediments into the atmosphere has been suggested as a possible cause for rapid global warming events in the earth’s distant past. Yet recent results from polar ice core studies show that marine methane hydrates were stable at least over the past 40,000 years, indicating that they were not involved in the abrupt increases of atmospheric methane during the last glacial cycle. We know that terrestrial vegetation is very sensitive to environmental changes, and thus the total amount of vegetation on the planet varies as the climate cools down and warms up during glacial cycles. In light of our findings, such variations should now be seriously considered as a possible cause of declines in methane levels during glacial periods and rises during the interglacials.
Our discovery also led to intense speculation that methane emissions by plants could diminish or even outweigh the carbon storage effect of reforestation programs. But our calculations show that the climatic benefits gained by establishing new forests to absorb carbon dioxide would far exceed the relatively small negative effect of adding more methane to the atmosphere (which may reduce the overall carbon uptake of the trees by 4 percent at most). The potential for reducing global warming by planting trees is most definitely positive. A more legitimate concern is whether the methane produced by vegetation can have an impact on climate in the near future. Although plants are not responsible for the massive increase of methane in the atmosphere since preindustrial times, they do tend to grow faster. As we can expect methane emissions from vegetation to increase with temperature, this would lead to even more warming. This vicious cycle would be a natural phenomenon except for its speed, which is accelerated mainly by anthropogenic activities such as burning fossil fuels. The large plant feedback to global climate change that most likely happened in the past, however, is probably unlikely today because so many forests have been cut down. The problem is not the plants; it is the global large-scale burning of fossil fuels.
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发表于 2016-3-22 12:12:15
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