There are hidden factors which scientists call "feedback mechanisms". No one knows quite how they will interact with the changing climate. Here's one example: plants and animals adapt to climate change over centuries. At the current estimate of half a degree centigrade of warming per decade, vegetation(植物)may not keep up. Climatologist James Hansen predicts climate zones will shift toward the poles by 50 to 75 kilometres a year— faster than trees can naturally migrate. Species that find themselves in an unfamiliar environment will die. The 1,000-kilometre-wide strip of forest running through Canada, the USSR and Scandinavia could be cut by half. Millions of dying trees would soon lead to massive forest fires, releasing tons of CO
2
and further boosting global warming.
There are dozens of other possible "feedback mechanisms". Higher temperatures will fuel condensation and increase cloudiness, which may actually damp down global warming. Others, like the "albedo" effect, will do the opposite. The "albedo" effect is the amount of solar energy reflected by the earth's surface. As northern ice and snow melts and the darker sea and land pokes(戳)through, more heat will be absorbed, adding to the global temperature increase.
Even if we were to magically stop all greenhouse-gas emissions tomorrow the impact on global climate would continue for decades. Delay will simply make the problem worse. The fact is that some of us are doing quite well the way things are. In the developed world prosperity has been built on 150 years of cheap fossil fuels.
Material progress has been linked to energy consumption. Today 75 percent of all the world's energy is consumed by a quarter of the world's population. The average rich world resident adds about 3. 2 tons of CO
2
yearly to the atmosphere, more than four times the level added by each Third World citizen. The US, with just 7 percent of the global population, is responsible for 22 percent of global warming.
单选题
"Feedback mechanisms" in Paragraph 1 most probably refers to______.
单选题
James Hansen predicts that the shift of climate zones will be accompanied by______.
【正确答案】
D
【答案解析】解析：文章第一段中指出“Climatologist James Hansen predicts climate zones will shift toward the poles by 50 to 75 kilometres a year--faster than trees can naturally mi—grate．Species that find themselves in an unfamiliar environment will die．”气候学家詹姆斯·汉森预计，气候带将每年向极地移动50公里到75公里，比树木可能自然迁移的速度要快。那些发现自己生活于一个不熟悉的环境的物种将会灭绝。可见，气候带的迁移使树木不能适应其速度而灭绝。D项符合文章的意思。B和C都与文章的意思相反。A项的内容是文中举例来说明气候带的迁移对树木的影响，并不是气候带迁移将伴随的状况，所以A项不对。因此本题的正确答案为D。
单选题
We can learn from the passage that______.
【正确答案】
A
【答案解析】解析：文章第一段“There are hidden factors which scientists call‘feedback mechanisms’．No one knows quite how they will interact with the changing climate．”有一些隐形因素，科学家叫做“反馈机制”。没有人完全了解它们将如何与变化的气候相互作用。第二段接着讲到“There are dozens of other possible‘feedback mechanisms’．Higher temperatures will fuel condensation and increase cloudiness，which may actually damp down global warming．Others，like the‘albedo’effect，will do the opposite．”可能还有许多其他的“反馈机制”。更高的温度将加速凝结，增加朦胧度。实际上，这可能抑制全球变暖。其他的机制，如“反射”效应，其作用相反。可见，“反馈机制”中有的可能促进全球变暖，有的可能抑制全球变暖。A项符合文章的意思。B、C项的内容与文意不符，D项不属于文章中表述的内容。因此本题的正确答案为A。
单选题
It can be inferred from the passage that______.
【正确答案】
B
【答案解析】解析：文章最后一段中指出“The average rich world resident adds about 3．2 tons ofCO
2
yearly to the atmosphere， more than four times the level added by each Third World citizen．”由此可知，第三世界国家每人每年向大气中排放的二氧化碳不足3．2吨的1／4，也就是不到1吨的二氧化碳。B项的内容符合文意。A项的内容在文章中没有提及。文章第三段说“Even if we were to magically stop all greenhouse—gas emissions tomorrow the impact on global climate would continue for decades．”可见，即使我们现在停止温室气体的排放，温室气体对全球气候的影响也不会立即消失，而是要持续几十年，地球的气候也不会不久就获得平衡。所以C项不对。D项的内容不符合文意。所以应该选B。
单选题
Which of the following is the main topic of the passage?