托福模拟试题听力 - TPO20 - 讲座2

时间 : 2013-08-12 09:57来源 : VOA官网 收听下载次数 :
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TPO20 Lecture2-Environmental Science  

Professor:I’d like to take you back about 11 thousand years ago when Earth entered the latest interglacial period. Interglacial periods are, typically periods of time between Ice Ages, when the climate warms, and the glacial ice retreats for a time, before things cool off again and another Ice Age begins. And for over the past several million years, Earth’s sort of default climate has actually been Ice Age, but we have experienced periodic regular thaws, and the last one, the one we are in now, started about 11 thousand years ago. Now, the typical pattern for an interglacial period, and we have studied several, is that the concentration of carbon dioxide and methane gas actually reaches it... its peak, that is, there is the most carbon dioxide and methane gas, uh, greenhouse gases in the atmosphere just after the beginning of the interglacial period. And then, for reasons which are not entirely clear , the concentration of greenhouse gases gradually goes down. Now, the climate continues to warm for a while because there is a lag effect. But uh, gradually as the concentration of greenhouse gases goes down, Earth starts to cool again, and eventually you slip back into an Ice Age.

Um, however , for the latest interglacial period, the one we are in now, this pattern did not hold, that is, the concentration of carbon dioxide and methane dipped a little bit after, uh, uh, after peaking at the beginning, near the beginning of the interglacial period, but then it began to rise again. Um ... What was different about this interglacial period than the other ones? Well, one of the big differences is human activity. People began to raise crops and animals for food instead of hunting for them. This is the agricultural revolution. And it began to happen in the earliest stages about 11 thousand years ago.

Now, scientists have tended to regard ... the ... uh ... agricultural revolution as a beneficiary of the ... uh ... fortuitousshift in climate. However , some new theories of climate, new theorists of climate have proposed that perhaps humanity was having an effect on the climate as far back as the beginnings of the agricultural revolution. When you grow crops and uh, pasture your animals , one of the things you do is you cut down the forests. If you cut down the forests, when you burn the trees for fuel and don’t replace them with other trees, or when you just leave them to rot and don’t allow other trees to grow, you end up with a lot more carbon in the form of carbon dioxide getting into the atmosphere. Um ... another gas associated with the spread of agriculture is methane. Methane forms in large concentration above wetlands, and as it turns out, the cultivation of certain grains creates vast areas of artificial wetlands, and probably drastically increases the amount of methane getting into the atmosphere, over and above what would be there. So, um... agriculture, the ... the spread of agriculture, you know we are talking over thousands of years, um... but this could very well had a profound effect on the composition of Earth’s atmosphere. It’s kind of ironic to think that absent that effect, it maybe that we would be heading into an Ice Age again. In fact, back in the 1970s, a lot of theorists were predicting that, you know, the climate would start to cool and we’d slowly enter into the new Ice Age. And then they were puzzled as to why it didn’t seem to be happening.

Umm... now, what are the implications for the future? Well, um... it is a little tricky. I mean, you could say, well, here is an example of ... um ... human activity, the agricultural revolution which actually was beneficial, we altered the climate for the better , perhaps, by preventing an Ice Age. But then industrialization, of course, has drastically increased the amount of carbon dioxide that humans are putting into the atmosphere, the burning of fossil fuels tends to put a lot of CO2 into the atmosphere. Um... so we are entering into uncharted3 territory now, in terms of the amount of carbon dioxide, the concentrations of carbon dioxide that are now being put into the atmosphere as a result of industrialization and the use of fossil fuels.

 

1 What is the lecture mainly about?

A. The effect of ice ages on the development of agriculture

B. A theory about a change in Earth’s climate cycle

C. Strategies to prevent Earth from entering another ice age

D. Some effects of industrialization on Earth’s atmosphere 

 

2 What does the professor imply about Earth’s climate over the last several million years? Click on 2 answers.

A. Ice ages have alternated with warmer periods.

B. Recent ice ages have not been as cold as earlier ice ages.

C. Interglacial periods have become cooler and cooler overtime.

D. Previous interglacial periods were shorter than the current interglacial period.



3 According to the professor, what factor is extending the duration of the current interglacial period?

A. A shift in the locations of wetlands and forests

B. The relatively mild temperatures of the most recent ice age

C. The increased absorption of certain atmospheric gases by farm crops

D. An increase in the quantity of certain gases in Earth’s atmosphere 


 
4 According to the professor, what activities associated with the beginnings of agriculture may have slowed or prevented the onset of a predicted ice age? Click on 2 answers.

A. The clearing of trees

B. The burning of fossil fuels

C. The domestication of certain animals

D. The cultivation of certain grains 

 

5 What is the professor’s attitude toward industrialization?

A. He thinks that its effect on Earth’s climate will decrease overtime.

B. He is worried that it may speed the arrival of the next ice age.

C. He thinks that it may reduce the effect of agriculture on Earth’s climate.

D. He is unsure about its long-term effects on Earth’s climate.