托福模拟试题听力 - TPO23 - 讲座2

时间 : 2013-10-23 08:49来源 : VOA官网 收听下载次数 :
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TPO23 Lecture2 - Environmental Science (Earth Budget)

Professor:Basically, a cloud either contributes to the cooling of Earth's surface or to its heating. Earth's climate system is constantly trying to strike a balance between the cooling and warming effects of clouds.It's very close, but overall the cumulative effects of cloud are to cool Earth rather than heat it. And this balance between the amount of solar radiation, energy from the Sun, that's absorbed by Earth, and the amount that's reflected back into space. We call this Earth's radiation budget. And one way we keep track of the radiation budget is by looking at the albedo of the different surfaces on the planet.A surface's albedo is the percentage of incoming solar energy, sunlight, that's reflected off that surface back into space. Oceans have a low albedo, because they reflect very little energy. Most of the solar energy that reaches the ocean gets absorbed and heats the water. Um... rainforests also have low albedos. Well, by contrast, deserts and areas covered by ice and snow, these places have high albedos. And clouds, in general, cloud also have high albedos. That means that a large percentage of the solar energy clouds receive is reflected into space.OK. Now, when we say that clouds have a high albedo. We are talking about the effect of all the clouds on earth averaged together. But different types of clouds have different reflective properties, they have different albedos.

Student:So which type of clouds cools Earth? And which type heat it?

Professor:Well, high thin clouds contribute to heating while low thick clouds cool Earth. High thin clouds are very transparent to solar radiation, like, uh, clear air. So they mostly transmit incoming solar energy down to Earth. There's not much reflection going at all. At the same time, these clouds trap in some of Earth's heat. Because of the trapped heat, these clouds have an overall heating effect.

Student:Oh. OK. Since low thick clouds are not transparent to radiation...

Professor:Exactly. They block most of the solar energy so it never reaches Earth's surface. They reflect much of it back out into space.

Student:So that's how they contribute to cooling?

Professor:Yep. And as I said earlier, this cooling effect predominates. Now, what if there was a process that could control the type of clouds that form?

Student:Are you talking about controlling the weather?

Professor:Well, I am not sure I would go that far. But we recently noticed an increase in cloud cover over an area of the ocean waters around Antarctica. An increased area of low thick clouds, the type that reflects a lare portion of solar energy back to space and cools the Earth.
Well, the reason for this increased cloud cover, it turns out, is the exceptionally large amount of microscopic marine plants. Well, the current hypothesis is that these microorganisms produce a chemical, dimetho sulfide that interacts with the oxygen in the air, creating conditions that lead to the formation of the low thick clouds we observed. Well, that's true. It could have huge implications. So, maybe we are talking about controlling the weather. Perhaps, if the microorganisms near Antarctica really are responsible, perhaps we can accelerate the process somehow.

 

1 What is the lecture mainly about?

A. Ways of identifying different types of clouds

B. Recent research findings about the causes of global warming

C. The impact of clouds on global temperatures

D. The impact of human activity on cloud formation



2  According to the professor, what is Earth’s radiation budget?

A. The average temperature difference between land masses and bodies of water

B. The balance between incoming solar energy and reflected solar energy

C. The percentage of incoming solar energy that gets trapped in clouds

D. The portion of marine species that has been affected by global warming



3  Why does the professor discuss albedo?

A. To point out that different surfaces have different reflective properties

B. To suggest that the reflective surfaces on Earth should be increased

C. To demonstrate how a cloud's thickness is measured

D. To explain why clear air reflects a large amount of solar energy back to space



4 What can be inferred from the lecture about the effects of different types of clouds on Earth's climate?

A. Low, thick clouds increase ocean temperatures much more than high, thin clouds do

B. The cooling effect of low, thick clouds is stronger overall than the heating effect of high, thin clouds

C. The effect of low, thick clouds is understood better than the effect of high, thin clouds.

D. The effect of low, thick clouds is much more variable than the effect of high, thin clouds.



5 What does the professor say about microscopic plants in the ocean near Antarctica?

A. They have been raising the ocean's albedo.

B. Their population is increasing due to global warming.

C. They grow more rapidly when cloud cover is thin.

D. They produce a chemical that leads to cloud formation



6 Why does the professor say this So, maybe we are talking about controlling the weather.

A. To reintroduce a topic from a previous lecture

B. To correct a common misunderstanding

C. To encourage students to express their own opinions

D. To revise his previous response to a student's question