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21世紀(jì)大學(xué)英語(yǔ)讀寫(xiě)教程第一冊(cè)Unit9內(nèi)容介紹
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Hothouse Earth
Kevin McKean
Headlines warned of rising temperatures and melting polar ice caps.
Scientists issued reports on the severe climate changes that could result from the "greenhouse effect" — the gradual warming of the atmosphere caused by an increase in carbon dioxide levels from the burning of fossil fuels, saying that average global temperatures could start to rise within a few decades and reach levels nine degrees Fahrenheit higher than today's temperatures by the end of the next century. This, experts said, could create dangerous changes to global weather patterns. For instance, it could change annual amounts of rainfall, swell or dry up rivers, and raise the level of the seas.
While admitting that this forecast was somewhat uncertain, scientists warned against treating it as a cry of wolf. Although there is considerable debate over how severe the greenhouse effect will be, one thing seems certain: Carbon dioxide levels are on the rise.
Who or what is to blame? Scientists conclude that it is the burning of coal, oil, synthetic fuels, and natural gas. These fossil energy sources release an estimated five and a half billion tons of carbon into the atmosphere each year as colorless, odorless CO2 gas.
The increased carbon dioxide could profoundly affect the way the earth is heated by the sun. The sun's energy strikes the earth mainly in the form of visible light. As the earth heats up, it radiates this energy back into space, but at the much longer wavelengths of infrared light, or heat. Carbon dioxide lets the visible light pass through, but absorbs energy at infrared wavelengths. Thus, the more carbon dioxide there is in the atmosphere, the more the earth's heat is blocked from escaping — just as a blanket holds in the heat of a sleeper's body. In the late 1800s, a Swedish scientist gave this phenomenon its name when he compared it to the way glass shuts in air heated by the sun in a greenhouse.
Some scientists think the greenhouse effect already has begun: Average global temperatures have risen about one degree Fahrenheit in the past ninety years (with a dip from the mid-1940s to 1970). Others argue that the rise could be due to natural temperature ups and downs.
Nevertheless, most scientists agree that the accumulation of carbon dioxide has reached the point where an increase in temperature is sure to take place. One study said average global temperatures probably would rise nearly four degrees by the twenty-first century — a total warming greater than that since the last ice age.
Rising temperatures would be just the beginning. The heating would shift global rainfall patterns, bringing drought to some now-fertile areas and irrigating some deserts. Likewise, mountain glaciers and polar ice caps could melt substantially, causing the seas to rise two feet by the end of the century. Many low-lying communities could be flooded. Worst of all, the effect may be irreversible.
Some have maintained that the world faces such great dangers from population growth, diminishing food supply, and the spread of nuclear weapons that the greenhouse threat seems mild by comparison. Others argue that since the earth has endured a long string of ice ages in the last two million to three million years, any warming is likely to be temporary. Even so, those who try to minimize the problem must also explain away the harsh conditions on the planet Venus. There, a runaway greenhouse effect is thought to account for surface temperatures approaching 900 degrees Fahrenheit; Venus's cloud-shrouded atmosphere is about 97 percent carbon dioxide.
Although few scientists think the earth will go the way of Venus, most agree that the greenhouse problem should be tackled now. City planning should be revised; dykes and reservoirs should be built; an eye should be kept open on the thermometer for the first definite sign that the greenhouse era has arrived.
Second Listening
Listen to the tape again. Then, choose the best answer to each of the following questions.
1. Which of the following topics does the listening passage mainly discuss?
A) The dangers caused by changes in the atmosphere.
B) Problems on the planet Venus.
C) The damage done by different types of pollution.
D) Ways of growing flowers in the winter.
2. What does the term "greenhouse effect" refer to?
A) A "blanket" of green glass being built over some low-lying cities.
B) O1d trees being cut down in order to build houses.
C) A warming of the earth's temperatures.
D) A cloud of green dust on the planet Venus.
3. Which of the following is mentioned as a reason for the buildup of carbon dioxide in the atmosphere?
A) Burning of fuels by cars and factories.
B) A large increase in the number of trees in some areas.
C) A large decrease in the number of trees in some areas.
D) Pollution in the earth's rivers and streams.
4. What changes in global weather patterns might the greenhouse effect create?
A) An increase in rain in some places.
B) A decrease in rain in some places.
C) A shift in the patterns of ocean tides.
D) Both A) and B).
Pre-reading Questions
1. Looking at the title, what do you guess the passage is about? Make predictions, and then read the first paragraph to find out what the "greenhouse effect" is.
2. In the discussion of the "greenhouse effect", what do scientists disagree about? And, what points do they agree on? Skim paragraphs 3 and 4 to look for your answers.
3. How serious of a threat do you consider the "greenhouse effect" to be? Give reasons for your answer.
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