大学英语精读第二册 Unit 5 The Villain in the Atmosphere
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There is one gas present in the air we breathe that is essential to life.Unfortunately,one can have too much of a good thing and the growth in carbon dioxide threatens to warm up our planet to a dangerous extent.Isaac Asimov introduces us to this villain in the atmosphere,explaining how it works and what can be done about it.UNIT 5 The Villain in the AtmosphereThe villain in the atmosphere is carbon dioxide.It does not seem to be a villain. It is not very poisonous and it is present in the atmosphere in so small a quantity — only 0.034 percent — that it does us no harm.What’s more, that small quantity of carbon dioxide in the air is essential to life. Plants absorb carbon dioxide and convert it into their own tissue, which serve as the basic food supply for all of animal life (including human beings, of course). In the process they liberate oxygen, which is also necessary for all animal life.But here is what this apparently harmless and certainly essential gas is doing to us:The sea level is rising very slowly from year to year. In all likelihood, it will continue to rise and do so at a greater rate in the course of the next hundred years. Where there are low-lying coastal areas (where a large fraction of the world’s population lives) the water will advance steadily, forcing people to retreat inland.Eventually the sea will reach two hundred feet above its present level, and will be splashing against the windows along the twentieth floors of Manhattan’s skyscrapers. Florida will disappear beneath the waves, as will much of the British Isles, the crowded Nile valley, and the low-lying areas of China, India, and Russia.Not only will many cities be drowned, but much of the most productive farming areas of the world will be lost. As the food supply drops,starvation will be widespread and the structure of society may collapse under the pressure.And all because of carbon dioxide. But how does that come about? What is the connection?It begins with sunlight, to which the various gases of the atmosphere (including carbon dioxide) are transparent. Sunlight, striking the top of the atmosphere, travels right through miles of it to warm the Earth’s surface. At night, the Earth cools by radiating heat into space in the form of infrared radiation.However, the atmosphere is not quite as transparent to infrared radiation as it is to visible light. Carbon dioxide in particular tends to block such radiation. Less heat is lost at night, for that reason, than would be lost if carbon dioxide were not present in the atmosphere. Without the small quantity of that gas present, the Earth would be distinctly cooler, perhaps uncomfortably cool.We can be thankful that carbon dioxide is keeping us comfortably warm, but the concentration of carbon dioxide in the atmosphere is going up steadily and that is where the villainy comes in. In 1958, carbon dioxide made up only 0.0316 percent of the atmosphere. Each year since, the concentration has crept upward and it now stands at 0.0340 percent. It is estimated that by 2020 the concentration will be nearly twice what it is now.This means that in the coming decades, Earth’s average temperature will go up slightly. As a result, the polar ice caps will begin to melt.Something like 90 percent of the ice in the world is to be found in the huge Antarctica ice cap, and another 8 percent is in the Greenland ice cap. If these ice caps begin to melt, the sea level will rise, with the result that I have already described.But why is the concentration of carbon dioxide in the atmosphere steadily rising?To blame are two factors. First of all, in the last few centuries, first coal, then oil and natural gas, have been burned for energy at a rapidly increasing rate. The carbon contained in these fuels, which has been safely buried underground for many millions of years, is now being burned to carbon dioxide and poured into the atmosphere at a rate of many tons per day.To make matters worse, Earth’s forests have been disappearing, slowly at first, but in the last couple of centuries quite rapidly. Right now it is disappearing at the rate of sixty-four acres per minute.Whatever replaces the forest — grassland or farms or scrub — produces plants that do not consume carbon dioxide at an equal rate. Thus, not only is more carbon dioxide being added to the atmosphere through burning of fuel, but as the forests disappear, less carbon dioxide is being removed from the atmosphere by plants.But this gives us a new perspective on the matter. The carbon dioxide is not rising by itself. It is people who are burning the coal, oil, and gas. It is people who are cutting down the forests. It is people, then, who are the villains.What is to be done?First, we must save our forests, and even replant them.Second, we must have new sources of fuel that do not involve the production of carbon dioxide. Nuclear power is one of them, but if that is thought too dangerous, there are other alternatives. There is the energy of waves, tides, wind, and the Earth’s interior heat. Most of all, there is the direct use of solar energy.All of this will take time, work, and money, to be true, but nations spend more time, work, and money in order to support competing military machines that can only destroy us all. Should we object to spending less time, work, and money in order to save us all?。