Book 2 Unit 5
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.
The Villain in the Atmosphere
Isaac Asimov
The 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?
课文翻译
在我们呼吸的空气中，有一种气体对生命是必不可少的。遗憾的是，一样好东西我们可能会拥有得太多，而二氧化碳的增长威胁着我们，使地球变暖到一种危险的程度。艾萨克·阿西莫夫向我们介绍了大气层中的这个坏蛋，向我们解释了它是怎样活动的以及对付它的办法。
大气层中的恶棍
艾萨克·阿西莫夫
大气层中的恶棍就是二氧化碳。
二氧化碳看上去不像一个恶棍。它毒性不大，在大气层中的含量极小——只占0.034％——不会对我们造成任何伤害。
再者，空气中的那一点点二氧化碳对生命至关重要。植物吸收二氧化碳并将其转化成它们自己的组织，充当所有动物（当然也包括人类）的基本食物供给。在这一过程中，植物释放氧气，而氧气又是所有动物生命所不可缺少的。
然而，这一看上去无害而且无疑又必不可少的气体却正在对我们产生影响。
年复一年，海平面正在慢慢上升。它很可能继续上升，而在今后数百年间，会以更快的速度上升。在那些低洼的沿海地区（在这些地区居住着世界上很大一部分人口），海水会稳步向前推进，迫使人们向内陆退居。
最后，海水将会高出目前海平面两百英尺，一阵阵海浪将会拍打曼哈顿摩天大楼二十层楼的窗户。佛罗里达将会沉没在海浪之下，英伦三岛的大部分，人口稠密的尼罗河流域，还有中国、印度和俄罗斯的低洼地区也都将遭到同样的命运。
不仅许多城市将被淹没，而且世界上大部分盛产粮食的地区也将会失去。由于食品供应下降，到处都会出现饥荒，在这种压力下，社会结构有可能崩溃。
而这一切都是因为二氧化碳。可怎么会出现这种情况呢？两者之间又有什么联系呢？
首先是太阳光，大气层中的各种气体（包括二氧化碳）对于太阳光来说是透明的。太阳光照射大气层的顶部，径直透过数英里的大气层，温暖着地球的表面。在夜间，地球将热量以红外线的形式放射到外层空间而冷却下来。
然而，大气层对红外线来说并不像它对可见光那样透明。二氧化碳特别会阻挡这样的热量辐射。因此，在夜间失去的热量要比在大气中没有二氧化碳的情况下失去的要少。要是没有少量的二氧化碳存在，地球就会明显冷得多，说不定就冷得不舒服了。
我们该感到欣慰，二氧化碳给我们温暖使我们舒舒服服，但是大气中二氧化碳的浓度正在稳步升高，其恶迹也就由此而生。1958年，二氧化碳只占大气总量的0.0316％。此后，其浓度逐年悄悄攀升，而现在已达到0.0340％。据估算，到2020年，二氧化碳的浓度将接近现在的两倍。
这就意味着，在未来几十年间，地球的平均温度将要稍许升高。极地冰盖因此将开始融化。
世界上大约90％的冰都聚积在巨大的南极冰盖中，另有8％在格陵兰冰盖。如果这些冰盖开始融化，海平面将要升高，其结果就是我上面描述的那个样子。
可是大气中的二氧化碳浓度为什么正在不断升高呢？
难辞其咎的有两个因素。首先，在近几个世纪中，先是煤，其后是石油和天然气，以快速增长的态势被用作燃料获取能量。这些燃料中所含的碳，在过去数百万年的岁月里一直安全地埋在地下，而现在正被烧成二氧化碳，并以每天数吨的速率大量排放到大气中。
更糟的是，地球上的森林在不断消失，起先是慢慢地消失，但在近一两个世纪里其消失的速度相当快。现在，森林消失的速度是每分钟64英亩。
不管取代森林的是草地、农田，还是灌木丛，其生产的植物消耗二氧化碳的速率与森林是不相等的。因此，不仅是通过燃料的燃烧使更多的二氧化碳被释放到大气中，而且，随着森林的消失，植物从大气中吸收的二氧化碳也减少了。
但是这也给了我们一个新的视角来考察这个问题。大气中二氧化碳并不是自行上升的。是人在烧煤、烧油和烧气。是人在砍伐森林。所以，人才是真正的元凶。
怎么办呢？
首先，我们必须拯救森林，乃至重植森林。
第二，我们必须有新的不产生二氧化碳的燃料源。核能就是其中之一，如果认为核能太危险，也还有其他选择。有波浪能，潮汐能，风能，还有地球内部的热能。尤其是，还可以直接利用太阳能。
诚然，这一切将需要时间、努力和金钱，但是，各个国家却把更多的时间、努力和金钱花在了对抗性的军事器械上，而这些军备只能毁灭我们大家。为了拯救我们大家而减少在这方面时间、努力和金钱的花费，难道我们应该反对吗？
本文由王树振老师编辑整理，图片来自网络
