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?
課文翻譯
在我們呼吸的空氣中，有一種氣體對生命是必不可少的。遺憾的是，一樣好東西我們可能會擁有得太多，而二氧化碳的增長威脅著我們，使地球變暖到一種危險的程度。艾薩克·阿西莫夫向我們介紹了大氣層中的這個壞蛋，向我們解釋了它是怎樣活動的以及對付它的辦法。
大氣層中的惡棍
艾薩克·阿西莫夫
大氣層中的惡棍就是二氧化碳。
二氧化碳看上去不像一個惡棍。它毒性不大，在大氣層中的含量極小——只佔0.034％——不會對我們造成任何傷害。
再者，空氣中的那一點點二氧化碳對生命至關重要。植物吸收二氧化碳並將其轉化成它們自己的組織，充當所有動物（當然也包括人類）的基本食物供給。在這一過程中，植物釋放氧氣，而氧氣又是所有動物生命所不可缺少的。
然而，這一看上去無害而且無疑又必不可少的氣體卻正在對我們產生影響。
年復一年，海平面正在慢慢上升。它很可能繼續上升，而在今後數百年間，會以更快的速度上升。在那些低洼的沿海地區（在這些地區居住著世界上很大一部分人口），海水會穩步向前推進，迫使人們向內陸退居。
最後，海水將會高出目前海平面兩百英尺，一陣陣海浪將會拍打曼哈頓摩天大樓二十層樓的窗戶。佛羅裡達將會沉沒在海浪之下，英倫三島的大部分，人口稠密的尼羅河流域，還有中國、印度和俄羅斯的低洼地區也都將遭到同樣的命運。
不僅許多城市將被淹沒，而且世界上大部分盛產糧食的地區也將會失去。由於食品供應下降，到處都會出現饑荒，在這種壓力下，社會結構有可能崩潰。
而這一切都是因為二氧化碳。可怎麼會出現這種情況呢？兩者之間又有什麼聯繫呢？
首先是太陽光，大氣層中的各種氣體（包括二氧化碳）對於太陽光來說是透明的。太陽光照射大氣層的頂部，徑直透過數英裡的大氣層，溫暖著地球的表面。在夜間，地球將熱量以紅外線的形式放射到外層空間而冷卻下來。
然而，大氣層對紅外線來說並不像它對可見光那樣透明。二氧化碳特別會阻擋這樣的熱量輻射。因此，在夜間失去的熱量要比在大氣中沒有二氧化碳的情況下失去的要少。要是沒有少量的二氧化碳存在，地球就會明顯冷得多，說不定就冷得不舒服了。
我們該感到欣慰，二氧化碳給我們溫暖使我們舒舒服服，但是大氣中二氧化碳的濃度正在穩步升高，其惡跡也就由此而生。1958年，二氧化碳只佔大氣總量的0.0316％。此後，其濃度逐年悄悄攀升，而現在已達到0.0340％。據估算，到2020年，二氧化碳的濃度將接近現在的兩倍。
這就意味著，在未來幾十年間，地球的平均溫度將要稍許升高。極地冰蓋因此將開始融化。
世界上大約90％的冰都聚積在巨大的南極冰蓋中，另有8％在格陵蘭冰蓋。如果這些冰蓋開始融化，海平面將要升高，其結果就是我上面描述的那個樣子。
可是大氣中的二氧化碳濃度為什么正在不斷升高呢？
難辭其咎的有兩個因素。首先，在近幾個世紀中，先是煤，其後是石油和天然氣，以快速增長的態勢被用作燃料獲取能量。這些燃料中所含的碳，在過去數百萬年的歲月裡一直安全地埋在地下，而現在正被燒成二氧化碳，並以每天數噸的速率大量排放到大氣中。
更糟的是，地球上的森林在不斷消失，起先是慢慢地消失，但在近一兩個世紀裡其消失的速度相當快。現在，森林消失的速度是每分鐘64英畝。
不管取代森林的是草地、農田，還是灌木叢，其生產的植物消耗二氧化碳的速率與森林是不相等的。因此，不僅是通過燃料的燃燒使更多的二氧化碳被釋放到大氣中，而且，隨著森林的消失，植物從大氣中吸收的二氧化碳也減少了。
但是這也給了我們一個新的視角來考察這個問題。大氣中二氧化碳並不是自行上升的。是人在燒煤、燒油和燒氣。是人在砍伐森林。所以，人才是真正的元兇。
怎麼辦呢？
首先，我們必須拯救森林，乃至重植森林。
第二，我們必須有新的不產生二氧化碳的燃料源。核能就是其中之一，如果認為核能太危險，也還有其他選擇。有波浪能，潮汐能，風能，還有地球內部的熱能。尤其是，還可以直接利用太陽能。
誠然，這一切將需要時間、努力和金錢，但是，各個國家卻把更多的時間、努力和金錢花在了對抗性的軍事器械上，而這些軍備只能毀滅我們大家。為了拯救我們大家而減少在這方面時間、努力和金錢的花費，難道我們應該反對嗎？
本文由王樹振老師編輯整理，圖片來自網絡