Today, we live in a balmy epoch, 10,000 years after the last major glaciation. In this climatic spring, our species has flourished, we now cover the entire planet and are altering the very appearance of our world. Lately-whithin the last century or so-humans have acquired, in more ways than one, the ability to make major change in that climate upon which we are so dependent. The Nuclear Winter findings are one dramatic indication that we can change the climate-in this case, in the spasm one slower, more subtle and arising from intention that are wholly benign. When sunlight strikes the Earth, part is reflected back into the sky; much of the rest is absorved by the ground and heats it- the darker the ground, the greater the heating. The ground radiates back upward in the infrared. Thus, for an airless Earth, the temperature would be set solely by a balance between the incoming sunlight absorbed by the surface and the infrared radiation that the surface emits back to space. When you put air on a planet, the situation changes. The Earth's atmosphere is, generlly, still theransparent to visible light. That's why we can see each other when we talk, glimpse distant mountains and view the stars. But in the infrared, all that is different. While the oxygen and nitogen in the air are transparent in both the infrared and the visible, minor constiuents such as water vapor(H₂O) and carbon dioxide(CO₂) thed to be much more opaque un the in frared. Accordingl, if you add air to a world, you heat it: the surface now has difficulty when it tries to radiate back to space in the infrared. The atmosphere tends to absorb the infrared radiation, keeping heat near the surface and providing an infrared blanket for the world. There is very little Co₂in the Earth's atmosphere-only 0.03%. But that small amount is enough to make the Earth's atmosphere opaque in important ragions of the infrared spectrum. CO₂ and H₂O are the reason the global themperature is not well below freezing.. We owe our comfort-indeed, our very existence-to the fact that these gases are present and are much more transparent in the visible than in the infrared. Our lives depend on a delicate balance of invisible gases. Too much blanket, or too little, and we're in trouble. The greenhouse effect-what it is and isn't. Thisproperty of many gases to absorb strongly in the infreared but not in the visible and there by to heat their surroundings, is called the "greenhouse effect". A florist's greenhouse keeps its planty inhabitants warm. The phrase "greenhouse effect" is widely used and has an instructive ring to it, reminding us that we in a planetary scale greenhouse and recalling the admonition about living in glass houses and throwing stones. But, in fact, florist's greenhouses do not keep warm by the greenhouse effect; they work mainly by inhibiting the movement of air inside, another matter altogether. When humans burn wood or "gossil Furl"(coal, oil, natural gas, ect.), they put carbon dioxide into the air. One carbon atom(C) combines whit a molecule of oxygen(O₂) to produce CO₂. The development of agriculture, the conversion of dense forest to comparatively sparsely vegetated farm, has moved carbon atoms from plants on the ground to carbon dioxide in the air. About half of this new CO₂is removed by plants or by the layering down of carbonates in the oceans. On humam thim-scales, these changes are irreversible; Once the CO₂is in the atmosphere, human techology is helpess to remove it. So the the overall amount of CO₂in the air has been growing-at least since the industrial revolution. If no other factors operate, and if enough CO₂is put into the atmosphere, eventullay the averge surface themperature will increase perceptibly. As the climate warms, glacial ice melts. Over the last 100 years, the level of the world's oceans has risen by 15 centiometers. A global warming of 3℃... or 4℃... over the next century is likely to bring a future rise in the average sea level of about 70 ccentimeters. An increase of this magnitude could produce major damage to ports all over the world and induce fundamental changes in the patterns of land development. A serious speculation is that greenhouse temperature increases of 3℃...or 4℃...could, in addition, trigger the disintergration of the West Antarctic Ice Sheet, with huge puantities of polar ice falling into ocean. This would raise sea level by some 6 meters over a period of centuries, with the eventual inundation of all coastal cities on the planet. The importance of thengking globally. The problem is daifficult for at least three diffrernt reasons: (1) We do not yet fully understand how severe the greenhouse consequences will be. (2) Althought the effect are not yet strikingly noticeable in everyday life, to deal with the problem, the present generation might have to make sacrifices for the next (3) The problem cannot be solved except on an international scale: The atmosphere is ignorant of national boundaries. South Africa carbon dioxide warms Taiwan, and Soveit coalburning practice affect agricultural productiviy in America. The largest coal resources in the world are found in the Soviet Union, the United States and China, in that order. What incentives are there for a nation such as hold back on the burning of fossil fuel because the result might, decades later, be a parched American sunvelt or still more ghastly starvation in sub-Saharan Africa? Would countries that might benefit from a warmer climat be as vigoraous in restarining the burning of fossil fuels as natrions likelt to suffer greatly? Fortunately, we have alittle time. A great deal can be done in decades. Some argue that government subsudues lower the price of fossil fuel, inviting waste; more green-house problem. Prats of the solution might involve alternative energy sources, wheere appropriate: solar power, for example, or safer nucler fisson reactors, which, whatever their other awaited advent of commercial nuclear fusion power might happen before the middle of the next century. However, any technological solution to the looming green-house problem must be worldwide. It would not be sufficient for the United Stares or the Soviet Union, say, to develop safe and commercially feasible fusion power plants: That technology would have to ve diffused world wide, on terms of cost and reliability that would be more attractive to developing to developing nations than a reliance on fossil fuel reserves or imports. During the last few milloon years, human technology, spurred in part by climatic change, has made our species a force to be reckoned with on a planetary scale. We now find, to our astonishment, that we pose a danger to ourselves. The present world order is, infortunatelt, not designed to deal with gloval scale dangers. Nations tend to ve voncerned about themselves, not about the palnet; they tend to have short-term rarher rather than long-them ovjectives. Un problem such as the increasing green house effect., on nation or region might benefit while another suffers. In other global environment issues, such as nuclear war, all nations lose. The problems are connected: Constructive interanational efforts to understand and resolve one will be benefit the others. Further is a global consciousness- a view that transcends our exclusive identification with the generation and political groupings into which, by accident, we have been born. The solution to these problems requires a perspective that embraces the planet and the future. We are all in the greenhouse together.
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