GreenhouseEffect.doc

Greenhouse Effect Climatic conditions are delicately adjusted to the composition of the Earths atmosphere. If there were a change in the atmosphere - for example, in the relative proportions of atmospheric gases - the climate would probably change also. (2) A slight increase in water vapor, for instance, would increase the heat-retaining capacity of the atmosphere and would lead to a rise in global temperatures. In contrast, a large increase in water vapor would increase the thickness and extent of the cloud layer, reducing the amount of solar energy reaching the Earths surface. (3)The level of carbon dioxide in the atmosphere has an important effect on climatic change. Most of the Earths incoming energy is short-wavelength radiation, which tends to pass through atmospheric carbon dioxide easily. The Earth, however, reradiates much of the received energy as long-wavelength radiation, which carbon dioxide absorbs and then remits toward the Earth. This phenomenon, known as the greenhouse effect, can result in an increase in the surface temperature of a planet. An extreme example of the effect is shown by Venus (4), a planet covered by heavy clouds composed mostly of carbon dioxide, whose surface temperatures have been measured at 430. If the carbon dioxide content of the atmosphere is reduced, the temperatures fall. According to one respectable theory, if the atmospheric carbon dioxide concentration were halved, the Earth would become completely covered with ice. Another equally respectable theory, however, states that a halving of the carbon dioxide concentration would lead only to reduction in global temperatures of 3.If, because of an increase in forest fires or volcanic activity, the carbon dioxide content of the atmosphere increased, a warmer climate would be produced. Plant growth, which relies on both the warmth and the availability of carbon dioxide, would probably increase. As a consequence, plants would use more and more carbon dioxide. Eventually carbon dioxide levels would diminish and the climate, in turn, would become cooler. With reduced temperatures many plants would die; carbon dioxide would thereby be returned to the atmosphere and gradually the temperature would rise again. Thus if this process occurred, there might be a long-term oscillation in the amount of carbon dioxide present in the atmosphere, with regular temperature increases and decreases of a set magnitude.Some climatologists argue that the burning of fossil fuels has raised the level of carbon dioxide in the atmosphere and has caused a global temperature increase of at least 1. But a supposed global temperature rise of 1 may in reality be only several regional temperature increases, restricted to areas where there are many meteorological stations and caused simply by shifts in the pattern of atmospheric circulation. Other areas, for example the Southern Hemisphere Oceanic Zone, may be experiencing an equivalent temperature decrease that is unrecognized because of the shortage of meteorological recording station.温室效应 (Greenhouse Effect)气候条件微妙地与地球的大气成分相适应。假如大气发生了变化，比如在大气中各种气体相对比例方面发生变化，气候也可能会发生变化。例如，水蒸气稍有增长就会增加大气的存热能力，并会导致全球性气温升高。以此相对，水蒸气的大量增加会增加云层的厚度和幅度，而减少太阳传到地球表面的能量。大气中二氧化碳的含量对于气候变化具有重要影响。地球摄入的大部分能量是短波辐射线，这些辐射线往往容易穿过大气中的二氧化碳。然而地球将所收到能量的大部分以长波射线再辐射出去。二氧化碳将其吸收然后传回地球。这一现象被称为温室效应，它可以导致一颗行星表面温度的上升。对于这一现象，金星就是极其典型的一个例子。这个行星是由厚厚的主要由二氧化碳组成的气层所覆盖，已测出其表面温度达430。如果大气中的二氧化碳含量减少，温度便降低。根据一种著名理论，如果地球大气中二氧化碳含量减半，地球就会完全被冰层所覆盖。然而，另有一种同样重要的理论指出，现有二氧化碳含量减半仅会使全球温度减低3。如果由于森林火灾或火山喷发次数的增加使大气中二氧化碳含量增加，就会产生温暖的气候。植物生长要靠温度和对二氧化碳的吸收，生长可能会加快。进而植物会吸收越来越多的二氧化碳，最后二氧化碳的含量就会降低，从而导致气候降温。温度下降了，许多植物就会死亡，因此二氧化碳又会回到大气中，温度又会逐渐上升。因此，如果发生这样的过程，大