How well can we predict long-term effect? Because weather has been studied for a period of time that is miniscule compared with the age of the earth, the factors that control the earth's climate in the long range are not clearly understood. For example, we do not understand what causes the earth's periodic ice ages. So, indeed, it is difficult to estimate the impact of the increasing carbon dioxide levels. In fact, the variation in the earth's average temperature over past century is somewhat confusing. In the northern latitudes during the past century, the average temperature rose by 0.8℃ over a period of 60 years, then cooled by 0.5℃ during the next 25 years, and finally warmed by 0.2℃ in the past 20 years. Such fluctuations do not match the steady increase in carbon dioxide. However, in southern latitude and in areas near the equator, the average temperature showed a steady increase totaling 0.4℃ over the past century. This figure is in reasonable agreement with the predicted effect of the increasing carbon dioxide concentration over that period. Another significant fact is that the last 10 years of the twentieth century appear to be the warmest decade on record. Although the exact relationship between the carbon dioxide concentration in the atmosphere and the earth's temperature is not known at present, one thing is clear: The increase in the atmospheric concentration of carbon dioxide is quite dranatic. We must consider the implications of this increase as we consider our future energy needs. " "() 你知道什麼是噹噹噹嗎？ --

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