2 A UNCERTAINTIES CONCERNING CLIMATIC CHANGE Despite the efforts of researchers to study the various aspects of past and present climate and man’s role in producing or enhancing climatic change, there are many uncertainties that prevent confident predictions of climatic change in the near future. Some of the uncertainties result from a lack of information; presumably these can be addressed with increasing research efforts. However, the major uncertainties exist as a result of the extremely complex nature of the earth-atmosphere system and the interrelations between the various parts of the system. These uncertainties may never be resolved well enough to allow reliable forecasts of future climate. 2.4.1 Feedback Mechanisms Radiative-convective models are useful in determining the immediate effect of a change in the atmospheric concentration of a given pollutant. However, in addition to assessing first-order effects, it is necessary to assess how coupled second-order processes, or "feedback mechanisms," might either enhance or suppress first-order effects on the climate. Effects that accentuate the first-order climatic effect are referred to as positive feedback mechanisms, whereas those that suppress the initial effect are called negative feedback effects. Some of the major climatic feedback mechanisms are summarized in Table 2.9. The major uncertainty is probably how increased temperatures relate to global cloudiness and how a change in cloudiness will act to either further warm the climate or suppress the initial warming trend. An increase in lower and middle clouds will produce lower surface temperatures,6^ because the amount of absorbed solar energy will be reduced due to reflection from the cloud tops, and because absorption and reradiation to space from the clouds. The decrease of incoming solar energy because of cloud cover may outweigh the decrease in terrestrial infrared radiation, to produce a net cooling. However, this may not be the case for very high, thin cirrus clouds with relatively low albedo. The response of polar ice to temperature increases is as important as the temperature-cloudiness feedback effect. There is a large difference between the albedo of the surface ocean and the albedo of polar ice. A reduction of ice cover due to melting would decrease the albedo of the earth
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