2.1.2 Global Impacts Although it is apparent that anthropogenic heat rejection to the environment on a global scale will increase severalfold by the year 2000, the important issue is whether this increase may have significant climatic implications. If noticeable climatic impacts do not occur by the year 2000, it is quite possible that they will occur beyond 2000 when heat rejection may be two orders of magnitude greater than it is at present. Thus, it is important to establish the magnitude of waste heat rejection at which climatic impacts may become an issue and the point in time at which this magnitude might be achieved. Perkins-Ll attempted to put global heat rejection into perspective by comparing global energy use with the solar input to the earth-atmosphere system. Solar input is estimated at 17.3 x 10^-^ W, of which about 35% is reflected back to space, leaving a net solar input of 11.2 x 10^^ W.$ In comparison to this number, the energy figures in Table 2.1 are quite small. A crude estimate of the atmospheric response to these heat inputs can be made by considering that thermal radiation from a black body is proportional to the fourth power of the absolute temperature: If the black-body radiation temperature of the earth-atmosphere system is taken as 255 K, then the impact of a heat rejection of 3.35 x lO^ W by the year 2000 can be calculated to produce a global warming of 0.019 K. This is far below the magnitude of natural climatic fluctuations and would not be a noticeable impact. Weinberg and Hammond'si ultimate heat rejection estimate of 4 x 10^ W would produce an estimated warming of 0.22 K. Although this is not a substantial global warming, it approaches the magnitude necessary to produce a noticeable change in global climate. Rottyl^ also estimated that noticeable climatic change from thermal pollution can occur with a heat rejection of approximately Other estimates of the global impact of heat rejection have been made, and several are summarized in Table 2.2. Kellogg^ compared the heat released by human activities to the amount of solar energy absorbed at the earth’s surface. Although man currently releases only 0.01% of the solar
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