than that in the developed world, the difference in per capita energy consumption has not changed markedly, indicating that the aggregate energy consumption by the developing countries is becoming a larger fraction of the world total as times goes on (Figure 6.1).

This trend, if it persists, will lead to a more rapid increase of energy flux densities in the developing countries than in the developed nations. Indeed, aggregate consumption of all fuels by the developing nations will equal that among the present developed nations in less than 120 years (United Nations Statistical Papers, 1973), if both groups maintain the average annual increase in energy use typical of the past 15 years. No one is suggesting that such trends can easily continue, particularly in the absence of clearly adequate and acceptable alternatives to the fossil fuels; however, pressure on the world’s social systems will be to maintain the trends to the degree possible (i.e., continue to improve standards of living via energy expenditures). If anything, the energy conservation strategies being explored in many developed countries may reduce the time to energy equity to significantly less than 120 years.

In suggesting that the upward trend of energy use may persist in the developing countries, we are not assuming a rapid rise in the numbers of automobiles, televisions, air conditioners, and the like throughout the world. The pressure to feed the increasing population will provide the main thrust. Providing India’s people with the minimum 3000 kcal/day considered necessary would require that nation to devote more energy to agriculture than it currently uses for all purposes combined. To raise the caloric intake of all the world’s people to this level would demand that 80 percent of the world’s current total energy consumption be devoted to agriculture (Steinhart and Steinhart, 1974). The problem is monumental, but the effort will probably be made to solve it.

Without concern at this point for possible solutions and the details of new technologies that may contribute to, or the extent to which rapidly depleting fossil fuel reserves may impede, the implementation of potential solutions, it must be recognized that man-made energy flux densities

FIGURE 6.1 Ratio of energy use by developed countries (EA) to energy use by developing countries (EB), 1960– 1971.

will likely continue to increase, with those in the developing countries increasing more rapidly than elsewhere. These increases seem sure to continue through this century and, with obviously less certainty, well into the twenty-first century.

Our interest here is directed toward what the current trends in energy flux densities may suggest concerning the earth’s climate on various scales ranging from convective to synoptic, i.e., from areas smaller than 102 km2 to those 106 km2 or larger (Figure 6.5). As Hosler and Landsberg point out in Chapter 5, the effects of man’s activities in modifying the weather on a microclimate scale (areas up to several hundred km2) are well documented. Microclimate effects due to heat generated by cities and major electric generating stations have been previously noted in the literature. Included among the observed effects have been increments in various atmospheric parameters ranging from cloud cover and temperature to the frequency of thunderstorms and tornadoes. The important point is that changes in these indicators also occur without the benefit of man’s intervention; so it is essential to assess carefully whether man-made heat rejected to the atmosphere over small areas, such as cities, really produces significant departures from ordinary fluctuations resulting from natural energy inputs to the atmosphere. The evidence seems substantial that on the convective scale it certainly does (Landsberg, 1956; Hosler, 1971; Changnon, 1973).

Whether the same conclusion is valid for larger areas is another question. In Chapter 2, Mitchell observes that the size of the region over which the climate is affected by a given factor and the geographical extent of that factor are rather closely related. Changnon (1973) noted observable effects on rainfall, thunderstorms, and hail frequency over areas of urban dimensions (St. Louis, Chicago, etc.), which reject heat to the atmosphere with energy flux densities of the order of 10 11–1012 Btu/km2-year. For similar effects to occur on a continental or global scale, presumably man-made energy flux densities of similar magnitude would be necessary over the larger region, unless, of course, there are potential positive feedbacks not yet recognized that could become significant at less than macrodimensions. In the absence of such feedbacks, it does not seem likely that man’s production of heat energy at current levels will have any influence on climate that can be distinguished from effects arising from natural causes at other than microclimate scales.

The key phrase in the last sentence of the preceding paragraph is “at current levels.” As pointed out earlier in this paper and by Perry and Landsberg in Chapter 1, neither current levels of energy consumption nor current global patterns of energy flux density are likely to continue. Although the mix of fuels will change in a way not yet clear, total consumption will undoubtedly continue to rise, and higher energy flux densities will probably become more widely distributed geographically.

As one example of how the energy flux density patterns might change in the future, we have computed flux densities for 1970, 2000, 2025, 2050, and 2075, those after 1970 being projected on the basis of present values and recent trends in per capita energy consumptions and population

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