anticipate a broad-scale electrification of autos, home heating, etc. The replacement value of existing vehicles and furnaces is of the order of $1012, and most of this is personal property which is not subject to amortization via tax writeoffs for depreciation. So much for the present energy crisis. However, one finds a different picture a century or so ahead; this is the second energy crisis. Zimen and Altenhein have estimated the world's exploitable fossil-fuel reserves as equivalent to 7.1 x 1012 tons of carbon. If these reserves are exploited with 5% annual production increase (the value which held from 1960 to 1970), then by 2060 production will top out, and we will be in the same situation we face today with petroleum. Even before we face such physical exhaustion, we may face a crisis due to the climatic effects of burning fossil fuels. When C02 is released from such combustion, some 50% remains in the atmosphere; the balance dissolves in seawater, or is taken up in enhanced plant growth. This atmospheric C02 traps heat by the greenhouse effect, raising surface temperatures. Figure 1 shows historical annual C02 production rates; Figure 2, measured increases in atmospheric C02. Wetherald and Manabe have used a three-dimensional general-circulation model of the atmosphere to determine the effect of doubling the atmospheric C02 level, as have other investigators. The consensus of opinion is that a mean temperature increase of 2° to 4°C would result, and that this increase would be amplified 3- to 4-fold in polar regions. It is widely believed that such an effect would produce broad shifts in patterns of winds and of rainfall. Even more serious would be a possible partial melting of the polar caps. Bretherton has stated the region of greatest risk would be the West Antarctic ice sheet (Figures 3, 4), whose underlying bedrock lies below sea level. Melting or disintegration of this ice sheet would raise worldwide ocean levels by 5 meters, inundating many coastal regions. Siegenthaler and Oeschger have addressed the question of limits on future combustion of fossil fuels, in order not to exceed specified C02 limits. Figure 5 shows that if the C02 level is to be held to a 50% increase, there must be drastic reductions in fossil-fuel use early in the next century. An alternate scenario (Figure 6), in which all recoverable fossil fuels are burned, shows the atmospheric C02 level increasing tenfold by the early 22nd century. Laurmann has noted that market penetration considerations limit the range whereby noncarbon-based energy sources can reduce fossil-fuel consumption. Figure 7 shows his curves for C02 increase, given that it takes 50 years or more for a new energy source to advance from 1% to 50% of the energy market. It thus is suggested that even today is none too soon to begin a major commitment to such noncarbon-based energy sources, if we are to avoid the potential consequences of a 21st century atmospheric C02. buildup. It must be noted that study of these C02 effects is still in its early stages. In particular, Newell and Dopplick as well as Idso, using independent approaches have recently proposed that a C02 doubling would produce only a 0.25°C global temperature rise -- an order of magnitude less than in the Manabe-Wetherald models. Much also remains to be learned about the world's ice sheets. However, one may conclude that even today, prudence would dictate due attention to noncarbon-based energy sources, including the power satellite.
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