5.5% per year. This corresponds to an increase by a factor of five every 
thirty years. Even if the current growth rate is not maintained, it is con- 
ceivable that consumer demand for energy in the year 2050 may be more 
than twenty-five times what it is today. The energy we use ultimately 
appears as heat which is either radiated immediately into space, stored in 
the biosphere, or stored in the atmosphere and the oceans. At present, the 
total manmade thermal load is so small compared to the solar heat load 
as to be insignificant. However, the local manmade load is already becoming 
sizeable in heavily industrialized regions. 
The balance between radiant energy received from the sun and that 
radiated out again determines the earth’s temperature. If we take the 
energy which has been locked up as fossil fuel over hundreds of millions 
of years and release it in a few centuries, we could push up the earth’s 
temperature. 
For the year 1970, the amount of heat released by man’s energy con- 
sumption activities, averaged over the whole globe, was estimated to be 
about 0.016% of the net solar radiation.* If the present rate of growth 
were to continue, then a century from now the global average would be 
more than one hundred times what it is today, or about 2% of the net 
solar load, and the continental average would be close to 7%. ‘These 
figures correspond to temperature rises of approximately 2.5° and 9°F, 
respectively. Clearly, continuation of the present growth of energy usage 
implies the possibility of global climatic upset in only a century or so. 
Climate, like all of global geophysics, is much more complex than a 
mere statement of the gross inflow of solar energy and the reradiation of 
most of it into space. Various feedback mechanisms exist which may 
serve to amplify or diminish the impact of man’s activities. For example, 
the increased temperatures resulting from the manmade thermal load may 
lead to increased cloudiness and a decrease in solar energy reaching the 
earth’s surface, resulting in only a slight change in surface temperature. 
On the other hand, in arctic regions a small amount of warming may melt 
some of the highly reflective ice and snow cover, so that less solar radiation 
is reflected away from the surface and temperatures rise even higher. The 
detailed effects of such changes on climate patterns are beyond our ability 
to predict today. This constitutes further evidence of the need for a major 
effort to develop a predictive climatology, as discussed in the previous 
section. 
A temperature rise resulting from man’s activities will not be distributed 
evenly over the globe. The problem of climatic “hot spots” is being 
aggravated by the tendency to build power plants of ever-increasing 
* Figures on energy consumption are drawn from “Inadvertent Weather Modifica- 
tion. Report of the Study of Man’s Impact on Climate.” MIT Press, Cambridge, 
Mass., 1971. 
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