184 rSSUEs IN INADVERTENT WEATHER AND CLIMATE MODIFICATION CLIMATIC BARRIERS TO LONG-TERM ENERGY GROWTH Revelle and Suess (1957) stated: Human beings are now carrying out a large scale geophysical experiment. of a kind that could not have happened in the past nor be repeated -in, the- ftture. Within a few centuries we are returning to the atmosphere and ocean the concentrated organic carbon stored in the, sedimentary rocks over hundreds of -millions of years. This experiment may yield a far-reaching insight into the processes of determining weather and climate." Thus stated is the case for diligent observation of the consequences of the man-generated flux of carbon dioxide to the atmosphere.. Left unstated is perhaps the greater need to anticipate the consequences well enough to keep them within acceptable limits. Even though carbon dioxide makes up a small fraction (less than one one-thousandth of the total atmospheric mass) of the gases that comprise the atmosphere, it is crucial in determining the Earth's temperature because it traps some of the Earth's heat to produce the so-called greenhouse effect. Worldwide industrial civilization may face a major decision over the next few decades-whether to continue reliance on fossil fuels as principal sources of energy or to invest the research and engineering effort, and the capital, that will make it possible to substitute other energy sources for fossil fuels within the next 50 years. The second alternative presents many difficulties, but the possible climatic consequences of reliance on fossil fuels for another one or two centuries mayv be critical enough as to leave no other choice. The climatic questions center around the increase in atmospheric carbon dioxide that might result from continuing and increasing use of fossil fuels. In 110 years since about 1860 a 12-perceilt increase in the concentration of carbon dioxide had taken place, but because of the exponential nature of the consumption of energy and the burning of fossil fuels the next 10-12 percent increase would take only about 20 years and the next 10-12 percent increase beyond that only about 10 years. By this time the climatic impact of the carbon dioxide should (according to model calculations) cause a climatic warming. of about 10C (1.80F). Four questions are crucial: 1. What concentrations of carbon dioxide can be expected in the atmosphere at different times in the future, for given rates of combustion of fossil fuels? 2. What climatic changes might result from increased atmospheric carbon dioxide? 3. What would be the consequences of such climatic changes for human societies and for the natural environment? 4. What, if any, countervailing human actions could. diminish the climiatic changes or mitigate their consequences? 71 Wh'lether such a warming would influence the extent of ice and snow at~ the polar caps or influence the level of the world ocean cannot be '7 Revelle, R. and H. E. Suess, "Carbon Dioxide Exchange Between the Atmosphere and Ocean,"' and the "Question of an Increase in Atmospheric Carbon Dioxide During, the Past Decades," Tellus. vol. 9, No. 1, 1957, P. 18. SNational Research Council, Geophysics Research Board, "Energy and Climate," p. 1.