262 ANlSrUAL REPORT SMITHSONIAN INSTITUTION, 1950 



ENERGY PER CAPITA 



Prior to 1800 most of the energy available to man was that derivable 

 from his food, the labor of his animals, and the wood he used for 

 fuel. On a world-wide basis it is doubtful if the sum of these ex- 

 ceeded 10,000 kilogram-calories per man per day, and this was a 

 several-fold increase over the energy from food alone. 



After 1800 there was superposed on these sources the energy from 

 fossil fuels. From a world average of 300 kilogram-calories per 

 capita per day in 1800 the energy from coal and petroleum increased 

 to 9,880 by 1900, and to 22,100 by 1940. In the areas of high indus- 

 trialization this quantity is much larger. In the United States, for 

 example, the energy from coal and petroleum consumed per day per 

 capita amounted in 1940 to 114,000 kilogram-calories (2), and from, 

 coal, petroleum, and natural gas 129,000. 



PHYSICAL LIMITS TO EXPANSION 



From the foregoing data it should be clear that while we are con- 

 cerned with a progression of ancient origin, the developments within 

 the last century, and especially within the last few decades, are de- 

 cidedly exceptional. One cannot refrain from asking, "How long 

 can we keep it up ? Where is it taking us ?" 



This leads us to consider what physical limitations there may be 

 upon the quantity of various types whose expansion we have noted. 

 In the case of the fossil fuels the answer is simple. As remarked 

 before, these fuels represent an accumulation over 500 million years 

 of geologic time, and any additional accumulation that may be ex- 

 pected w^ithin the next 10,000 years is negligible. Wlien these fuels 

 are burned, their material content remains upon the earth in a rela- 

 tively useless form, but the precious energy, after undergoing a se- 

 quence of degradations, finally leaves the earth as spent, long-wave- 

 length, low-temperature radiation. Hence, we deal with an 

 essentially fixed storehouse of energy, which we are drawing upon at 

 a phenomenal rate. The amount that remains at any given time 

 equals the amount initially present less that which has been consumed 

 already. 



The amount consumed up to any given time is proportional to the 

 area under the curve of annual production plotted against time. This 

 area may approach but can never quite equal the amount initially 

 present. Thus we may announce with certainty that the production 

 curve of any given species of fossil fuel will rise, pass through one or 

 several maxima, and then decline asymptotically to zero. Hence, 

 while there is an infinity of different shapes that such a curve may 

 have, they all have this in common : that the area under each must 

 be equal to or less than the amount initially present. 



