260 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1950 



The energy content of the coal and petroleum that have been con- 

 sumed, expressed in kilogram-calories, is shown in figure 3. From 

 these two sources the energy amounted to 15 X 10 ^^ or 15 thousand 

 trillion kilogram-calories per year in 1939. Approximately four- 

 fifths of this amount was contributed by coal, and one-fifth by 

 petroleum. 



WORLD PRODUCTION OF ENERGY FROM COAL AND PETROLEUM 



1880 

 Time (Years) 



FlQUHK 3. 



Because of the lack of world-production statistics the energy from 

 natural gas has not been included. In the United States about 400 

 cubic meters of natural gas are produced for each cubic meter of oil, 

 with an energy content of about 0.4 of that of oil. Since oil and gas 

 are genetically related it may be presumed that this approximate 

 ratio is valid for the rest of the world also. Hence, the energy from 

 the natural gas that has been produced may be assumed to be at least 

 40 percent of that of petroleum. 



GROWTH OF POPULATION 



In the introductory remarks it was intimated that one of the most 

 disturbing ecological influences of recent millennia had been the 

 human species' proclivity for the capture of energy, resulting in a 

 progressive increase of the human population (4, 5). This is borne 

 out by the growth curve of human population since 1650, shown in 

 figure 4, based on the studies of Carr-Saunders (6), and the recent 



