ENERGY FROM FOSSIL FUELS — HUBBERT 



261 



estimate of Davis (7) . According to these estimates the world popu- 

 lation has increased from about 545 millions in 1650 to 2,171 millions 

 by 1940. The greatest rate of increase during this period has been 

 that of the last half century during which the world population has 

 been increasing at such a rate as to double itself once a century, or 

 at an annual rate of increase of 0.7 percent. 



GROWTH OF WORLD POPULATION 



TIME (Y<oi> 



FlGUKIO 4. 



That such a rate is not "normal" can be seen by backward extra- 

 polation. If it had prevailed throughout human history, beginning 

 with the Biblical Adam and Eve, only 3,300 years would have been 

 required to reach the present population. If, on the contrary, we 

 assume that the human race has been in existence for a million 

 years, and has increased at a uniform exponential or geometrical 

 rate, starting with a single pair, the present population would be 

 reached in that time by a rate of increase of 2.1 X 10"^ percent per 

 year, or a rate of growth that would require 33,000 years for the 

 population to double. At such a rate it is doubtful whether any 

 census could detect a change in the population during one man's 

 lifetime. 



That the present rate of growth cannot long continue is also evident 

 when it is considered that at this rate only 200 more years would be 

 required to reach a population of nearly 9 billion — about the maxi- 

 mum number of people the earth can support. In fact, at such a 

 rate, only 1,600 years would be required to reach a population density 

 of one person for each square meter of the land surface of the earth. 



