According to Cohen, there are 67 cases where the supporting resources of the earth were figured in the past. Considering these studies, the smallest number is 1 billion, and the largest number was 1000 billion. The largest number is as 1000 times as larger than the smallest one and its range is quite wide. There are various methods of projecting, but the most popular method among them is to first, calculate the maximum quantity of food the world can produce, and then divide that number by quantity of food necessary for a person. Another method among them is to obtain the number by figuring out how much fresh water, instead of food, can be obtained. According to Cohen, among 67 projections, many numbers are centered around between 4 billion and 16 billion, and the average of the projected value within this range is 12 billion. This figure is even closer to those population projections, previously mentioned made by U.N. and Bank of World. By considering above all, it can be said that index of population carrying capacity of the earth is approximately 12 billion.
There is no more room to discuss further about the carrying capacity of the earth here, but one thing can be surely said, that is at the present stage, no definite answer for supporting power of the earth can be given. Two factors come up for the reason. The first factor is, we cannot anticipate how far scientific technology will progress into the 22nd century. "The Limits to Growth" (1972), a famous publication by the Club of Rome, gave the warning that the mankind will be destroyed because of destruction of the earth environment before a food shortage crisis hits. However in the book, scientific technology is mainly considered as bad, which only amplifies environmental pollution when coupled with manufacturing and agriculture production. By the way, Ehrlich's (Paul R. Ehrlich) well- known formula I=PAT, that is the impact for environmental destruction, is assumed as a multiplicative product of P(population), A(affluence), and T(technology), and here again technology is considered as only bad.
However, scientific technology is not necessiarily all bad. It has a lot of
