Population can not grow indefinitely within the finite constraints of a nation's borders. Similarly, population can not grow indefinitely within the finite constraints of planetary land mass.
Humans are the most populous large mammal on Earth today, and probably in all of geological history. This World Population Day, humans number in the vicinity of 7.5 to 7.6 billion individuals....
In an environment with unlimited natural resources, population size grows exponentially. One characteristic feature of exponential growth is the time a population takes to double in size.
Exponential growth of world population
It took 127 years for the world population to double from one billion to two. By contrast, it took only 47 years, from 1927 to 1974, to double from two billion to four. Since 1960, world population has grown by about one billion every 13 years. Each point represents an additional one billion people....
For real populations, doubling time is not constant. Humans reached 1 billion around 1800, a
doubling time of about 300 years; 2 billion in 1927, a doubling time of 127 years; and 4 billion in 1974, a doubling time of 47 years.
On the other hand, world numbers are projected to reach 8 billion around 2023, a doubling time of 49 years, and barring the unforeseen, expected to level off around 10 to 12 billion by 2100.
This anticipated leveling off signals a harsh biological reality: Human population is being curtailed by the Earth’s
carrying capacity, the population at which premature death by starvation and disease balances the birth rate....
[see the original article for interactive graphs]
For real populations, doubling time is not constant. Humans reached 1 billion around 1800, a doubling time of about 300 years; 2 billion in 1927, a doubling time of 127 years; and 4 billion in 1974, a doubling time of 47 years.
On the other hand, world numbers are projected to reach 8 billion around 2023, a doubling time of 49 years, and barring the unforeseen, expected to level off around 10 to 12 billion by 2100.
This anticipated leveling off signals a harsh biological reality: Human population is being curtailed by the Earth’s carrying capacity, the population at which premature death by starvation and disease balances the birth rate....
Ecological implications
... According to the Worldwatch Institute, an environmental think tank, the Earth has 1.9 hectares of land per person for growing food and textiles for clothing, supplying wood and absorbing waste. The average American uses about 9.7 hectares.
These data alone suggest the Earth can support at most one-fifth of the present population, 1.5 billion people, at an American standard of living. ...
We cannot wish natural resources into existence. ... As a mathematician, I believe reducing birth rates substantially is our best prospect for raising global standards of living. As a citizen, I believe nudging human behavior, by encouraging smaller families, is our most humane hope.
