Re: How long does it take for the World population to double?

Dear Eric,

the doubling time of any population can be calculated based on the growth rate, assuming that the population is growing exponentially. Mathematically, we can represent exponential population growth with the equation N = N₀e^rt where

• N₀ is the starting population size
• N is the population after a certain time interval
• t is the time interval, and
• e is the constant 2.71828... (the base of natural logarithms).

When a population has doubled, N = N₀ x 2.

The world population is currently about 6.6 billion, and the growth rate is approximately 1.3%. Dividing 0.69 by this rate, we get a doubling time of 53 years: the world population could reach 13.2 billion by 2061, and 26.4 billion by 2114.

However, these calculations assume that the population will keep growing exponentially forever. Continued exponential growth depends on a limitless supply of resources. Ecologists generally model population growth with the logistic growth equation. In this case, the finite supply of resources imposes a carrying capacity: the population cannot grow above a certain level, because there would not be enough resources to support it. Applying the logic of a carrying capacity to the global human population, the Population Reference Bureau estimates that the human population will probably level off at around 12 billion in the next hundred years.