We Can’t Grow On Like This

It took perhaps two million years to add the first billion people to the population of the world -- a number reached about 1830. It took only 100 more years to add the second billion people (1930), and just thirty more years to add the third billion (1960).

The global population counter clicked past four billion by 1975, five billion by 1987, and six billion by 1999. 

World population will climb past eight billion within the next 3 years.