The notebook page shown below depicts the growth, billion-by-billion, of the human population. From the earliest traces of Homo sapiens in the anthropological record, it took 150,000 to 200,000 years for the population to grow to one billion (in 1800).
The table shows the year that the population added each billion and the number of years it took to do so. The peak growth rate seems to have occurred during the last 35 years. This is where the slope of the graph is the steepest and where the intervals to add a billion people are the shortest.
Demographers (including the UN) predict the population will grow to 9.6 billion by 2050 and perhaps 10-11 billion by 2100.
No one, except a few wildlife biologists, are predicting that the population will "level off" in the near future. Wildlife biologists are thinking that in the next 37 years we will add another 2.5 billion people, 35% more than now, but we are not likely to increase the productive surface of the Earth by 35% to provide them with the resources (on a per-capita basis) that the 7.1 billion current residents of the planet have. Wildlife biologists often use a term called "carrying capacity."
The growth of the Earth's human population truly defines our times.
Refer to the blog on Wednesday, February 13, 2013 for "The Human Population I" (Current Size and Growth Rate).