The UN calculates that there are more than 7 billion living humans on Earth, yet 200 years ago we numbered less than 1 billion. Recent estimates suggest that 6.5 percent of all people ever born are alive right now. This is the most conspicuous fact about world population growth: for thousands of years, population grew only slowly, but in recent centuries it has jumped dramatically. Between 1900 and 2000 the increase in world population was three times greater than the entire previous history of humanity– an increase from 1.5 to 6.1 billion in just 100 years.
A picture of world population in the very long-run fits the pattern of exponential growth (when a population grows exponentially the rate of growth is proportional to the size of the population). Yet an empirical observation of how growth rates have developed in the course of the last century reveals that this pattern no longer holds. The annual rate of population growth has recently been going down. A long historical period of accelerated growth has thus come to an end; the annual world population growth rate peaked in 1962, at around 2.1%, and has come down to almost half since.
Based on these observations, world history can be divided into three periods marked by distinct trends in population growth. The first period (pre-modernity) was a very long age of very slow population growth. The second period, beginning with the onset of modernity (with rising standards of living and improving health) and lasting until 1962, had an increasing rate of growth. Now that period is over, and the third part of the story has begun; the population growth rate is falling and will likely continue to fall, leading to an end of growth towards the end of this century.
In order to study how the world population changes over time it is useful to focus on the rate of change (rather than just levels). The following visualization presents the annual population growth rate, superimposed on the total world population, for the period 1750-2010 (plus projections up to 2100). This is the period in history when population growth changed most drastically. Before 1800 the world population growth rate never exceeded 0.5%, while in the course of the first fifty years of the 20th century it went from 0.8% to 2.1% – the highest annual growth rate in history, recorded in 1962. After this point, it has been systematically going down with projections estimating an annual rate of growth of 0.06% for 2100. Since the rate of growth corresponds to the slope of the line tracing the total world population over time, this means that under these projections we should expect an inflection in growth around the year 2100. In other words, under the assumption that the population growth rate will continue falling more or less at the current pace, population will stop growing before the end of this century.