At the turn of the twenty-first century, there were almost 400 cities in the world that had over one million citizens.

200 years ago there were less than one billion humans living on earth. Today, according to UN calculations there are over 7 billion of us.1 Recent estimates suggest that today's population size is roughly equivalent to 6.9% of the total number of people ever born.2 This is the most conspicuous fact about world population growth: for thousands of years, the 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 during the entire previous history of humanity—an increase from 1.5 to 6.1 billion in just 100 years.

How the world population is changing is of great importance for humanity’s impact on the Earth’s natural environment, but it also gives reasons to hope for a good future. This is because we have a bigger team of better educatedpeople who can contribute to the solutions that improve global well-being.

A picture of the world population in the very long-run shows extremely rapid growth. Indeed, for a long time the world population grew at an increasing rate. However, if we focus on the last couple of decades, we see that this pattern no longer holds, as the annual rate of population growth has been recently going down. 1962 saw the growth rate peak at 2.1%, and it has since fallen to almost half. A long historical period of accelerated growth has thus come to an end.

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—which was characterized by rising standards of living and improving health—had an increasing growth rate that continued to rise through 1962. Today, the second period is over, and the third period is unfolding; the population growth rate is falling and will likely continue to fall, leading to an end of population growth towards the end of this century.