One hundred years ago, there were less than two billion humans living on Earth. Today, there are over seven billion. How many will there be 100 years from now?
A study published in Science in September shed some light on this important question. Using the United Nations’ most recent data, researchers projected, with 95 percent confidence, that the world population will fall between 9 and 13.2 billion people in 2100, with 11 billion as the most likely outcome. Additionally, they projected with 70 percent confidence that the world population will not stabilize this century.
Swedish statistician and science communicator Hans Rosling does an excellent job explaining the study’s findings in this short video:
Population growth studies have been plagued by uncertainties for quite some time, but a lot of progress has been made in just the last few years. For example, there are zero mentions of the year 2100 in the 2008 U.N. World Population Prospects report, but in the 2010 report there are 1,258.
That report projected that the world population would surpass 9 billion in 2050 and 10 billion in 2100. The numbers were somewhat encouraging due to the slow projected growth in world population from 2050 to 2100, in what appeared to be a near stabilization of world population at around 10 billion people (see the solid line in the graph below).
This led many to believe that the world population could peak before the end of the century, but the 2012 U.N. report revised the numbers upward, putting world population at close to 11 billion in 2100 (blue line below).
While the probability study shows that it’s unlikely that population will stabilize before 2100, there is some good news hidden in the data. In a longer video produced by his nonprofit organization, Gap Minder, Rosling shows that decreased fertility rates in developing countries have already brought us to “peak child.” The number of children under the age of 15 peaked around 2010 and has stabilized at roughly 2 billion. That means that all population growth in the coming decades will be due to what Rosling calls “the inevitable filling-up of adults.”
Basically, we’re heading for a world population of around 11 billion people before stabilization and there’s very little we can do about it, so we better start the process of figuring out how we’re going to support them all.