The United Nations yesterday revealed unsettling news about the world's population: Instead of leveling off at around 9 billion by 2050, the population will now reach 10.1 billion people by 2100 and keep growing. That projection from the U.N. Population Division reflects revised estimates of fertility particularly in developing countries. Demographer John Bongaarts, a vice president of the Population Council in New York City, spoke with ScienceInsider about why the outlook has changed:
Q: What have previous U.N. population reports said?
J.B.: The U.N. makes projections to the year 2050 every 2 years and every 4 or 5 years they make a longer year projection. Throughout the 2000s, there were two reports where they predicted a peaking in the low 9 billions, then a decline. The big news here is that there's no peaking and no decline, and continued increases over the entire century to 10 billion. Then it doesn't say. It's still growing in the year 2099.
Q: Why did the projections change?
J.B.: The main reasons are that in the poor countries, particularly in Africa, the fertility declines that they had expected are not materializing as rapidly as they originally projected. The U.N. has a set of assumptions about what happens to fertility over time as countries develop. Africa is not following the script as precisely as expected.
It's both fertility being a little bit higher and mortality being a little lower. In the '90s some epidemiologists predicted that the population of Africa would decline because of AIDS. That has not happened. There have been a lot of deaths due to AIDs, but population momentum is so strong that we're going to have a billion more people in Africa by 2050 and 3.5 billion people in Africa by 2100.
That raises of course the question, "Can you feed all these people? Will this lead to a crisis of some kind?" That is quite possible. The U.N. does not take that into account in their projections. [So it could change] if you end up with massive civil wars in that region or you run out of food or there's another AIDS-like epidemic or another virus or something.
Q: Why is fertility a little higher than expected?