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?
J.B.: One reason is that African governments have neglected to invest in family planning programs. ... There are exceptions. Kenya had a program starting in the 1970s that did some good, but was underfunded in the last decade. A success story that is now being followed very closely is Rwanda. The Rwandan government in the last few years has made a major investment in health and in family planning, so that is bringing down the fertility rate.
But most governments in Africa do almost nothing in family planning or very little.
Q: Do people blame that on the governments, or donors or both?
J.B.: It's a complicated story. It's partly the AIDS epidemic. In the '90s everybody said the sky's falling and people are dying, so what's the point of having a family planning program. The other problem is that conservative governments, the Bush Administration, the Vatican, and so on have strongly opposed family planning programs.
The third factor is that economists have objected to investing in this. They don't think family planning programs work. For example, the World Bank, which was a very strong supporter of family planning in the '70s and '80s, has gone entirely missing in action in the last 2 decades.
Q: Is that starting to change?
J.B.: After 2 decades of neglect there's suddenly a resurgence of this. The Obama Administration has increased very substantially aid for international family planning programs. The British have made family planning programs one of their top priorities. The World Bank has started an entirely new reproductive health program, including family planning, which is something surprising from them. And Melinda Gates talks about family planning now.
There is suddenly a return of interest. This also has to do with the fact that food prices and energy prices are rising, we now have much clearer evidence for global warming. All of that together brings this issue back in focus.