This week, the United Nations Population Division made a radical shift in its population projections. Previously, the organization had estimated that the number of people living on the planet would reach around 9 billion by 2050 -- and then level off. Now everything has changed: Rather than leveling off, the population size will continue to grow, reaching 10 billion or more at century's end.
Why is this happening? Put simply, fertility rates. Across much of the world, women are having fewer children, but in African countries, the decline is far slower than expected. Part of this shift was supposed to come from preferences about family size and better access to family planning to make that possible. Sadly, however, that access hasn't come. Another factor, many expected, would come from the deleterious impact of high HIV/AIDS rates. But even Uganda -- with one of the highest numbers of AIDS cases in sub-Saharan Africa -- is projected to almost triple its population by 2050. In fact, outside a handful of countries, HIV/AIDS has only a tiny impact on overall population. Consider this: In the first five months of this year, the world population grew by enough to equal all the AIDS deaths since the epidemic began 30 years ago.
Rapid population growth is bad news for the continent, as it will likely outstrip gains in economic development. It's also a wake-up call: If the world doesn't begin investing far more seriously in family planning, much of our progress fighting poverty in sub-Saharan Africa over the last half-century could be lost.
Demographic projections are just that -- predictions. They only tell us what can happen if we make a variety of policy decisions and investments. As is the case with these projections, they include a lower and higher estimate -- and where we end up in that range depends upon what we do in the meantime. Hence, it would be a mistake to focus only on the medium U.N. projection of 9.3 billion people by 2050 as most commentators do. The high projection would take us to 10.6 billion in 2050. The low projection would mean 8.1 billion. (Just for a sense of scale: The difference between these high and low variants is equivalent to the entire global population in 1950.)
That 2050 figure is vital in determining how large the population will grow by 2100 -- either as high as 15.8 billion or as low as 6.2 billion. With so many people reproducing, very small differences in family size have a dramatic impact over time. The difference between a world of 6.2 billion and 15.8 billion will depend on a change in the average number of children that women have -- a change that is so small that demographers are reduced to using the odd image of "half a child" to describe it. Over the coming 40 years, however, if the average woman bears half a child more, on average, it will have an almost unimaginably profound effect on virtually everything else that happens in the 21st century.