Jeff asks: “And this is a good thing why? I mean I love the idea of overpopulation and depleting resources the same as everyone else but…” (Referring to my half-serious suggestion to promote a higher birthrate in the US.)

Overpopulation is a non-issue, at least on a global scale. The world is pretty close to the replacement fertility rate (2.5 children per woman currently vs. 2.2 replacement rate) and should get there around 2050 (though the error bars are pretty wide). There is a lag between the fertility rate and the population growth rate, so the world’s population will keep growing for a while after we reach replacement.

Fertility stats on p.9 of the UN’s “World Population Prospects.”The population growth rate has been declining for a long time. We are seeing a lengthening of the period between each new billion.

However, these world averages cover up the differences between countries. The 50 poorest countries will see their populations double by 2050, the rest of the developing countries will grow more modestly, and the developed countries will be stagnant (UN medium estimate). I’m not too worried about high growth rates in poor countries. I tend to see high fertilities rates as a function of the circumstances that exist in a country. Where children are a big asset, people tend to have lots of them. Where children are a huge cost (college, etc.) — not so much. The issue is that when a parent has more children, there may be costs to society that are not borne by the parents, i.e. externalities. Just like traffic congestion! But the effect of more people is not at all clear. The externalities may actually be positive on net.

This highlights the benefits of a higher population level.

But here’s the bigger problem: the populations of the developed (and most of the developing) countries will “age” over the next 50 years, quite dramatically in the case of developed nations. This is a big problem for countries with retirement programs, like Social Security and Medicare in the US. To quote the UN’s report: “Furthermore, in the more developed regions, the population aged 60 or over is expected to nearly double (from 245 million in 2005 to 406 million in 2050) whereas that of persons under age 60 will likely decline (from 71 million in 2005 to 839 million in 2050). ” (p. v)

This demographic shift is the source of the projected problems with SS and Medicare. Ironically, these programs and their counterparts in other developed countries help to suppress the fertility rate. One reason for having more children is to provide for your retirement. If the government takes care of that for you, you will have fewer kids.

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