Global depopulation is the looming existential threat that no one is talking about.

The world currently has 7.8 billion people, and that total is expected to rise to 10.9 billion by 2100.  The population may begin falling in the 22nd century, but I wonder if it’s a bit early to begin planning for something so far out in the future, which is so hard to predict.  Back in 1970, most experts were worried about overpopulation, at a time when the world had less than half as many people as today.

What is the optimal global population?  I just completed Schopenauer’s 1200 page magnum opus on philosophy, which argues that the correct answer is zero.  At the other extreme, some argue that all human life is wonderful, pointing to the fact that even people living in horrible conditions—say North Korean concentration camps—typically do not commit suicide.  Both claims are plausible, but I’m not entirely convinced by either extreme.  I remain agnostic on the question.

We could apply the utilitarian criterion that the optimal number of humans is the one that maximizes aggregate global utility (perhaps including animal utility in the calculation.)  I have no principled objection to that approach, but I don’t see how to implement it.

People often criticize utilitarianism by pointing to the fact that utility cannot be measured.  I accept their point, but still find it to be a useful policy guide for real world public policy decisions.  While we cannot measure utility exactly, we can have well informed views that one situation has a higher utility level than another.  Thus is seems very plausible that South Korean public policies produce higher utility than North Korean public policies.  But when I use utilitarian reasoning I always implicitly hold the population fixed.  I find it almost infinitely more difficult to think about utility in an absolute sense.  How many Swiss people does it take to have the same total utility as 100 residents of rural Pakistan?  I wouldn’t even hazard a guess, and thus would be extremely reluctant to advance any public policy agenda on that basis.

Some population boosters point to polls suggesting that Americans would prefer to have more children. OK, but why don’t they?  Presumably there are some barriers related to the resources (time, money, etc.) required to raise children.  But then what are the public policy implications?  People would also prefer to have more money, bigger houses, more vacations, and lots of other good things.  Should public policies subsidize those goods?  For children the answer might be yes, as there’s a sort of “positive externality” aspect to raising kids.  But that just pushes us back to the optimal population question in the title of this post.  What is the answer?

Another possibility is that we should keep population roughly where it is, as change can cause problems.  Thus keep Japan’s population at roughly 125 million, Britain at roughly 68 million, and New Zealand at roughly 5 million, even though these three island groups have roughly equal ability to support human life.  But I’m not convinced that the disruption caused by Japan gradually declining in population and New Zealand gradually growing in population is all that bad.  Yes, you can point to downsides from population aging, but also some upsides (less crime, less traffic congestion, less pollution, more living space.)  So I’m not convinced by the claim that while we don’t know the optimal population, surely we know that population decline is bad.

People worry that Europe will turn into a sort of museum.  I love museums!

PS.  Suppose it turned out that the “correct” utilitarian answer to the question in the post title was that the world should become populated until living standards fell to those of a North Korean concentration camp, because all life is basically wonderful.  At that point I suspect Cowen and Douthat would jump ship, but Hanson would stick with the utilitarian logic of the analysis.

PPS.  I had always assumed that the Christian religion had a sort of “be fruitful and multiply” ethic, but Schopenauer points out that this is the Old Testament, and argues that the New Testament has a very different perspective.  Can anyone confirm?

PPPS.  Schopenauer’s The World as Will and Representation is highly recommended for disillusioned people.  Optimists might like his book on how to be happy, which is perhaps just as impressive, but in a radically different way.