Population and the Environment

Last year the theory that population growth was the single most dangerous threat to the environment and human existence became suddenly quite popular with the publication of a few review articles on the topic.

It is clearly a good idea to improve environmental conditions, both for biodiversity and human well-being. Since it is politically unlikely (and anyway undesirable) that this will be feasible by prematurely constraining consumption, the most promising approach is the development of new technology - i.e. finding new ways to produce the consumption goods and services that we need while polluting less and using fewer resources, and discovering ways of reversing previous environmental damage.

If you even partially accept that innovation will play a major role in the ability of humans to maintain and increase both well being as well as environmental conditions, then the focus in this popular literature on population size seems rather bizarrely misplaced. In particular, it has mostly ignored the single largest and arguably most fundamental causal impact of a larger population: increased innovation rates. Across countries we generally associate higher incomes with fewer children, but over the very long run, as the graph below (from the excellent 2009 working paper by Jones and Romer) illustrates, a larger population size increases the rate of technological innovation for all the reasons outlined in the paper and which we have explored in DV409 lectures. An article today in the New York Times reminded me of this again.

However be careful about the policy implications of this result: it does not mean that each and every family should have lots and lots of children (!). It does mean that low fertility rates in the wealthy world are not necessarily so good for the future of the environment. As Jones and Romer calculate (and as we reviewed in DV409), the increased innovation and resulting increase in per capita wealth from the introduction of 1.3 billion Chinese into the modern global economy should (by a rough back of the envelope calculation) much more than compensate for the costs of carbon mitigation, even at today's mitigation costs (which will likely decrease significantly when all those Chinese put their heads to it).

So, yes, if we could hold the rate of technological innovation constant and decrease the number of people on earth, we would use fewer resources. However that is a false hypothetical experiment, as the two variables are so closely linked.