By Lyman Stone
We can’t solve our climate-change problems by having fewer babies.
In response to a Vox column of mine suggesting that the United States needed a pro–population growth agenda, many readers from across the political spectrum responded by raising fears about overpopulation.
Clearly, fear of overpopulation is widespread.
But the truth is that overpopulation in the United States is not even close to a serious problem. Even globally, overpopulation is an overstated problem.
It’s simplest to start with just the United States. How many people can the country support? Because I am an agricultural economist by profession, my bias is to first think about food. One simple question is how many people can the United States feed? Well, our net agricultural exports account for about 25 percent of the physical volume of agricultural production, which suggests that if we redirected those exports internally, the US could probably support approximately 25 percent more people. That’s assuming current technology and current diets and current land use.
In short, we could feed more than 400 million people, total, merely by consuming locally what we now export.
If you assume that a growing population induces more land to be shifted to food production (because farming becomes more profitable), that food imports can rise, and that agricultural innovation continues apace, it becomes clear that our land can physically support even more people than that — I estimate as much as double our current population. And given that agricultural yields are far lower in the developing world today than in the United States, thanks to the much lower level of technological advancement and managerial expertise in those countries, the truth is that the rest of the world has plenty of potential for increased food production: more than enough to feed itself and provide imports for a more populous United States. Merely tweaking foreign land use rules could unlock large gains in agricultural production.
I also approach this problem as a regional economist specializing in migration, so I also think of the American population issue through the lens of population density comparisons. Consider that the European Union has approximately 300 people per square mile, making it as dense as the ninth-densest US state (that is, similar to Pennsylvania or Florida). The continental United States on the whole has about 110 people per square mile (excluding Alaska, an outlier), making the US less than one-third as densely peopled as the EU. Yet the European Union, too, has roughly balanced or even slightly positive agricultural trade. That suggests that Europe, too, has no trouble feeding itself despite being three times as densely settled as the United States.
If the continental United States were as heavily settled as the EU, the US would have nearly a billion people living in it. Granted, the Western US is extremely dry and thus might not support an EU-density population. (Again, I assume we aren’t going to populate remote Alaska.) Nonetheless, if just the states east of the Mississippi had European-style population density, and the other states maintained current population, then the United States would still have more than 400 million people.
Every time I show Americans these calculations, they respond with surprise, but the truth is that getting European-style densities wouldn’t require technological change. It wouldn’t even require any non-voluntary lifestyle changes or new regulations: Simple deregulation of the housing industry would do the trick. Reducing parking requirements for new apartment buildings, removing height limits, altering restrictive lot sizes (namely lot minimums), and generally just allowing landowners to build freely on their property would greatly reduce the cost of living and boost population growth and density. It would prompt Americans to move to denser areas while also lowering housing prices and easing family budgets — which would itself increase fertility. (Recall that many American families wish they could afford more children.)
Population growth is the least influential part of the climate change calculation
The concern with overpopulation, naturally, often dovetails with concerns about climate change. Won’t higher population devastate the environment? We can answer that question fairly easily, making use of forecasts of population, GDP per capita, and emissions intensity per dollar by country. We can come up with some scenarios and then compare them to estimates of emissions needed to keep global warming manageable.
I show a daunting number of scenarios above, but they’re color-coded to make following them easier. The greenish lines show emissions under different population scenarios. The most steeply climbing line assumes only a modest decline in global fertility rates, while the lowest (green) scenario assumes a very rapid decline in total fertility rates — frankly, an unattainable decline.
The teal line assumes that fertility rates in every country go directly to replacement rate in 2016 (down for most poor countries, up for rich ones), and stay there. The central green line assumes fertility declines in the future following the historic trend. As you can see from these crude extrapolations, fertility rates do have substantial long-run effects on emissions.
But note those two gray lines. They’re important: They show where emissions need to go in order to prevent sharp rises in global temperatures. The paler of the two shows emissions required for less than 2 degree Celsius increase, broadly seen as the benchmark for a “serious” global warming solution. The darker gray line would get us down to a 2.5 to 2.7 degree increase, which is more or less what the Paris climate agreement committed participating countries to strive for. No amount of population control achieves those goals.
One challenge is that lower fertility leads to higher consumption and economic output
One complication is that fertility decline tends to increase GDP per capita, as families invest more in human capital for each child. What happens if GDP growth is much faster than in my baseline scenario? That sharply rising purple line shows emissions if we retain baseline fertility but global GDP per capita rises to $100,000 real dollars. (It is under $12,000 today.) …read more
Read more here: Why you shouldn’t obsess about “overpopulation”