One Reason the World Isn’t Ending

Bill Gates recently recommended the book Factfulness by Hans Rosling, a man who, about a year ago, changed my perspective about the future of the world. I’m not exactly a devout Malthusian, but I thought some aspects of Malthus’ arguments are compelling. If the earth’s population grows exponentially—as it has in the past century—and the earth’s resources are limited—which is obviously true—then at some point, one should expect a reckoning as the earth’s population exceeds the capacity of the earth to support it.

Rosling disabused me of that notion with this excellent video. While there are many things to worry about, I now believe that overpopulation isn’t one of them.

The historical problem

Historically, families would on average have six kids. Exponential growth is tricky to understand, but even basic back of the napkin calculations make it clear that there is a big problem with this birth rate.

The world’s population in 1AD was estimated to be about 300 Million. If you assume on average, children are born when the mother is twenty-five years old, then that means between that time and 2000 AD, there were about 80 generations. If each pair increases the population by approximately three times (a man and a woman making six children), then the 300M population quickly becomes extremely large—roughly a trillion multiplied by a trillion multiplied by a trillion multiplied by a trillion multiplied by ten trillion.

Of course, the population on earth is nowhere near that 10 to the power of forty-six number. In fact, the earth’s population grew extremely slowly, only reaching a billion by the early 1800s and two billion by 1925. The reason for the discrepancy is that many kids—the majority in fact—died without reproducing. Only slightly more than two of those six kids would actually have their own children. As a result, population growth was slow.

Hitting the wall

The problem arose, of course, when those kids started surviving. In Canada, as a result of improvements in healthcare and safety, only about 1% of people die before the age of 25. And, while fewer children dying is a good thing, if everyone’s having six kids and they’re all surviving, the exponential growth quickly creates problems.

But those problems didn’t actually arise because people in Canada are having fewer kids. In Canada, the average woman has about 1.6 kids, well below the rate of repopulation. The only reason the country’s population is growing at all is because of immigration.

But the world’s population is still growing. When I was in grade school, the population topped 4 billion, and today it’s almost double that. So, even if Canadians aren’t having a lot of kids, other people are. Therefore, overpopulation is still a threat, right?

Nope

Rosling’s answer is a definitive “No!” While the earth’s population is still growing, Rosling looks at the relationship between development, wealth, and the number of births and makes the argument that as people get wealthier—and more children survive—people have fewer children. In fact, most developed countries are at or below the repopulation rate, and pretty well every country has a falling birth rate.

As poorer countries become wealthier and gain access to better healthcare, their birth rates will continue to fall, approaching those of developing countries. In fact, Hans Rosling argues that right now, we have hit the level of “peak children”, that we’re in a situation where birth rates have fallen to the extent that the number of children alive today is likely to be greater than or equal to the number of children alive any time in in the next hundred years.

In other words, right now, birth rates are at a repopulation level, but no higher.

The earth’s population will continue to increase for a while because, even with births exactly equal to the replacement rate, it takes a couple of generations before flattening birth rate makes it through the higher age groups. Suppose the 50-year-old cohort today came from 50 million births fifty years ago. If for the next 100 years we have 100 million births per year, then in 50 years, the 50-year-old cohort will be from a group of 100 million births and will therefore be larger than the 50-year-old cohort today. Thus, even if births are identical for 100 years, we will still have the population grow until the smaller generations are replaced by the bigger generation.

Some interesting consequences

In a way, the flattening of the world’s population growth makes sense. If parents were having six children because they expected four to die, then intuitively, you’d expect them to only have two kids if they expect all their children to survive. But the fact that this hypothesis appears to be true in practice is nevertheless reassuring.

In fact, it’s great news, because it means that one major risk, that the world would become an overpopulated Fifth Element wasteland with billions fighting for scare resources, will not come to pass. That’s one less thing to worry about.

This outcome does have its own problems, of course. Our society is built on the assumption that population growth will increase indefinitely. Social programs like pensions are designed to have the numerous young people provide an income to the few older people. If the young don’t outnumber the old, then the math behind our pensions breaks, and they have to be redesigned. A similar problem exists with government spending. Government debt is far less onerous if you know that simple population growth will lead to GDP growth that can be harvested to pay interest on that debt.

So, society and governments will have to figure out ways to address this major change. In Canada, the government’s approach seems to be largely about not tackling the issue head-on, but rather importing a bunch of immigrants and temporary foreign workers to keep the old models working for as long as possible. Even so, it seems likely that, in my lifetime, we will need to create sustainable new models that work in a world where population growth is zero.