Are we too many people or too few?

[This is a transcript of the video embedded below. Some of the explanations may not make sense without the animations in the video.]

There’s too many men, too many people, making too many problems. That’s how Genesis put it. Elon Musk, on the other hand, thinks there are too few people on the planet. “A lot of people think there’s too many people on the planet, but I think there’s, in fact, too few.” Okay, so who is right? Too many people or too few? That’s what we’ll talk about today.

This graph shows the increase of world population in the past twelve-thousand years. Leaving aside this dip in the 14th century when the plague wiped out big parts of the population in Europe and Asia, it looks pretty much like exponential growth.

If we extrapolate this curve, then in a thousand years there’ll be a few trillions of us! But this isn’t how population growth works. Sooner or later all species run into resource limits of some kind. So when will we hit ours?

When it comes to the question how close humans are to reaching this planet’s resource limits the two extremes are doomsters and boomsters. Yes, doomsters and boomsters sound like rival gangs from a rock musical that are about to break out in song, but reality is a bit less dire. We’ll look at what both sides have to say and then we look at what science says.

The doomsters have a long tradition, going back at least to Thomas Malthus in the 18^th century. Malthus said, in a nutshell, the population is growing faster than food production and it’ll become increasingly more difficult to feed everyone. If that ever does happen, it’d be a huge bummer because, I don’t know about you guys, but I’d really like to keep eating food. Especially cheese. I’d really like to keep eating cheese.

Malthus’ problem was popularized in a 1968 book by Paul Ehrlich called The Population Bomb, title says it all. Ehrlich predicted that by the 1980s famines would be commonplace and global death rates would rise. As you may have noticed, this didn’t happen. In reality, death rates have dropped, continue to drop, and on the average calorie consumption has globally increased. Still Ehrlich claims that he was in principle right, it’ll just take somewhat longer than he anticipated.

Indeed, the Club of Rome report of 1972 predicted that we would reach the “limits to growth” in the mid 21^st century, and population would steeply decrease after that basically because we weren’t careful enough handling the limited resources we have.

Several analyses in the early 21^st century found that so far the business as usual predictions from the Club of Rome aren’t far off reality.

The Earth Overshoot Day is an intuitive way to quantify just how bad we are at using our resources. The idea was put forward by Andrew Simms from the University of Sussex and it’s to calculate by which date in each calendar year we’ve used up the resources that Earth regenerates in that year. If that date is before the end of the year, this means that each year we shrink the remaining resources which ultimately isn’t sustainable.  

In this figure you see the Earth Overshoot Days since 1970. As you can see, in the past ten years or so we used up all renewable resources in early August. In 2020, the COVID pandemic pushed that date temporarily back by a couple of days but now we’re back on track to reach Overshoot Day sooner and sooner. It’s like groundhog day meets honey, I shrunk the resources, clearly not something anyone wants.

So the doomster’s fears aren’t entirely unjustified. We’ve arguably not been dealing with our resources responsibly.  Overpopulation isn’t pretty and it’s very real already in some places. For example, the population density in Los Angeles is about 3000 people per square kilometer but that of Manila in the Philippines is more than ten times higher, a stunning 43 thousand people per square kilometer. There’s so little space, some families have settled in the cemetery. As a general rule, and I hope you’ll all agree, I think people should not have to sleep near dead bodies when possible.

Such extreme overpopulation benefits the spread of diseases and makes it very difficult to enforce laws meant to keep the environment clean, which is a health risk. You may argue the actual problem here isn’t overpopulation but poverty, but really it’s neither in isolation, it’s the relation between them. The number of people grows faster than the resources they’d need to keep the living standard at least stable. 

On the global level, the doomsters argue, the root problem of climate change and the loss of biodiversity that accompanies it is that there’s too many people on the planet.

You may have seen the headlines some years ago. “Want to fight climate change? Have fewer children!” “Scientists Say Having Fewer Kids Is Our Best Bet To Reduce Climate Change” “Science proves kids are bad for earth”. These headlines summarized a 2017 article that appeared in the magazine Environmental Research Letters. Its authors had looked at 39 peer-reviewed papers and government reports. They wanted to find out what lifestyle choices have the biggest impact on our personal share of emissions.

Turns out that recycling doesn’t make much of a difference, neither makes changing your car or avoiding transatlantic flight, which is unfortunate for those of you who are scared of flying, as not flying to protect the environment is no longer a good excuse. The one thing that really made a difference was not having children. Indeed, it was 25 times more important than the next one which was “live car free”. The key reason they arrived at this conclusion is that they assumed you inherit half the carbon emissions of your children and then a quarter of your grandchildren, etc.

Fast forward to the headlines of 2022 and we read that men are getting vasectomies so they don’t have to feel guilty if they keep driving a car. Elon Musk has meanwhile fathered eight children, though maybe by the time I’ve finished this sentence he has a few more. So let’s then look at the other side of the argument, the boomsters.

The boomsters’ fire is fueled by just how wrong both Malthus and Ehrlich were. They were both wrong because they dramatically underestimated how much technological progress would improve agricultural yield and how that in return would improve health and education and lead to more technological progress. Boomsters extrapolate this past success and argue that human ingenuity will always save the day.

To illustrate this point, the economist Julian Simon has developed what’s called the Simon Abundance Index. You may think it tells you if there is an abundance of Simons, but no, it tells you instead the abundance of 50 basic commodities and their relation to population growth. His list of basic commodities contains every-day needs such as uranium, platinum, and tobacco, but doesn’t contain cheese. Seems that Mr Simons and I don’t quite have the same idea of basic commodities.

The index is calculated as the ratio of the price of the commodity and the average hourly wage, so basically it’s a measure of how much of the stuff you’d be able to buy.

The index is normalized to 1980 which marks one hundred percent. In 2020, the index reached 708 point 4 percent. And hey, the curve goes mostly up, so certainly that’s a good thing. Boomsters like to quote this index to prove something.

Now, this seems a little overly simplistic and you may wonder what the amount of tobacco you can buy with your earnings has to do with natural resources. Indeed, if you look for this index in the scientific literature you won’t find it – it isn’t generally accepted as a good measure of resource abundance. What it captures is the tendency of technology to increase efficiency, which leads to dropping prices so long as resources are available. Tells you nothing about how long the resources will last.

However, the boomsters do have a point in that pessimistic predictions from the past didn’t come true and that underpopulation is also a problem. Indeed, countries like Canada, Norway, and Sweden, have an underpopulation problem in their northern territories. It’s just hard to keep up living standards if there aren’t enough people to maintain them, that’s true for infrastructure but also education and health services. A civilization as complex as the one we currently have would be impossible to maintain with merely some million people. There’d just not be enough of us to learn and carry out all the necessary tasks, like making youtube videos!

Another problem is the age distribution. For most of history, it’s had a pyramid shape, with more young people than old ones. This example shows the population pyramid for Japan and how it changed in the past century. When people have fewer children this changes to an “inverted pyramid”, with more old people than young ones, which makes it difficult to take proper care of the elderly.

The transition is already happening in countries such as Japan and South Korea and will soon happen in most of the developed world. But the inverted pyramid comes from decrease in population, not from underpopulation, so it’s a temporary problem that should resolve once a population stabilizes.

Okay, so we’ve seen what the doomsters and boomsters say, now let’s look at what science says.

A useful term to talk about overpopulation is the “carrying capacity” of an ecosystem, that is the maximum population of a given organism that the ecosystem can sustain indefinitely. So what we want to know is the carrying capacity of Earth for humans.

Scientists disagree about the best and most accurate way of determining that number and estimates vary dramatically. Most estimates lie  in the range between four and 16 billion people, but some pessimists say the carrying capacity is more like 2 billion so we’ve long exceeded it and some optimists think we can squeeze more than 100 billion people on the planet.

These estimates vary so much because they depend on factors that are extremely hard to predict. For example, how many people we can feed depends on what their typical diet is. Earth can sustain more vegans than it can sustain Jordan Petersons who eat nothing but meat, though some of you may think even one Jordan Peterson is too much. And of course the estimates depend on how quickly you think technology improves together with population increase which is basically guesswork.

The bottom line is that the conservative estimate for the carrying capacity of earth is roughly the current population, but if we’re very optimistic we might make it to a hundred billion. Another thing we can do is try to infer trends from population data.  

The graph I showed you in the beginning may look like an exponential increase, but this isn’t quite right. If you look at the past 50 years in more detail you can see that the rate of growth has been steady at about one billion people every 12 years. That’s not exponential. What’s going on becomes clearer if we look at the fertility rate in different regions of the planet.

The fertility rate is what demographers call the average number of children a woman gives birth to. If the number falls below approximately 2 point 1, then the size of the population starts to fall. The 2.1 is called replacement level fertility. It’s worth mentioning that the 2.1 is the replacement fertility in developed countries with a low child mortality rate. If child mortality is high, the replacement fertility level is higher.  

Current fertility rates differ widely between different nations. In the richest nations, fertility rates have long dropped below the replacement level for example, the current fertility rate in the USA is 1.81 and in Japan 1.33. But in the developing world fertility rates are still high for example in Afghanistan 6.01; and in /niːˈʒeə/ 7.08. How is this situation going to develop?

We don’t know, of course, but we can extrapolate the trends. In October 2020, The Lancet published the results of a massive study in which they did just that. A team of researchers from the University of Washington made forecasts for population trends in 185 countries from the present to the year 2100. They used several models to forecast the evolution of migration, educational attainment, use of contraceptives, and so on, and calculated the effects on life expectancy and birth rate.

According to their forecast, global population will peak in the year 2064 at 9.73 billion and gradually decline to 8.79 billion by 2100. By then, the fertility rate will have dropped to only 1.66 globally (95% 1.33-2.08).

This is remarkably consistent with the Club of Rome report. They also looked at individual countries. For example, by 2100 China is forecasted to decrease its population by 48 percent to the small, measly number of 732 million people. No wonder Xi Jinping is asking Chinese people to have more babies.

Both the US and the UK are expected to keep roughly the same population thanks mostly to immigration. Japan is expected to stay at its current low fertility rate and consequently its population will decrease from the current 128.4 million to only 59.7 million.

Just a few weeks ago Musk commented on this, claiming that Japan could “cease to exist”. Well, we have seen that Japan will indeed likely halve its population by the end of the century and if you extrapolate this trend indefinitely then, yeah, it’ll cease to exist. But let’s put the numbers into context.

This figure shows the evolution of the Japanese population from 1800 to the present. It peaked around 10 years ago at about 130 million. If that doesn’t sound like much, keep in mind that Japan is only about half the size of Texas. This means its population density is currently about ten times higher than that of the United States. The Lancet paper forecasts that Japan will remain the world’s 4th largest economy even after halving its population and no one expects the population to continue shrinking forever. So the future looks nice for Japanese people, regardless of what Musk thinks.
 

What’s with Europe? The population of Germany is expected to go from currently 83 to 66 million people in 2100. Spain and Portugal will see their population cut by more than half. But this isn’t the case in all European countries, especially those up north can expect moderate increases. Norway, for example, is projected to go from currently 5.5 to about 7 million, and Sweden from currently 10 to 13 million.

But the biggest population increase will happen in currently underdeveloped areas thanks to both high fertility rates and further improvements in living conditions. For example, according to the Lancet estimates Nigeria will increase from currently 206 million to a staggering 791 million. That’s right, by 2100 there will be more Nigerians than Chinese. Niger will explode from 21 to 185 million.

Overall the largest increase will be in sub-Saharan Africa, which will go from currently 1 billion to 3 billion, but even there the fertility rate is projected to decrease below the replacement rate by the end of the century. If you want to check the fertility forecast for your country just check out the paper.

Those extrapolations assumed business as usual. But the same paper also considers an alternative scenario in which the United Nations Sustainable Development Goals for education and contraceptive are met. In that case the population would start decreasing much sooner, peak in 2046 at 8.5 billion and by the year 2100 the world population would be between 6.3 and 6.9 billion.

What do we learn from this? According to the conservative estimates for the carrying capacity of the world and extrapolations for population trends, it looks like the global population is going to peak relatively soon below carrying capacity. Population decrease is going to lead to huge changes in power structures both nationally and internationally. That’ll cause a lot of political tension and economic stress. And this doesn’t even include the risk of killing off a billion people or so with pandemics, wars, or a major economic crisis induced by climate change.

So both the doomsters and boomsters are wrong. The doomsters are wrong to think that overpopulation is the problem, but right in thinking that we have a problem. The boomsters are right in thinking that the world can host many more people but wrong in thinking that we’re going to pull it off.  

And I’m afraid Musk is right. If we’d play our cards more wisely, we could almost certainly squeeze some more people on this planet. And seeing that the most relevant ingredient to progress is human brains, if progress is what you care about, then we’re not on the best possible track.