NPR. Here are two seemingly contradictory truths about the people of planet Earth.
The first is that over the past century, the world's population has exploded, going from around 2 billion people to 8 billion people today.
day. Truth number two is even as the Earth's population has boomed, the average fertility rate has declined.
And if things keep going that way, a few decades from now, the world's population will actually start to shrink.
And just as the world's population spiked in recent centuries, it could also crash.
And our guests today say that we're living near the very edge of this crash.
This is The Indicator from Planet Money.
I'm Adrian Ma. Today on the show, our guests are are economists Dean Spears and Mike Jerusalem.
They've co -authored a forthcoming book called After the Spike, Population, Progress, and the Case for People.
And when we come back, they'll explain why, population -wise, the human party will soon peak, and why that's a problem.
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For economists who study population growth and decline, the fertility rate is a very important metric.
The fertility rate is the average number of children a woman has in a lifetime.
time. And here, two is kind of the magic number.
That's what demographers call the replacement rate.
And when the global fertility rate falls below two for long enough, that leads over time to something called depopulation.
Depopulation is the name for what happens when birth rates are low enough that the population shrinks decade by decade and generation by generation.
This is Dean Spears, an economist at the University of Texas at Austin.
And while fertility rates vary from country to country, on a global scale, they've actually been declining for centuries.
And in fact, the vast majority of people on earth today live in a country where that rate is below two.
Mike Jeruso is also an economist at UT Austin.
I think something that's important to understand here is that depopulation wouldn't require people having smaller families than they do today.
Family sizes like today's would be enough to cause depopulation.
And Mike says this trend of fertility rates falling below an average of two is happening all over the world in North America, Latin America, Europe, and even in countries like China, Russia, and India.
So Mike and Dean have run the numbers.
They estimate somewhere around the year 2080, the world's population will peak around 10 billion.
And then over the next 300 years or so, the population will drop off to just 2 billion.
So that sounds pretty drastic, but I guess the threshold question here is, is a smaller population necessarily a bad thing?
Dean, what do you think?
Well, one big consequence of depopulation is that it would mean less progress on all the things that we all care about.
The world's become a safer, richer place over the same narrow span of human history when the population's been booming, and that's not a coincidence.
I mean, one way you've both distilled this argument in your book is to say that more people equals a more prosperous planet.
And you break down this idea into a couple of economic concepts, one being idea generation and the other being fixed costs.
So, Mike, can you just talk about why these concepts lead you to conclude that more people are better?
Yeah. The concept of idea generation, creating economic progress, was something that economist Paul Romer won the Nobel Prize for in 2018.
And the notion was that ideas are an endlessly renewable resource.
Once you or I discover or learn something, we can share it, and that can be reused over and over again.
And innovation doesn't just mean high tech. So yes, like tailored gene therapies come from human innovation, but so does the technology of how to organize a construction crew or a kindergarten classroom.
And so that's one reason why we should care about global depopulation, because it means fewer people collaborating, learning, sharing knowledge that has basically been a tide that's lifted all boats in the past couple hundred years.
Okay. And Dean, what about the other concept of fixed costs?
How does that translate into an argument for more people?
So many of the things that we value have this property that economists call fixed costs, where the cost is all in creating it once and for all.
And there isn't a very high cost or any cost at all for an extra person to use it.
And so one of these things with high fixed costs, you need other people to want it or need it just like you do, and then everybody can use it.
and so one of the ways that we might lose out in a smaller world is that there wouldn't be so many people who want the things we want or need the things we want and paying the fixed costs to make it happen.
So you know one of the things that we talk about cheekily in the book is that we have a vaccine for RSV, we have a vaccine for chickenpox, we have a vaccine for COVID.
We have those vaccines because it made sense to invest in them because those diseases affect many people.
There's no vaccine for sealpox because, you know, only a few people a year get sealpox and it's, you know, people that are working in marine rehabilitation facilities who get bitten by a seal.
But it sort of demonstrates that you really need a critical mass of people to justify the investment in finding cures for diseases, in building great public works, in doing all sorts of things that have these wide public benefits.
So you've just laid out the argument for why a a bigger population is better for people's living standards.
But I know some people are listening and thinking, could a population that's smaller be better for the planet?
What do you say to that?
I think sometimes we think about this wrong.
Think about climate change.
Even on our current path towards depopulation, humanity's numbers are probably going to keep growing for the next 50 years or so.
That would be way too late to support our climate goals and targets.
The only path to successfully addressing climate change and other issues is to take them head on, to reduce per capita pollution, to reduce per capita greenhouse gas emissions.
So you're saying population decline, climate change, these should be separate issues?
I think that's right.
I think it's a totally separate issue.
Okay. So if we accept that depopulation is something we should try to avoid and that somehow reversing the trend of falling fertility rates is key, what's the solution?
Because in your book, what's interesting is you talk about how there are a lot of countries where governments actually have policies aimed at supporting parents and families with children.
But even those countries see falling rates.
So what's the answer here?
Perhaps the surprising answer is that we don't think anybody has a solution to this problem, at least not in the sense of… Oh, good.
Okay. Okay. We're at the very beginning of even there being a broad public understanding that depopulation is a problem.
Okay. Okay. But still, do you have a sense of what the future would look like in a world where we've managed to avoid exponential depopulation?
I want to jump in. This is Dean.
I mean, a future in which we avoid depopulation, a future where the population stabilizes at some level, is going to be a future in which people choose to have an average of two kids per two adults.
And for people to be making that choice, they're going to have to be growing up and seeing a society, a different society, where parents get more of the support that they need.
Then maybe they will choose to have more kids.
And that word choice is important.
We should We should all be wary of any form of pro -natalism that proposes to turn back the clock on gender progress.
But we also shouldn't accept the traditionalist premise that that would even get us there, that children are women's responsibility, children are everyone's responsibility.
And perhaps if more of us saw that all along, we'd be in a different situation right now.
In short, Dean and Mike say, we all benefit from a big world.
Thanks to Dean Spears and Mike Druso for coming on the show.
Their book After the Spike, Population, Progress and the Case for People is out July 8th.
This episode was produced by Corey Bridges and engineered by Sina Lafredo.
It was fact -checked by C .R.
Juarez and edited by Julia Ritchie.
Cake and Cannon is our show's editor and the indicators for production of NPR.
