We're nearing 'peak population.' These economists are worried.

Summary

The Indicator from Planet Money: We're Nearing 'Peak Population.' These Economists Are Worried

Release Date: July 1, 2025

In this insightful episode of The Indicator from Planet Money, host Adrian Matthew delves into the pressing issue of global population trends with esteemed economists Dean Spears and Mike Gerusso from the University of Texas at Austin. Together, they explore the concept of "peak population," the potential consequences of a shrinking global population, and the interconnectedness of population dynamics with economic progress and environmental challenges.

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Understanding Population Growth and Decline

The episode kicks off with Dean Spears highlighting a paradoxical trend:

"Over the past century, the world's population has exploded, going from around 2 billion people to 8 billion people today. Even as the Earth's population has boomed, the average fertility rate has declined." (00:11)

Spears explains that while the global population has surged, the average number of children per woman has been decreasing, a phenomenon observed across continents—from North America to Asia. This decline in fertility rates poses a long-term risk of depopulation, where the global population could eventually shrink after peaking.

Mike Gerusso adds nuance to the discussion:

"Depopulation wouldn't require people having smaller families than they do today. Family sizes like today's would be enough to cause depopulation." (03:31)

Their collaborative research projects a peak population of approximately 10 billion by 2080, followed by a gradual decline over the next three centuries down to about 22 billion. This projection underscores the fragility of current population trends and the looming challenges they present.

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The Impact of Depopulation on Economic Progress

Spears and Gerusso argue that a declining population could impede economic and societal advancements. Gerusso emphasizes:

"Depopulation 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." (04:21)

The economists identify two key economic concepts to support their case for a larger population:

1. Idea Generation: Building on Paul Romer's Nobel Prize-winning work, they assert that a higher population fosters innovation and economic growth. Every individual contributes to the pool of ideas, driving advancements not just in high-tech fields but also in everyday technologies and organizational methods.

   "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." (05:00)

2. Fixed Costs: Many societal advancements involve high initial investments with minimal incremental costs for additional beneficiaries. Examples include vaccine development and public infrastructure. A larger population ensures a critical mass that justifies these fixed costs, enabling widespread benefits.

   "We have a vaccine for RSV. We have a vaccine for chickenpox, vaccine for Covid. ... there's no vaccine for sealpox because only a few people a year get sealpox." (06:29)

Gerusso further illustrates how essential a sizable population is for maintaining and advancing these public goods.

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The Relationship Between Population and Climate Change

Addressing potential counterarguments, Spears and Gerusso tackle the notion that a smaller population might benefit the planet. Gerusso counters:

"Think about climate change... humanity's numbers are probably going to keep growing for the next 50 years or so. ... 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." (07:25)

Spears clarifies that population decline should be considered separately from environmental challenges:

"Population decline, climate change, these should be separate issues." (07:52)

Their stance emphasizes that mitigating climate change relies more on reducing individual carbon footprints and advancing sustainable technologies rather than merely decreasing the number of people on the planet.

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Possible Solutions and Future Prospects

When prompted about solutions to the declining fertility rates, the economists admit uncertainty:

"Perhaps the surprising answer is that we don't think anybody has a solution to this problem." (08:26)

However, they suggest that societal shifts are necessary to encourage balanced family sizes. Spears envisions a future where:

"People choose to have an average of two kids per two adults. ... parents get more of the support that they need." (08:45)

This involves fostering a society where child-rearing is a shared responsibility, and extensive support systems are in place to make raising children more feasible and appealing without reverting to outdated gender roles.

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Conclusion

Spears and Gerusso's exploration of "peak population" underscores the intricate balance between population dynamics, economic growth, and environmental sustainability. Their discussion sheds light on the often-overlooked implications of declining fertility rates and the urgent need for societal adaptations to maintain a prosperous and innovative global community.

As the world approaches this critical juncture, understanding and addressing the factors influencing population trends will be paramount in shaping a sustainable and thriving future for humanity.

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For a deeper dive into these topics, Dean Spears and Mike Gerusso's forthcoming book, "After the Spike: Population Progress and the Case for People," is set to release on July 8th.

Transcript

[Adrian Matthew]

NPR.

[Dean Spears]

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. 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 Matthew. Today on the show, our guests are economists Dean Spears and Mike Gerusso. They've co authored a forthcoming book called after the 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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[Dean Spears]

Who study population growth and decline, the fertility rate is a very important metric. The the fertility rate is the average number of children a woman has in a lifetime. 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 2 for long enough, that leads over time to something called depopulation.

[Mike Girusso]

Depopulation is the name for what happens when birth rates are low enough that the population shrinks decade by decade and generation by generation.

[Dean Spears]

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 2. Mike Girusso is also an economist at UT Austin.

[Mike Girusso]

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 deposition population.

[Dean Spears]

And Mike says this trend of fertility rates falling below an average of 2 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 22 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?

[Mike Girusso]

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.

[Dean Spears]

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?

[Mike Girusso]

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.

[Dean Spears]

Okay, and Dean, what about the other concept of fixed costs? How does that translate into an argument for more people?

[Mike Girusso]

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 cost to make it happen.

So 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, 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 only a few people a year get sealpox. And it's 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. In doing all sorts of things that have these wide public benefits.

[Dean Spears]

So you've just laid out the argument for why 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?

[Mike Girusso]

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.

[Dean Spears]

So you're saying population decline, climate change, these should be separate issues.

[Mike Girusso]

I think that's right. I think it's a totally separate issue.

[Dean Spears]

Okay, so if we accept that depopulation is something we should try to avoid and, 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?

[Mike Girusso]

Perhaps the surprising answer is that we don't think anybody has a solution to this problem. At least not in the sense of.

[Dean Spears]

Oh, good, okay.

[Mike Girusso]

We'Re at the very beginning of even there being a broad public understanding that depopulation is a problem.

[Dean Spears]

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?

[Mike Girusso]

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 all be wary of any form of pronatalism 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.

[Dean Spears]

In short, Dean and Mike say we all benefit from a big world. Thanks to Dean Spears and Mike Girusso 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 Lofredo. It was fact checked by Ciara Juarez and edited by Julia Ritchie. Cake and Cannon is our show's editor and the indicators for production of npr.

[Adrian Matthew]

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