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If you only have 80,000 people left, they’re probably randomly all over the world and they’re probably not going to end up in one place that quickly.

So then things like earthquakes, they just won’t affect the different groups — it’s hard to have a thing that affects all of them. Climate effects plausibly get closer to affecting all of them, but even climate effects just don’t affect the whole world equally, basically, ever.

Luisa Rodriguez

If modern human civilisation collapsed — as a result of nuclear war, severe climate change, or a much worse pandemic than COVID-19 — billions of people might die.

That’s terrible enough to contemplate. But what’s the probability that rather than recover, the survivors would falter and humanity would actually disappear for good?

It’s an obvious enough question, but very few people have spent serious time looking into it — possibly because it cuts across history, economics, and biology, among many other fields. There’s no Disaster Apocalypse Studies department at any university, and governments have little incentive to plan for a future in which almost everyone is dead and their country probably no longer even exists.

The person who may have spent the most time looking at this specific question is Luisa Rodriguez — who has conducted research at Rethink Priorities, Oxford University’s Future of Humanity Institute, the Forethought Foundation, and now here, at 80,000 Hours.

She wrote a series of articles earnestly trying to foresee how likely humanity would be to recover and build back after a full-on civilisational collapse.

In addition to being a fascinating topic in itself, if you buy philosopher Derek Parfit’s argument that the loss of all future generations entailed by human extinction would be a much greater moral tragedy than the deaths of even as many as 99% of humans alive, it’s also a question of great practical importance.

Luisa considered two distinct paths by which a global catastrophe and collapse could lead to extinction.

The first is direct extinction, where, say, 99.99% of people die, and then everyone else dies relatively quickly after that.

There are a couple of main stories people put forward for how a catastrophe like this would kill every single human on Earth — but as we’ll explain below, Luisa doesn’t buy them.

Story One:

Nuclear war has led to nuclear winter. There’s a 10-year period during which a lot of the world is really inhospitable to agriculture, and it takes a lot of ingenuity to find or grow any alternative foods. The survivors just aren’t able to figure out how to feed themselves in the time period, so everyone dies of starvation or cold.

Why Luisa doesn’t buy it:

Catastrophes will almost inevitably be non-uniform in their effects. If 80,000 people survive, they’re not all going to be in the same city — it would look more like groups of 5,000 in a bunch of different places.

People in some places will starve, but those in other places, such as New Zealand, will be able to fish, eat seaweed, grow potatoes, and find other sources of calories. Likewise, people in some places might face local disease outbreaks or be hit by natural disasters — but people will be scattered far apart enough that other groups won’t be affected by regional disasters.

It’d be an incredibly unlucky coincidence if the survivors of a nuclear war — likely spread out all over the world — happened to all be affected by natural disasters or were all prohibitively far away from areas suitable for agriculture (which aren’t the same areas you’d expect to be attacked in a nuclear war).

Story Two:

The catastrophe leads to hoarding and violence, and in addition to people being directly killed by the conflict, it distracts everyone so much from the key challenge of reestablishing agriculture that they simply fail. By the time they come to their senses, it’s too late — they’ve used up too much of the resources they’d need to get agriculture going again.

Why Luisa doesn’t buy it:

We’ve had lots of resource scarcity throughout history, and while we’ve seen examples of conflict petering out because basic needs aren’t being met, we’ve never seen the reverse.

And again, even if this happens in some places — even if some groups fought each other until they literally ended up starving to death — it would be completely bizarre for it to happen to every group in the world. You just need one group of around 300 people to survive for them to be able to rebuild the species.

———

The other pathway Luisa studied is indirect extinction: where humanity stabilises things and persists for hundreds or thousands of years, but for some reason gets stuck and never recovers to the level of technology we have today — leaving us vulnerable to something like an asteroid or a supervolcano.

But Luisa isn’t too worried about that scenario either.

Luisa’s best guess for how long it might take to recover — given that we’d already have the knowledge that agriculture and even more advanced technologies are possible, as well as artifacts to reverse engineer — is a couple thousand years at the longest.

And because it seems like the natural rate of extinction for humanity as a hunter-gatherer species has to be pretty low — otherwise we probably wouldn’t have been around in one form or another for 100,000 to a million years — it just seems like humanity would probably have plenty of time to rebuild.

When Luisa started this project, she thought, “I don’t know how to do any of the stuff we’d need to survive — I couldn’t grow a potato if my life depended on it, let alone reestablish more complex technologies. We’d be doomed.” But some wild examples of human ingenuity from the past made her realise that maybe other people are a bit more practical than she is, such as:

  • During the Serbian bombing of Bosnia, people generated electricity by pulling engines out of cars and putting them into rivers in a way that generated hydropower.
  • After the fall of the Soviet Union, Cuba realised they were going to lose their access to trucks — so they spent years breeding oxen to manually plough fields, which allowed them to keep generating food.
  • In World War II, people in POW camps built radios out of things like gum wrappers and pennies — allowing them to listen to music and the news.

Even just the fact that two billion people alive today practise subsistence farming — and therefore already know much more than she does about producing food — made Luisa realise that while she might be especially poorly equipped to survive a catastrophe, that doesn’t mean everyone else would be.

And having collected all this knowledge, Luisa admits that she too will now be a valuable member of a post-apocalyptic world!

In this wide-ranging and free-flowing conversation, Luisa and Rob also cover:

  • What the world might actually look like after one of these catastrophes
  • The most valuable knowledge for survivors
  • What we can learn from fallen ancient civilisations and smaller-scale disasters in modern times
  • The risk of culture shifting against science and tech
  • How fast populations could rebound
  • Implications for what we ought to do right now
  • ‘Boom and bust’ climate change scenarios
  • And much more.

Get this episode by subscribing to our podcast on the world’s most pressing problems and how to solve them: type 80,000 Hours into your podcasting app. Or read the transcript below.

Producer: Keiran Harris
Audio mastering: Ben Cordell
Transcriptions: Katy Moore

Highlights

What the world might look like after a catastrophe

Luisa Rodriguez: So regardless of the scenario, a thing that kept coming up as important was the fact that catastrophes will kind of inevitably be non-uniform in their effects. So I guess if you have a catastrophe that’s so big that it’s actually uniform in its effects and it’s really severe, it’s going to kill everyone. So that would be a catastrophe like an asteroid that actually really impacted the Earth. Or maybe actually like —

Rob Wiblin: It’s like even bigger than the one that killed the dinosaurs or something like that?

Luisa Rodriguez: Yeah. So that is one where you can imagine having consistent mortality rates everywhere, consistent climate effects everywhere. But for the catastrophes that interest us — so the ones that don’t actually kill everyone at once, but leave some survivors — the reason that happens is because the catastrophe is going to have non-uniform effects. And I think for lots of catastrophes, they could just be very non-uniform, where you might get some entire continents that are much, much less affected than others, both in terms of population death and in terms of climate effects.

Luisa Rodriguez: So an example in nuclear winter that’s kind of well known is you have some continents where agriculture becomes near impossible, and then you have others where it’s like, maybe even a bit better, because it’s colder and otherwise it was too hot for agriculture. Mostly you wouldn’t get better. It just wouldn’t be quite as devastating as other places.

Rob Wiblin: So this non-uniformity is super central, if you’re thinking about if it will kill 100% of people. Because even if there’s just like 1% of people living in some place that’s largely unaffected, then that basically answers the question for you.

Luisa Rodriguez: Exactly. And I think sometimes it’s slight non-uniformity that makes a bit of difference — maybe isn’t decisive. So like with nuclear winter, you’ll have some areas that are cold and some areas that are slightly less cold. But some catastrophes would cause extremely non-uniform effects, where like even if you had really, really enormous population losses, and actually the collapse of society and political systems — all of these systems that we think of as critical collapsed on one continent, I think you might see society continue on others. And I think that’s something that I didn’t intuitively have in my head when I first started thinking about this, is just some places might really be kind of unfazed.

Rob Wiblin: Right. Thinking about New Zealand again, I suppose it’s also Tasmania… Are there any other things that we should have in mind? I guess it’s like Pacific islands.

Luisa Rodriguez: Pacific islands. Yeah, I think depending on the thing again… In some scenarios you really want coastlines because fishing is a key source of food. So like Chile looks kind of good in a couple of scenarios. I think those are the main ones.

Grace period

Luisa Rodriguez: I think just a really interesting emergent finding is that the number of survivors really does interact in a kind of funny way with other things. Where yeah, I think this applies to things beyond just supplies left. So supplies left is a good example, where if you have lots of survivors, the supplies go very quickly. But then on the other hand, if you have lots of people dying, which would be terrible in some respects, and makes it a bit harder to rebuild industry and harder to make sure that you… Well, ideally that you’d keep some of the necessary knowledge and skills — you’d want to at least eventually rebuild industry. When you are down to tens of thousands or hundreds of thousands of people, it’s less guaranteed that you’ll keep all of those skills. And so you just get these kind of tradeoffs. And I think, mostly, I felt like it worked in favor of survival.

Rob Wiblin: Okay. So this kind of relates to this concept that you have called the “grace period,” which I think you got from The Knowledge, right? So I guess the grace period is this temporary time after some disaster where a bunch of people are now dead, but I guess you still have this overhang of supplies from the pre-apocalypse world. And I guess other things like cars are around, other infrastructure, so this potentially helps you to stick around and then rebuild. Yeah, do you want to elaborate on that?

Luisa Rodriguez: Yeah, sure. So again, it kind of depends on the catastrophe, but at least in some places in most catastrophe scenarios, you have maybe all of the infrastructure that you did otherwise: you have a power grid that still exists (even if it’s not working), you have grocery stores with food in them, you even have petrol stations that still have petrol in them and that you can siphon out pretty easily.

Luisa Rodriguez: So you have things that mean that you can kind of survive in a reasonably easy and accessible way. And just how long that period lasts, again, depends on how many people there are. But I think you’d be surprised how much stuff you can still access, with the limitations being the power grid will stop working. But even water will still run for at least a while, and even maybe for a long while in some places, where the water supply isn’t run by electricity and gravity.

Rob Wiblin: Yeah, so the more people you have, the more people you have to try to rebuild stuff, but the less supplies you have per person. And then like the reverse in the other case: if most people are dead, then you’re potentially short of the expertise that you might need to get things running, but the grace period is longer. Yeah, is there any way of giving a sense of how long it is, or what kind of stuff might we run out of first?

Luisa Rodriguez: So if you have 50% population loss, I think that, theoretically, if you actually allocated all of the supermarket food and grain stocks and water — kind of literally rationed it — then it would only last days, like under a week. If you actually just divide the US, China, some of the really big food suppliers, over everyone.

Luisa Rodriguez:. We used to have a much greater volume of food stocks than we do now, especially during the Cold War, kind of unsurprisingly. But currently, lots of countries have about six months of grain reserves, and then lots have basically none. And so it seems to come out to a week or a couple of weeks for grain.

Rob Wiblin: Okay. So that means that if you have a situation where 99% of people suddenly die, then now you can last years with that kind of food.

Luisa Rodriguez: Yeah. So it’s years if you make a few assumptions about how you prioritize the order, basically, in which you eat things.

The most valuable knowledge for survivors

Luisa Rodriguez: Luckily, there is kind of an inverse correlation between how valuable knowledge is and how few people have it. This isn’t perfectly true, so there are some things that would be really useful for survivors to know, like… What’s a common one? I guess there are some weird things about telecommunications that like six people know. And so we’ll probably lose those facts.

Luisa Rodriguez: But mostly, like, even though there are many fewer brain surgeons than general practitioners or something, brain surgery is just less important than all the knowledge that general practitioners have. And that just does a lot of work. So we’ll lose lots of sophisticated knowledge of some types of medicine, but it’s hard to imagine why we’d lose germ theory, and even some basic things that will make maternal health better during childbirth, for example. And even that will be a huge improvement on where our ancestors were at similar population levels.

Rob Wiblin: Yeah. How many people know things like how to keep a car running or how to run a power station, or how to run the electrical grid, or get that back up and running? Things that kind of stand out, as maybe there’s not enough people in that group?

Luisa Rodriguez: Yeah. Those were good candidates for… I called them “critical skillsets,” and I guess it’s just kind of hard to think about. One reason it’s hard is no single person knows how to run a power grid — it’s really distributed knowledge. And leadership at a plant might have more knowledge of the bigger picture, but it’s still distributed — not just in the many individuals who know the different steps, but also it’s going to be in manuals and some of those will survive.

Luisa Rodriguez: So it’s hard to think of really critical knowledge that’s super concentrated in a couple of people. And I tried to do some back-of-the-envelope calculations to be like… What is concentrated and what could we lose? And I would love for someone else to try doing this research in a way that produces more interesting results than what I did. I ended up doing things like, maybe… Like we think advanced chemistry would be really nice to have. So I was like, “How many PhD chemists are there?” and try to think of it this way. And when you think of it that way, and you just make some naive assumptions about where they live, you still have lots of PhD chemists, even in a world where 99% of people have died.

Luisa Rodriguez: That’s where you start to hypothesize. I think I just don’t know enough about how critical infrastructure works to be like, “What’s the job? What’s the one job that’s scarce, but super critical?” But you can think about it just theoretically, like, maybe there are some jobs like that, and you do get to the 99.99% population loss level before you start thinking that there are jobs like that that you’ll definitely lose.

Luisa Rodriguez: I think maybe there’s some evidence that when you get really small populations, when you try to pass down skills between generations… In a way you’re making copies of information, and when you try to teach it, if the number of people learning it is small enough, the copies will get lower and lower fidelity.

Luisa Rodriguez: The more people you have, the more people innovate, and then you get improvements that make up for losses in the basic skill. But yeah, I think the way you can think of it is if someone’s teaching you to shoot an arrow, lots of people will be worse at it than the master, and you need enough people learning it to have some people exceed —

Rob Wiblin: So that in the next generation, there’s someone as good as the best person in the previous time.

Luisa Rodriguez: Yeah, exactly. And so, some examples of knowledge degrading over time that were interesting, I think one was Polynesian Islanders lost the ability to build boats and then got stuck. And apparently this is the way in which at least one group of Tasmanians lost the ability to build fire.

Would people really work together?

Luisa Rodriguez: I guess I do feel a bit “peace and lovey” when I talk about this, but I think you even pointed me to the research on how people react to crises, according to sociologists who have looked into post-crisis response. And again, this is hard to generalize from because it’s not actually a case where maybe the world’s going to end; it’s sociologists looking at how individuals and groups respond to tsunamis and hurricanes. It’s just almost unanimously not violent. Like looting is a kind of famous trope, but almost never happens. Same with people fighting over resources.

Luisa Rodriguez: I think it did feel intuitive to me that there would be lots of violence because people would be facing death. But not only does that not look like the case empirically, it also just doesn’t look like a very… I mean, it looks like a strategy that might help some individuals survive if you just think about it theoretically, but it really doesn’t seem like a strategy that would be good for the majority of people to take on.

Luisa Rodriguez: Because most people will really benefit from cooperation that lets them grow more food — like an individual will have a very hard time producing enough food for themself. And there’s a reason that we live in cities, it’s because we specialize and produce more stuff for the number of people, and so cooperation has these clear benefits, especially in the context of agriculture.

Luisa Rodriguez: And insofar as there will be some selection for survival strategies, it seems like lots of people would benefit from taking this cooperation-y strategy, and that there will be some cheaters or people who use violence to get a bunch of resources. But on the whole that’s not going to be a very persistent survival strategy, because you’ve got to have someone to steal from.

Rob Wiblin: Are there other case studies that we can point to where people cooperated to a surprising extent?

Luisa Rodriguez: So both Hiroshima and Nagasaki suffered just horribly. I don’t think I fully understood before looking into the details, but basically, a third of the population died. I think the population started around 400,000, and maybe a quarter of those people died instantly. And then another set of tens of thousands of people died from radiation poisoning in the weeks after. So that already was horrible, of course, and shocking to learn, and especially to learn about the details. And then I just remember being really surprised that 90% of the city’s buildings were either totally incinerated or reduced to rubble. So just like this huge infrastructure loss.

Luisa Rodriguez: And then at the same time, I also learned that the recovery was just shockingly quick. So the analogy doesn’t totally work, but if you kind of imagine these as cities whose societies basically collapsed — how quickly they were able to recover is just really astounding to me. I think power was restored to at least homes that weren’t completely destroyed within like a month or so. Water pumps were restored within… I think it was just a few days. Actually, maybe what surprised me even more was some intermediate services were back within the next two or three days.

Luisa Rodriguez: Trains running on like day two. I remember learning that the bank, there was a bank where I think… God, this is awful. I think literally all of the employees were killed immediately. But the bank was able to reopen a few days later. And those services were actually just really important to getting things up and running again. Other things too… like telecommunications, so they had phones back I think on day two or three.

How fast could populations rebound?

Luisa Rodriguez: So population growth is an example of how hard it is to grasp, or how hard it is to intuitively understand, how quick compounded growth is. But if you think the population would grow at the fastest level that it ever has — which is in the 1960s, that was about 2.2% per year — then you’d get about a tenfold increase in population every 100 years. So if you lost 90% of the population, you’d be back to current levels within 100 years.

Luisa Rodriguez: And then if you think that population is going to grow slower, so maybe the level it did when humans were just agriculturalists, then you could recover a population from 90% population loss to current levels in about 240 years. Which is still really, really fast.

Rob Wiblin: Yeah. It’s kind of shockingly fast. It seems like it should take ages, but yeah, I suppose just the magic of exponential growth means that it doesn’t take quite as long as you’d think.

Luisa Rodriguez: Exactly. Yeah. So even the most pessimistic scenarios we thought of were if 99.999% of people died, which is a huge number of people dying. Then at that 1% population growth — so agriculturalist-level of population growth — you’d still expect the population to reach current levels in about 1,200 years.

Rob Wiblin: Okay. So I suppose we could compound all these scenarios into an even more pessimistic one where you have 99.9% gone. And you’re only growing at the hunter-gatherer level, which was 0.1%… We would get back to the original population in 7,000 years. But I guess maintaining a 0.1% population growth rate the entire time just seems very strange. It seems like it should either be below zero or more above zero than that. That’s just like knife-edge level.

Luisa Rodriguez: It would be really surprising if at six billion, we were still going at hunter-gatherer levels of growth rates.

Rob Wiblin: Yeah. But even then, 7,000 years, it’s not so long such as that, even in a very negative-case scenario, it’s still very, very, very possible to rebuild. How would you be most likely to be wrong?

Luisa Rodriguez: In general, I think I’m biased toward optimism. So I’m more likely to think that if something is technologically possible, it will also be what happens — especially if it seems intuitively advantageous for it to. And that’s not always the case. Yeah, so I guess something like, in some systematic ways, the survivors are much worse at taking advantage of all the things working in their favor than I’ve predicted.

Boom and bust climate change scenarios

Luisa Rodriguez: So the boom refers to using a bunch of fossil fuels, which translate to high emissions and high temperature effects and other climate effects. And then the bust at least broadly is referring to, for some reason, not being able to bring carbon in the atmosphere back down to make those climate changes tolerable, mitigated.

Luisa Rodriguez: Specifically, Will MacAskill and John Halstead came up with two ways that that could happen. So in one scenario, I think Will calls it the “rise and fall scenario” — I think he’s alluding to Rome — where there’s no single catastrophe that means that we don’t have climate-mitigating technologies. It’s just that our technological progress on climate mitigation stagnates before we’re able to get to the level necessary to get to carbon neutral, and then to suck more carbon out of the atmosphere to get temperature levels even lower, if we’ve already gone up higher than we want to be. So that’s one.

Luisa Rodriguez: The other one is a bust caused by some kind of catastrophe. And I think Will calls this one a “double catastrophe,” with a first catastrophe is something like… I think his best guess at how this happens is something like there’s a great power conflict that is both demanding of technological innovation and attention — so brain power. I think basically he’s imagining a scenario where much of our resources are being devoted to developing new military technologies to basically win some arms race. And because arms races are super energy intensive, we’re also burning maybe even more fossil fuels than we would otherwise. And at the same time, that conflict is so politically charged that we are not following through with climate agreements. So basically we just stopped trying to bring carbon levels down and in fact are increasing them.

Luisa Rodriguez: And then maybe that particular conflict becomes a hot conflict, by which I mean war actually erupts — could be a nuclear war, could be use of bioweapons — but something causes society to collapse more significantly in like a single event. And then in that scenario, you’ve had all this carbon being released into the atmosphere, making everything hot and without a way to take it out. So things are just going to keep getting hotter.

Luisa Rodriguez: And you’re now in a collapse scenario where we don’t have the technology we’d need to, again, pull it out. And I think because we don’t have the technology to pull it out, I guess the idea there is it’s basically too hot in almost all areas of the world to exist without air conditioning as humans, but also to have livestock without air conditioning, and then also to grow some types of crops. And we don’t have air conditioning technology. So we’re really in a tricky spot.

Implications for what we ought to do right now

Luisa Rodriguez: We should think more about where we want to conserve both physical resources and information, given the types of catastrophes that we think are likely. Like maybe a nuclear war between Western countries or just countries in the Global North. Think about what things we want to keep. So the Svalbard seed bank does a great job of keeping heirloom seeds, which are seeds that do produce viable seeds when grown, prioritizing those seeds. Keeping, in like a similar vein, stocks of things that would be both useful to use and also useful to learn from in a more intentional and curated way. Like on the same theme of banks, like what do we want them made of?

Rob Wiblin: Technology banks or something. Here’s tons of artifacts, all nicely conserved. They’re going to last quite a long time. And next to each thing is a book describing how it works.

Luisa Rodriguez: Exactly. And then just being deliberate about distributing those globally.

Rob Wiblin: Sticking them under mountains and places that can still be accessed.

Luisa Rodriguez: Making sure they get preserved. I would love one on a sub. I’d love one in Antarctica, who knows. Yeah. So something a bit more strategic there.

Luisa Rodriguez: I think there are concrete things that can be done to make infrastructure more resilient. And there are organizations and cities trying to make their infrastructure more robust to things like cascading power outages caused by weather or something. And probably there are really targeted things you could do to make infrastructure have fewer interdependencies.

Luisa Rodriguez: Some components of the project would be maybe interviewing experts to see what kinds of technologies you’d want stored. Thinking about the types of knowledge, so like which books you’d want to have. Maybe going back and reading Lewis Dartnell’s The Knowledge and thinking of more examples of things like heirloom seeds or yeast or things that would just be kind of a leapfrog… Save you some trouble to have stored somewhere.

Luisa Rodriguez: So like thinking of the things is one step, building the things is obviously a costly step, deciding where to put the things I think would be really achievable. I think in general, you can’t go wrong with like, distributed all over the world. And then there’s some pretty clear other factors that might push you toward certain places that don’t… Yeah, that I think you could just work out places that seem like they’d be more likely to have survivors.

Luisa Rodriguez: And then governments have plans that you can download online that are like, “What should I do if there are massive disasters that force me to leave my home?”, and basically maybe there aren’t services for a long time. I can imagine advocating for something to be inserted into those plans, that’s like just a location of where these vaults are or something. Yeah.

Luisa Rodriguez: I think David Denkenberger talked about food stocks. We used to have way more. It’d probably be good if we had way more again. It’d probably be good if more countries had more, and I don’t know how hard that’d be to advocate for, but yeah, it’s something that we’re doing worse on than we were even 40 years ago. So it just seems like we could improve upon that again. I guess in general, I’m in favor of all the research being done into alternative foods.

Articles, books, and other media discussed in the show

Luisa’s work:

Mitigating the risks and effects of civilisational collapse:

Book and movie recommendations:

Other 80,000 Hours Podcast episodes:

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About the show

The 80,000 Hours Podcast features unusually in-depth conversations about the world's most pressing problems and how you can use your career to solve them. We invite guests pursuing a wide range of career paths — from academics and activists to entrepreneurs and policymakers — to analyse the case for and against working on different issues and which approaches are best for solving them.

The 80,000 Hours Podcast is produced and edited by Keiran Harris. Get in touch with feedback or guest suggestions by emailing [email protected].

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