‘A lively guide to the many existential risks faced by 21st-century humanity’ SIMON MUNDY
The Pocket Guide to PLANETARY PERIL
‘Fascinating’
HOWARD DAVIES
‘Eye-opening’
BEN CALDECOTT
JAKOB THOMÄ
The Pocket Guide to PLANETARY
PERIL
The Pocket Guide to PLANETARY PERIL
WH Allen
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Originally published in Germany as Das kleine Buch der großen Risiken by Klett-Cotta in 2024
This edition published by WH Allen in 2025 1
Copyright © Jakob Thomä 2025 Illustrations © Vyki Hendy
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INTRODUCTION
We live in a time where people are bombarded by stories about the plethora of risks and vulnerabilities of modern life. It is not without reason that the words ‘polycrisis’ and ‘permacrisis’ are now staples in political debates and the boardrooms of large companies. The CEO of Moody’s, one of the largest credit-rating agencies in the world and perhaps the premier global institution when it comes to measuring risk, talks about the ‘era of exponential risk’.1 The British use the word ‘omnishambles’ – and doesn’t it feel like it, a lot of the time?
All this makes us feel vulnerable. Partly because these risks are real and in some cases are an active threat. But partly also because, despite the barrage of existential risk news clippings, we are often left in the dark when it comes to how these risks work, how relevant they actually are for our lives, and what we can do about them. Society engages with big, existential risks a little bit like it’s last orders in the pub. A somewhat frantic affair involving ill-advised decision making and the occasional ill-timed blackout, always mysteriously catching us by surprise. That is why I wrote this book: to lift the veil on what I think
are the 26 biggest ‘planetary perils’. It’s a pocket guide, a neutral compass for navigating the world of big disasters, pointing to which dangers we can put to bed and which ones should make us get out of bed.
Crucially, this is not a doomsday, everything-is-awful book. For starters, it is just very unlikely that the world will literally end in our lifetime. We would have to be really, really unlucky for that to happen to us! Dinosaurs are among the most successful species to have ever called this place home, roaming Earth for well over 100 million years. To put that number into context, Homo sapiens (that’s us!) has been around for a little less than 300,000 years, depending on when you start counting. Even if we only manage to survive 1 per cent as long as the dinosaurs, we still have around 700,000 years left to try to finally win that dumb stuffed animal toy in one of those claw machines in your local arcade.
What is more, we now have the technological capacity to shoot asteroids off course to prevent them crashing into Earth. I am sure dinosaurs would have liked a piece of that gadget. In fact, humans thrive in all types of places, on ice, on sand, on water, on land. After all, the adaptability of mammalian life is what ultimately allowed our forefather rodents to survive the asteroid that killed dinosaurs.
While this isn’t, then, a doomsday book, it is an attempt for us to be more clear-eyed about the future risks – and our role in shaping them. And just because it is unlikely that literally every single human will die does not mean we are not going to be exposed to a range of life-altering, earth-shattering perils, many of which have a meaningful likelihood of materialising in our lifetime.
To graduate from the car crash that is our daily news and social media feed, permanently reminding us that everything is a mess, we have to confront and understand these risks. What does the potential collapse of ocean currents actually imply for modern life in Britain and what can we do about it? How real are the risks related to quantum computing? We are at the cusp of (and some would argue amid) a technological revolution that has the potential to destroy like no generation before us. While the dinosaurs did not have asteroid redirection technology, they also did not have to contend with rogue artificial intelligence (AI), salted nuclear weapons, technology empowering large-scale social control and manipulation, and runaway heat and climate change. What might all of that look like and what societal response is at our disposal?
One of the things I’ve learned in a professional lifetime of thinking about threats and perils is that there is perhaps no concept that our Stone Age brains struggle to process more than ‘risks’. No example illustrates this better than the concept of expected loss in finance. A £100 portfolio that has a 90 per cent chance of losing 10 per cent and a 10 per cent of chance of losing nothing has an expected loss of £9. If that same portfolio then had a 10 per cent chance of losing 90 per cent and a 90 per cent chance of losing nothing, the expected loss is still £9. It goes without saying that those two scenarios are pretty different. The same is true for the risks in this book. Some are very likely to happen but perhaps have less dramatic impacts than, say, a planet-sized asteroid hitting Earth. Building a career in finance trying to get people to understand and care about these types of risks has also
taught me that, as counterintuitive as it sounds, it’s better not to try to convince them. Rather, my job is to take them along for the ride, to embark on the journey of discovery together.
This is what I want to do with this book, too. I will provide my assessment for each chapter (it is a guide, after all), but ultimately my goal is not to convince you that all the risks are about to crash down on us, or that there is nothing to worry about. It is to show you what we know about these risks, what we don’t know, and, ultimately, when your bones are exhibited in some future natural history museum as a species that became extinct 20 million years ago, to have an idea of what eventually did us in.
So that when it does end up being last orders in the pub … oh wait, who am I kidding, it’s going to be a shitshow no matter what. But at least you won’t be surprised …
A ATOMIC BOMBS
THE RISK IN ONE SENTENCE
What is effectively unlimited energy (the splitting or ‘fusion’ of atoms) becomes either an uncontrolled chain reaction that destroys the planet or a controlled weapon wielded in a civilisation-destroying conflict.
SHOULD I CARE?
Uncontrolled chain reactions do not seem feasible given our current knowledge of physics. Somebody over the next thousand years deciding to detonate one of these things is much more likely. If you believe in a modicum of human sense, then that is the worst of it. But I for one don’t love your odds …
We will explore the big and the small in this book, from super ‘planet-killing’ asteroids several hundreds of kilometres across to tiny nanobots building self-replicating machines that will turn our planet into ‘grey goo’. But nothing illustrates the power of small quite like the energy stored in an atom. A milligram of mass – the equivalent of one small snowflake or a grain of sand – stores roughly five times the energy the average British person consumes in an entire year. Next time you walk on the beach, take a
second to pick up a grain, just one, no more, hold it in your hand and marvel at the power stored within. It’s power enough for five years of your life’s energy demands, the heating of your home, the lights, your washing machine and dishwasher, your car and transport, everything, for five years, all stored in a grain of sand.
Now drop that grain of sand and run your hand through the beach again, this time picking up an entire handful with each hand. That two handfuls of sand will now contain 20,000 grains, enough energy to power a small town for a year. Imagine the energy that you are holding in your two hands. Now imagine the force and destruction it can unleash. The nuclear bomb dropped in Hiroshima weighed more than 64kg, but the energy from the explosion came from just half a gram, the weight of a butterfly.1 That is why people fear the atom, nuclear energy and the nuclear bomb. And why ‘A – Atom Bombs’ is the first chapter of this book. No potential existential risk sets the scene quite like the building block of all matter and by extension all modern life: the atom.
We are, of course, here firmly on the grounds of the most famous equation in the world: E = mc2. Energy equals mass times the speed of light squared. This equation hints at why small things store so much energy. Multiplying anything by the speed of light squared is going to give a big number. This is also a neat reminder of why nuclear energy is so much more powerful than fossil-fuel energy. Fossil fuels release energy through their unpaired electrons in the outer shell. Nuclear energy comes from splitting atoms. It’s the difference between cutting off a branch for firewood or cutting down the whole forest. Which is
why we need much less material for nuclear power than for fossil-fuel energy. We don’t split atoms when we burn fossil fuels. If an atom is a lemon, our fossil fuel energy is the equivalent of a pinch of lemon zest.
Happily, splitting atoms isn’t a trivial exercise. And so, by extension, we can count two nuclear bombs, two (or three) major nuclear accidents from nuclear reactors, and a bunch of lucky misses as the total damage this technology has wrought on humanity.2 As always, our ledger has two sides: consider these costs next to the prosperity that nuclear power has brought to humanity by being a low-carbon energy source. Some even believe that the nuclear bomb has contributed to less war, given its role in creating ‘Mutually Assured Destruction’ during the Cold War. I would just say that if this is ‘less war’, then I’m not sure I’m all that excited about it. Either way, the fear remains that the atom and the guided or unguided energy it may unleash may be the end of us.

How exactly does this weapon work? The nuclear energy is freed by breaking up an atom in the process of shooting atoms at each other, ideally unstable atoms3 like uranium or plutonium. An atom weighs significantly less than a gram or even a milligram, so the energy really only becomes serviceable when it sets off a chain reaction. In fact, this particular feature was one of the original fears that the scientists working on the first nuclear bomb in Los Alamos had: that a chain reaction would jump to nitrogen and hydrogen (the material in our atmosphere) as part of
an uncontrolled chain reaction that would effectively set the world on fire and melt the planet.
The debates around this are fascinating, especially if we put ourselves in the minds of the scientists at the time of the Manhattan Project during the Second World War, who literally didn’t know whether their experiment would destroy Earth. It is now settled science that such reactions are effectively impossible, requiring temperatures equivalent to the inner core of the Sun to even fathom such a process (incidentally, the Sun is one continuous chain reaction …).
But we don’t need to set the world on fire through an uncontrolled chain reaction in order to imagine the calamities of atom bombs (just conduct a simple YouTube search for Hiroshima and Nagasaki). Consider the hypothetical of exploding all existing nuclear bombs. There are currently roughly 10,000 of them,4 and exploding all of them all at once would be enough to destroy every city of a meaningful size (>100,000 inhabitants) in the world.5 Billions would die from the bombs and the ensuing nuclear winter. It is hard to imagine modern civilisation after such an event, but fascinating to consider that this explosive force still pales in comparison to the asteroid that killed the dinosaurs. In any case, it is unclear what the rationale for piling all nuclear weapons together and setting them on fire at the same time in the same place (the asteroid equivalent) would be.
Of course, the hypothetical of a nuclear war even approximating that size would imply a deterioration of global political stability, where the issue would not be constrained to nuclear weapons. It seems reasonable to assume that forces would intervene before such an escalation would materialise – or if they couldn’t, that the level
of anarchy this implies would be just as damaging as the nuclear bombs themselves. An uncontrolled war of nuclear powers would come with depravity exceeding anything humanity will ever have witnessed.
I cheated a tiny bit a moment ago when discussing nuclear energy and the splitting of atoms. Most of us think this is how nuclear bombs work when, in fact, modern nuclear bombs (or hydrogen bombs) don’t involve the splitting of atoms but the fusion of atoms. Whereas nuclear fission bombs (aka bombs involving the splitting of atoms) have some hypothetical upper yield or explosive power limit due to the complexity of putting a bunch of critical mass in one place that deteriorates, nuclear fusion bombs (aka hydrogen bombs aka bombs that involve the merging of atoms) do not have a known upper constraint. The largest nuclear bomb ever tested – the Tsar Bomba in 1961 – had a fireball radius of roughly 3.5km.6 Put differently, that is over 1,000 times more powerful than the Hiroshima and Nagasaki bombs combined (!) and ten times more powerful than the entire stock of conventional weapons exploded during the Second World War. Here is the rub: the bomb was altered such that the fallout would be reduced by 50 per cent.7 If applied in the way it was originally designed, it would have had twice the destructive force. There is no upper limit to nuclear fusion bombs, operating under the same principle of releasing mass in exchange for what is effectively unlimited energy in the context of two atoms joining together (fusion).
It is not clear why bombs of this size would be built, or even bombs a multiple of that size, to achieve reasonable military and security objectives. There is a reason the
United States ended its nuclear tests at 15 megatons with the Castle Bravo test (little less than a third of the Tsar Bomba).8 But the unreasonable rule the world. It is not just – as Mr Wonka himself informs us in Roald Dahl’s Charlie and the Chocolate Factory – that ‘Mr Wonka is being unreasonable’. It is all of us. We have only learned to manipulate weapons of this power very recently. There is time to be unreasonable yet.
It is important in all of this to highlight that the civilisational risk from nuclear fusion bombs is unreasonably linked to nuclear power and fusion power. While fusion power – currently in the research phase – can supply what is effectively unlimited energy, it somewhat curiously has almost zero risk. Because of the tiny amounts of material required to generate fusion energy and the ability for this material to be fed continuously, any system failure in a nuclear fusion power plant would immediately be containable. This is different to traditional nuclear power, where unspent fuel can cause radiation – like in Chernobyl – for decades.
Nuclear power is scary. But it has not and will not in the future represent a civilisational risk. While nuclear accidents are likely to return, there is no meaningful mortality risk from previous disasters measured to date. That doesn’t mean societies may not consider nuclear power a risk not worth taking, but that would be a political choice, not a scientific one. But from a civilisational risk perspective, the track record for nuclear power is clear.
Inevitably, the discussion of nuclear fusion brings us back to the imaginary ledger that we use to account the good and the bad in this world. Nuclear fusion, through
atom bombs, is currently the only known technology that humankind could wield to destroy the entire planet completely. But nuclear fusion power once (efficiently and economically) deployed would arguably by itself solve the climate crisis. The effectively unlimited power it would generate, at potentially very, very, very low costs, represents zero-carbon power for our heating, our lighting, our transport, and even the technology-based solutions designed to extract carbon from the atmosphere and reverse global warming. As we will discover, it can also unleash some other pretty crazy technological applications. On the other hand, simply dismissing nuclear fusion as safe without recognising its potential role as a gateway drug to nuclear weapons would be naive. It seems reasonable that, as with any other technology, the more research we do and the better we understand it, the higher the risk that it might fall into the wrong hands.9
Obviously, the best way out of this risk is if we could negotiate a world without nuclear weapons. A truly novel idea! Why hasn’t anyone else thought of this? But joking aside, while a world without nuclear weapons may seem like a fantasy, we shouldn’t give up on the anti-nuclear movement. A less dangerous world with fewer nuclear weapons is still a worthwhile fight.
So, to sum up: nuclear power (fusion or traditional) is not in and of itself a civilisational threat. To the best of our knowledge, it is also not a significant threat to mortality or global health or even regional health (although of course it will have local health impacts in cases of calamities). Traditional nuclear bombs, however, can destroy all major cities. Nuclear fusion bombs (or hydrogen bombs)
can hypothetically destroy regions or even countries and, once of sufficient size, the planet itself. If you believe in the fundamental rationality of humanity, then we will never cross that line. If you don’t, well, we can’t all live as long as the dinosaurs …
B BLACK HOLES
THE RISK IN ONE SENTENCE
A black hole will eat us up.
SHOULD I CARE?
No, but you are welcome to read this chapter anyway!
Working across finance and risks, I permanently struggle with how to communicate information. Numbers are often unspeakably large (hundreds of millions of potential future climate refugees) or vanishingly small (the greenhouse gas emissions content in the atmosphere is measured in a few hundred parts per million, with only marginal increases causing dramatic climate change).
Space is also like that. You probably don’t spend a ton of time thinking about the Milky Way. Assuming you live in a city, you probably don’t see much of it to begin with. The Milky Way, of course, has its etymological origin in Greek mythology. Zeus put the mortal Hercules on his wife’s breast while she was asleep, so that Hercules could drink her divine milk and become immortal. When Hera became wise to the trick, she pushed Hercules away and the spilled milk – you guessed it – formed the Milky Way.