A massive volcano erupts in Southeast Asia. Ash fall delays flights and destroys crops, while pyroclastic flows wipe out entire towns. Over the following weeks, the sulfur dioxide pumped out turns into a haze of fine acid droplets, eventually wrapping around the entire planet, scattering sunlight back to space. The sun turns pale, shadows go soft, the sky glows violet after sunset and the ground below cools. The next summer never appears. Harvests fail from the American Midwest to the monsoon belt in Asia. Countries close their borders, and people who have never heard of the volcano begin to starve.

This nightmare scenario has yet to happen, but it's not a matter of if but when a world-changing event like this will hit, and governments need to start preparing for global catastrophes that could disrupt the food system on an unprecedented scale.

There are three main steps we need to take soon: put events like nuclear war, a huge volcanic eruption and a continent-wide blackout into national risk assessments; agree to trade rules for such an emergency before it arrives; and fund pilot projects now for foods so we know what can be produced at scale without much sunlight or without fertilizer.

Florian Ulrich Jehn is a senior researcher in environmental science specializing in food security, climate impacts, and civilizational resilience.

Following doctoral studies in hydrology, Florian’s research expanded to extreme climate change scenarios and innovative approaches to prevent global famine after catastrophic events. He currently works at the FernUniversität in Hagen, developing a new university course about global catastrophic risk.

Beyond academic research, Florian writes the research newsletter Existential Crunch and delivers public lectures on food security and global risks.

We've been faced with turbulent times the last few years with COVID, the Russian invasion of Ukraine and the Iran war. And the current outlook indicates there's more trouble ahead — the closure of the Strait of Hormuz alone could disrupt global food production, for example. A significant part of the world's traded fertilizer passes through it, and the United Nations Food and Agriculture Organization has warned that the shortfall will cut yields into 2027.

This shows that in today’s interconnected world, regional crises will influence countries far away from it. With larger catastrophes, these ripple effects in the global system would be more widespread, quicker to take hold and on a higher magnitude.

Critics might question why we need to prepare for such Black Swan events. But global catastrophes are not as unlikely as they feel. Ice cores enable us to count large eruptions of the past. On that basis, volcanologists put the chance of a magnitude-7 eruption — the size of Tambora in 1815, which caused a "year without summer" — at roughly 1 in 6 this century. Estimates for a repeat of the 1859 Carrington solar storm, which could disrupt power grids on a continental scale, run from about 1% to 12% per decade. Nuclear-armed states are almost constantly engaged in conflicts, risking nuclear war.

Each of these events might seem unlikely. But in combination, they add up to a significant chance that at least one of them will happen this century.

What they all have in common is that they all would drastically impact the food system. A volcanic eruption, the firestorms of a nuclear war or a large asteroid impact all push particles into the upper atmosphere that block sunlight, which would lead to colder, drier growing seasons that could result in harvest losses up to total failure. In the most extreme nuclear war scenario, researchers estimate that global calorie production could drop by around 90%. A long blackout, caused by a powerful solar storm for example, works differently but has the same consequence: no fertilizer, no pesticides, no fuel, and the sharpest yield losses exactly where we produce most food today.

Hardly anyone is assessing these risks. Even the countries doing it best fall short. The U.K. and Switzerland are good examples. The U.K. National Risk Register lists 89 risks, including volcanic eruptions, severe space weather, pandemics and a nuclear miscalculation abroad. However, the catastrophic events it considers are all relatively small-scale — with a "reasonable" worst-case scenario of over 1,000 deaths and a cost of tens of billions of pounds — and the register does not even begin to consider events like a global famine or a nuclear war that could lead to tens of millions of deaths and cost trillions of pounds.

Switzerland's national risk analysis, meanwhile, covers 44 hazards including a solar storm, a foreign volcanic eruption and a meteor strike. Again, the scale is too small. The volcano is a moderate European eruption and the meteor is 66 feet (20 meters) across, comparable to the Chelyabinsk impact in 2013. Many other countries do not even consider risk on these limited scales.

No country can solve this alone. In a review, my colleagues and I highlighted the key factors that would make countries and communities more resilient to various global catastrophes. These include food self-sufficiency, decentralization, geographic isolation and governance quality — meaning working institutions, low corruption and low inequality. Australia scores best, but even Australia would struggle without imported fuel, medicine and fertilizer. Nowhere is a refuge on its own.

Countries will need international collaboration to make it through a crisis of this scale. Export bans have been a common reflex in food crises of the past. After a global catastrophe, they would only isolate countries from each other and lead to further damage, as export bans can easily lead to the situation where enough food is still around, but nobody is trading it and so people starve.

We need to work on rules to govern trade under those circumstances before a global emergency occurs.

You might say the probabilities are too small to justify the cost, and that money spent on hypothetical volcanoes is money not spent on floods, hospitals and defense. This criticism might land if you only look at a single catastrophe. However, there is a whole portfolio of events that could lead to global catastrophe. In combination, there is a good chance that one of them will hit, and if it does, we better be prepared. Also, many of the preparations needed are not even that expensive. Low-input farming, decentralized grids, a diverse food supply and more exhaustive risk assessment are within grasp of most countries.

This needs to happen now. Starting work on resilient foods or better international agreements when a global catastrophe has already occurred is too late. You cannot start an industry in the month the harvest fails. Clearly, prevention is better than resilience, but some of these events cannot be prevented at all. When one of them arrives, the difference between the societies that prepared and those that did not will be measured in lives.

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