WHAT IS THE chance that your hobby will kill you? This isn’t something you need to think about if you’re into, say, knitting, but most base jumpers will have felt the niggling fear that each jump could be their last. Intuitively, we know that some hobbies really are way riskier than others.
In 1980, a Stanford engineering professor named Ronald Howard came up with a simple way to convey this difference in risk: He coined a unit of measurement called the micromort. Each micromort equals a one-in-a-million chance of death. Scuba diving, for example, is pretty risky at 5 micromorts per trip, but nowhere near as dangerous as base jumping, which will net you 430 micromorts per jump. Traveling 230 miles by car would add up to 1 micromort, but you’d only need to go 6 miles by motorcycle to expose yourself to the same risk of death.
The reason we have micromort estimates for these activities is because we have pretty good data on how people die. Other risks are much harder to quantify. Take, for example, the prospect of dying in a nuclear war. It’s not something that most people want to contemplate, but we know that the risk isn’t zero. Nuclear weapons were used to kill people in Hiroshima and Nagasaki, and since then there have been a handful of close calls. During the Cuban missile crisis, John F. Kennedy estimated that the chance of a nuclear conflict was “between one in three and even.” With the war in Ukraine and Putin’s escalating nuclear rhetoric, the prospect of nuclear conflict has once again risen uncomfortably to the fore. And whether we like to admit it or not, behind every discussion of nuclear war looms the same worrying question: How likely is it that a nuclear weapon will kill me?
Micromorts can help us here, too. Thinking about the prospect of nuclear war in terms of personal risk might sound callous, but getting to grips with probabilities might help us make better decisions about our own lives and also provide hints about how we can avoid nuclear conflicts in the future.
There’s a whole field of research that deals with trying to assign probabilities to hard-to-predict future events. It’s called super fore casting, and it really started to take off in the mid-2010s after the Canadian academic Philip Tetlock coauthored an influential book on the topic. The general gist is that even experts in a particular field are quite bad at knowing what will happen in the future, but some people are unusually good at making verifiable predictions across a broad range of topics. These people are often labeled “super fore casters,” and governments are increasingly interested in tapping their expertise to help make smarter policy decisions.
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Calculating the likelihood of dying in a nuclear conflict sounds like an impossible task, but it could give us a whole new way to think about the risk.

Early on in the war in Ukraine, one set of superforecasters was particularly interested in trying to figure out the likelihood that the conflict would escalate into a nuclear war that would kill someone in London. Most of the forecasters involved are part of a group called Samotsvety that has a strong track record at predicting future events. In 2020, the Samotsvety group won one of the top forecasting competitions in the world, in which teams are asked to predict arcane future scenarios such as the number of O-1 US visas granted to Chinese nationals and the combined revenues of the top tech firms. The group won the competition again in 2021, and currently holds the top place in the ongoing 2022 competition. In late February, the forecasters bet around $14,000 that Russia would invade Ukraine by the end of the year. They ended up winning just over $32,000.
In March, the Samotsvety group turned to their next big question: What is the risk of death in the next month due to a nuclear explosion in London? The forecasters broke this down into a series of smaller questions, such as the chance of nuclear war between NATO and Russia and the likelihood of dying if a nuclear bomb were to drop on London. Each forecaster wrote down their own prediction for each question and then returned to the group to discuss their reasoning. After that, they updated their answers again and averaged their predictions using a method of calculating averages that’s popular with group forecasters.

The Samotsvety forecasters concluded that there was a 0.01 percent chance that London would be hit by a nuclear weapon between mid-March and mid-April 2022. On a per-person level they estimated that the risk of dying in London during those four weeks was roughly 24 micromorts. In other words, staying in London posed about the same level of added risk as riding a motorcycle for 144 miles or going hang gliding three times. Since the average daily risk of death for a young adult is around 1 micromort anyway, the war in Ukraine roughly doubled a young healthy Londoner’s risk of sudden death.
But micromorts aren’t an exact guide to decisionmaking. “Maybe you value your time much less if there is a nuclear war,” says NuñoSempere, a Samotsvety forecaster who normally works as a researcher at the Quantified Uncertainty Research Institute. If everyone you love is in London, then you might require a very high micromort risk in order to consider leaving the capital. Or if you consider yourself a survivalist, you might value your contribution to a postapocalyptic society so highly that you would set a very low threshold for leaving London. When the war in Ukraine broke out, some did choose to leave London after weighing up the risks versus the personal cost of leaving.
David Spiegelhalter, chair of the Winton Centre for Risk and Evidence Communication at the University of Cambridge, liked that the Samotsvety group deconstructed the risk of a nuclear attack into smaller questions. “It’s a very good way of dealing with a big problem,” he says. To make their predictions, the Samotsvety forecasters also considered the history of close calls in the past as well as the specifics of the current situation in Ukraine. One of the forecasters, MishaYagudin, is Russian, and put an emphasis on considering how Russian elites would react to the prospect of Putin using a nuclear weapon.
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In October, the Samotsvety group updated their predictions. In a blog post published on October 3, they estimated that the chance of London being hit with a nuclear weapon in the next three months was now around 0.02 percent. Since their previous prediction only covered a single month, it’s hard to directly compare these forecasts in terms of micromorts, but Sempere estimates that their projected risk for a Londoner over the next one-to-three months may now be around 40 micromorts. Other superforecasters have made their own forecasts about nuclear war. In London, the Swift Centre for Applied Forecasting estimates the likelihood of a nuclear weapon being detonated somewhere in Europe before April 30, 2023 to be 9.1 percent. The crowdsourced forecasting platform Metaculus puts the likelihood of a nuclear detonation in Ukraine by 2023 at 4 percent.
Putting a percentage on the likelihood of a nuclear disaster can feel icky—like you’re boiling down the immensity of human suffering into a spreadsheet. “I think what people dislike about this is that people are thinking about the unthinkable,” says Spieghalter. But confronting the unthinkable is unavoidable if we want to reduce the risk of nuclear war now and in the future. “The risk of nuclear war is probably much higher than many of us might want to assume,” says Anders Sandberg, who researches risk at the University of Oxford’s Future of Humanity Institute. If we know how different factors contribute to the probability of a nuclear detonation, we can start to think of ways that we might defuse some of that risk.
Take accidents as one example. In 1981, the US Department of Defense released a report counting 32 known accidents involving nuclear weapons. In March 1958, a B-47 bomber carrying an unarmed nuclear weapon accidentally jettisoned its bomb over South Carolina. The bomb exploded in someone’s garden, destroying their home and blowing a crater 50 feet in diameter. In that case the bomb didn’t contain nuclear material, but four years later two nuclear bombs that were many times more powerful than the one detonated over Hiroshima accidentally fell from a B-52 bomber flying over Goldsboro, North Carolina. One of those weapons broke apart, and a section containing uranium sank into waterlogged farmland and was never recovered. The other bomb went through all but one of its arming mechanisms—an accidental detonation was only one step away. In the wake of the accident, the US added new safety devices to its weapons and encouraged the Soviets to do the same.
The history of nuclear accidents tells us that one way we can minimize the risk of a disaster happening is by making weapons much less likely to accidentally detonate. We can apply a little of the same thinking to future scenarios to figure out where risks might escalate. The Samotsvety forecasters estimate that if tactical weapons are dropped in Ukraine, that would increase the risk of someone in London dying from a nuclear attack by about 10 times—at that point, leaving the city might start to look like a very sensible decision. The Swift Centre forecasters broke down their predictions into a series of steps, looking at how the risk of nuclear conflict might change depending on which cities Ukrainian troops manage to retake. Most of their forecasters thought that if Russia was going to use nuclear weapons, it would do so before Ukraine retook Mariupol, but if Russia hadn’t used nuclear weapons before that point, it was unlikely to do so afterward. Considering these branching pathways might help us know where to focus our risk reduction efforts
Shortly after Russia invaded Ukraine, some of Sandberg’s friends started asking him whether they should move out of London. He put together a quick model of how he thought the war might shake out. Back then he was glum about Ukraine’s chances of holding out against Russia, and so concluded that the risk to London was extremely low. Of the possible outcomes spread out in front of him .

Reference https://www.wired.com/