Furthermore, the atomic bombings of Hiroshima and Nagasaki occurred 77 years ago, under circumstances that no longer apply. There has only been one previous nuclear war – World War Two – and one data point is not enough. The risk of you dying in a nuclear war cannot be calculated in the same way. Without this and similar data, the insurance industry couldn't operate their business. You personally have never died in a car crash, but many other people have, and those data make for reliable risk quantification. For example, to quantify the risk of you dying in a car crash, one can use abundant data on past car crashes and segment them according to various criteria such as where you live and how old you are. Common risks can be quantified using past event data. Risk is generally quantified as the probability of some adverse event occurring, multiplied by the severity of the event if it occurs.

So, how do we approach these uncertainties, and what can it tell us about how to interpret present-day events? Reconciling this tension between the importance of evaluating nuclear war risk and the difficulty of doing so is a primary focus of my research. However, whether an event will result in nuclear war is deeply uncertain, as are the consequences. For the individual: should I take shelter somewhere relatively safe? For human society: should global food production systems prepare for nuclear winter? In the worst-case scenario, a nuclear war may cause the collapse of global civilisation, potentially resulting in massive harm into the distant future. Whether the invasion of Ukraine or any other event will result in nuclear war raises desperately important questions. My country, the United States, supports Ukraine, making it a potential target of a Russian nuclear attack. In the first few days of Russia's invasion of Ukraine, the conflict was escalating so fast that it could have conceivably gone all the way to nuclear war. It's rare, however, that I have gone to sleep wondering whether the very next day will bring an exchange of nuclear weapons.

'OK good,' I said to myself, 'we made it through the night without a nuclear war.' I work for the Global Catastrophic Risk Institute, a US-based think tank, where it's my job to think about humanity's gravest future threats. My neighbourhood in the New York City area was calm and normal. One day last week, I woke up in the morning and looked out the window to see the Sun was shining.

Fallout shelter list weapons by damage