Nuclear deterrence and taboo?

Nuclear weapons were created about 80 years ago, and they were used almost immediately after their creation, in August 1945: twice against the Japanese cities of Hiroshima and Nagasaki by the United States in the closing days of World War II. Eighty years later, we want to explain why that is still the only time that nuclear weapons have been used in armed conflict. We now have nine states in the international system that possess nuclear weapons that they could use in armed conflict, and they haven't.

A taboo is a particular kind of moral prohibition, one that we can best think of as categorical. It is a prohibition that is not sensitive to the expected consequences of doing or not doing something. Many prohibitions, for instance on using violence, can be overridden if we expect particularly good consequences, so if using violence is the lesser evil. A taboo or a categorical prohibition cannot be overridden. Certain types of acts are in a category so evil that we never contemplate undertaking them, even if they would have good consequences, or even if not undertaking them has really bad consequences. A categorical prohibition is a prohibition where a lesser evil justification is not available. There are very few taboos that are widely shared. The two examples people often give of taboos are incest and cannibalism. These are acts that we tend not to contemplate even if we thought we would get away with them – even if not engaging in these acts might have bad consequences. One explanation for the non-use of nuclear weapons is that there is a taboo against using them.

In principle, a nuclear taboo could be something that only elite political decision makers subscribe to. They believe that it is categorically wrong to use nuclear weapons, but the societies around them don't necessarily believe that. That would be quite surprising, because taboos are such strong prohibitions that for a person to buy into them without the society around them believing something to be wrong is unlikely. Often taboos involve emotional disgust. It would be surprising if only the American politicians who make decisions about nuclear use had that reaction to nuclear use.

International law outlaws some weapons with specific treaties. There is a treaty that prohibits the use of nuclear weapons, which was adopted in 2017. Unfortunately, none of the states that possess nuclear weapons have ratified the treaty. So they are not bound by it.

We do not know very much about how states plan to use nuclear weapons. Nuclear plans are, by and large, classified. We know most about nuclear plans in the United States because of a consistent effort to research that, for reasons of declassification, and because the United States communicates much more about its nuclear posture than most other nuclear armed states.

For some people, that ends the discussion: since the United States no longer engages in countervalue targeting, nuclear plans are unproblematically compliant with international humanitarian law. However, that is not the case, because there are also the principles of necessity and proportionality to consider. The principle of necessity, for instance, implies that when it is possible to destroy a particular target in ways that create less civilian harm, then this is obligatory. Whenever a particular nuclear target could in principle be neutralized with a conventional weapon, on the assumption that conventional weapons cause less civilian harm, particularly through radiation and fallout, then a conventional weapon would have to be used.

If we held the attacks of Hiroshima and Nagasaki to the legal standards that prevail today, they would not be compliant with international law. Interestingly, when President Truman justified the first attack publicly, he spoke of a military base as the target, but it is quite clear that the weapon was aimed at the center of Hiroshima. These attacks would violate the principle of distinction as we see it today. Principles of necessity and proportionality are harder to judge, but basically, these attacks would not be compliant with international law as we understand it today.

A threat to resort to a war that would be illegal if carried out is an illegal threat in international law. It is slightly less clear whether a threat to use a nuclear weapon in a war that could be legal overall, for instance because it is a war of self-defense, is illegal if the nuclear attack would violate international humanitarian law. Whether an articulation of a nuclear plan for the purpose of deterrence is illegal as a threat, if that attack plan if carried out would violate international humanitarian law, is, to some extent, contestable.

I think the most important question for us is: what is the best package of means that we should rely on to prevent nuclear war? What raises the nuclear threshold the most? What I learned from my research into the nuclear taboo is that we can't take comfort from the notion that the public in democratic states would be constraints on a hawkish leader that is tempted to use nuclear weapons. We know that, particularly in democracies, but even in autocracies, public opinion or perceived public opinion can influence how political leaders make important decisions about the use of force. If we thought that there was a strong nuclear taboo, we might take comfort in the assumption that the threshold for political leaders to resort to nuclear weapons is high, because they do not want to incur the wrath of a population that has internalized a nuclear taboo. The findings of our research suggest that there is a dislike of nuclear weapons but not a categorical prohibition. We cannot rely on the public alone then. Neither do I think we should only rely on deterrence. Deterrence is really important, but it also has costly consequences. To shore up deterrence, nuclear states are consistently tempted to invest in more nuclear weapons and to adopt ever more aggressive and forward-leaning postures, which raises the risk of an accident or unwanted escalation. Both deterrence and moral arguments about nuclear weapons are important, but neither is alone sufficient to prevent nuclear use. We need a large concerted effort to delegitimize nuclear weapons, to educate the public about the consequences of nuclear weapons and to renew efforts to institutionalize non-use of nuclear weapons.

I have studied attitudes towards the use of force across different countries, in Western countries but also in conflict-affected countries like in Ukraine, Iraq and Afghanistan. The one lesson I take away from that is that it is a mistake to think of public opinion as some kind of repository for moral truth or guidance. Often, people embrace views that are quite problematic; many people are not particularly well informed. They can't be, because not everybody can spend all their time thinking about the politics or morality of war. At the same time, it is equally a mistake to ignore public opinion or to not try to figure out what people think, because the morally best and politically and strategically effective answer to most policy problems must take into account what the people who are affected by those answers think. It may not be a satisfying answer, but the answer to the question of what we learned from studying public opinion on war is that we must study it. Understanding what people think about complex moral and strategic problems like war also gives us some indication of what it takes to cue people to have pro-humanist and pro-peace attitudes.

If we fully appreciate the immense destructive power of nuclear weapons use, including the risk of nuclear winter, but also simply the effects of nuclear exposure on the human body, then to me, there can be no doubt that the morally ideal solution to the problem of nuclear weapons is abolition.

What is the least bad outcome we can work towards right now? I think we need a multi-pronged strategy. One prong is to educate the public about the consequences of nuclear use.

A misconception is that the public underestimates the likelihood of a mistake or unwanted escalation. We tend to think that the biggest risk is that a personalist autocrat sitting on a pile of nuclear weapons decides one day to use them and launches a bolt out of the blue. In fact, the biggest risk is either nuclear escalation from an ongoing conventional armed conflict or a mistake, an accident. The propensity for something like that to happen in the long run is quite high, and I don't think we are sufficiently alive to that unfortunate reality.