In the early Cold War, weapons were not very accurate and intelligence collection often wasn’t very good or up to date. If you were a war planner, the advent of the hydrogen bomb solved a lot of problems for you: even if you didn’t know exactly where a target was, and even if your weapon could miss by hundreds of meters, with a large enough nuclear yield, you could still guarantee the destruction of whatever targets you hoped to hit.

But with giant yield weapons, comes massive collateral damage, likely far beyond what is required to deter decision makers. The difference between a TSAR bomb (or its modern equivalent) and the lowest settings of a mini-nuke is still an order of magnitude larger than the difference between the conventional “mother of all bombs” and a hand grenade. The Beirut explosion last year was the size of the hand grenade blast in this analogy… but if you feel the need to visualize the differences more precisely, you can use NUKEMAP.

Massive yield weapons aren’t just big explosions: they produce more radioactive nuclear fallout that can spread over thousand miles and kill people for years, larger (though less efficient) electromagnetic pulses that can disable electronic grids and large electronic devices over millions of square miles, and mushroom clouds that can reach the stratosphere, contributing to nuclear winter.

With the proliferation of sensors, precision weapons, and fusion of information by narrow artificial intelligence, giant weapon yields may no longer necessary to assure deterrence. In my view, this presents the opportunity the reduce the risk of nuclear winter, but how would you achieve that?

In “Winter-Safe Deterrence” Seth Baum argues that limiting the global nuclear arsenals to ~50 weapons may be a path that allows a degree of deterrence while not threatening enough cities to threaten the global climate. To dig in to more detail and slightly contest the paper: it is not a limit of 50 weapons per say that assures the climate, but rather how large the weapons are and what they are aimed at. Since large yield weapons can loft dust straight to the stratosphere, they don’t even have to produce firestorms to start contributing to nuclear winter: once you get particles that block sunlight to an altitude that heating by the sun can keep them lofted, you’ll block sunlight a very long time and start harming crop yields. To get soot high enough otherwise, certain kinds of cities with large enough fire loads/fuel density would have to be hit to produce firestorms that loft soot high enough that it won’t just quickly fall or be rained back out of the sky. If a bomb knocks over buildings, a lot of the fuel often won’t be available to burn as collapse prevents oxygen from getting to it. With large yield hydrogen bombs where the radius of burning can significantly exceed the radius at which buildings will be knocked over, fires can do much better at sustaining firestorms and burning all available fuel. Lastly, for rural and wild lands, fuel density is normally too low for firestorms: meaning that missiles landing in the middle of nowhere trying to hit silos, submarines, air bases, and mobile launchers probably won’t wreck the global climate, but if they did, it would require very large yields.

Overall, my argument is that nuclear winter is uncertain with current arsenals and targeting plans, but that it could be made extremely unlikely without getting rid of nukes, or even shifting to very small numbers of nukes. Countries with lots of weapons are more likely to employ counterforce targeting to limit damage in the event of nuclear war (aiming at military forces, command and control, etc.) while if you have fewer weapons you are more likely to do counter value targeting for pure deterrence value: neglecting precision, increasing weapon yield, and targeting cities (how you produce nuclear winter). Low yield weapons are still orders of magnitude worse than conventional weapons and can provide plenty of deterring power. If you thought current nuclear deterrence was insufficient, would your solution be to replace all warheads with Tsar Bombs? Probably not, you could increase the yield of some weapons selectively if you have intelligence problems, or instead get better intelligence, increase precision, and get more low yield weapons.

While arms races are undesirable, arms races between superpowers raise the cost of military competition for everyone else, deterring some other arms races and attempts to get nuclear weapons in the first place. The fewer actors there are in military competitions, the fewer security dilemmas you have, and the fewer points there are to initiate conflict. If you think mutually assured destruction works, but that eventually someone will make a mistake or irrationality will change the calculus, then the last thing you want is for everyone to have nukes and magnify the odds that such mistakes will happen. Likewise, if you want to negotiate to reduce the risks of escalation or catastrophic damage then the last thing you want is to multiply the number of parties that have to negotiate. If early attempts at building nuclear arsenals can be halted even fairly late with low collateral damage, that may serve as a last line in deterring nuclear proliferation beyond diplomatic measures and sanctions. In general, I think it is good for the world that nukes are excessively expensive: thought experiments about what happens when they aren’t have fairly dystopian implications. In the grand scheme of things, even through the Cold War the world kept spending less of its wealth on weapons, and even with the Reagan build-up, the costs were highly concentrated on the Soviet Union, bringing the competition to a close for sometime without war. Cost imposition strategies that disproportionately punish totalitarian regimes, advance technology for democracies, and let everyone else enjoy more economic growth sound good to me (when they work).

Bringing this all together, I think a good path for nuclear modernization would be to generally reduce nuclear weapon yields while increasing precision: this makes the weapons more credible that you will use them, and enhances deterrence in that manner while decreasing the odds of global nuclear winter if something ever goes wrong somehow. For tiny states, this creates a far more credible threat of counter force nuclear targeting: dis-incentivizing proliferation, while for large states targeting problems would become far more difficult due to the number of weapons, and thus counterforce targeting would be much more difficult. I don’t think smaller weapons do any less good of a job at deterring decision makers: at point blank range these weapons produce absurdly high overpressure that will crush any bunker, removing the need for extreme yield weapons to take out out hardened bunkers while missing by hundreds of meters. I think it is better if deterrence shifts to deterring decision makers and militaries rather than inherently threatening entire societies. I don’t hold these ideas with extreme certainty, but they should at least be debated, and if wrong, thoroughly debunked.

I think there are two reasons this debate doesn’t really happen: the first is political warfare, and the second is the asymmetries in attachment to reality and interests between military strategists and activists.

In my view, political warfare and active measures created a lot of problems with anti-nuclear activism during the Cold War: activism can get weaponized, hijacked, or coopted in a naïve risk increasing directions, by those seeking to increase their own power, and once groupthink gets started, it can keep going with its own force. Deterrence held up by neutron bombs would have posed far less long-term radiation and nuclear winter risk, but Soviet hijacked peace activism ended that option by rebranding neutron bombs “capitalism bombs.” By bolstering anti-nuclear campaigns against neutron bombs (asymmetric U.S. advantage vs. USSR), and nuclear power (more NATO energy independence) Soviet influenced activism seems to have directly contributed to both planetwide nuclear risk and climate change. Maybe the peace/green movements would have gone that way on their own… but it seems strange when the outcome achieved aligns with higher risk/worse environment and more relative power for an authoritarian state. Beyond these efforts, the Soviet Union also pursued active measures to shift peace group messaging from “no missiles” to “no more missiles” to lock in their advantages in Europe. This made negotiating weapons out far more difficult, and to this day Russia has a huge number of tactical nuclear weapons that people usually don’t count/ignore because they aren’t counted by arms control treaties (I have made this mistake before). Overall, influence operations and disinformation campaigns do target existing rifts in society, and sometimes rely on locals blowing them out of proportion to have effect… but anti-nuclear activism easily could have focused on other directions and doing so would likely have been much better for the environment.

Why did political warfare work at all in hijacking peace activism when often it is so ineffective? Though some peace activists had sympathy to communism, many just were good people that wanted to reduce the risks of millions or billions of people dying. This is where I think asymmetry of interest and attachment to reality comes in: those that enter the military are more likely to have a competitive mindset on military subjects, while peace activists are far less likely to. The military mind may miss opportunities for de-escalation, while the pacifist mind will miss the entire game because it has little interest in plotting out in detail how to invade a country, win a war, or thoroughly imagine the motivations of someone who does such things. Both types of minds will miss many opportunities: the peace activists because they aren’t wrestling with the concrete details of military competition, and the military planners because they have a psychological disposition toward winning with their preferred tools. If you want things to improve, the sort thought leaders you’d want in peace activism would be able to keep their larger goals in mind while thinking much more deeply about the specifics of technology and competition.

Overall, the particular form of arms control I’m arguing for here may be extremely difficult or infeasible due to enforcement issues, but that same problem doesn’t stop activists from pushing for arms control on subjects where enforceability is even harder yet and where the benefits aren’t as clear (e.g. lethal autonomous weapons). This post isn’t terribly detailed or rigorous, but it’s pretty far ahead of most conversations I have had on arms control in the past 5 years: I think it’s time for a new look for ways to improve nuclear arms control, and for the best arguments to get fleshed out and win.


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"I think a good path for nuclear modernization would be to generally reduce nuclear weapon yields while increasing precision"

I am unsure about this. I have the feeling that this is in part the trend going on right now, and that geopolitics experts are very worried, because it gives a path to gradual escalation and makes nuclear war more likely. When nuclear bombs were large and inaccurate, they were kept only as last option of deterrence: it was clear that any use would be followed by a devastating counter-strike with ~100% probability. In contrast, when a military has smaller, well-targeted tactical nukes, there is a temptation to use them for a limited strike, maybe to military installations, thinking that at worst the other country will do the same (that's what the "tactical" word means in this context after all). But the country on the receiving may very well react with an all-out nuclear counter-strike, especially if their capabilities for a tactical strike are limited or absent (or crippled by the first country's attack).

This is very much a real-world worry, btw. Only an year of two ago the risk of this scenario was discussed for an India-Pakistan war, after Pakistan increased its tactical nuke capabilities if I remember correctly. In fact, given the stated policies of the two countries and their respective capabilities, it is what would likely happen if no-one is bluffing. (In detail: India overwhelms Pakistani conventional forces and attempts a quick, deep invasion of Pakistan to disable nuclear installations and/or force surrender -> Pakistan destroys the invading force or cripples the logistic chain with tactical nukes -> India uses its own nukes, not ruling out targeting major cities.)

Of course the complete elimination of larger "strategic" arsenals, like you propose, would ease this worry somewhat. However, in a world where military technology levels are not equal everywhere, it may be impossible to convince the less-advanced military to give up what they think as their only deterrence. 

I generally agree with this thought train of concern. That said, if the end state equilibrium is large states have counterforce arsenals and only small states have multi-megaton weapons, then I think that equilibrium is safer in terms of expected death because the odds of nuclear winter are so much lower.

There will be risk adaptation either way. The risk of nuclear war may go up contingent on their being a war, but the risk of war may go down because there are lower odds of being able to keep war purely conventional. I think that makes assessing the net risk pretty hard, but I doubt you'd argue for turning every nuke into a civilization ender to improve everyone's incentives: at some point it just isn't credible that you will use the weapons and this reduces their detergent effect. There is an equilibrium that minimizes total risk across sources of escalation, accidents, etc. and I'm trying to spark convo toward figuring out what that equilibrium is. I think as tech changes, the best equilibrium is likely to change, and it is unlikely to be the same arms control as decades ago, but I may be wrong about the best direction of change.

The difference between a TSAR bomb (or its modern equivalent) and the lowest settings of a mini-nuke is still an order of magnitude larger than the difference between the conventional “mother of all bombs” and a hand grenade. The Beirut explosion last year was the size of the hand grenade blast in this analogy

I didn't quite understand the last sentence here. Are you saying A) that the Beirut explosion was about the same size as a mini-nuke blast would be, or that B) MOAB : hand grenade :: TSAR bomb : Beirut explosion? (In which case the Beirut explosion would be larger than a mini-nuke explosion, if your claim about relative differences in the first sentence is correct.)

In other words, I take the first part of what you wrote to be saying that (TSAR bomb / mini-nuke) > (MOAB / grenade), but then I'm not sure whether the second part is saying that A) (TSAR bomb / Beirut explosion) = (TSAR bomb / mini-nuke), or B) (TSAR bomb / Beirut explosion) = (MOAB / grenade).

Is one of either A or B correct? (Or did you mean something else entirely?)

I meant A. The Beirut explosion was about the yield of a mini-nuke.

Does this post endorse self-interested unilateral action or a multilateral arms control treaty?

I could imagine unilateral action to reduce risk here being good, but not in violation of current arms control agreements. To do that without breaking any current agreements, that means replacing lots of warheads with lower yields or dial yields, and probably getting more conventional long-range precision weapons. Trying to replace some sub-launhed missiles with low yield warheads was a step in that direction.

There's a trade-off between holding leverage to negotiate, and just directly moving to a better equilibrium, but if you are the U.S., the strategy shift may just increase your negotiating power since the weapons are more useable.

The main thing I want to advocate is for people to debate these ideas to see if there is a potentially better equilibrium to aim for, and to chart a path to it. I don't want people to blindly assume I am right.

Thanks for this thought-provoking post. I found the discussion of how political warfare may have influenced nuclear weapons activism particularly interesting.

Since large yield weapons can loft dust straight to the stratosphere, they don’t even have to produce firestorms to start contributing to nuclear winter: once you get particles that block sunlight to an altitude that heating by the sun can keep them lofted, you’ll block sunlight a very long time and start harming crop yields.

I think it's true that this could "contribute" to nuclear winter, but I don't think I've seen this mentioned as a substantial concern in the nuclear winter papers I've read. E.g., I don't think I've seen any papers suggest that nuclear winter could occur solely due to that effect, without there being any firestorms, or that that effect could make the climate impacts 20% worse than would occur with firestorms alone. Do you have any citations on hand for this claim? 

Some of the original papers on nuclear winter reference this effect, e.g. in the abstract here about high yield surface burst weapons (e.g. I think this would include the sort that would have been targeted at silos by the USSR).

A common problem with some modern papers is that they just take soot/dust amounts from these prior papers without adjusting for arsenal changes or changes in fire modeling.

Any proposal that brings us closer to hundred million dollars nuke will probably be bad for preventing nuclear incident of the mushroom cloud kind. I think your proposal of reducing the size and yield of nuclear weapons also reduces its cost. 

A country like North Korea is unlikely to strike first with nuclear weapons precisely for reasons you mentioned. But possession of them is a significant deterrent against invasion by a conventional military force or insurrection aided by an outside military force, such as ones happened in Iraq and Libya. Any government concerned by a threat of such invasion or insurrection would love to emulate North Korean example now that it is clear that any other safety guarantees are insufficient. Any major actor that actively pursues the strategy of making its nuclear weapons smaller and cheaper must take care that they are not so small and cheap, that any government with a hundred million dollar budget can afford one. 

Precision isn't cheap. Low yield accurate weapons will often be harder to make than large yield inaccurate weapons. A rich country might descend the cost curve in production, but as long the U.S. stays in an umbrella deterrence paradigm that doesn't decrease costs for anyone else, because we don't export nukes.

This also increases the cost for rogue states to defend their arsenals (because they are small, don't have a lot of area to hide stuff, etc.), which may discourage them from gaining them in the first place.

USA is not the only nuclear power. Other nuclear powers which begin to descend their cost curves might be tempted to export the cheaper tech, especially if the expensive precision components are not wanted by the buyer. See the nuclear tech connection between Pakistan and North Korea, but make the cost of technology an order of magnitude smaller. 

Limiting the spread of cheap nuclear weapons will never become as impossible as banning firearms, but it will become harder.

This is what the non-proliferation treaty is for. Smaller countries could already do this if they want, as they aren't treaty limited in terms of the number of weapons they make, but getting themselves down the cost curve wouldn't make export profitable or desirable because they have to eat the cost of going down the cost curve in the first place and no one that would only buy cheap nukes is going to compensate them for this. Depending on how much data North Korea got from prior tests, they might still require a lot more testing, and they certainly require a lot more nuclear material which they can't get cheaply. Burning more of their economy to get down the cost curve isn't going to enable them to export profitably, and if they even started it could be the end of the regime (due to overmatch by U.S. + Korea + Japan). The "profit" they get from nukes is in terms of regime security and negotiating power... they aren't going to throw those in the trash. They might send scientists, but they aren't going to give away free nukes, or no one is going to let planes or ships leave their country without inspection for years. The Cuban missile crisis was scary for the U.S. and USSR, but a small state making this sort of move against the interest of superpowers is far more likely to invite an extreme response (IMO).