Why I think nuclear war triggered by Russian tactical nukes in Ukraine is unlikely

post by Dave Orr (dave-orr) · 2022-10-11T18:30:08.110Z · LW · GW · 7 comments

Contents

  Initial nuclear strike
  Strategic considerations
  Estimate
None
7 comments

This is a response to Max's post Why I think there's a one-in-six chance of an imminent global nuclear war [LW · GW].

Max's thesis is that Putin is likely to use nuclear weapons if the war in Ukraine goes badly for Russia, that the west will retaliate, and both sides will continue to escalate until we have a full nuclear exchange. In particular, he estimates a 30% chance that Ukraine is nuked, an 80% chance of a significant conventional retaliation, and a 70% chance that things further escalate from there all the way to KABOOM.

I think the first and last terms in that equation are much too high. I think the center term is perhaps slightly too low (it's hard to believe that nuclear weapon use will be tolerated because it sets up terrible incentives for future nuclear weapon use), but I won't explore that here in depth.

Initial nuclear strike

An initial use of tactical nuclear weapons is unlikely because:

1. There is no military purpose served by nuclear weapon use
2. There are very large downsides to using nuclear weapons, including the scenario Max outlines
3. Because of points 1 and 2, such a use will not win Putin political points at home

The war against Ukraine can't really be won by bigger explosions. The Ukrainian military is broadly dispersed across a huge front, operating on both sides of the line. Similarly their equipment is not stored in a small number of supply depots. 

Infrastructure and logistical networks can be disrupted with conventional explosives, and both Ukraine and Russia are attacking enemy logistics (Ukraine with rather more success than Russia). But the Russian ineffectiveness is due to missiles getting shot down and poor targeting, neither of which is helped by nukes.

And of course there are significant downsides to using nukes, which is that it risks a serious escalation with the west, one that could endanger Russia's future as a country and Putin's leadership and life, as well as losing support domestically, allowing Putin's political rivals to argue (perhaps correctly!) that he is a madman taking irrational and highly risky actions, and needs to be stopped.

There is exactly the case that he is a madman to worry about. I think this is unlikely; perhaps he has been corrupted by power, or is succumbing to dementia, but absent those Putin has showed himself to be a careful strategic actor in the past.

Overall I put the likelihood of an initial tactical nuclear strike by Putin to be south of 5%. Most of the probability mass is the possibility that Putin is mentally unstable, or that there's a series of mistakes / bad judgments that lead to a very ill-considered decision.

Strategic considerations

I think my fundamental disagreement with Max on an apocalyptic cycle of escalation is this: Putin and his advisors don't want a nuclear war (that's terrible for Russian and Putin personally), and are very familiar with game theory, since that's the framework that's governed strategic nuclear weapon use for many decades. Similarly, nobody in the west wants a nuclear war either. The logic of nuclear standoffs is such that there are strong incentives to go to the brink, but not to go over, so I think in general tense situations feel scarier than they actually are. And we should expect lots of threats and posturing, because signaling that you are willing to go over the edge gives you negotiating leverage.

Therefore the most likely analysis is that Putin is essentially bluffing -- his nuclear threats are not credible. 

(To be clear, I think this dynamic is awful, because it puts us in a position where mistakes are much more likely to have terrible consequences; therefore escalatory situations do make nuclear war more likely. However 80% is a huge overestimate.)

We've seen brinksmanship in the past, and it hasn't resulted in nuclear war, though in the Cuban missile crisis it came close. But note the dynamic: a nuclear weapon was almost used due to a mistake, not due to a decision by leadership. The Cuban crisis was much scarier because the US felt that this was an existential threat and were willing to go all the way; nothing in Ukraine is like that, at least for now.

Of course history is not necessarily a clear guide, due to the anthropics problem that if nuclear war had happened we wouldn't be here to talk about it. Nonetheless, while there were many close calls, it is still the case that at no point did leadership decide to start a nuclear war, and really only in the Cuban missile crisis was it remotely plausible.

I think that almost all of the probability mass of a nuclear war is some kind of accident. After all, the entire logic of mutually assured destruction is to ensure that nobody has an incentive to start a nuclear war.

How much more likely is some kind of accident in a time of high tensions and active conflict, such as a NATO retaliation for some kind of Russian atrocity? Many times more likely but over a very low baseline. Call it 5% -- maybe 1% chance that such an accident will happen over the rest of the conflict, and the rest is just uncertainty about how rational all the actors are.

Estimate

Using Max's framework, my estimate is 5% x 90% x 5% = about a quarter of a percent.

This is far enough below e.g. prediction market estimates that I think it's probably a bit higher, but overall I believe that the game theoretical considerations (nobody wants nuke war) and the tactical considerations (nothing really is served by using tactical nukes) both point towards risk being much lower than outlined elsewhere.

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