(Below written by Peter in collaboration with Josh.)

It sounds like I have a somewhat different view of Knightian uncertainty, which is fine—I’m not sure that it substantially affects what we’re trying to accomplish. I’ll simply say that, to the extent that Knight saw uncertainty as signifying the absence of “statistics of past experience,” nuclear war strikes me as pretty close to a definitional example. I think we make the forecasting challenge easier by breaking the problem into pieces, moving us closer to risk. That’s one reason I wanted to add conventional conflict between NATO and Russia as an explicit condition: NATO has a long history of confronting Russia and, by and large, managed to avoid direct combat.

By contrast, the extremely limited history of nuclear war does not enable us to validate any particular model of the risk. I fear that the assumptions behind the models you cite may not work out well in practice and would like to see how they perform in a variety of as-similar-as-possible real world forecasts. That said, I am open to these being useful ways to model the risk. Are you aware of attempts to validate these types of methods as applied to forecasting rare events?

On the ignorance prior: 

I agree that not all complex, debatable issues imply probabilities close to 50-50. However, your forecast will be sensitive to how you define the universe of "possible outcomes" that you see as roughly equally likely from an ignorance prior. Why not define the possible outcomes as: one-off accident, containment on one battlefield in Ukraine, containment in one region in Ukraine, containment in Ukraine, containment in Ukraine and immediately surrounding countries, etc.? Defining the ignorance prior universe in this way could stack the deck in favor of containment and lead to a very low probability of large-scale nuclear war. How can we adjudicate what a naive, unbiased description of the universe of outcomes would be?

As I noted, my view of the landscape is different: it seems to me that there is a strong chance of uncontrollable escalation if there is direct nuclear war between Russia and NATO. I agree that neither side wants to fight a nuclear war—if they did, we’d have had one already!— but neither side wants its weapons destroyed on the ground either. That creates a strong incentive to launch first, especially if one believes the other side is preparing to attack. In fact, even absent that condition, launching first is rational if you believe it is possible to “win” a nuclear war, in which case you want to pursue a damage-limitation strategy. If you believe there is a meaningful difference between 50 million dead and 100 million dead, then it makes sense to reduce casualties by (a) taking out as many of the enemy’s weapons as possible; (b) employing missile defenses to reduce the impact of whatever retaliatory strike the enemy manages; and (c) building up civil defenses (fallout shelters etc.) such that more people survive whatever warheads survive (a) and (b). In a sense “the logic of nuclear war” is oxymoronic because a prisoner’s dilemma-type dynamic governs the situation such that, even though cooperation (no war) is the best outcome, both sides are driven to defect (war). By taking actions that seem to be in our self-interest we ensure what we might euphemistically call a suboptimal outcome. When I talk about “strategic stability,” I am referring to a dynamic where the incentives to launch first or to launch-on-warning have been reduced, such that choosing cooperation makes more sense. New START (and START before it) attempts to boost strategic stability by establishing nuclear parity (at least with respect to strategic weapons). But its influence has been undercut by other developments that are de-stabilizing. 

Thank you again for the thoughtful comments, and I’m happy to engage further if that would be clarifying or helpful to future forecasting efforts.

Thanks for the reply and the thoughtful analysis, Misha and Nuño, and please accept our apologies for the delayed response. The below was written by Peter in collaboration with Josh.

First, regarding the Rodriguez estimate, I take your point about the geometric mean rather than arithmetic mean and that would move my probability of risk of nuclear war down a bit — thanks for pointing that out. To be honest, I had not dug into the details of the Rodriguez estimate and was attempting to remove your downward adjustment from it due to "new de-escalation methods" since I was not convinced by that point. To give a better independent estimate on this I'd need to dig into the original analysis and do some further thinking of my own. I'm curious: How much of an adjustment were you making based on the "new de-escalation methods" point?

Regarding some of the other points:

• On "informed and unbiased actors": I agree that if someone were following Rob Wiblin's triggers, they'd have a much higher probability of escape. However, I find the construction of the precise forecasting question somewhat confusing and, from context, had been interpreting it to mean that you were considering the probability that informed and unbiased actors would be able to escape after Russia/NATO nuclear warfare had begun but before London had been hit, which made me pessimistic because that seems like a fairly late trigger for escape. However, it seems that this was not your intention. If you're assuming something closer to Wiblin's triggers before Russia/NATO nuclear warfare begins, I'd expect greater chance of escape like you do. I would still have questions about how able/willing such people would be to potentially stay out of London for months at a time (as may be implied by some of Wiblin's triggers) and what fraction of readers would truly follow that protocol, though. As you say, perhaps it makes most sense for people to judge this for themselves, but describing the expected behavior in more detail may help craft a better forecasting question.
• On reasons for optimism from "post-Soviet developments": I am curious what, besides the New START extension, you may be thinking of getting others' views on. From my perspective, the New START extension was the bare minimum needed to maintain strategic predictability/transparency. It is important, but (and I say this as someone who worked closely on Senate approval of the treaty) it did not fundamentally change the nuclear balance or dramatically improve stability beyond the original START. Yes, it cut the number of deployed strategic warheads, which is significant, but 1,550 on each side is still plenty to end civilization as we know it (even if employed against only counterforce targets). The key benefit to New START was that it updated the verification provisions of the original START treaty, which was signed before the dissolution of the Soviet Union, so I question whether it should be considered a "post-Soviet development" for the purposes of adjusting forecasts relative to that era. START (and its verification provisions) had been allowed to lapse in December 2009, so the ratification of New START was crucial, but the value of its extension needs to be considered against the host of negative developments that I briefly alluded to in my response.

Peter says: No, I live in Washington, DC a few blocks from the White House, and I’m not suggesting evacuation at the moment because I think conventional conflict would precede nuclear conflict. But if we start trading bullets with Russian forces, odds of nuclear weapons use goes up sharply. And, yes, I do believe risk is higher in Europe than in the United States. But for the moment, I’d happily attend a conference in London.