Why I think there's a one-in-six chance of an imminent global nuclear war

Last spring, I predicted that once loss of occupied territory loomed, he would annex what he controlled and start talking about nuclear defense of Russia's new borders – and here we are. 

Citation/link please? "Trust, but verify."

I view it as highly unlikely (<10%) that Putin would accept "Vietnam" without first going nuclear, because it would almost certainly result in him being overthrown and jailed or killed.

This seems overconfident to me. So many people made confident predictions about what Putin would or wouldn't do (or Trump, or Obama, or Xi for that matter) and were wrong. It's hard to predict world leader behavior even in cases with somewhat of a precedent, which this is not. Example: Early in this war I thought "Belarus will almost certainly join the war sooner or later, because Putin can have Lukashenko assassinated, along with loads of higher-ups in the government, if he wants." Welp, I was wrong. Don't know why yet. Similarly I think that if Putin were to accept a "vietnam" he'd probably still remain in power. You might think that there'd be a revolution, and there totally might, but I don't know how you can be almost certain.

 

On the other hand, I also view it as highly unlikely (<10%) that the West would accept a "Kosovo" scenario where Russia is granted a peace deal where it keeps everything it's annexed, because if the powers that be in the West were that appeasement-minded, they would presumable have opted for a "Cuba" scenario in 2021 by acquiescing to Russia's demand that Ukraine never join NATO. 

I can't square my model of Russia with the idea that Russia genuinely invaded Ukraine because they were afraid of NATO expansion. Pre-invasion, Ukraine was unlikely to join NATO and NATO itself was likely only to become smaller and less significant.

Up until the invasion NATO was increasingly perceived as a relic - an organization that lost the reason for its creation. It was hard for me to even imagine chain of events would revitalize NATO. But then Russia sends columns of tanks straight to the capital of the largest country in Europe and yeah, I guess that would do it. Give every country near Russia's the strongest possible reason and urgency to join NATO and increase their defense budgets.

That result seems likely even if Russia had conquered the entire country in 3 days. In fact I believe Putin felt comfortable invading Ukraine, knowing this would massively boost NATO, because he had absolutely no genuine concerns about NATO invading RUSSIA itself.

Regarding your Twitter comment about Musk's proposals:

Here's why I think there's now a one-in-six chance of an imminent global #NuclearWar, and why I appreciate @elonmusk and others urging de-escalation, which is IMHO in the national security interest of all nations

The real issue with backing down from nuclear threats is what happens when you back down.

Let's say we force Ukraine to allow Putin to keep the annexed territory because of nuclear weapons. This gives him, every Russian and every dictator around the world a clear message: nuclear weapons are the winning strategy.

It would make Putin and all warmongers like Prigozhin or Kadyrov look like geniuses. They stood against the whole world and won! Everyone inside Russia who was opposing the use of nuclear weapons would have to admit that it worked. So they need to use this trick more! It costs nothing. You just need to be a true believer in the greatness and ruthlessness of mother Russia. 

Hitler also looked like genius of strategy after annexation of Austria and Sudetenland. From German perspective in Summer of 1939 he obviously knew what he was doing and should be trusted.

So, how far are you willing to back down?

Is Poland valuable enough for you? Poland was not valuable enough for UK and France in 1939 despite them pledging "all support in their power". They got war anyway gaining only a bit of time.

And to illustrate that Russia's imperial goals are not limited to Ukraine you have to remember that Russia's demands in the first place were not limited to Ukraine.

From Article 4 of the draft of the "Agreement on measures to ensure the security of The Russian Federation and member States of the North Atlantic Treaty Organization":

The Russian Federation and all the Parties that were member States of the North Atlantic Treaty Organization as of 27 May 1997, respectively, shall not deploy military forces and weaponry on the territory of any of the other States in Europe in addition to the forces stationed on that territory as of 27 May 1997.

To Poles and Balts this was unacceptable under any circumstances. We would never sign it.

From my perspective if nuclear threat wins Putin anything significant then Poland will need to try to obtain strategic nuclear weapons as soon as possible and at any cost. We lost every fifth person after 1939 because we trusted foreign powers when we should not have. Russian soldiers did not leave Poland until 1993 and we do not want them back.

The way out of nuclear escalation is convincing Russia that they have nothing to gain and everything to lose after using nuclear weapons. They need to back down from their mistake.

We’re still only a few hours post the bridge attack, but worth noting that when given the opportunity to massively escalate with a ‘red line’ being crossed, the Russian government are talking about how this was a terrorist attack and traffic will be up and running within hours (playing down the impact). This suggests to me they’re extremely unwilling to move up to tactical nuclear weapons right now.

Thank you for this post, Max.

My background here:

• I've watched the Ukraine war very closely since it started.
• I'm not at all familiar with nuclear risk estimations.

Summary: I wouldn't give 70% for WW3/KABOOM from conventional NATO retaliation. I would give that 2-5% in this moment (I spent little time thinking about the precise number).

Motivation: I think conventional responses from NATO will cause Russia to generally back down. I think Putin wants to use the threat of nukes, not actually use them.

Even when cornered yet further, I expect Putin to assess that firing off nukes will make his situation even worse. Nuclear conflict would be an immense direct threat against himself and Russia, and the threat of nuclear conflict also increases the risk of people on the inside targeting him (because they don't want to die). Authoritarians respect force. A NATO response would be a show of force.

Putin has told the Russian public in the past that Russia couldn't win against NATO directly. Losing against NATO actually gives him a more palatable excuse: NATO is too powerful. Losing against Ukraine though, their little sibling, would be very humiliating. Losing in a contest of strength against someone supposedly weaker is almost unacceptable to authoritarians.

I think the most likely outcome is that Putin is deterred from firing a tactical nuke. And if he does fire one, NATO will respond conventionally (such as taking out the Black sea fleet), and this will cause Russia to back down in some manner.

You think it is likely/possible that a nuclear war kills almost everyone in the US and Europe. Since you estimate the chance of this happening to 1 in 6, are you moving to South America or Australia for a year or two? 

I strongly disagree with this post but I think it's well written conditional on the views of the author, so now I'm divided between whether I should upvote or downvote it.

If only we had agreement karma at the post level, not just the comment level...

I view it as highly unlikely (<10%) that Putin would accept "Vietnam" without first going nuclear, because it would almost certainly result in him being overthrown and jailed or killed.

Why are you saying "almost certain" instead of giving a probability? 

Many people who have power in Russia have power because they were over decades loyal to Putin. They are likely going to lose power if Putin would be overthrown.

I recently heard from a Ukrainian that part of the demands of the EU for what Ukraine would need to do in terms of minority protection of Russian speakers is pro-Russian propaganda. The Ukrainians pretend that Elon Musk that spends gifted them ~80 million worth of StarLink is anti-Ukrainian. 

One interesting aspect of the reaction to Musk's proposal in German media, is the absence of citing anyone from the German government. As winter progresses the pain from lack of Russian gas will rise in Europe, moving troops in Winter in the Ukraine is harder. That shifts the politics into making a peace deal more likely.

It's quite clear why it's worth suffering when Russland attacks parts of Ukraine that don't want to be Russian. On the other hand, the case for why European should suffer to support Ukraine to retake Crimea when Crimeans don't want to be part of Ukraine is much harder.

This months leak that they admonished an Ukrainian operation for assassinating a Russian citizen in Moscow. That suggests that even the US is not willing to let the Ukrainians just do whatever they want.

On the other hand, I also view it as highly unlikely (<10%) that the West would accept a "Kosovo" scenario where Russia is granted a peace deal where it keeps everything it's annexed, because if the powers that be in the West were that appeasement-minded, they would presumable have opted for a "Cuba" scenario in 2021 by acquiescing to Russia's demand that Ukraine never join NATO.

Russia asked for more than just NATO expansion. They also asked for decentralization of power to protect the Russian minority. It would be easy for the West to agree not to expand NATO but not to get Ukraine to provide decentralization. 

Russia also wanted to withdraw of US troops from the baltic states which is also a nonstarter. 

>I view it as highly unlikely (<10%) that Putin would accept "Vietnam" without first going nuclear, because it would almost certainly result in him being overthrown and jailed or killed.

Not obvious to me that this is true. If it was, I would have expected more escalation/effort from Russia already by this point.

I view it as highly unlikely (<10%) that Putin would accept "Vietnam" without first going nuclear, because it would almost certainly result in him being overthrown and jailed or killed.

Much of the analysis hinges on this, so I think it needs to thought through more deeply.  I would argue that the odds of Putin "being overthrown and jailed or killed" are higher if he gives the order to use nukes, than if he accepts "Vietnam". 

The NATO response to nukes would be catastrophic. Any remaining support from China/India would disappear. Further, the war is becoming less popular within Russia.  Russia escalating to nukes and the possibility of all out war weakens Putins position both internally and externally.

My guess is that withdrawal would also be met with a certain degree of "relief" from a significant portion of the Russian population.

There is a long history of Goliaths accepting and surviving embarrassing defeats. The level of control Putin exerts internally makes it more likely he would survive and spin "Vietnam" into something not too embarrassing for him personally, instead pinning the blame on an incompetent and corrupt military. Much of the Russian news media is already taking this approach.

You haven't factored in the possibility Putin gets deposed by forces inside Russia who might be worried about a nuclear war and conditional on use of tactical nukes, intuitively that seems likely enough to materially lower p(kaboom).

EDIT: Removed "nuclear arsenal not working because Russia didn't bother to maintain them" as I don't find that especially likely on reflection.

An aside on the level of destruction we can anticipate: Nuclear war is not an existential threat. ^[1]Fears of nuclear winter, which may be an existential threat^[2],  are likely overblown as the well known soot production model is based on poor research. Soot production in the high atmosphere is like 1-2 orders of magnitude below what the original studies suggested.

Strategy suggests that military targets, ports and sites of industrial production would serve as far better targets than highly populated regions or areas with large amount of flammable material which could create soot. Some important military bases, like missile silos, are hardened against nuclear weapons and would require two consecutive strikes to confidently take down. Which reduces the number of war heads available for non-military targets.

Nuclear warheads are shrinking in number, and are quite difficult to maintain so there are fewer usable warheads than you might expect. Moreover, the most famours soot production studies make a wide variety of errors, which later simulations didn't bear out. The amount of suit produced by nuclear war is much lower due to strategic reasons, the difference between usable nuclear weapons and ones which could theoretically be used, an incorrect scaling law for the burn area-nuclear yield relationship, improperly accounting for oxygen starvation and the low likelihood of foot reaching the upper troposphere which is crucial to the nuclear winter mechanism. 

That said, there hasn't been enough research on the topic and we can't be too sure of what would happen if there was all out nuclear war. Maybe some exotic effects would occur and instead of hundreds of millions of deaths it would be billions. Or perhaps the damage to logistic chains and global norms would be enough to cripple our civilization. But the soot production thing? Probably not going to kill us all.

1. ^{^}

   They're by Bean, a commentator on ACX and datasecretslox. The thread he started on nuclear winter has some good discussion on the topic.

2. ^{^}

   Bostrom, "Existential Risks" v.3, 1.1.1

 My estimate is quite high (80%) that NATO's response will be forceful enough to include a non-nuclear military strike against Russia, because key NATO leaders have already made strongly worded statements to this effect.

Here, my estimate is much lower (about 25%). Talk is cheap, so strongly worded statements in itself are only weak evidence for future intentions if carrying out those threats poses threats on this level (and I do think it to be likely that the relevant players in NATO are aware of the level of risk). 

I notice I am most confused on the Expansion -> KABOOM 70%.

I have been in a model that Expansion would be limited within Ukraine, annexed territories including Crimea included. Therefore I have (completely subjectively) estimated Expansion -> KABOOM to 1/1000 or lower?

It seems to me that as Russia has moved its nuclear weapon submarines from Crimea to Russian mainland port, that this could be a shared model also in Russia.

MaxTegmark:

1. Why do you see Expansion to include attacks on Russian mainland?
2. If no attacks on Russian mainland, does this alter your previous estimation of 70% of Expansion -> KABOOM?

One question in the back of my mind regarding the likelihoods here about Russia's demonstrated maintenance performance in its military. Yes, strategic systems will have to have both a higher priority and, one might think, higher quality professionals performing all the tasks and management. But is that really a safe assumption?

Is there really any reason to believe that the corruption that has hamstrung a the Russian military in general is not also pervasive in strategic weapons? Seems to me that would be driven by the underlying culture of autocratic regimes which seem poorly suited to maintaining high quality and honest assessments of actual state.

I view it as highly unlikely (<10%) that Putin would accept "Vietnam" without first going nuclear, because it would almost certainly result in him being overthrown and jailed or killed.

Two points:

• This is why Biden is looking for an "offramp" for Putin. Is this included in your "<10%" figure?
• If Putin wants to avoid being jailed or killed, a nuclear attack that by your own logic leads to a 56% chance of WWIII seems worse for him. Would ordering his military to escalate in this way be more likely to result in compliance, or a coup?

I would like to see stronger argumentation for that 10% figure, explicitly factoring in the likelihood of an "offramp," the threat of a coup if Putin attempts to go nuclear, and justifying why Putin couldn't halt the invasion while still hanging onto power.

Who'd be doing the jailing? Whoever replaces him in Russia? Whatever powers in Russia are likely to effect Putin's replacement can't accomplish this if Putin ignites WWIII, and so they are incentivized to offer him an offramp into peaceful retirement, or even simply an end to the war with Putin still in power.

My estimate is quite high (80%) that NATO's response will be forceful enough to include a non-nuclear military strike against Russia, because key NATO leaders have already made strongly worded statements to this effect. My most likely (70%) scenario after that is Russian counterstrikes followed by rapid escalation via retaliatory actions from both sides

Obama said that if Assad used chemical weapons in Syria, that would be a "red line" that would lead to US military involvement. That's a strongly worded statement that didn't happen. If we didn't invade Syria, a country that doesn't have nuclear weapons, then why do you think it's so likely that we'd take a military action leading to such a high probability of WWIII? Ukraine isn't in NATO.

You frame your 70% probability of escalation from expansion to to WWIII as having two components:

• Rapid escalation
• Global freakout causes de-escalation

I think you are lacking a third option:

• Delay tactics. The US and Russia look for the minimal "retaliations" that appease hawks while avoiding progression toward WWIII. More sanctions, cyberattacks, proxy fighting, weapons in Ukraine, spying, providing incentives for Russians to flee the country.

My 70% estimate factors in that the long history of nuclear near misses has convinced me that both the US and Russia are much less competent in de-escalation than in escalation. 

If anything, the list should make you feel relaxed. Consider the pattern:

Peace -> tension -> nuclear brinksmanship -> nuclear war

At any step, successful de-escalation brings you to an earlier one.

Items on the list you cite are pre-selected for being escalated. So far, only in WWII has a nuclear attack actually occurred. And this was in the unique historical context of the USA being the only country to have nukes.

In every other case, de-escalation successfully moved the conflict toward a lower level, and ultimately back to peace.

The more items on the list of nuclear near-misses, the more convinced you should be that de-escalation works, no matter how close we get to nuclear war.

You should, however, increase your likelihood of nuclear war the more escalated we become in the current situation.

Two thoughts:

1. I'm not at all well-calibrated enough to evaluate your probabilities. They feel sensible to me, but good forecasters seem to give much lower probabilities, so I think they might be right. A naive alternative would be to just evenly spread it out by the number of options, so maybe 1/6 for transitioning to kaboom, 1/5 for transitioning to expansion, and 1/5 for transitioning to KABOOM, leading to 0.7% probability.
2. On the other hand, there's probably a ton of correlations in the probabilities for each step. If the nations involved are more inclined to escalations, then all of the steps become more likely. The sort of probabilities I gave above become terribly inaccurate in reductionistic models if the correlations are not correctly modelled. So I would wonder what effects the correlations have; presumably they would raise the probability a lot up from 0.7%.

Overall I would like to see more evaluation of the risk of imminent global nuclear war.

Perhaps a nuclear war today would reduce the possibility of human extinction within this century. It appears that AGI is close, without substantial progress in AI Safety. A nuclear war, would, I believe cause a major slowdown in AI progress, increasing the probability of getting an aligned AI at the end. 

I think this modeling assumes Russia can escalate conventionally and that the conventional NATO response would be perceived as escalatory by Russia even if it destroyed their army. Russia can't escalate conventionally: they have run out of tanks and men.

Ukraine is already doing a great job of destroying Russia's army with NATO weapons, and Russia hasn't used nukes to stop it. In the aftermath of usage, increasing the rate of that destruction is just more of the same. Even if Russia would like to escalate more, they need to actually stop the army from liberating Ukraine, and nukes are not good at that. Jumping up the ladder to attacking NATO territory is unlikely, especially if NATO views edge cases as reasonable self-defense not worth starting something over  (e.g. firing on a radar targeting a Russian airplane from Poland). The threat to nuke NATO isn't credible, and Russia has downplayed its threats as Ukraine succeeds more, saying things like it doesn't know yet where the border it is defending is.

I think there are a great many actions NATO could take that would hurt Russia to the point of quick victory and are unlikely to be worth war, without loosing essential credibility that would force Russia into nuclear escalation.

• Smashing stuff up in Syria
• Sending Ukraine even better weapons: GMLRS are nice and all, but we've not broken out the CBU-97's for them, or clustered artillery, or the fun new warhead for the HIMARS.
• Bombing Russian ground forces in Ukraine semicovertly
• Sending MBTs to Ukraine
• Giving Ukraine cruise missiles
• Sending in ground reinforcements, with very clear "we are not going further then the deliniated boundary" signalling

While these all go beyond what has happened so far, they aren't the kind of provocation that invites more nukes, and Russia can't really use nuclear weapons to stop them because nuclear weapons are not good at stopping these things. There's a reason we don't have tactical nukes in the US, and that's because conventional smart weapons can do the same job better.

Ultimately I think Russia is attempting to use the nuclear threat because they can't use nukes to get what they want, and I don't think they can threaten to stop Ukraine and assistence credibly.

If Putin uses a nuke in Ukraine, NATO will respond by decimating the Russian invasion force in Ukraine (probably excluding Crimea) with conventional air power. That should be seen as de-escalating, since 1) only a nuclear response can really be an escalation to a nuclear provocation, and 2) Russia’s pre-war border is not violated. It will allow the Ukrainians to take back their land to pre-war boundaries (“Vietnam”). Putin knows this (it’s probably been “explained” to him by Western leaders), so the likelihood he would choose that path is small. Even if he does, I think the likelihood he would opt for further nuclear escalation with a first strike beyond Ukraine is much smaller than you claim. The West would never opt for a nuclear first strike, because of their clear conventional advantage.

I think we need to view it from Putin's angle. What will keep him in office (because if he loses office, he might very well lose his life, certainly his freedom)? 
One possibility is that by dropping a small nuke, that hopefully will only be met with a conventional weapons response, Russia will then be isolated from the world, and Putin imagines he can survive in power, 'forever' raging against the West, much like North Korea, or Iran to some extent.
Other options are that Russians themselves remove Putin before he can drop a bomb, or that somehow he negotiates a withdrawal, but I don't see other Russians allowing that, but maybe there's more resistance within Russia than I realise. 
Scary times indeed!

What % are the 70% that Ukraine doesn't get nuked composed of?

I think Russia has already suffered quite a lot of embarrassment and hasn't nuked yet. According to your model, why not?

Of the 4 NS pipelines ( 2 NS1, 2 NS2), 3 are off line, one is still operational, hence I think we shouldn’t rule out the scenario where gas flow from Russia to Germany would resume

I will return with thoughts on adjusting Max's assigned probabilities, but prefer to start with two more 'qualitative' arguments. First, I am not persuaded by statements and events to date that Russia is experiencing severe setbacks in the last 1-2 weeks. I noted a Ukrainian boast - hard to credit it with a milder term - that it has recovered 900 square kilometers of Russian-annexed territory. If true, that amounts to roughly 18 by 18 miles, a rather insignificant amount of steppe. Eventual negotiations can be expected to haggle over much larger chunks of territory, and in the half-forgotten lexicon of European great power competition, such adjustments do not throw possible outcomes into either the 'Vietnam' or the 'Kosovo' bin - more like Alsace-Lorraine.

Second, it is very important to look closely at the actual correlation of forces. Even before it crossed into Ukraine, Russian military capability was inferior to NATO's, and Russia's GDP and demographics promise no chance of significantly altering that imbalance. The only exceptions are in the near parity of nuclear forces, and in minor advantages in the numbers of certain conventional ground combat systems such as field artillery that do not translate into significant offensive military power. Russia does not dare (and has not, since February 2022, dared) to provoke direct war with NATO. Hence, by the way, their very real concern since the mid-90s with NATO eastern expansion.

In that context, Putin's recent references to nuclear weapons are simply restatements of Russia's national strategic doctrine since before he came to power in 1999 - and both represent weakness, not power. Russia can, quite demonstrably, barely prosecute one regional war against a third-rate contiguous neighbor. The prospect of direct NATO intervention - a prospect heightened logically not by Ukrainian success but by Ukrainian weakness and exhaustion well-concealed by Western media and leaders - is very frightening to Putin. Hence what I call the 'Blazing Saddles' ploy of holding a gun to his own head. Putin cannot fight NATO conventionally, and cannot prevail in a nuclear war either. He can only hope to engender the response that Cleavon Little got in the movie: "Don't move, men - he might be crazy enough to do it!" Hence, I reject the notion that Putin would see any advantage in any form of nuclear weapons use in Ukraine. As another commenter noted, talk is cheap. Putin's "threats" are no worse than those of Biden and other senior NATO leaders and spokesmen.

The unspoken rule since 1949 has been that nuclear powers do not engage in direct combat with one another, proxy wars, insurgency/counterinsugency, bluffs and bluster notwithstanding. That rule is an important firebreak holding nuclear war at bay, needs to be maintained, and in my estimation will be.

The outcome I consider most likely - unless the US and NATO continue to prevent it - is a negotiated solution that will involve considerable compromise on both sides.

This analysis  assumes that if Russia uses nuclear weapons:

1. Military response from NATO is the worst outcome and largest deterrent, and 
2. China, India and the rest of the world don't have interest in the nuclear issue and their relations with Russia would not change.

For Russian nuclear brinkmanship to be effective, atomic weapon use would need an outcome without complete isolation and regime collapse after a military win.  Becoming another North Korea would be huge  loss for Russia and put the Putin's regime in danger.  

Putin's regime wants to frame the war as NATO-Russia military conflict. Refusing to play the game and communicating that the response for Kaboom would be maximum pain and no gain is more likely [1]

WH is  working trough China and India to communicate that using nuclear weapons would result a crippling unified economic and diplomatic response, even from Russia’s friends and neutral parties.  

China has already signaled and messaged to everyone that China will consider the use of nuclear weapons unacceptable.  

Dangers of giving up to nuclear blackmail:

1. Russia can use the same tactic again to get some other thing. 
2. It sets global precedent (North Korea and others are watching).  

[1]: During Obama's presidency  NSC wargamed against Russia’s new nuclear strategy.  Russia invades Baltics and uses low-yield nuclear weapon against German weapons storage.  Principals level wargame chose not to use nuclear response. source: "The Bomb: Presidents, Generals, and the Secret History of Nuclear War" (2020) by Fred Kaplan.  

I think there is one scenario you have left out, where the shooting war sort of stagnates, but is still fairly intense, and Russia bleeds itself out economically and socially maintaining the war. So, neither escalation nor de-escalation. I don't consider it to be a deescalation (Ie. "Libya"), because it's a form of loss for Russia, but it's slow enough that it doesn't necessarily register immediately as a "Vietnam" and there's time for internal unrest. At some point they will implode internally (coup/revolution/whatever), or they will escalate, or both. No idea of probabilities.

The global elites and media either think that nuclear war is impossible, or they are strongly influenced by the current environmentalist zeitgeist that considers humans to be overpopulated parasites on Mother Earth. I think this makes nuclear war much more likely, as they are disconnected enough from reality that they think bad things won't happen, or they are deluded that the bads things are good in some way.

Nice post Mr. Tegmark, ty! Regarding your statement

"...(80%) that NATO's response will be forceful enough to include a non-nuclear military strike against Russia, because key NATO leaders have already made strongly worded statements to this effect"

would you (or can anyone else?) kindly supply direct quotes (please not merely citations of news articles that paraphrase or that quote less than complete sentences) of some such statements? For the ones not cited or quoted, maybe Mr. Tegmark will clarify whether he means key current NATO officials or merely key current officials of NATO member countries, or whether perhaps retired former officials is what was instead meant? Fwiw the reason for my request, besides the obvious one that the claim is a key one in the analysis, is that the only people from whom I've read the claimed statements are current couch-sitters and not even "NATO leader" ones. At most they are former nonmilitary govt officials. Have retired generals such as Hodges or Hertling said NATO direct military response is highly likely? If the only such opinions that could be found were of this "armchair" variety, I'd say they'd give some grounding to Mr. Tegmark's remarkably high "80%" estimate. (So far I see a quote from Hodges that characterizes his probability estimate as US "could well" do this or that direct military action", which is laughably different to the "WILL" (no kidding, all-caps) stated in the headline of the newspaper article in which the actual quote is sort of eventually dribbled out.)

Edited to add: [Here's a retired general] (https://mobile.twitter.com/mccaffreyr3/status/1568769530658435072) whose probability estimate seems to go a bit higher than Hodges' "could well...". I'm really starting to think that such couch surfers (no offense to couch surfers) are actually who Mr. Tegmark rather slyly means by "key NATO leaders" but if he did mean actual NATO officials then I'd consider that to be a huge difference.

I agree with the underlying logic of your argument, but see the percentages as quite arbitrary. What would you consider the margin of error (perhaps "error" is the wrong word here) for your percentage estimates? Surely you are not professing to be certain on the exact numbers. 

What are your market positions? What bets have you made in response to this knowledge? 

There's potential paths that this model doesn't include. I have to believe that the Five Eyes have done some amount of work to find ways to hamstring Russias nuclear capabilities (I recall stories that "we" were able to sabotage chips in in the supply chain for Iraq's missiles, for example).  Meaning, there's a chance Russia does some kind of nuclear launch and it's horribly botched for one reason or another.  Their own incompetence, supply chain sabotage, etc. They may, then, be reluctant to launch another.

I don't know what a reasonable prior is to set on this. Much has been made of the out-dated technology the US has to manage our own nuclear arsenal, and we spend an awful lot more on our military than Russia does. Who really knows what they're capable of here? So far, they haven't accurately estimated their own military strength.

There are probably other outcomes we haven't thought of. 1/6 seems high, but I take the point that we could be underestimating the threat here. 

EDIT: Will take that this is an unpopular opinion, but not sure why?

What are the numbers based on, especially 30% of Ukraine winning? So far, the retired US and NATO generals have voiced that Ukraine has achieved "irrevesible momentum" of winning. 

Any evidence you can counter argue that with?

In the past, we've often seen that officers in charge of nukes don't launch them (Archipov, the Generals in the Trump admin seemed minded to ensure they got a look in before launch). What probability do you assign that when told to launch a nuke, the Russian officers don't?

I doubt France & Germany, let alone Hungary or Turkey are going to consent to a NATO retaliation. So I think the relevant question is whether US/UK/Eastern Europe are going to go it alone.

Marginally Compelling had a great podcast episode with Josh Centers back in March of this year on surviving a nuclear attack. https://polimath.substack.com/p/get-ready-for-nuclear-war-with-josh#details

I haven’t seen it mentioned, so I’m mentioning it.

Dear Max Tegmark,
I read your risk assessment with an abstract mathematical scenario model with great interest, but was also very worrying, because your result does not bode well and gives no prospect of a possible happy ending.
However, I see a number of errors in the approach or better it does not reflect our current world situation. There's just a bunch of undisclosed facts that put everything in a different light. In your statement, dear Max Tegmark, these developments in the world have not been taken into account. Your model turns out to be like a model for the Cuban Missile Crisis. So it's stuck with a look back at the sixties. It's like Hans Rosling's book "Factfulness": we always have to learn that the world is different today than it was in the past.
I believe that, on the one hand, we a r e already in the midst of a war between East and West; only the war is conducted differently today. And furthermore, both sides have a "new general" sitting at the war map tables today: I consider the development of artificial intelligence to be so advanced that it is definitely used for tactical consultation and strategic planning, and if that is not the case yet, it will shortly be involved in war planning and decisions.
Of course, Russia has similar support, only they are in a far weaker position as the US leads by miles in AI development. Alpha-Zero, the super chess-playing, self-learning system, like Alpha-Star, is ideal for transferring to "similar problems". And a constantly changing war situation poses similar problems. Here, too, it's basically about the best use of matter, space and time; and about tactics and strategies. The self-learning system is fed with data from space surveillance, the news from Ukraine and Russia and learns extremely quickly how wars are waged and won by absorbing all previous wars and battles in history, recorded on the Internet and in literature, and uses millions of battle simulations against itself for achieving highest levels to the point that his tactics and strategy are largely invincible, at least bringing Russia to the edge of defeat. At the same time, all measures and recommendations must be dosed in such a way that a psychological system component keeps Putin's potential decision on a nuclear strike as low as possible.
I think that's how warfare works today. And it is real, no SF.
And we saw the first results recently, with everyone wondering how Ukraine managed to launch such a successful counteroffensive.
Of course, a nuclear escalation by Russia cannot be ruled out 100%, but the probability is well below your 1:6 model.
If that were to happen, the possible consequences would be Armageddon, perhaps like Harlan Ellison's 1968 Hugo-winning story "I have no mouth and I must scream" (https://en.wikipedia.org/wiki/I_Have_No_Mouth, _and_I_Must_Scream) described. The status of today's AI leads not only to the best game players, whether chess, go or video games, the best medical scientists or chemical, biological inventors and future predectors, but also to the best war advisors, which the Pentagon has likely just integrated into the General Staff. Only with  AI ​​the Ukraine problem can and will be solved. And we will see that soon. At least in 2023 you will remember my words.
Rudolph Angeli, Hamburg

What are your candidates for targets for a tactical nuclear use, and your estimate of the yield of the strike?

What is the specific military need that will be met by setting off a nuclear weapon on the current battlefield which would be unmet by precision conventional strikes or massed fires from artillery or aviation?

A professional would have an answer to these questions.

I know this is an estimate for imminent global nuclear war (for which I'd give a lower estimate, but even if it were 100x lower, 0.17% -- and it isn't -- that would be wholly unacceptable) but I don't want global nuclear war in my lifetime.

So it's necessary to also consider how various outcomes of the current war may have on the liklihood of global nuclear war in the next decades. In this vein, the best argument for ensuring that Ukraine wins in spite of Russian nuclear threats, is that allowing Russia to achieve a relatively favorable outcome on the basis of its nuclear threats incentives proliferation -- of nukes, and of nuke threats. This would surely increase the liklihood of global nuclear war in the next decades, whether through error or escalation.

The best outcome of the war in my opinion would be a restart of global nuclear weapon elimination. It's even conceivable (though I'm not wishing for it!) that escalation to use of nukes in Ukraine is the insult that the world needs to eliminate nukes, and any leader who makes any move toward getting them.

To be honest I would like to understand a little bit more on why and how the parameters of this little model were "tuned". I mean, I am not saying that the model is wrong (because the outcomes are forcibly those) but I would like to understand more on how those probabilities were tuned or at least estimated.

Let's put in this way: to possibly have an hint to calculate and have a reasonable estimate I think we should consider the chicken game scenario. Because at the moment we are in a stage of the war that is a "chicken game", in which neither Ukraine, neither Russia wants to divert from the road that leads to the brink. In addition we should consider one thing (this is not a position that says that NATO is wrong or so, but is a matter of fact), both the opponents want to keep going in the war, based on game theory: if they will sit down to a peace agreement both will earn less than they can earn winning the war, and this scenario was possible only with the western armaments. At the beginning of the invasion, who was more determined for sitting down on a peace table was Ukraine, because Ukr could still take back some territories that were invaded with a negotiated peace agreement.

So my suggestion to try to understand the closeness of the probabilities to the reality is to understand in human behavior the "chicken game" outcomes in other situations, because the human reasoning probably is the same and to understand how much the mankind would go to the brink (or, in Italian "Muoia Sansone e tutti i filistei", from biblic tales of Sanson) avoiding to be a "chicken".

On the impact of WW3, I think that the scenario depends on how extended will be the war. If you consider the seminal studies of Turco and Sagan, I think that the nuclear winter would be far more dangerous, leading the human race to the brink of extinction. 

Lots of interesting opinions in the comments - these days it is rare to read comments about this war without lots of emotional stuff.

However, I must point out that many of the points are based on what people think about Putin as a person. And their opinions are heavily based on what western media want them to think. 

I think in the grand scheme it is not important what Putin's personal traits are. The most important is who are the parties in this war and what are their interests. Putin is just a figure that some internal russian parties agreed on, its not like he's on his own.

As it happened before, world capitalism tries to solve a huge number of unsolved problems through the war.

Major parties(of course, just my personal view) in this war are(and when I mention country, I don't mean people, I mean capital in the first place): 

1. US. Sky-high debt and endless dollar printing finally got to the point when the internal economy is starting to crack under pressure. EU has become too much of a competition and needs to be weakened. Huge numbers of refugees from the countries devastated by US did the first step. Second step was "green energy". And third step is removing cheap russian energy. As a result - some of the european industry players have already moved factories to US, some are preparing to do the same. Does US want a nuclear conflict? No, I don't think so. There's no gain from that for them, and lots of potential losses. They have lots of interest in keeping Ukraine on fire, but that fire don't have to be nuclear.
2. EU. Decades of using cheap energy allowed european industry to thrive. But this age has finished, and there seems to be no going back from that. Large capitals are about to be moved out from Europe in different directions, mostly to the US. But while there, they're not interested in keeping the war going. And obviously, they don't have any interest in nuclear war starting out - the US have chances at least to survive it, the EU doesn't.
3. UK. They didn't have such a big dependency on energy from russia, but lots of cheap gas in Europe kept other gas sellers from raising prices. So UK is losing cheap energy too, but as far as I know, they have much more sustainable economics foundation(this doesn't mean regular people won't suffer). And they made wise move with the Brexit - first rat out of the sinking ship. Do they want nuclear war? I think not, but I also think that they don't care about it on the same level as other europe does. Unless the Island is targeted directly, they have lots of chances to survive through that - and thrive afterwards, major competitors being kicked to the stone age. But the risks are enormous and the prize is very ghostly.
4. Russia. Last 10+ years I saw increasing number of links with the western world being cut. When I speak to my friends colleagues in Europe, US and UK, it seems that they're always imagining picture somewhat like  Biff's Future from BTtF2 or something like that. But the life is going on normally - roads are getting better, houses are being built. People are going to work. People discuss the war a lot, and there's lots of different opinions. Nobody is being jailed just because of their point. Usually, it happens when expression of the point takes extreme measures - but if you do that in any "free and democratic" country - one will face the same or even worse consequences. People are getting tired of war. People are getting tired of constant lies - both by russian government and and western media. The war has been started by oligarchs and its being kept on by them. Do they want nuclear war? No, this would be the end of the world as we know it.

So, out of four major actors, not a single one, as far as I can see, will benefit from nuclear war. Almost nobody will gain nothing useful from it, and the losses are incredibly high. The "regular" war effort, however is very handy for everyone (except Ukraine). This makes me think nuclear strikes are very unlikely to happen. I wouldn't even give it 5%, not to say 30%.

If it were up to regular people to decide - the Earth would've been perished already.

There's an implicit assumption in this line of reasoning that military response is inherently escalatory but you are demonstrating with this line of reasoning that fear of military response is de-escalatory! 

The assumption beneath that is that you are rational but your counterparty is unlike you and cannot be trusted to be rational - but if this is the case then you are trapped in a room with a madman with a knife and the only rational move is first strike.

The only nuclear target map thus far declassified by the United States suggested that China would also be targeted even in a US-Russia war, to prevent it from emerging as the strongest post-war economy.

Wait, what? 

If true, this seems to strongly undermine the credibility of the U.S. in the eyes of most world leaders.

Especially the leaders of India, Africa, Brazil, etc., who would almost certainly share fears of being next on the chopping block.

I can't see how this is possibly advantageous for the US government to suggest.

If Putin values his life more than victory, then he will, at each time, follow the path which minimizes the probability of his death as outcome, as estimated by him.

For the time being he can follow any of 3 possible paths: Withdrawal_before_Ukr, Conv_War_on_Ukr, and Tac_nukes_on_Ukr (kaboom).

The Conv_War_on_Ukr path has 2 possible outcomes: Victory or Defeat_by_Ukr.

The Tac_nukes_on_Ukr path has 2 possible outcomes: Victory or Conv_NATO_strike. After Conv_NATO_strike, Putin can follow any of 3 possible subpaths:

• Withdrawal_before_NATO,
• Conv_war_on_NATO (plus ongoing Tac_nukes_on_Ukr), with 2 possible outcomes: Victory (close to 0) or Defeat_by_NATO_Conv (close to 1),
• Tac_nukes_on_NATO (plus ongoing Tac_nukes_on_Ukr), with 2 possible outcomes: Victory (if NATO folds) or Strat_NATO_strike (KABOOM).

The Withdrawal and Defeat paths/outcomes have Putin's death as a possible outcome. KABOOM implies everyone's death with certainty.

The probabilities of Putin dying in each path are:

• Withdrawal_before_Ukr: P(I_die/Withdrawal_before_Ukr)
• Conv_War_on_Ukr: P(Defeat_by_Ukr/Conv_War_on_Ukr) x P(I_die/Defeat_by_Ukr)
• Tac_nukes_on_Ukr: P(Conv_NATO_strike/Tac_Nukes_on_Ukr) x 
       min({P(I_die/Withdrawal_before_NATO), 
                 P(Defeat_by_NATO_Conv/Conv_War_on_NATO) x P(I_die/Defeat_by_NATO_Conv),
                 P(Strat_NATO_Strike/Tac_Nukes_on NATO)})

If Putin values victory more than his life, then he will, at each time, follow the path which minimizes the probability of Russian defeat as outcome, as estimated by him. In this case the Withdrawal paths vanish and the probabilities of Russian defeat in each path are:

• Conv_War_on_Ukr: P(Defeat_by_Ukr/Conv_War_on_Ukr)
• Tac_nukes_on_Ukr: P(Conv_NATO_strike/Tac_Nukes_on_Ukr) x 
      min({P(Defeat_by_NATO_Conv/Conv_War_on_NATO),
                P(Strat_NATO_Strike/Tac_Nukes_on NATO)})

The above assumes that Putin perceives the KABOOM outcome as defeat. But if he perceives it as victory, then the Tac_nukes_on_NATO subpath leads always to victory, so that, as soon as Putin perceives that a Russian defeat by Ukraine in a conventional war has become likely, it is certain that he will follow the Tac_nukes_on_Ukr path, and that if NATO strikes Russian targets in response, he will then follow the Tac_nukes_on_NATO subpath.
 

The officially stated position of Russia is not to get involved in a conventional war with NATO (that Russia knows it can't win) and immediately escalate to a "limited" nuclear war (that they believe they can win). It appears that (from the Russian standpoint) the nuclear "escalation ladder" looks as this:

- kaboom

- Tactical nuclear strike against a single (non-nuclear) NATO state in Western Europe

-Massive tactical nuclear strikes against  (non-nuclear)  NATO state(s) in Western Europe

-Tactical nuclear strike(s) against nuclear NATO states, but outside the territory of US, GB and France

-KABOOM 

and, from Russia's standpoint, an advance from one step of the ladder to the next are not automatic. 

On the other hand, from the US  military planner's standpoint, the movements from one step of the ladder to the next are also not automatic, but even the second step of the ladder poses such a huge problem that a non-military response to "kaboom", e.g. an attempt to persuade India and China to join sanctions and further isolate Russia, seems more likely than  a direct military response. 

In addition,  the process can be deescalated at any step of the ladder, at least in theory. It follows that the probability of moving from "kaboom" to "KABOOM" is (much) lower than you assume.  

not bad

Max is clearly a highly intelligent person, who's highly respected with a great track record. I believe we all should be taking his arguments seriously and discussing how we can create better outcomes through action, rather than focusing our intellects on breaking apart his logic and trying to convince ourselves that everything is fine.

WW3 is a suicide pact. The #1 thing that defines modern Russia is cynical self-interest. Putin won't die for his professed ideals(which he does not believe in anyway). If he gives the order the people around him won't be willing to die and they'll just kill him. I view this all as extreme brinksmanship that will ultimately lead nowhere. 

Russia's oligarch billionaires aren't incinerating their Swiss mansions over some dead proles on the Ukrainian front.

Non-military deterrents:

How about turning off Moscow’s lights for a few hours? Or wider-scale?

Or seizing ALL Russian assets in the West?

Darker deterrent:

Seize all children of Putin & Russian generals & elite who reside or school or vacation in the West?

—O.S.

Humans have maintained a compulsion dubbed in Edgar Allan Poe's The Black Cat as " The Spirit of Perverseness" or something better known as Sin. Whereas in almost every major science fiction story that our world goes through a catastrophe, either we abandon all hope, and become dedicated toward anarchy, in some others we strive toward peace, through either a better sense of community and a proper rebuild, or, a means of peace through government control. Our most recent test was Covid. I asked myself "Where is the War?" And now we have not one major War, but many, across the world. From China and Taiwan, N. Korea, Russia and the U.S., but also so many other conflicts, and then more mainstay crisis upon crisis upon crisis upon crisis. This is what it boils down to - Ascension. We humans are addicted to Repentance into Sin, Peace into Chaos. We, as a species, refuse to stop this cycle, unified, ready to ascend to the next major purpose of our species. We are a cancer to this planet, or the proper balance/test Nature itself needs to survive the next asteroid. There are no longer any major icons (Susan B. Anthony, Galileo, Gandhi, MLK Jr., Malcolm X, Mother Teresa, Vera Lynn). No more hunger strikes, and in the U.S. - There is no longer a need to amend our Constitution, which in turn, by default, is a relinquishment of "rights". We slave ourselves to debt with Money (This note is legal tender for all debts, public and private), to give ourselves a unified "pat on the back" that we are not "poor" (poverty/lack of abundance; wealth/overabundance). Simply put, if we cannot get ourselves as a species to defy this monotonous cycle of the status quo, then human behavior itself is the key to the answer to such subject matters as nuclear war. It is imminent and necessary, to possibly get this species to the next ascended step. Nietzsche explains that Confrontation produces Genius. This seems to be a very unfortunate truth.

Thousands of people in the West understand all this but the population in kept blind by most of the media. If we think our population can't handle the truth then we effectively claim democracy failed. I already hear Xi laughing in the background.

I don't know how someone can claim to know with what likelihood an event will occur when we have no historical precedent for Russia using nuclear weapons. We have never seen their doctrine in action. In fact, the only examples we have regarding Russia and nukes are two events where Soviet soldiers REFUSED to launch nukes. So you should actually have a 0% chance for your kaboom scenario.

So now, we have 0%  80% * 70% = 0%

Also, it's incredibly disingenuous coming from a person that supposedly knows science to not include error bars and not mention the fact that even a slightly different number for each of the scenarios would drastically decrease the total likelihood. You could have chosen whichever number you liked and made the total likelihood any number you like.

In reality, the likelihood of total nuclear war is somewhere between 0% and 100% and you claiming to know what the number is shows how ignorant you truly are.