Welcome to The Nonlinear Library, where we use Text-to-Speech software to convert the best writing from the Rationalist and EA communities into audio. This is: Can a war cause human extinction? Once again, not on priors, published by Vasco Grilo on January 25, 2024 on The Effective Altruism Forum.

Summary

Stephen Clare's classic EA Forum post

How likely is World War III? concludes "the chance of an extinction-level war [this century] is about 1%". I

commented that

power law extrapolation often results in greatly overestimating tail risk, and that fitting a power law to all the data points instead of the ones in the right tail usually leads to higher risk too.

To investigate the above, I looked into historical annual war deaths along the lines of what I did in

Can a terrorist attack cause human extinction? Not on priors, where I concluded the probability of a terrorist attack causing human extinction is astronomically low.

Historical annual war deaths of combatants suggest the annual probability of a war causing

human extinction is astronomically low once again. 6.36*10^-14 according to my preferred estimate, although it is not

resilient, and can easily be wrong by many orders of magnitude (

OOMs).

One may well update to a much higher extinction risk after accounting for inside view factors (e.g.

weapon technology), and indirect effects of war, like increasing the likelihood of

civilisational collapse. However, extraordinary evidence would be required to move up sufficiently many orders of magnitude for an

AI,

bio or

nuclear war to have a decent chance of causing human extinction.

In the realm of the more anthropogenic

AI,

bio and

nuclear risk, I personally think underweighting the

outside view is a major reason leading to overly high risk. I encourage readers to check David Thorstad's series

exaggerating the risks, which includes subseries on

climate,

AI and

bio risk.

Introduction

The 166th

EA Forum Digest had Stephen Clare's

How likely is World War III? as the classic EA Forum post (as a side note, the rubric is great!). It presents the following conclusions:

First, I estimate that the chance of direct Great Power conflict this century is around 45%.

Second, I think the chance of a huge war as bad or worse than WWII is on the order of 10%.

Third, I think the chance of an extinction-level war is about 1%. This is despite the fact that I put more credence in the hypothesis that war has become less likely in the post-WWII period than I do in the hypothesis that the risk of war has not changed.

I view the last of these as a

crucial consideration for

cause prioritisation, in the sense it directly informs the potential

scale of the benefits of mitigating the risk from

great power conflict. It results from assuming each war has a 0.06 % (= 2*3*10^-4) chance of causing

human extinction. This is explained elsewhere in the post, and in more detail in the curated one

How bad could a war get? by Stephen and Rani Martin. In essence, it is 2 times a 0.03 % chance of war deaths of combatants being at least 8 billion:

"In Only the Dead, political scientist Bear Braumoeller [I recommend

his appearance on The 80,000 Hours Podcast!] uses his estimated parameters to infer the probability of enormous wars. His [

power law] distribution gives a 1 in 200 chance of a given war escalating to be [at least] twice as bad as World War II and a 3 in 10,000 chance of it causing [at least] 8 billion deaths [of combatants] (i.e. human extinction)".

2 times because the above 0.03 % "may underestimate the chance of an extinction war for at least two reasons. First, world population has been growing over time. If we instead considered the proportion of global population killed per war instead, extreme outcomes may seem more likely. Second, he does not consider civilian deaths. Historically, the ratio of civilian-deaths-to-battle deaths in war has been about 1-to-1 (though there's a lot of variation across wars). So fewer than 8 billion battle deaths would be...