In this post, I investigate whether the TPNW is likely to have an impact on nuclear deproliferation through formal legal channels — for example, by keeping countries that might have considered building nuclear weapons programs from doing so.[1] To do this, I first looked into whether any of the countries that are currently doing things that would be banned by the TPNW might ratify the treaty in the next 20 years (and stop doing those things). Next, I looked into whether the TPNW will keep any countries that ratify the treaty from becoming non-compliant — for example, by trying to get a sense of whether the treaty could counterfactually cause them not to pursue nuclear weapons.

In this post, I estimate the number of fatalities caused directly by nuclear detonations in the US/NATO and Russia. I model these effects in Guesstimate using expert surveys and interviews, forecasts made by Good Judgment Project superforecasters, academic research, and media coverage of international relations, along with academic research into the effects of nuclear war and nuclear weapons policy.

My previous posts address how bad a nuclear war is likely to be, conditional on there being a nuclear war, but they don’t consider the likelihood that we actually see a US-Russia nuclear exchange unfold in the first place. In this post, I get a rough sense of how probable a nuclear war might be by looking at historical evidence, the views of experts, and predictions made by forecasters. I find that, if we aggregate those perspectives, there’s about a 1.1% chance of nuclear war each year, and that the chances of a nuclear war between the US and Russia, in particular, are around 0.38% per year.

Nuclear attacks on cities would likely produce much more smoke than attacks on missile silos, military bases, and other nuclear arsenal targets. This is mainly because cities have much more flammable material to burn than the remote wildlands — mostly cropland and grasslands — that surround, for example, missile silos. This leads me to conclude that a nuclear war between the US and Russia would likely produce closer to 31 teragrams of smoke (90% confidence interval: 14 Tg to 68 Tg of smoke) — suggesting that nuclear winter is not as synonymous with US-Russia nuclear war as many effective altruists seem to assume. The ~31 teragrams of smoke that would be vaulted into the atmosphere would undoubtedly produce severe climate effects, likely leading to food shortfalls and regional famines, and killing between 36% and 96% of the world population.

The degree to which a nuclear war between the US and Russia could escalate depends on how many of their nuclear weapons would survive a first strike. For decades, both the US and Russia have been able to maintain a secure second strike by hiding their nuclear weapons on submarines, armored trucks, and aircraft. If improvements in technology allowed either country to reliably locate and destroy those targets, they would be able to eliminate the others’ secure second strike, thereby limiting the degree to which a nuclear war could escalate.

A nuclear exchange may have the potential to kill millions or billions of people, and possibly lead to human extinction. In this post, I rank plausible nuclear exchange scenarios in terms of their potential to cause harm based on three factors: 1) The size of the involved countries’ nuclear arsenals; 2) The size of the involved countries’ populations; 3) The probability of the given nuclear exchange scenario. Based on my rough prioritization, I expect the following nuclear exchange scenarios have the highest potential for harm: Russia and the US, India and Pakistan, and China and either the United States, India, or Russia.