EA - Nuclear winter - Reviewing the evidence, the complexities, and my conclusions by Michael Hinge

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: Nuclear winter - Reviewing the evidence, the complexities, and my conclusions, published by Michael Hinge on August 25, 2023 on The Effective Altruism Forum.Nuclear winter is a topic that many have heard about, but where significant confusion can occur. I certainly knew little about the topic beyond the superficial prior to working on nuclear issues, and getting up to speed with the recent research is not trivial. Even then there are very large uncertainties around the topic, and different teams have come to different conclusions, which are unlikely to be resolved soon.However, this does not mean that we cannot draw some conclusions on nuclear winter. I worry that the fact there are still uncertainties has been taken to the extreme that nuclear winters are impossible, which I do not believe can be supported. Instead, I would suggest the balance of evidence suggests there is a very serious risk a large nuclear exchange could lead to catastrophic climate impacts. Given that the potential mortality of these winters could exceed the direct deaths, the evidence is worth discussing in detail, especially as it seems that we could prepare and respond.This is a controversial and complex topic, and I hope I have done it justice with my overview. Throughout this article I should however stress that these words are my own, along with any mistakes.Headline results, for those short on timeThis is a very long post, and for those short on time the thrust of my argument is summarized here. I've also included the relevant section(s) in the post that back up each point for those who wish to check my working on a specific piece of analysis.Firestorms can inject soot effectively into the stratosphere via their intense plumes. Once there, soot could persist for years, disrupting the climate (see "The case for concern: Firestorms, plumes and soot").Not every nuclear detonation would create a firestorm, but large nuclear detonations over dense cities have a high risk of causing them (see "The case for concern: Firestorms, plumes and soot").Not every weapon in arsenals will be used, and not all will hit cities. However, exchanges between Russia and NATO have the potential to result in hundreds or thousands of individual detonations over cities. This has the potential to result in a large enough soot injection that catastrophic cooling could occur (see "Complexities and Disagreements: Point one").The impacts of soot injections on the climate are nonlinear, and even if the highest thresholds in the literature are not met there still could be serious cooling. My personal estimates are that around 20-50 Tg of soot could be emitted in the event of a full-scale exchange between Russia and NATO with extensive targeting of cities. This is less than the upper threshold of 150 Tg from other sources, however that would still cause catastrophic crop losses without an immediate and effective response (see "Synthesis").There are disagreements between the teams on the dynamics of nuclear winters, which are complex. However, to date these disagreements center on a regional exchange of 100 weapons of 15 kt each, much smaller than Russian and NATO strategic weaponry. Some of the points raised in the debate are therefore far less relevant when looking at larger exchanges, where fuel loads would be higher, weapons are much more powerful and firestorms more likely (see "Complexities and Disagreements: The anatomy of the disagreements, followed by Synthesis").This means that nuclear winter is not discredited as a concept, and is very relevant for the projected mortality of nuclear conflict. There are uncertainties, and more research is needed (and possibly underway), however it remains a clear threat for larger conflicts in particular (see "Synthesis").Overall, although highly uncertain, I would expec...