EA - The Precipice Revisited by Toby Ord

The Nonlinear Library

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: The Precipice Revisited, published by Toby Ord on July 12, 2024 on The Effective Altruism Forum. I'm often asked about how the existential risk landscape has changed in the years since I wrote The Precipice. Earlier this year, I gave a talk on exactly that, and I want to share it here. Here's a video of the talk and a full transcript. In the years since I wrote The Precipice, the question I'm asked most is how the risks have changed. It's now almost four years since the book came out, but the text has to be locked down a long time earlier, so we are really coming up on about five years of changes to the risk landscape. I'm going to dive into four of the biggest risks - climate change, nuclear, pandemics, and AI - to show how they've changed. Now a lot has happened over those years, and I don't want this to just be recapping the news in fast-forward. But luckily, for each of these risks I think there are some key insights and takeaways that one can distill from all that has happened. So I'm going to take you through them and tease out these key updates and why they matter. I'm going to focus on changes to the landscape of existential risk - which includes human extinction and other ways that humanity's entire potential could be permanently lost. For most of these areas, there are many other serious risks and ongoing harms that have also changed, but I won't be able to get into those. The point of this talk is to really narrow in on the changes to existential risk. Climate Change Let's start with climate change. We can estimate the potential damages from climate change in three steps: 1. how much carbon will we emit? 2. how much warming does that carbon produce? 3. how much damage does that warming do? And there are key updates on the first two of these, which have mostly flown under the radar for the general public. Carbon Emissions The question of how much carbon we will emit is often put in terms of Representative Concentration Pathways (RCPs). Initially there were 4 of these, with higher numbers meaning more greenhouse effect in the year 2100. They are all somewhat arbitrarily chosen - meant to represent broad possibilities for how our emissions might unfold over the century. Our lack of knowledge about which path we would take was a huge source of uncertainty about how bad climate change would be. Many of the more dire climate predictions are based on the worst of these paths, RCP 8.5. It is now clear that we are not at all on RCP 8.5, and that our own path is headed somewhere between the lower two paths. This isn't great news. Many people were hoping we could control our emissions faster than this. But for the purposes of existential risk from climate change, much of the risk comes from the worst case possibilities, so even just moving towards the middle of the range means lower existential risk - and the lower part of the middle is even better. Climate Sensitivity Now what about the second question of how much warming that carbon will produce? The key measure here is something called the equilibrium climate sensitivity. This is roughly defined as how many degrees of warming there would be if the concentrations of carbon in the atmosphere were to double from pre-industrial levels. If there were no feedbacks, this would be easy to estimate: doubling carbon dioxide while keeping everything else fixed produces about 1.2°C of warming. But the climate sensitivity also accounts for many climate feedbacks, including water vapour and cloud formation. These make it higher and also much harder to estimate. When I wrote The Precipice, the IPCC stated that climate sensitivity was likely to be somewhere between 1.5°C and 4.5°C. When it comes to estimating the impacts of warming, this is a vast range, with the top giving three times as much warming as the bottom. Moreover, the...