RCP 8.5: Why did the climate change model get it wrong?

Whether we like it or not, global warming is happening. The global temperature has already gone up, and it’s going to go up more, because the atmosphere is already full of carbon dioxide and other greenhouse gases, and we’re continuing to add to that stock. Quite how much it will increase by is a very important question for all of us. Until relatively recently, during much of the 2010s and into the 2020s, many scientists claimed that if we kept on going down the path we were on, if we just kept on with business as usual, then by the end of the century global temperatures would increase by almost five degrees centigrade. This projection was based on something called RCP 8.5, a statistical scenario used by scientists to model the future of the climate. You can still find scientific papers published in 2025 that make the same claim. However, there’s a good case that RCP 8.5 should never have been used as the business-as-usual scenario. And in hindsight it doesn’t look like an accurate vision of the future at all. So what’s going on? Dr Zeke Hausfather, a climate scientist and the climate research lead at Stripe, explains the argument. Presenter: Tim Harford Series producer: Tom Colls Sound mix: Donald MacDonald Editor: Richard Vadon