Since I’ve discussed climate sensitivity on a number of occasions, it seems worth highlighting the new paper that assesses climate sensitivity using multiple lines of evidence. The authors include many who will be familiar to my regular readers.The key figure is on the right and shows that the likely range for the Equilibrium Climate Sensitivity (ECS) is 2.6-3.9K, and the 5-95% range is 2.3-4.7K. Essentially, this now largely rules out very low ECS values (below 2K) and also makes the higher values (>5K) also somewhat less likely.
I don’t need to say much more, since this has been covered extensively elsewhere. I’ll provide links at the end of this post. What I thought I would briefly mention is why I think this illustrates the issue with the general narrative being promoted by people like Shellenberger and Lomborg. They’re essentially suggesting that although climate change is real, it’s manageable. We can deal with sea level rise, and disasters aren’t getting worse. The global economy is going to continue to grow, so people will be more capable of dealing with climate related events in the future than they are now. It’s important, but let’s not do anything too drastic.
Of course, it is possible that we will be able to effectively deal with the impacts of climate change. However, it’s also possible that it will be much more difficult to deal with than people like Shellenberger and Lomborg suggest. Given the results in this new paper, it’s clear that it will be incredibly challenging to limit warming to 2oC above pre-industrial levels. On our current trajectory, we’re probably heading for something like 3oC and that’s assuming that climate sensitivity isn’t on the high side of the range. Even on our current trajectory, we can’t rule out that we’ll end up more than 4oC above pre-industrial levels. There are also various carbon cycle feedbacks that could amplify this even further.
So, yes, we shouldn’t suddenly panic and turn everything off. However, we also shouldn’t – in my view – assume that we will easily deal with whatever climate change happens to throw at us (technically, since we’re doing this, what we’re throwing at ourselves). We actually don’t really know what a 2oC world will be like, let alone a 3oC, or a >4oC world. A key thing to bear in mind, is that once we get there, there is no easy way of going back.
Some amount of future climate change is unavoidable, but how much we experience is largely up to us. I can see why the optimism presented by the likes of Shellenberger and Lomborg is appealing; we’re innovative, we can deal with anything. However, rather than being optimistic that we can deal with any possible climate change impacts, why not be optimistic that we can do innovative things that limit how much climate change we will actually face?
An assessment of Earth’s climate sensitivity using multiple lines of evidence – Paper by Sherwood et al. 2020.
Back to the future – post by James Annan.
Climate Sensitivity: A new assessment – Realclimate post.
Just how sensitive is the climate to increased carbon dioxide? Scientists are narrowing in on the answer – Conversation article by Richard Betts, Jason Lowe and Timothy Andrews.
Guest post: Why low-end ‘climate sensitivity’ can now be ruled out – Carbon Brief article by Piers Forster, Zeke Hausfather, Gabi Hegerl and Steven Sherwood.
Global heating study rules out best and worst case scenarios – Guardian article about the new paper.