I know Eli has already beaten me to it, but I thought I would also post the video of Andrew Dessler’s at the recent meeting on Earth’s Climate Sensitivity. It includes a talk by Bjorn Stevens called Some (not yet entirely convincing) reasons why 2K < ECS < 3.5K. This is a little ironic given that his recent paper on aerosol forcing is being used by some to argue that ECS is probably less than 2K.
Andrew Dessler’s talk is essentially also arguing that ECS > 2K. It’s quite interesting in that he’s trying to use short-term variability to estimate ECS. This has the advantage that the change in external forcing will be small, allowing it to be ignored. It does, however, require having some idea of how short-term estimates compare to longer-term estimates, which is obtained through comparing forced model runs, with unforced control runs. What he also did was to consider, initially, the feedbacks about which we have some confidence (water vapour, lapse rate, surface albedo) and showed that these alone would suggest an ECS of about 2K. There are then some reasons why cloud feedbacks are likely positive, which would then suggest that the ECS is probably greater than 2K. I don’t quite know the arguments for why cloud feedback is likely positive, so if anyone else does, it would be useful to get an idea of what they are.
Anwyay, that’s all I was going to say. The talk is quite good and clear, so just watch the video 🙂