Sean Cohen (Columbia): “Why increases in CO2 cool the stratosphere and how this amplifies radiative forcing”
Maya Chung (Princeton): “Runaway Cooling from Large Solar Reductions Modulated by Ocean Overturning Circulation and Heat Uptake”
Florian Roemer (ETH Zurich): “How to think about the clear-sky shortwave water vapor feedback”
00:30:10 Christopher S Bretherton: Maya, nice talk. Have either of your models done LGM simulations, and if so can you see any hints of the same difference in behavior?
00:30:22 Nadir: Maya interesting talk. I’m just wondering how you square the unstable feedbacks for CM2.1 with the fact that there doesn’t seem to be runaway cooling in that model
00:31:48 gaschmid: Missing the LW absorption of upwelling LW!
00:32:28 Maya Chung: Hi Christopher, we don’t have LGM simulations but it would be interesting to look at. Would be cautious though because LGM has many differences with he modern climate besides solar radiation
00:34:06 Maya Chung: Thanks Nadir, I didn’t show this but when we add the atmosphere and ocean components together (“climate resistance” = alpha + kappa) we find an unstable state in FLOR and stable in CM2.1.
00:52:12 Nadir: Reacted to "Thanks Nadir, I didn..." with 👍
00:55:03 Moritz Günther: @Sean: Basically, my comment was aimed to raise the point that the stratosphere is not just in radiative equilibrium, but in radiative-dynamic equliibrium, and in the full equation there appears a dynamic cooling term (at least in the upwelling regions of the Brewer-Dobson circulation). The BDC is robustly projected to accelerate under CO2 forcing, changing the dynamic cooling (even ignoring atmospheric composition changes). It would be interesting to explore how that term affects everything you presented. But even without the dynamic component I think your konrad results are really interesting, just understanding the radiative contributions is valuable in itself.
00:59:52 seancohen: Great point. I should have clarified that we are only considering global-annual mean temperature, for which dynamic terms integrate to zero and radiative equilibrium holds. Outside the global-annual mean, you are correct that changes in dynamical heating become incredibly relevant.
01:00:52 Moritz Günther: Reacted to "Great point. I shoul..." with 👍
01:01:29 seancohen: We haven’t yet studied these effects (we effectively assume FDH) but we are most definitely interested in doing so moving forward.