I’m not going to say anything about this research because I’ve not read the paper, but it looks important. If someone out there writes something up I’ll put a link here.
Here’s the deal. Climate sensitivity is, very oversimplified, how much the surface of the planet heats up as we add CO2 and other greenhouse gasses to the atmosphere. More specifically, equilibrium climate sensitivity is the number of degrees C the atmosphere at face height and the sea surface heat up with a doubling of CO2 from pre-industrial levels.
If our atmosphere had just nitrogen and CO2 and that’s it, the number would be fairly low. But live would not exist here because there would be no water, so we would not be having this conversation. The fact that we are having this conversations suggests the existence of water vapor, which cranks up sensitivity quite a bit, because more CO2 means more heat means more water vapor. That is just one of a number of “positive” (read not good) feedbacks on climate sensitivity.
I’ve noted before that if you offer a group of informed climate scientist the chance to guess a single number for climate sensitivity, using the Free Beer method, is something like 2.5. Certainly not less than 2.0. But it could just possibly be much higher, like 6. The chances of climate sensitivity being 6 are small, and if it turned out to be, then we are truly Doomed. But here’s the thing. The upper range of possible values for this important number is what is sometimes called a “fat tail.” The chances are low, but not so low they can be ignored.
Here’s a picture of a fat tail.
(Our blog platform is broke so I can’t insert that graphic. Go click on it and come right on back.)
Even a value of 4 or 5 would be bad, and the chances are not vanishingly small that this would be the value.
So, about the latest research.
Authors: Chengxing Zhai, Jonathan H. Jiang, Hui Su
Abstract: The large spread of model equilibrium climate sensitivity (ECS) is mainly caused by the differences in the simulated marine boundary layer cloud (MBLC) radiative feedback. We examine the variations of MBLC fraction in response to the changes of sea surface temperature (SST) at seasonal and centennial time scales for 27 climate models that participated in the Coupled Model Intercomparison Project phase 3 and phase 5. We find that the intermodel spread in the seasonal variation of MBLC fraction with SST is strongly correlated with the intermodel spread in the centennial MBLC fraction change per degree of SST warming and that both are well correlated with ECS. Seven models that are consistent with the observed seasonal variation of MBLC fraction with SST at a rate −1.28 ± 0.56%/K all have ECS higher than the multimodel mean of 3.3 K yielding an ensemble-mean ECS of 3.9 K and a standard deviation of 0.45 K.
Potential meaning: Ruh roh.
These results are not particularly unexpected. But one would hope that more research would show a lower number, because we really don’t want this to be a higher number.
from ScienceBlogs http://ift.tt/1Wv2wOz
I’m not going to say anything about this research because I’ve not read the paper, but it looks important. If someone out there writes something up I’ll put a link here.
Here’s the deal. Climate sensitivity is, very oversimplified, how much the surface of the planet heats up as we add CO2 and other greenhouse gasses to the atmosphere. More specifically, equilibrium climate sensitivity is the number of degrees C the atmosphere at face height and the sea surface heat up with a doubling of CO2 from pre-industrial levels.
If our atmosphere had just nitrogen and CO2 and that’s it, the number would be fairly low. But live would not exist here because there would be no water, so we would not be having this conversation. The fact that we are having this conversations suggests the existence of water vapor, which cranks up sensitivity quite a bit, because more CO2 means more heat means more water vapor. That is just one of a number of “positive” (read not good) feedbacks on climate sensitivity.
I’ve noted before that if you offer a group of informed climate scientist the chance to guess a single number for climate sensitivity, using the Free Beer method, is something like 2.5. Certainly not less than 2.0. But it could just possibly be much higher, like 6. The chances of climate sensitivity being 6 are small, and if it turned out to be, then we are truly Doomed. But here’s the thing. The upper range of possible values for this important number is what is sometimes called a “fat tail.” The chances are low, but not so low they can be ignored.
Here’s a picture of a fat tail.
(Our blog platform is broke so I can’t insert that graphic. Go click on it and come right on back.)
Even a value of 4 or 5 would be bad, and the chances are not vanishingly small that this would be the value.
So, about the latest research.
Authors: Chengxing Zhai, Jonathan H. Jiang, Hui Su
Abstract: The large spread of model equilibrium climate sensitivity (ECS) is mainly caused by the differences in the simulated marine boundary layer cloud (MBLC) radiative feedback. We examine the variations of MBLC fraction in response to the changes of sea surface temperature (SST) at seasonal and centennial time scales for 27 climate models that participated in the Coupled Model Intercomparison Project phase 3 and phase 5. We find that the intermodel spread in the seasonal variation of MBLC fraction with SST is strongly correlated with the intermodel spread in the centennial MBLC fraction change per degree of SST warming and that both are well correlated with ECS. Seven models that are consistent with the observed seasonal variation of MBLC fraction with SST at a rate −1.28 ± 0.56%/K all have ECS higher than the multimodel mean of 3.3 K yielding an ensemble-mean ECS of 3.9 K and a standard deviation of 0.45 K.
Potential meaning: Ruh roh.
These results are not particularly unexpected. But one would hope that more research would show a lower number, because we really don’t want this to be a higher number.
from ScienceBlogs http://ift.tt/1Wv2wOz
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