by Judith Curry
The story surrounding Spencer & Braswell has gotten more interesting with the pre-publication of the rebuttal paper by Dessler.
The Dessler (2011) paper is in press at Geophysical Research Letters. Dessler et al. is a critique of Spencer and Braswell (2011), and also Lindzen and Choi (2011). Spencer and Braswell (2011) is a critique of Dessler (2010). Dessler (2010) is a critique of Spencer and Braswell (2010).
Here is the abstract and conclusion for Dessler (2011):
Cloud variations and the Earth’s energy budget
Abstract: The question of whether clouds are the cause of surface temperature changes, rather than acting as a feedback in response to those temperature changes, is explored using data obtained between 2000 and 2010. An energy budget calculation shows that the energy trapped by clouds accounts for little of the observed climate variations. And observations of the lagged response of top-of-atmosphere (TOA) energy fluxes to surface temperature variations are not evidence that clouds are causing climate change.
Conclusions. These calculations show that clouds did not cause significant climate change over the last decade (over the decades or centuries relevant for long-term climate change, on the other hand, clouds can indeed cause significant warming). Rather, the evolution of the surface and atmosphere during ENSO variations are dominated by oceanic heat transport. This means in turn that regressions of TOA fluxes vs. ΔTs can be used to accurately estimate climate sensitivity or the magnitude of climate feedbacks. In addition, observations presented by LC11 and SB11 are not in fundamental disagreement with mainstream climate models, nor do they provide evidence that clouds are causing climate change. Suggestions that significant revisions to mainstream climate science are required are therefore not supported.
I just checked Roy Spencer’s blog, and I don’t see a response from him yet, but I suspect that one will be forthcoming.
Blogospheric analyses of the Dessler paper are starting to emerge. Steve McIntyre provides an analysis of Dessler (2010) and (2011), which is well worth reading. RealClimate has a new post that mentions Dessler (2011) but focuses on the broader brouhaha surrounding S&B.
I’ve done a quick read of Dessler (2011). I have the same problem with Dessler’s paper that I had with S&B and LC. These analyses don’t really tell us anything about cloud feedback, although they are interpreted as doing so. The simple energy balance model upon which equation (1) is useful (at best) only for black box thermodynamics only analyses of the climate system. Cloud feedback is frequency dependent, and the key issue S&B are trying to address is the role of natural internal variability in modulating clouds, which in turn modulates the radiative balance and surface temperature; it is in this sense that they then refer to clouds as a “forcing.” This inconsistency arises from trying to use the black box energy balance feedback model to make inferences about the impact of internal dynamical variations on clouds and the energy balance.
So how to do a sensible observational analysis of cloud feedback remains elusive. The most significant element of all of these papers is the comparison of satellite data with models. A key issue is which models to select. S&B select models with highest and lowest sensitivity. Dessler (2011) seems to select the models that best match the satellite observations. IMO the best way to select the models would be to conduct an a priori analysis of the 20th century simulations for the period of interest, and compare the simulations with major circulation features of relevance to the large-scale cloud field, such as ENSO, the NAO, etc. Then look at the relevant radiation and cloud fields for these models.
IMO, none of these papers are of particular scientific interest, although they have become important in the public debate. The broader issue is that we need more papers comparing satellite observations to climate model simulations, and need to design better ways of using these data to evaluate processes of relevance to cloud feedback.
Bottom line: S&B and LC papers do have flaws, as discussed on previous Climate Etc. threads. Dessler (2011) adds relatively little to this debate. None of these papers are particularly useful in evaluating the sign or magnitude of the cloud feedback.
Nevertheless, all this stuff is like crack cocaine for the climate blogosphere :).
Moderation note: this is a technical thread, moderated heavily for relevance. Make your general comments on the Part II thread.