- Bishop Hill blog

Thanks to Anthony for forwarding me the Dessler comment on response to Spencer and Braswell. I'll post the same excerpts as AW has so that readers here can discuss.

Cloud variations and the Earth’s energy budget
A.E. Dessler
Dept. of Atmospheric Sciences
Texas A&M University
College Station, TX

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.

Introduction
The usual way to think about clouds in the climate system is that they are a feedback — as the climate warms, clouds change in response and either amplify (positive cloud feedback) or ameliorate (negative cloud feedback) the initial change [e.g., Stephens, 2005]. In recent papers, Lindzen and Choi [2011, hereafter LC11] and Spencer and Braswell [2011, hereafter SB11] have argued that reality is reversed: clouds are the cause of, and not a feedback on, changes in surface temperature. If this claim is correct, then significant revisions to climate science may be required.

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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.

Acknowledgments: This work was supported by NSF grant AGS-1012665 to Texas A&M University. I thank A. Evan, J. Fasullo, D. Murphy, K. Trenberth, M. Zelinka, and A.J. Dessler for useful comments.

Dessler, A. E. (2011),

Cloud variations and the Earth’s energy budget, Geophys. Res. Lett., doi:10.1029/2011GL049236, in press. [Abstract] [PDF paywalled] (accepted 29 August 2011)