Thursday, August 23, 2012

New paper finds unjustified assumptions on clouds in most climate models

A paper published today in Earth System Dynamics finds that due to large uncertainties and limited data it is not possible "to rule out either the positive [cloud] feedback present in most climate models or a strong negative cloud feedback." This huge unknown could alone be responsible for all global warming due a tiny 1-2% natural change in global cloud cover. Climate models conveniently assume clouds are a positive feedback that accelerates global warming, but this paper and many others show this is an unjustified assumption and that cloud feedback could instead be "strongly negative."

Earth Syst. Dynam., 3, 97-107, 2012
www.earth-syst-dynam.net/3/97/2012/
doi:10.5194/esd-3-97-2012


On the determination of the global cloud feedback from satellite measurements
T. Masters
School of Engineering and Applied Science, UCLA, Los Angeles, California, USA
 Abstract. A detailed analysis is presented in order to determine the sensitivity of the estimated short-term cloud feedback to choices of temperature datasets, sources of top-of-atmosphere (TOA) clear-sky radiative flux data, and temporal averaging. It is shown that the results of a previous analysis, which suggested a likely positive value for the short-term cloud feedback, depended upon combining all-sky radiative fluxes from NASA's Clouds and Earth's Radiant Energy System (CERES) with reanalysis clear-sky forecast fluxes when determining the cloud radiative forcing (CRF). These results are contradicted when ΔCRF is derived using both all-sky and clear-sky measurements from CERES over the same period. The differences between the radiative flux data sources are thus explored, along with the potential problems in each. The largest discrepancy is found when including the first two years (2000–2002), and the diagnosed cloud feedback from each method is sensitive to the time period over which the regressions are run. Overall, there is little correlation between the changes in the ΔCRF and surface temperatures on these timescales, suggesting that the net effect of clouds varies during this time period quite apart from global temperature changes. Given the large uncertainties generated from this method, the limited data over this period are insufficient to rule out either the positive feedback present in most climate models or a strong negative cloud feedback.

 Final Revised Paper (PDF, 626 KB)   Supplement (168 KB)   Discussion Paper (ESDD)   




Related: 
Paper showing that the models are pathetic at representing clouds:
Others on clouds and water vapor as negative feedbacks:

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