ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-1923-2010 Estimations of climate sensitivity based on top-of-atmosphere radiation imbalance Lin B. 1 Chambers L. 1 P. Stackhouse Jr. 1 Wielicki B. 1 Hu Y. 1 Minnis P. 1 Loeb N. 1 Sun W. 2 Potter G. 3 Min Q. 4 Schuster G. 1 Fan T.-F. 2 NASA Langley Research Center, Hampton, VA 23681, USA SSAI, One Enterprise Parkway, Hampton, VA 23666, USA University of California at Davis, Davis, CA 95616, USA State University of New York at Albany, Albany, NY 12222, USA 19 02 2010 10 4 1923 1930 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/10/1923/2010/acp-10-1923-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/1923/2010/acp-10-1923-2010.pdf

Large climate feedback uncertainties limit the accuracy in predicting the response of the Earth's climate to the increase of CO<sub>2</sub> concentration within the atmosphere. This study explores a potential to reduce uncertainties in climate sensitivity estimations using energy balance analysis, especially top-of-atmosphere (TOA) radiation imbalance. The time-scales studied generally cover from decade to century, that is, middle-range climate sensitivity is considered, which is directly related to the climate issue caused by atmospheric CO<sub>2</sub> change. The significant difference between current analysis and previous energy balance models is that the current study targets at the boundary condition problem instead of solving the initial condition problem. Additionally, climate system memory and deep ocean heat transport are considered. The climate feedbacks are obtained based on the constraints of the TOA radiation imbalance and surface temperature measurements of the present climate. In this study, the TOA imbalance value of 0.85 W/m<sup>2</sup> is used. Note that this imbalance value has large uncertainties. Based on this value, a positive climate feedback with a feedback coefficient ranging from &minus;1.3 to &minus;1.0 W/m<sup>2</sup>/K is found. The range of feedback coefficient is determined by climate system memory. The longer the memory, the stronger the positive feedback. The estimated time constant of the climate is large (70~120 years) mainly owing to the deep ocean heat transport, implying that the system may be not in an equilibrium state under the external forcing during the industrial era. For the doubled-CO<sub>2</sub> climate (or 3.7 W/m<sup>2</sup> forcing), the estimated global warming would be 3.1 K if the current estimate of 0.85 W/m<sup>2</sup> TOA net radiative heating could be confirmed. With accurate long-term measurements of TOA radiation, the analysis method suggested by this study provides a great potential in the estimations of middle-range climate sensitivity.

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