A new framework for isolating individual feedback processes in coupled general circulation climate models. Part II: Method demonstrations and comparisons
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We here use a coupled atmosphere-surface single column climate model to illustrate how the CFRAM, a new climate feedback analysis framework formulated in Part I of the two-part series papers, can be applied to isolate individual contributions to the total temperature change of a climate system from the external forcing alone, and from each of individual physical and dynamical processes associated with the energy transfer with the space and within the climate system. We demonstrate that the isolation of individual feedbacks in the CFRAM is achieved without referencing to a virtual climate system as in the online feedback suppression method. We show that partial temperature changes estimated by the online feedback suppression method include the “compensating effects” of other feedbacks when the feedback under consideration is suppressed. The partial temperature changes are addable in the CFRAM but they are not in the online feedback suppression method. We also apply the CFRAM to isolate the contributions to the lapse rate feedback from individual physical and dynamical feedback processes. We show that the lapse rate feedback includes not only the partial effect of each feedback that directly contributes to energy flux perturbations at the TOA (such as water vapor feedback), but also the total effects of those feedbacks that do not contribute to energy flux perturbations at the TOA (such as evaporation and moist convection feedbacks). Because the contributions to the lapse rate feedback from various physical and dynamical processes tend to cancel one another, the net lapse rate feedback is a residual of many large terms. This leads to a large uncertainty not only in estimating the lapse rate feedback itself, but also in other feedbacks whose effects are either partially or totally lumped into the lapse rate feedback.
The authors are indebted to Dr. Qiang Fu who provided us the radiative transfer model (Fu and Liou 1993), which is the core part of the coupled atmosphere-surface single column climate model used in this study. We are grateful for constructive comments from two anonymous reviewers. This work is supported by grants from the NOAA/Office of Global Programs (GC04-163 and GC06-038).
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