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An Assessment of Climate Feedbacks in Observations and Climate Models Using Different Energy Balance Frameworks

This study evaluates the performance of Coupled Model Intercomparison Project (CMIP) phase 5 and phase 6 models by comparing feedbacks in models to those inferred from observations. Overall, we find no systematic disagreements between the feedbacks in the model ensembles and feedbacks inferred from observations, although there is a wide range in the ability of individual models to reproduce the observations. In particular, 40 of 52 models have best estimates that fall within the uncertainty of the observed total feedback. We quantify two sources of uncertainty in the model ensembles: (1) the structural difference, due to the differences in model parameterizations, and (2) the unforced pattern effect, due to unforced variability, and find that both are important when comparing to an 18-year observational data set. We perform the comparison using two energy balance frameworks: the traditional energy balance framework, in which it is assumed that changes in energy balance are controlled by changes in global average surface temperatures, and an alternative framework that assumes the changes in energy balance are controlled by tropical atmospheric temperatures. We find that the alternative framework provides a more robust way of comparing the models to observations, with both smaller structural differences and smaller unforced pattern effect. However, when considering the relation of feedbacks in response to interannual variability and long-term warming, the traditional framework has advantages. There are no great differences between the CMIP5 and CMIP6 ensembles’ ability to reproduce the observed feedbacks.