Quantifying the sources of spread in climate change experiments

[1] Energy-balance models (EBM) constitute a useful framework for summarizing the first-order physical properties driving the magnitude of the global mean surface air temperature response to an externally imposed radiative perturbation. Here the contributions of these properties to the spread of the temperature responses of an ensemble of coupled Atmosphere-ocean General Circulation Models (AOGCM) of the fifth phase of the Coupled Model Intercomparison Project (CMIP5) are evaluated within the framework of a state-of-the-art EBM. These partial contributions are quantified (in equilibrium and transient conditions) using the analysis of variance method. The radiative properties, particularly the strength of the radiative feedback to the global equilibrium surface warming, appear to constitute the most primary source of the spread. Moreover, the adjusted radiative forcing is found to play an important role in the spread of the transient response.