Climate feedbacks in CCSM3 under changing CO₂ forcing. Part I: Adapting the linear radiative kernel technique to feedback calculations for a broad range of forcings

One method to estimate feedbacks in global climate models is the radiative kernel technique, which is well suited for model intercomparison studies because of its computational efficiency. However, the usefulness of this technique is predicated on the assumption of linearity between top-of-atmosphere (TOA) radiative fluxes and feedback variables, limiting its application to simulations of small climate perturbations, where non-linearities can be neglected.

This paper presents an extension of the utility of this linear technique to large forcings, using global climate model simulations forced with CO2 concentrations ranging from twice to eight times present day values. Radiative kernels depend on the model's radiative transfer algorithm and climate base state. For large warming, kernels based on the present day climate significantly underestimate longwave TOA flux changes and somewhat overestimate shortwave TOA flux changes.