Revisiting the variation of the climate feedback parameter

Observations and models indicate a varying radiative response of the Earth system to CO₂ forcing. This variation introduces large uncertainties in the climate sensitivity estimates to increasing atmospheric CO₂ concentration. This variation is represented as an additional feedback mechanism in energy-balance models, which depends on more than only the surface temperature change. Models and observations also indicate that a spatio-temporal pattern in the surface warming controls this additional contribution to the radiative response. However, several authors picture this effect as a feedback change in the atmosphere, reducing the role of the ocean's enthalpy-uptake variations. I use a widely-known linearised conceptual energy-balance model and its analytical solutions to find an explicit expression of the radiative response and its temporal evolution. This explicit expression provides another timescale in the Earth system, as the ocean-atmosphere coupling modulates the radiative response. Thus, to understand the variation of the climate feedback parameter, we need not only to know its relation to the spatio-temporal warming pattern but an improved picture of the ocean-atmosphere coupling that generates the pattern.