Correlation between present-day model simulation of Arctic cloud radiative forcing and sea ice consistent with positive winter convective cloud feedback

A positive feedback on winter sea-ice loss, based on warming due to radiative forcing caused by the onset of convective clouds in response to sea-ice loss, has recently been proposed. This feedback has thus far been investigated using a hierarchy of climate models in high CO2 scenarios. This paper examines the possibility that such feedback may be active within present-day like Arctic variability, using model output from two reanalysis models. It is emphasized that Arctic surface fluxes, radiative fluxes and clouds are effectively unconstrained by observations in reanalysis products. Consequently, the results here should be viewed only as a model study of the feedback in present-day model climate variability. Model winter sea ice and cloud radiative forcing are found to co-vary strongly and locally, consistent with a strong convective cloud feedback, which may contribute to sea ice variability. Furthermore, the anti-correlation between the two variables is found to be as strong in the model output analyzed here as in the IPCC global climate models that simulate the convective cloud feedback most strongly at high CO2. In those IPCC models the convective cloud feedback contributes to a total loss of winter sea ice in a CO2 quadrupling scenario. These results do not necessarily prove that this feedback exists in the present-day Arctic and demonstrating this will require further study using actual Arctic observations.