Sensitivity of arctic sea ice thickness to intermodel variations in the surface energy budget

Sea ice simulations from an ensemble of climate models show large differences in the mean thickness of perennial Arctic sea ice. To understand the large thickness spread, we assess the sensitivity of thickness to the ensemble spread of the surface energy budget. Intermodel thickness and energy flux variations are related through a diagnostic calculation of thickness from surface temperature and energy fluxes. The calculation shows that an ensemble range of 60 W m^-2 in energy fluxes, as simulated by climate models, results in an approximate range of 1–5 m in ice thickness. The ensemble mean value of the melt season energy flux, together with a budget residual term that represents the effects of ocean heat exchange and ice divergence, are the key factors that determine the range in ice thickness owing to the flux spread. The ensemble spread in summertime energy flux is strongly related to the spread in surface albedo, while differences in longwave radiative forcing, due in part to cloud simulation errors, play a smaller role.