Biases in Climate Model Global Warming Trends Related to Deficiencies in Southern Ocean Sea Ice Evolution Over Recent Decades

Between 1985 and 2014 observations show an expansion of Southern Ocean sea-ice. This phenomena is not simulated in CMIP6 Atmosphere-Ocean General Circulation Models (AOGCMs). Here we quantify the impact of this discrepancy on radiative feedback and simulated global temperature trends. We find that both satellite reconstructions of the Earth's energy budget and atmosphere-only GCM simulations forced with observed Sea Surface Temperature (SST) and sea-ice trends support the hypothesis of a negative surface albedo feedback over the Southern Ocean. In contrast, declining sea-ice in AOGCMs gives rise to a positive feedback. We estimate that had the AOGCMs simulated the observed Southern Ocean sea-ice evolution their global feedback parameter would be less positive by 0.07–0.23 $\text{W}{\text{m}}^{-2}{K}^{-1}$ (which is 12%–29% of the total difference between AOGCM simulations and simulations forced with observed SST and sea-ice) and their global temperature trend over this 30 year period reduced by 0.01–0.06 K ${\text{decade}}^{-1}$.