A team of scientists from Princeton University, NOAA-GFDL, and UCAR performed global climate model simulations, using a newly developed coupled ocean–atmosphere model SPEAR (Seamless System for Prediction and Earth System Research). When this model was driven with changes in past radiative forcing, the model simulation did not reproduce the observed increasing trends in sea-ice concentration around the Antarctic. Instead, the model simulated a steady warming and Antarctic sea-ice loss as is commonly seen in multi-model mean results of Coupled Model Intercomparison Project Phase 5 (CMIP5) models. However, they showed that the observed sea-ice expansion during the past decades is within the range of natural variability in their 2000-year control simulation. Therefore, they concluded that natural variability in the Southern Ocean played a large role in the observed sea-ice expansion around Antarctica during the past decades.
Zhang, L., Delworth, T. L., Cooke, W., & Yang, X. (2018). Natural variability of Southern Ocean convection as a driver of observed climate trends. Nature Climate Change.