Projected Southern Ocean Sea Ice and Sea Surface Temperature Evolution beyond 2100

Abstract:

Sea ice in the Southern Ocean is an integral component of Antarctic climate and its evolution. It acts as a protective buffer to outlet glaciers and ice shelves while also supporting the function of critical phytoplankton communities and ice algal productivity. However, sea ice is not fully understood in the context of climate change dynamics. Here, we analyse the rate and spatial scale of sea ice changes in the extended runs (2300 AD) of the Coupled Model Intercomparison Project 5 and 6 (CMIP5 and CMIP6). Comparing CMIP5 and the first-released CMIP6 models, we evaluate the temporal and spatial changes in seasonal and annual-average sea surface temperature and sea ice extent in both historical simulations and the extended projections of the high greenhouse gas (GHG) and low GHG emission scenarios. In historical simulations, the CMIP6 models demonstrate less intermodel spread than CMIP5, but do not capture the high variability observed in 21^st century sea ice extent. Of the models investigated, both CMIP5 and CMIP6 retain modern sea ice extent in the low emission scenario, but CMIP5 shows greater sea ice extent in later years of the high emission scenario – suggesting that the CMIP6 models have higher sensitivity to GHG forcing than their predecessors. All models analyzed in this study show summer sea ice disappearing by ~2125 and winter sea ice disappearing by ~2200 in high emissions scenarios, with some of the low emissions scenarios exhibiting minimal change in sea ice extent relative to the historical period. In the high emissions scenarios, sea surface temperature increases linearly with sea ice decline in some models, but exponentially in others, indicating inconsistency in climate model behavior.