Yet on the other side of the planet in Antarctica, the sea ice seems to have evaded the global warming trend. Since 2010, there have been more interannual fluctuations than in the previous period. However, apart from a significant negative excursion in the years 2016 to 2019, the long-term mean sea-ice cover around the Antarctic continent has remained stable since 1979. As such, the observable reality does not match the majority of scientific simulations, which show a significant sea-ice loss over the same timeframe. “This so-called Antarctic sea-ice paradox has preoccupied the scientific community for some time now,” says first author Thomas Rackow from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). “The current models cannot yet correctly describe the behaviour of the Antarctic sea ice; some key element seems to be missing. This also explains why the Intergovernmental Panel on Climate Change, IPCC, concludes that the confidence level for model-based projections of future Antarctic sea ice is low.” In contrast, the models are already so reliable in the Arctic that the IPCC ascribes a high confidence level to their projections. “With our study, we now provide a basis that could make future projections for Antarctica much more reliable.”
In the course of the study, the team applied the AWI Climate Model (AWI-CM). Unlike other climate models, the AWI-CM allows certain key regions like the Southern Ocean to be simulated in far more detail – or in other words, in “high resolution”. As a result, mixing processes in the ocean, caused by smaller ocean eddies with diameters of 10 to 20 kilometres, can also be directly included.
“We used a broad range of configurations for our simulations. In the process, it became clear that only those simulations with a high-resolution description of the Southern Ocean encircling the Antarctic produced delayed sea-ice loss similar to what we are seeing in reality,” says Rackow. “When we then extended the model into the future, even under a highly unfavourable greenhouse-gas scenario the Antarctic sea-ice cover remains largely stable until mid-century. After that point the sea ice retreats rather rapidly, just as the Arctic sea ice has been doing for decades.”