Environmental Science and Engineering Seminar

Antarctic sea ice, after a period of sustained, steady growth, supplemented by several above average sea ice extents in winter and summer over the satellite-observed era has, since 2016, transitioned to a period of sharply reduced sea ice extent (SIE), manifested by extremely low SIE in summer (2017, 2022, 2023, 2024, 2025) and extremely low SIE in winter 2023, 2024 and 2025. Such unexpected behavior of the Antarctic sea ice system is not reproduced in climate models, which may indicate some major deficiencies in our understanding and in the skill of projections. However, it has prompted the questions - Is this a short-term change, or has there been a structural change in the sea ice system? Is this abrupt change associated with natural variability or a forced signal related to anthropogenic activities? To begin answer these questions, we place the present SIE variability within the context of SIE variability for the 20th century using an ensemble of SIE reconstructed using Bayesian statistics. We query the characteristics of the SIE to find out if the variability that we see fits the picture of structural change. Results indicate that there has been a structural change in the Antarctic sea ice system, specifically that SIE no longer reverts to the mean. Instead, it has become a system characterized by extremes. We discuss what that means for the future of Antarctic sea ice and the ecosystems which it supports and how certain are we about it.