This study examines the observational evidence for a regime shift in Antarctic sea ice during summer. The authors analyze satellite sea ice records and atmospheric reanalyses to assess the changes in sea ice variability and its drivers. They find that the standard deviation of summer sea ice cover has doubled from 0.31 million km² in 1979–2006 to 0.76 million km² in 2007–22, indicating increased variance. This increased variance is accompanied by a longer season-to-season sea ice memory, suggesting a change in the system's response to atmospheric forcing. While the atmosphere remains the primary driver of sea ice variability, a linear predictive model shows that sea ice changes cannot be fully explained by atmospheric drivers alone. The statistical changes, including increased variance and autocorrelation, along with increased spatial coherence noted by previous research, are indicators of a critical transition or regime shift in the Antarctic sea ice system. The study supports the hypothesis that Antarctic sea ice has undergone a regime shift, with implications for seasonal predictability and ecosystem impacts.This study examines the observational evidence for a regime shift in Antarctic sea ice during summer. The authors analyze satellite sea ice records and atmospheric reanalyses to assess the changes in sea ice variability and its drivers. They find that the standard deviation of summer sea ice cover has doubled from 0.31 million km² in 1979–2006 to 0.76 million km² in 2007–22, indicating increased variance. This increased variance is accompanied by a longer season-to-season sea ice memory, suggesting a change in the system's response to atmospheric forcing. While the atmosphere remains the primary driver of sea ice variability, a linear predictive model shows that sea ice changes cannot be fully explained by atmospheric drivers alone. The statistical changes, including increased variance and autocorrelation, along with increased spatial coherence noted by previous research, are indicators of a critical transition or regime shift in the Antarctic sea ice system. The study supports the hypothesis that Antarctic sea ice has undergone a regime shift, with implications for seasonal predictability and ecosystem impacts.