On February 21, 2023, the Antarctic sea ice extent dropped to its lowest level since satellite observations began 45 years ago. This drastic reduction in sea ice raises the question of whether it is a brief anomaly or an early indication of a long-term decline.
The Antarctic sea ice extent reached its seasonal minimum of 1.788 million km2 on February 21, 2023, setting a new record low since the late 1970s. This was observed against the backdrop of anomalously low ice extents since 2017, particularly after the previous record of 1.924 million km2 in 2022. By mid-March, strong heat waves brought warm anomalies to East Antarctica and coastal areas, keeping the ice extent below average in March, which was the second lowest on record.
From late May, the pace of seasonal ice growth decreased significantly, partly due to anomalous winds that transported warmer air and pushed the sea ice edge southward. Since October, the seasonal ice melt had been at a well-above-normal pace. This led to the second lowest December extent on record, followed by the lowest for two consecutive months (January and February 2023) on record.
Several atmospheric drivers associated with modes of climate variability might have contributed to the 2023 new record minimum. First, at mid- and high-latitudes, 2022 experienced a persistent positive Antarctic Oscillation (AAO, except June). Moreover, a very strong AAO occurred in September, November, and December 2022, and the strongest AAO for the month of January was set in 2023. This occurrence led to a persistent, stronger, and southwestward shift in the Amundsen Sea Low (ASL), which greatly reduced the sea ice in the Bellingshausen Sea and east of the Antarctic Peninsula. Second, in the tropics, there was a moderate La Niña event that occurred in 2022, but it had been unusually prolonged for three consecutive years, making it a rare triple-dip event. Third, the negative phase of the Interdecadal Pacific Oscillation and the positive phase of the Atlantic Multidecadal Oscillation also favored strengthening of the ASL through stationary wave dynamics.
The global ocean has absorbed most of the excess heat induced by human activity, and its temperature surged to a record high in 2022. The heat content of the Southern Ocean has increased faster than that of other oceans, and the subsurface south of ~55°S has been significantly warmer.
More importantly, the new record low Antarctic sea ice extent marks a reversal from the long-term positive trend to a negative trend for the time series of the minimum ice extent, indicating that Antarctic sea ice may enter a new era. This finding further raises the question of whether changes in Antarctic sea ice in the past several years are a brief anomaly due largely to natural climate variability or early evidence of a robust transition from long-term increasing Antarctic sea ice to decreasing sea ice.
Concern about a tipping point is enhanced by the fact that the latest generation of climate and earth system models projects a large decrease in Antarctic sea ice associated with increased greenhouse gases during the 21st century.
