Antarctic sea ice extent reached a new record low on 21 February 2023, marking the second year in a row that it has fallen below 2 million km2. This raises questions about whether this is a brief anomaly or a sign of a long-term decline. Sea ice in the Southern Ocean is highly variable, both seasonally and year to year, but recent changes could signal a new regime.
The decline in Antarctic sea ice has been significant since 2017, with anomalously low ice extents recorded immediately after the previous record in 2022. Strong heat waves in March 2022 brought warm anomalies to East Antarctica and coastal areas, keeping the ice extent below climatology. Anomalous northerly/northwesterly winds in various sectors of the Pacific, Atlantic, and Indian oceans also slowed the pace of seasonal ice growth. In 2023, Antarctic sea ice experienced a rare event, with the lowest extent for three consecutive months (June, July, and August) and the lowest for two consecutive months (January and February).
Several atmospheric drivers associated with modes of climate variability could contribute to the record minimum, including the persistent positive Antarctic Oscillation, a strong Amundsen Sea Low, and a moderate La Niña event. However, starting in June 2022, widespread negative sea ice concentration anomalies were observed, particularly in spring and summer, beyond the control of the anomalous Amundsen Sea Low. This could be due to human-caused global warming, which has caused the subsurface of the Southern Ocean to warm faster than other oceans. The circumpolar westerlies over the Southern Ocean have also intensified and are predicted to increase under anthropogenic forcing, which could enhance Ekman suction and facilitate warmer subsurface water being transferred upward.
The new record low Antarctic sea ice extent in 2023 marks a reversal from a long-term positive trend to a negative trend, indicating that Antarctic sea ice could be entering a new regime. This raises concerns about whether these changes are a brief anomaly due to natural climate variability or early evidence of a robust transition from long-term increasing Antarctic sea ice to decreasing sea ice, where anthropogenic forcing outweighs natural variability. Climate and earth system models project a large decrease in Antarctic sea ice associated with increased greenhouse gases during the 21st century, highlighting the need for more research to improve our understanding of how future Antarctic sea ice change could interact with the broader earth system.
A large reduction in Antarctic sea ice would have significant impacts on the Antarctic climate and ecosystem, including climate extremes, stability of ice shelves, the food chain and wildlife population, and global consequences such as sea level rise and carbon cycle feedback. Therefore, more research is needed to better understand these changes and their potential impacts.