Antarctica's Pause in Ice Loss Is Probably Temporary

The two-year slowdown in Antarctica's ice loss that began in 2021 was driven by an atmospheric link to unusually persistent warmth in a tropical patch of ocean known as the warm pool, not by the long-term increase in Antarctic snowfall expected under global warming, and the gain is "probably temporary," according to a study published Aug. 19 in Nature.

Satellite gravity measurements from GRACE and GRACE-FO show Antarctica losing 140.5 gigatons of ice a year, give or take 2.0, over 2003 to 2024. Between July 2021 and April 2023 that reversed: the ice sheet gained about 695 gigatons, which the paper calls the largest 22-month gain in the two-decade satellite record. About 68 percent of it, 470.3 gigatons plus or minus 29.1, fell on one sector of East Antarctica covering Queen Mary Land and Wilkes Land.

The cause the authors identify is remote. Sea surface temperatures in the tropical warm pool stayed unusually high from 2021 to 2023 compared with the previous two decades. Observations and model experiments reveal that this warming set off a domino effect of atmospheric waves traveling toward the pole, which built a high-pressure area over East Antarctica and steered moisture onto the continent, mostly from the mid-latitude Indian Ocean.

Warming-driven moistening accounts for a small share of the snowfall, on the paper's numbers. In a 40-member climate model ensemble representing the response to greenhouse-gas forcing, precipitation over that sector rose 32.3 gigatons during the event, about 9 percent of the 351.2 gigatons the ERA5 reanalysis puts on the observed anomaly.

Similar multiyear warming of the tropical warm pool recurs about once per decade in observations and historical simulations, and its effect on precipitation is distinct from that of global warming. Therefore, the gain does not yet reflect sustained, warming-driven moistening of Antarctica.

West Antarctica kept losing mass throughout. The paper puts that loss at 82 gigatons a year for 1992 to 2020, and reports Antarctica's net mass balance between 2021 and 2024 as close to zero.