State of the Climate in 2024. Antarctica and the Southern Ocean

In 2024, atmospheric conditions over Antarctica exhibited significant anomalies, and were marked by major surface and stratospheric warming and pressure fluctuations. The first half of the year (January–June) featured persistent below-normal surface pressure over the continent, a distinct zonal wavenumber-3 pattern with three deep atmospheric troughs extending over the Weddell Sea, Prydz Bay, and Ross Ice Shelf, and a positive phase of the Southern Annular Mode, with strong circumpolar westerlies. Surface pressure anomalies in February and April were particularly pronounced, with multiple stations recording record-low pressures. Strong stratospheric warming occurred in July followed by extreme surface warming in August. The surface warming was likely intensified by a compound event: 1) a strong ridge of surface high pressure along coastal East Antarctica advected warm maritime air into the continental interior, and 2) a significant positive geopotential height and temperature anomaly in the stratosphere propagated downward to the surface. As a result, multiple monthly records for high temperatures and pressure were set in August. The Antarctic Ice Sheet’s surface mass balance (SMB) in 2024 was shaped by contrasting periods of high snowfall and regional drought. The most significant anomaly occurred in May, when extreme snowfall led to record-high SMB gains across much of East and West Antarctica. Enhanced meridional moisture transport and atmospheric river events—which funneled moisture from the South Pacific and Atlantic Oceans toward the continent—supported/generated this extreme snowfall. In contrast, September emerged as the driest September on record, with a severe shortage of snowfall over the ice sheet. This was linked to an anomalously deep and eastward-shifted Amundsen Sea Low, which suppressed precipitation and led to below-average SMB across West Antarctica.