Melting on the Antarctic Ice Sheet for the 2024 to 2025 season began with above average melt extents in all regions, but melt extent dropped to nearly zero or below average from February 1 to March 15. Net accumulation of snow, part of the ice sheet’s surface mass balance, was far above average for the year ending in February 2025. Thus, extensive snowfall helped reduce the ice sheet’s net contribution to sea level rise for this period.
Current conditions
After setting records in December and January for melt extent in the 47-year satellite record, melt extents dropped abruptly by early February when conditions over the Antarctic Peninsula cooled. Overall, the number of melt days exceeded the 1991 to 2020 long-term average by approximately 10 days in the Larsen C Ice Shelf area, 15 days in the Fimbul Ice Shelf area, and over 30 days along the eastern side of the Amery Ice Shelf. Also notable were above average melt days in the West, Shackleton, and Totten Ice Shelf areas. The Sulzberger and Ross Ice Shelves were among the few areas with below average melt days for the austral summer season. Extensive ponding apparent in January in satellite images on the Larsen B remnant, known as Scar Inlet Ice Shelf, and northern Larsen C, all refroze in February; however, ponding and some surface melt flow were still visible on the Amery and Roi Baudouin Ice Shelves into March, although with a frozen surface at that point.
Colleagues at the University of Grenoble in France map daily melt extent using a different passive microwave sensor, the Advanced Microwave Scanning Radiometer 2 (AMSR2), similar to our Special Sensor Microwave Imager (SSMI). Their map pattern is very similar to ours although with a slightly higher number of melt days in all areas.
Conditions in context
Cool conditions over the Antarctic Peninsula later in the melt season brought on the sudden decline in melt extent and number of melt days. Conditions, however, remained warm compared to the average in Dronning Maud Land and West Antarctica, although temperatures rarely reached high enough to cause melt. East Antarctica was generally cooler than average, although a spurious region of persistently low temperatures and high air pressures in central Wilkes Land is likely related to data from a faulty weather station. Broader measures of climate, such as the Southern Annual Mode Index—a measure of the strength of the polar vortex surrounding Antarctica—were near neutral, indicating that the strong summer melting and low sea ice extent may plausibly be attributed to a warmer climate and ocean rather than an unusual pattern of air circulation.
Unusual heavy snowfall over the past 12 months may offset ice sheet losses this year
Total net accumulation of snow, known as the surface mass balance (SMB), has been far above average for the March 2024 to February 2025 period, by nearly 200 billion tons. SMB is the net contribution of snowfall, and a tiny amount of rainfall, minus the evaporation of snow and ice from the surface. The excess snowfall was primarily located along the Dronning Maud Land coast, central East Antarctica, and the Getz Ice Shelf area of West Antarctica. For reference, the average annual total surface mass balance for the continent is roughly 2,400 billion tons.
Maximum melt pond extent in recent years at two East Antarctic Ice Shelves
While the Larsen Ice Shelf and George VI Ice Shelf reached near-record melt pond extents in early January, the intensity of melting slowed as the month proceeded. However, for the Roi Baudouin and Amery Ice Shelves, near-record melt pond extents were observed into February.
Further Reading
Jezek K. C., C. J. Merry, and D. J. Cavalieri. 1993. Comparison of SMMR and SSM/I passive microwave data collected over Antarctica. Annals of Glaciology, 17:131-136, doi:10.3189/S0260305500012726.
Mottram, R., N. Hansen, C. Kittel, J. M. Van Wessem, C. Agosta, C. Amory, F. Boberg, W. J. Van De Berg, X. Fettweis, A. Gossart, and N. P. Van Lipzig. 2021. What is the surface mass balance of Antarctica? An intercomparison of regional climate model estimates. The Cryosphere, 15(8), 3751-3784, doi:10.5194/tc-15-3751-2021.
Picard, G., and M. Fily. 2006. Surface melting observations in Antarctica by microwave radiometers: Correcting 26-year time series from changes in acquisition hours. Remote Sensing of Environment, 104(3), 325–336, doi:10.1016/j.rse.2006.05.010.