How subtropical oceans fuel polar snow and ice
The polar regions have been warming for decades, with record-high temperatures increasingly accompanied by precipitation in the form of snow and rain. The Arctic has seen impacts ranging from thawing permafrost to sea-ice loss, and the Antarctic ice sheet has been losing mass, adding to global sea-level rise over time. But between 2021 and 2023, something strange was observed in Antarctica; the ice sheet actually gained mass due to increased precipitation. Why did the loss slow, and where did the precipitation come from?
It turns out that Antarctic ice sheet thaw was temporarily slowed by water molecules that had traveled all the way from the Indian Ocean. A warmer-than-usual pool of water in the Western Pacific and Eastern Indian Ocean triggered an atmospheric phenomenon known as a Rossby wave train, which brought alternating high- and low-pressure weather systems and resulted in a strong poleward airflow that persisted over time.
When the sun warms the ocean, water evaporates and travels through the atmosphere, sometimes to distant locations, and eventually precipitates back to the ground once it cools. Over the Eastern Antarctic Ice Sheet, this led to higher-than-usual snowfall, adding to the physical mass of the ice sheet and helping to offset melting.
Although it persisted for a few years, this event was temporary; it was part of the short-term variability of a changing climate.
Tom Ballinger is an IARC researcher and coauthor of the recent Nature cover article “Multiyear tropical warm pool warming drives slowdown in Antarctic mass loss,” led by Yunhe Wang of the Chinese Academy of Sciences and Qinghua Ding from the University of California, Santa Barbara. Ballinger is also a coauthor of The Arctic chapter of a recently published Bulletin of the American Meteorological Society.
“The ocean is a slow-acting thermostat that can take months or years to warm or cool. Longer-term patterns like the [20-30 year] Interdecadal Pacific Oscillation influence shorter-term events that can have big, intermittent impacts,” according to Ballinger.
These fluctuations tend to coincide with pockets of warmer ocean surface temperatures that can trigger extreme weather conditions and events on land.
The Arctic is also warming three times faster than the rest of the globe and getting wetter across all seasons, especially in autumn and winter. We also see dramatic spikes in precipitation, like the atmospheric river in January 2025 that brought heavy rains to the coast and snow to Alaska’s interior, driven by a surge of warm, moisture-laden air that traveled northward from the subtropical and tropical Pacific Ocean.
Researchers can sleuth out where precipitation comes from by simulating its journey through a process called moisture tagging, or water tagging, using a modeling framework of geographic areas. On the ground, ice cores and snow samples can be obtained and analyzed in the lab for chemical clues that confirm locations where water vapor originates. Water from a specific place has a sort of molecular fingerprint: a unique isotopic signature depending on where and when it formed. These water molecules with different isotopes evaporate and condense at various rates depending on temperature.
Here in Alaska, many of us rely on a mid-winter visit to the subtropics to help us get through the winter cold and dark, but it turns out we are even more connected to these regions. The water molecules that fall on our gardens and that we ski on in winter may have originated in our winter holiday destinations.
Reference
Wang, Y., Ding, Q., Li, X., et al. (2026). Multiyear tropical warm pool warming drives slowdown in Antarctic mass loss. Nature. https://doi.org/10.1038/s41586-026-10912-x
Andreassen, L. M., Askjaer, T. G., Ballinger, T. J., Berner, L. T., Bernhard, G. H., Bhatt, U. S., … Veasey, S. W. (2026). The Arctic. Bulletin of the American Meteorological Society, 107(8), S296–S351.