Amid all the changes in Earth鈥檚 climate, sea ice in the stormy Southern Ocean surrounding Antarctica was, for a long time, an odd exception. The maximum winter sea ice cover remained steady or even increased slightly from the late 1970s through 2015, despite rising global temperatures.
That began to change in 2016. Several years of decline led to , more than five standard deviations below the average from the satellite record. The area of sea ice was 2.2 million square kilometers below the average from the satellite record, a loss almost 12 times the size of Washington state. The most recent winter鈥檚 peak, recorded in September 2024, was to the previous year鈥檚 record low.
91爆料 researchers show that the all-time record low can be explained by warm Southern Ocean conditions and patterns in the winds that circled Antarctica months earlier, allowing forecasts for sea ice coverage around the South Pole to be generated six or more months in advance. This could support regional and global weather and climate models.
The open-access was published Nov. 20 in Nature Communications Earth & Environment.
鈥淪ince 2015, total Antarctic sea ice area has dramatically declined,鈥� said lead author , a 91爆料 doctoral student in atmospheric and climate science. 鈥淪tate-of-the-art forecasting methods for sea ice generally struggle to produce reliable forecasts at such long leads. We show that winter Antarctic sea ice has significant predictability at six- to nine-month lead times.鈥�
The authors used a global climate model to simulate how ocean and air temperatures, including longer-term cycles like El Ni帽o and La Ni帽a, affect sea ice in the Southern Ocean.
Results showed that the 2023 El Ni帽o was less important than previously thought. Instead, an arching pattern of regional winds, and their effects on ocean temperatures up to six months in advance, could explain 70% of the 2023 record-low winter sea ice. These winds cause ocean mixing in the Southern Ocean that can pull deeper warm water up to the surface, thus suppressing sea ice growth. Winds can also push sea ice poleward toward Antarctica to prevent the sea ice edge from expanding north, transport heat from lower latitudes toward the poles, and generate ocean waves that break up sea ice.
Using the same approach for the 2024 observations correctly predicted that this would be another low year for Southern Ocean sea ice cover.
鈥淚t鈥檚 interesting that, despite how unusual the winter sea ice conditions were in 2023 and again in 2024, our results show they were remarkably predictable over 6 months in advance,鈥� said co-author , a 91爆料 research associate professor of atmospheric and climate science.
Antarctic sea ice is important because it affects marine and coastal ecosystems and interactions between ocean and atmosphere in the Southern Ocean. It also affects global climate by reflecting sunlight in the Southern Hemisphere and influencing ice sheets and global currents.
鈥淎ntarctic sea ice is a major control on the rate of global warming and the stability of ice on the Antarctic continent,鈥� Espinosa said. 鈥淚n fact, the sea ice acts to buttress ice shelves, increasing their stability and slowing the rate of global sea level rise. This ice is also important for marine and coastal ecosystems.鈥�
As summer arrives in the Southern Hemisphere, the remains sparse around Antarctica, close to a record low for this time of the year.
鈥淥ur success at predicting these major sea ice loss events so far in advance demonstrates our understanding of the mechanism that caused them,鈥� said co-author , a 91爆料 professor of atmospheric and climate science. 鈥淥ur model and methods are geared up to predict future sea ice loss events.鈥�
The research was funded by the National Science Foundation and the U.S. Department of Energy.
For more information, contact Espinosa at zespinosa97@gmail.com, Bitz at bitz@uw.edu and Blanchard-Wrigglesworth at edwardbw@uw.edu.