In light of the ongoing shifts in Earth’s climate, the sea ice in the turbulent Southern Ocean encircling Antarctica had surprisingly remained stable. From the late 1970s to 2015, the maximum winter sea ice extent either stayed constant or even showed a slight increase, despite the rising global temperatures.
However, this trend began to reverse in 2016. Following several years of decline, 2023 recorded an unprecedented low, with sea ice levels plummeting over five standard deviations below the satellite-recorded average. Specifically, the sea ice area was 2.2 million square kilometers less than the average, which is nearly 12 times the area of Washington state. The peak of last winter, noticed in September 2024, was alarmingly close to the previous year’s record low.
Researchers from the University of Washington have pinpointed the reasons for this record low to warm conditions in the Southern Ocean and specific wind patterns that encircled Antarctica months prior. This allows for predictions regarding sea ice coverage around the South Pole to be made up to six months in advance, which may enhance both regional and global climate and weather models.
This study, which is freely accessible, was published on November 20 in Nature Communications Earth & Environment.
According to lead author Zac Espinosa, a doctoral student at UW specializing in atmospheric and climate science, “Since 2015, there has been a significant decline in the overall Antarctic sea ice area.” He emphasized, “Current top-tier forecasting techniques typically struggle to yield dependable forecasts over such extended periods. Our findings indicate that winter Antarctic sea ice is quite predictable with a lead time of six to nine months.”
The research team utilized a global climate model to explore how sea ice in the Southern Ocean is influenced by ocean and air temperatures, including long-term cycles like El Niño and La Niña.
The findings revealed that the 2023 El Niño’s significance was overestimated. Instead, a distinct regional wind pattern, along with its influence on ocean temperatures up to six months ahead, could account for about 70% of the record-low winter sea ice in 2023. These wind patterns promote mixing in the Southern Ocean, bringing warmer waters from below to the surface, thereby inhibiting sea ice formation. Furthermore, they can push sea ice towards Antarctica, limiting the expansion of the sea ice edge to the north, transport warmth from lower latitudes to the poles, and create ocean waves that break up the ice.
Using this same method, predictions for 2024 indicated another low year for Southern Ocean sea ice cover.
Co-author Edward Blanchard-Wrigglesworth, a research associate professor at UW, remarked, “It’s fascinating how our results illustrate that despite the unusual winter sea ice conditions in 2023 and again in 2024, they were strikingly predictable six months in advance.”
Antarctic sea ice plays a crucial role as it impacts marine life and coastal ecosystems, and mediates the interactions between the ocean and atmosphere in the Southern Ocean. It also contributes to global climate by reflecting sunlight in the Southern Hemisphere and affecting ice sheets and global ocean currents.
Espinosa noted, “Antarctic sea ice significantly influences the pace of global warming and the stability of the Antarctic landmass. Essentially, it serves to strengthen ice shelves, enhancing their stability and decelerating the rise in global sea levels. It is also vital for marine and coastal habitats.”
As summer approaches in the Southern Hemisphere, the current sea ice coverage around Antarctica remains low, nearing record lows for this season.
Co-author Cecilia Bitz, a UW professor focusing on atmospheric and climate science, stated, “Our ability to predict these significant sea ice loss events well in advance underscores our grasp of the mechanisms driving them. Our model and techniques are fine-tuned to anticipate future sea ice declines.”
The research received funding from the National Science Foundation and the U.S. Department of Energy.
