Sea ice levels in Antarctica have reached their lowest point since satellites started watching the region, a new study has found.
Per a report published in Advances in Atmospheric Sciences on Tuesday, sea ice in Antarctica reached a record low on Feb. 25, 2022 at just under 2 million square kilometers. According to the study, it’s the second time in five years that sea ice has taken a significant dive, with the previous event occurring in 2017.
Antarctic sea ice oscillates in volume throughout the year every year, swinging between around 7 million square miles during winter and around 1 million square miles during summer. But on February 25, toward the very end of its summer season, Antarctica’s sea ice was a mere 1.92-million square kilometers—the first time that the Southern Hemisphere has seen sea ice volumes so low since the poles were first recorded via satellite in 1978.
Across the region, sea ice volumes were nearly nearing 30 per cent lower than the annual average baseline, with regional variability. The researchers located “significant negative anomalies” in sea ice volume levels west of the continent: in the Bellingshausen, Amundsen and Weddell seas, and by the Western Indian ocean.
The researchers used a method called a sea-ice budget analysis to look at factors that would influence increases and decreases in sea ice loss to assess how the continent reached record lows. They found that, in the summertime, anomalies in the movement of heat toward the poles drag down ice volumes in the western part of Antarctica. According to the paper, the sea ice retreat started earlier than normal last year, and then experienced a delayed recovery in late February, leading to the low ice levels.
They also attribute sea ice melt to the albedo effect—the feedback loop created when light hits the surface of sea ice, and reflects it back into the atmosphere, keeping temperatures cool. Global warming, broadly, has thrown off this cooling mechanism, and as regions lose ice, they lose a key mechanism for managing temperature. Instead, the authors write, the ocean absorbs heat from the sun, leading to even more melting.
“Sea ice is whiter than the dark unfrozen sea, thus there is less reflection of heat and more absorption,” Qinghua Yang, a co-author of the study and professor at Sun Yat-sen University, said in a press release. “Which in turn melts more sea ice, producing more absorption of heat, in a vicious cycle.”
In the spring, Yang and his team found that on top of albedo, ice volume loss in the southwestern region of Antarctica pushes ice northward, toward the tropics, where temperatures are higher and more likely to spur melting. All of these phenomena occurred in tandem with La Niña, a weather event that takes place every two years in which winds blow warm ocean water from South America westward toward Indonesia and Australia.
The low ice volumes recorded are only temporary, and based on a range of variable factors. But Yang and his team’s findings are a sign that annual ice melt in the Southern Hemisphere is catching up with a trend that’s long occurred in the Northern Hemisphere. Arctic sea ice has long been in rapid decline as a result of global warming, while sea ice in Antarctica has seen steady growth. That could be changing, and Yang and his team hope their paper has helped land on why. Next, they’re setting their sights on figuring out what parts of the region are most vulnerable.
“If tropical variability is having such an impact, it’s that location that needs to be studied next,” said Jinfei Wang, co-author on the paper.