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August 31, 2017
While winter sea ice in the Arctic is declining so dramatically that ships can now navigate those waters without any icebreaker escort, the scene in the Southern Hemisphere is very different. Sea ice area around Antarctica has actually increased slightly in winter — that is, until last year.
A dramatic drop in Antarctic sea ice almost a year ago, during the Southern Hemisphere spring, brought its maximum area down to its lowest level in 40 years of record keeping. Ocean temperatures were also unusually warm. This exceptional, sudden nosedive in Antarctica differs from the long-term decline in the Northern Hemisphere. A new University of Washington study shows that the lack of Antarctic sea ice in 2016 was in part due to a unique one-two punch from atmospheric conditions both in the tropical Pacific Ocean and around the South Pole.
The study was published Aug. 24 in Geophysical Research Letters.
“This combination of factors, all these things coming together in a single year, was basically the ‘perfect storm,’ for Antarctic sea ice,” said corresponding author Malte Stuecker, a UW postdoctoral researcher in atmospheric sciences. “While we expect a slow decline in the future from global warming, we don’t expect such a rapid decline in a single year to happen very often.”
After increasing slightly in recent decades, the sea ice extent around Antarctica plummeted in 2016.Malte Stuecker/University of Washington
The area of sea ice around Antarctica at its peak in late 2016 was 2 million square kilometers (about 800,000 square miles) less than the average from the satellite record. Statistically, this is three standard deviations away from the average — an event that would be expected to occur randomly just once every 300 years.
The record low was not predicted by climate scientists, so UW researchers looked at the bigger picture in ocean and atmospheric data to explain why it happened.