Battering storms caused Antarctic sea ice to shrink at record pace

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Unusually severe storms in 2016 wrought the quickest meltdown of Antarctic sea ice ever seen during a Southern Hemisphere spring. This could explain why Antarctica’s sea ice extent hit a record low earlier this year.

Satellite images show that the extent of Antarctic sea ice decreased by an average of 75,000 square kilometers — almost the area of South Carolina — each day from September through December 2016. That was 18 percent faster than the previous record melt rate for this time of year and nearly 50 percent faster than average, researchers report online June 20 in Geophysical Research Letters.

Typically, the ring of sea ice surrounding Antarctica expands and contracts over the course of a year, usually peaking at around 18 million square kilometers in September, then shrinking to about 3 million by February. The average expanse of sea ice in a given year has increased since satellite monitoring started in 1979. So scientists were surprised that the sea ice shrank so radically this year. It hit 4.04 million square kilometers in January (SN Online: 2/17/17) and kept shrinking, dropping to about 2 million square kilometers by the beginning of March.

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The new study provides the first comprehensive analysis of why this drastic decline happened, says Walt Meier, a climate scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md., who was not involved in the work. Researchers examined weather data and found that a series of especially intense storms barraged the Southern Ocean during September, October and November 2016. Strong winds would have broken up the fragile sea ice, which is only about a meter thick, and bombarded it with warm air. Together, that hastened the usual springtime melting.

“People have said to us, ‘Is this global warming kicking in?’” says study coauthor Josh Turner, a climatologist at the British Antarctic Survey. But it’s impossible to pin one weird season on human-made climate change since scientists have been tracking sea ice extent for only a few decades — and it can vary widely from one year to the next.

“The big takeaway is that the Antarctic sea ice is very variable,” Meier says. “It has high highs and low lows, and we may not have seen the full range of it until now. Or maybe not even now.”