What to know about the huge losses of Antarctic sea ice
The giant donut of ice encircling Antarctica is volatile.
This ring of sea ice around the continent -- which grows each winter and largely melts each summer -- had been gradually increasing in size for 36 years, since reliable satellite measurements came online in 1979. But in late 2014, things changed dramatically. Between 2014 and 2017, the average sea ice extent plummeted, each year losing an area of ice (280,000 square miles) larger than the size of France.
"It’s just a huge decrease," marveled NASA scientist Claire Parkinson, who for over 40 years has used satellites to track sea ice trends in Earth’s frigid polar worlds.
On Monday, Parkinson published a new, comprehensive analysis of Antarctic sea ice in the journal Proceedings of the National Academy of Sciences. The research emphasizes how unpredictable the floating ice around Antarctica can be, and perhaps more so, raises questions about what’s driving the change. The sudden drop, after years of consistent growth, seems puzzling.
"I can assure you it’s been puzzling for the scientists also," said Parkinson.
Polar scientists are now investigating conditions in the ocean and atmosphere that could be responsible for the diminished ice. But the big takeaway, emphasized Walt Meier, a senior research scientist at the National Snow and Ice Data Center, is that the recent drop off shows Antarctic sea ice is prone to some immense swings in growth and loss. "The Antarctic is more variable than previously thought (or at least previously seen in the satellite record)," Meier, who had no involvement in the research, said over email.
Though, however notable Antarctica's sea ice loss has been since 2014, it’s nothing like what’s going on in the melting Arctic -- home to the most rapidly warming and changing region on Earth.
"[The study] definitely shouldn’t be read as the Antarctic suddenly showing a larger change than the Arctic," said Meier. "The Arctic sea ice environment has in many ways been completely transformed."
Stoked by warming oceans and air, Arctic sea ice is plunging to historic lows. "The 12 lowest extents in the satellite record have occurred in the last 12 years," NOAA's 2018 Arctic report underscored.
Meier has studied some of the earliest satellite imagery of Antarctica, from the 1960s. Though the old pictures are of lower quality and incomplete compared to modern satellite records, it does paint a picture of a highly variable Antarctic -- similar to what Parkinson has recently observed. There were almost certainly giant swings in the Antarctic sea ice some 60 years ago, with a big drop comparable to that occurring in recent years, he noted.
"In the Antarctic, it’s basically the same old story, with some fireworks (apropos for the [July 4] holiday I suppose) in recent years," Meier added.
What’s driving the changes?
It’s a compelling question. And it’s not so easily answered.
The Antarctic region is objectively a vastly different and more complicated region that the Arctic -- which unlike the Southern Ocean doesn’t have a massive, frozen continent sitting in the middle of its pole. Also, Antarctic oceans aren’t bound by big land masses -- namely Alaska, Canada, and Siberia -- like the Arctic. This leaves Antarctic sea ice all the more exposed to natural changes in circulating ocean and atmospheric conditions.
"It’s more complex," explained Ethan Campbell, a University of Washington Ph.D. student in physical oceanography who researches Antarctic ice. Campbell had no role in the NASA study.
Polar scientists have long been working to unravel the complexity. "There has been a lot of speculation about what could conceivably have been causing, for decades, an overall increase in sea ice in the Southern Ocean -- but there wasn’t ever a consensus viewpoint," said NASA’s Parkinson.
Now, after the abrupt reversal of ice growth, researchers have the opportunity to better examine what forces could drive such sustained ice increases, followed by such big losses, she explained.
One thing, however, is more certain. In stark contrast to the Arctic, it’s much too soon to say whether global warming is at fault. "Anyone who speculates conclusively that the new downward trends are related to climate change are far overstating the understanding we have," noted Campbell.
Scientists have proposed a number of ideas, noted Parkinson, linking ice losses to prominent El Niño events, longer-term temperature trends in the Pacific Ocean, the ozone hole over Antarctica, and shifts in atmospheric circulations over Antarctic seas. There is evidence that big Antarctic ice losses, at least in 2016, were stoked by the El Niño warming of tropical waters, which were then related to warmer seas around parts of Antarctica, explained Campbell.
But to really solve the conundrum, polar scientists must keep vigilantly watching the dynamic Antarctic. "We need sustained observations of the ocean," emphasized Campbell. "We need to continue the ice record."
For the past 40 years, Parkinson has used both NASA and Department of Defense satellites to monitor Antarctic sea ice. The satellites detected natural microwave radiation emanating from the ice and water, giving her a reliable record of constantly changing sea ice -- even when the bottom of the world is shrouded in clouds or months-long winter darkness. "We can get our data even if there’s no sunlight," she said.
"It’s a crowning achievement," noted Campbell, of the 40-year polar satellite record.
And it’s helped illuminate dramatic, puzzling changes in the volatile Antarctic -- changes that have stoked significant scientific curiosity.
"Everyone in the community is interested," said Campbell.
Mark was the science editor at Mashable. After working as a ranger with the National Park Service, he started a reporting career after seeing the extraordinary value in educating people about the happenings on Earth, and beyond.
He's descended 2,500 feet into the ocean depths in search of the sixgill shark, ventured into the halls of top R&D laboratories, and interviewed some of the most fascinating scientists in the world.
