Antarctic Winter Sea Ice Hits a Record Low ‘by a Wide Margin’

On September 10, the ice reached its lowest annual maximum in the books amid a record-smashing year that’s ringing “alarm bells” for polar ice

Chunks of ice float in water with a sunset reflecting off the water
Sheets of ice on top of the ocean in the Antarctic, photographed in February 2000. Sea ice reflects most of the sun's radiation that hits it, keeping the polar regions cool. Frances M. Ginter / Getty Images

At the end of each Antarctic winter, which occurs in September, the frigid continent’s sea ice has spread to its greatest extent of the year. This month, the ice reached its annual maximum on September 10—and it set a grim record.

Antarctic sea ice clocked its lowest annual maximum in recorded history “by a wide margin” this year, according to an analysis by the National Snow and Ice Data Center (NSIDC).

Researchers say the planet’s warming oceans could be the cause of the recent sea ice loss, and the decline could continue in years to come. The extent of summer sea ice in the Arctic is also shrinking, and it has been since the 1980s, per the NSIDC.

“It’s not great news,” Gail Whiteman, a researcher of sustainability and global risk at the University of Exeter in England, tells the Washington Post’s Kasha Patel. “Polar ice is one of the world’s biggest insurance policies against runaway climate change, and we can see in both the north and the south sea ice we’ve got problems, and alarm bells are ringing.”

Sea ice, which is frozen ocean water, grows and melts in the ocean and is typically covered with snow, per the NSIDC. On September 10, Antarctic sea ice was spread over 6.55 million square miles—an annual maximum that’s 676,000 square miles below the average from 1981 to 2010 and 398,000 square miles below the previous record low from 1986. The records date back to 1979.

“It’s not just a record-breaking year, it’s an extreme record-breaking year,” Walter Meier, a senior research scientist with the NSIDC who does sea ice remote sensing, tells Reuters’ Jake Spring.

The record for the lowest annual minimum sea ice was also broken this year, at the end of the Antarctic winter in February, according to the Guardian’s Graham Readfearn. Between April and August, the sea ice growth was significantly lower than it had been in any previous year on record. And it reached its maximum extent 13 days earlier than the median date from 1981 to 2010.

This low level of sea ice began in August 2016. While research found that the 2016 downturn was likely due to a series of storms, this year’s lack of ice growth is thought to be connected to warming of the ocean’s top layer, the NSIDC writes.

But other causes could be at play. “There is a chance that it’s a really freak expression of natural variability,” Robbie Mallett, who studies the decline of polar sea ice at the University of Manitoba in Canada, tells BBC News’ Georgina Rannard, Becky Dale and Erwan Rivault.

“As to why the sea ice has been so much lower than it has ever been on the record, we still don’t have a good grasp on that yet,” Ariaan Purich, a climate scientist at Monash University in Australia, tells the Guardian.

Human-caused climate change is leading Antarctic glaciers to melt, but scientists don’t have enough data yet to definitively prove it is melting the region’s sea ice, writes the Guardian. Antarctic sea ice grew between 2007 and 2016, according to Reuters, but the recent downward trend is consistent with climate change projections.

“There is some concern that this may be the beginning of a long-term trend of decline for Antarctic sea ice, since oceans are warming globally, and warm water mixing in the Southern Ocean polar layer could continue,” the NSIDC says in a statement.

Sea ice extent matters to the planet at large, because it keeps temperatures cool at the poles and plays a role in moderating the global climate, per the NSIDC. The bright surface of sea ice reflects between 50 and 70 percent of incoming solar radiation—and as much as 90 percent when it’s covered in snow. The darker ocean only reflects about 6 percent of sunlight, so when sea ice melts and exposes more water, the Earth absorbs more heat, exacerbating ocean warming and driving more melting.

Animals including seals, walruses, polar bears, arctic foxes and whales use sea ice to hunt, breed, forage and rest. A continued decline in sea ice could lead to the extinction of some species. Microorganisms rely on nutrients in the freshwater created by melting sea ice each year. And in the Arctic, Indigenous communities need sea ice for traveling and hunting, writes the NSIDC.

“To protect these frozen parts of the world that are really important for a whole number of reasons,” Purich tells Reuters, “we really need to reduce our greenhouse gas emissions.”

Get the latest stories in your inbox every weekday.