When Arctic sea ice extent hit its annual low-point for the year in September, it clocked in at the eighth lowest on record—far better than had been feared in projections earlier in the year. But that ranking doesn't tell the whole story.
As we enter December, the Chukchi and Bering Seas, which border Alaska on its western and northern sides, have unprecedented areas of open water and the least amount of ice ever recorded there.
"Certainly we've never seen anything quite like this before," said Mark Serreze, the director of the National Snow and Ice Data Center.
In recent years, the Chukchi Sea has reached 95 percent coverage about 2.5 weeks later than it did in the late 1970s, when satellites first started recording sea ice. This year, according to Rick Thoman of Alaska's Weather Service, it's falling even further behind.
"The thing is, we saw this coming," Serreze said. Last year, he co-published a study in the Journal of Geophysical Research that found that the timing of when warm water flows from the Bering Strait up to the Chukchi Sea is a strong indicator of how the sea ice will fare.
Early this summer, scientists aboard the research vessel Norseman II found an influx of warm, Pacific water near the Bering Strait about a month earlier than usual and measured water temperatures as high as 5 degrees Fahrenheit above the historical average. "There's just a hell of a lot of heat there," Serreze said.
As that water made its way up Alaska's coast, it was like a "double whammy," he said. The warm water flows in and helps melt the ice, and the dark water that's exposed absorbs heat from the Sun. Melting begets more melting, Serreze explained. "You're going to keep a lot of open water there for quite some time this year."
In addition to that warm water coming through the Bering Strait, Alaska has been hit by significant storms this fall. "The stronger winds and waves destroy the thinner ice," said Mary-Beth Schreck, a sea ice analyst with the National Weather Service Alaska Sea Ice Program.
Those storms have battered Alaskan coastal communities in recent months. One storm at the end of September in Utqiagvik resulted in an estimated $10 million in damage (read more about the toll climate change is taking on native hunting traditions and historic artifacts around Utqiagvik, formerly Barrow). Storms in October and November brought flooding to a number of communities. One caused such severe erosion in the island town of Shishmaref, near Nome, that officials declared a local disaster.
Scientists pay close attention to how much sea ice is left in September because that's when the summer shifts to fall—after a period of melting, the ice hits its lowest point before it starts to grow again. Sea ice in some areas of the Arctic fared better this year than they have in recent years (though still far below historical averages). The eighth-lowest ranking, on Sept. 13, came in large part because of how little sea ice was in a few key areas, including the Chukchi Sea. The Chukchi and Bering Seas have been slow to freeze in October and November, and Serreze said Arctic-wide sea ice levels today are among the lowest on historical record.
For the entire Arctic, "we're among probably the three or four lowest total extents right now," he said.