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Science & Environment

Explaining Record Low Sea Ice Isn't As Simple As It Seems

Sea ice in the Ross Sea, Antarctica.
Brocken Inaglory
Sea ice in the Ross Sea, Antarctica.

While New England is being pummeled by a series of winter storms, a different kind of storm has been wreaking havoc at the North Pole. For the third time this winter, a storm has pushed north from lower latitudes, bringing with it temperatures close to the melting point. It’s the kind of event that typically only happens once or twice each decade.

Meanwhile, sea ice – both Arctic and Antarctic – are at an all-time low for this time of year. What’s the connection? The short answer, of course, is it’s complicated.

Arctic sea ice has been declining for years. That trend has been most notable in the summer, when rising temperatures exacerbate the normal seasonal melting.

“At the end of summer there’s usually an area about the size of the U.S. left,” said Ted Maksym, a sea ice physicist at Woods Hole Oceanographic Institution. “This year, we had quite a low sea ice extent in the summer – not record low, but pretty close.”

Normally, the sea ice begins to rebuild and expand during the fall and through the winter. This year started off as expected, with rapid sea ice growth in September, but then it took an unusual turn.

In late October and November, Maksym says the growth of sea ice “stalled” and it’s been advancing very slowly all winter. The result has been record-low amounts of sea ice for three months running, from November through January.

“It’s been a record low far beyond anything we expect,” said Maksym. “About two million square kilometers of ice has been missing, essentially, which is about the area of Alaska and Texas combined.”

The warm storms aren’t the sole cause, but they’re part of the picture. In addition to bringing temperature spikes, those storms pack winds that can break up the ice.

All told, Maksym says the current sea ice conditions in the Arctic are unusual, but not surprising when you look at the long term.

Antarctica is another story. Record low summer (remember, it’s the opposite season there) sea ice is more of a surprise because sea ice there has actually been growing in recent years, for reasons that scientists don’t fully understand.

“That’s been an area of active research trying to figure out exactly why,” said Maksym. “There’s a complex connection between El Nino, possibly sone long-term changes in what’s going on in the ocean in the Atlantic, changes in the winds around the Antarctic, and probably a little bit of anthropogenic, or human, influence – both CO2 and ozone depletion.”

Research suggests ozone depletion may cause short term increases in sea ice, but scientists expect a long-term decline as the ocean warms.

To make things even more complicated, sea ice is only one part of the ice equation in Antarctica. There are land-based glaciers (the real concern for sea level rise). At their edges, they extend out over the ocean as floating ice shelves. And these different types of ice interact with each other in direct, and indirect, ways.

One theory about the increase in sea ice was that melting of land-based ice was injecting a layer of cold, fresh water that could freeze into sea ice. The only problem is, the places where the most melting was happening didn’t match up with the places where sea ice was growing.

“What’s more likely is that it’s just change in winds,” said Maksym. “In the Antarctic, because the sea ice is so exposed to the open ocean, winds move it around very easily.”

That means year-to-year variations are to be expected.

“This year is pretty weird, though,” Maksym said.