Arctic sea ice closes in on record low for the winter

Sea ice off the coast of Lapland, Finland, in June, 2014.
Image: DeAgostini/Getty Images

In another sign of how swiftly global warming is reshaping the Arctic, it is likely that scientists will declare a record low annual maximum sea ice extent as early as Thursday. This means that the sea ice cover, which has been in a steep decline in recent decades, built up to a record low level this winter.

The winter sea ice extent maximum usually occurs in March, but based on a recent decline in sea ice since the start of the month, as well as ocean temperatures in areas that currently lack sea ice cover, scientists are likely to declare that the maximum actually occurred on or about February 25.

"Previous years have seen a surge in Arctic ice extent during March (e.g., in 2012, 2014). However, if the current pattern of below-average extent continues, Arctic sea ice extent may set a new lowest winter maximum," the National Snow and Ice Data Center in Boulder, Colorado, which tracks sea and land ice, stated on its website on March 4.

Sea Ice Extent

Arctic sea ice extent for 2015 compared to other recent years and the recent average. The likely winter peak indicated with arrow.

Image: NSIDC/Mashable

The winter maximum is when the sea ice typically is at its most expansive and thickest, ahead of the increasingly intense melt season that lasts from spring through early fall.

The fact that this year's maximum is likely to be the lowest on record since consistent satellite monitoring began in 1979 is a warning sign that the longterm warming trend in the Arctic, which has been tied to the burning of fossil fuels such as coal and oil, continues to take its toll on the Far North.

The paltry peak in ice extent does not necessarily mean that 2015 will set a new record low summer ice extent, says Julienne Stroeve, a scientist at the NSIDC.

"In terms of what might happen this summer there's not necessarily a correlation between the two," she said in an interview, noting that ice thickness is a better predictor, since thicker sea ice is more difficult to melt in a single season.

A new study published in the journal Cryosphere found that Arctic sea ice has thinned out more significantly than previously reported, suggesting that the odds favor more record low summer melt seasons. The study, published in early March, found a 65% decline in sea ice thickness between 1975 and 2012.

"That's a more important factor than the total extent," Stroeve said.

Global warming has set off a positive feedback loop in the Arctic by melting sea ice via milder air and water temperatures, which exposes darker ocean waters to solar radiation, thereby allowing it to absorb more heat and then melt more sea ice.

This dynamic helped sea ice dip to a record low in 2012, with slightly higher ice extents observed since then.


The U.S.S. Scranton seen at the surface at the North Pole in 2001, after breaking through several feet of sea ice.

Image: U.S. Navy

Scientists have emphasized that although the longterm trend is toward thinner, sparser ice cover in the Arctic — which is already having major consequences in the realms of national security and energy resource extraction — there will be considerable variability from one year to the next.

"We might wait another day to see what happens," Stroeve said in an interview Wednesday, regarding the annual maximum ice extent declaration. "It's more likely to happen in March," she said, but at the same time, "It's not too unusual for the maximum to happen in February."

If it was so cold in parts of the U.S., how did Arctic sea ice not build up more?

As a frigid February caused large chunks of river ice to form on the Hudson River flowing past Manhattan, the same weather pattern affected the Arctic in different ways.

Think of the Arctic like a freezer, with sea ice and land-based glaciers locked inside. This winter, Mother Nature, through powerful jet stream winds, pried the freezer door open, allowing some of the ultra-cold air to escape, while sucking in comparatively mild air into the freezer compartment.

This pattern discouraged the buildup of a large, thick and resilient sea ice pack.

For example, sea ice extent was particularly low in the Bering Sea and the Sea of Okhotsk, which lies between Russia and Japan. This was tied to air temperatures that, during February, were as much as 11 degrees Fahrenheit above average.

Such unusually warm temperatures extended across most of northern Eurasia, Alaska and the Western U.S., as the jet stream was shunted far to the north of these areas. This allowed milder southerly winds to transport mild air into these regions. This weather pattern was tied in part to a pattern of atmospheric pressure over the North Atlantic, known as the Arctic Oscillation.

Air Temperature Anomaly

Air temperature anomalies on March 11, 2015, showing a large area of above average temperatures across the Arctic (orange/red hues).

Image: University of Maine/Climate Re-Analyzer

The positive phase of the Arctic Oscillation favors milder than average conditions in parts of the Arctic. It also can encourage the transport of older, thicker ice out of the Arctic through the Fram Strait, which lies between the west coast of Greenland and northeastern Canada, and Stroeve says there is evidence this took place in recent months as well.

Stroeve told Mashable that the winter featured regular injections of milder than average air into the Arctic from the North Atlantic, as storm after storm pummeled eastern Greenland and Iceland.

"With the Arctic Oscillation the way it's been there's been a lot of cyclones that have tracked up there," she said.

Unusually mild air moved into the Arctic in and around the Barents and Kara seas, which saw retreating ice cover since the end of February. Sea ice this winter was also below average in the Bering Sea off Alaska and the Sea of Okhost, which lies between the Kamchatka Peninsula and the Japanese island of Hokkaido.

What about Antarctica?

Although sea ice has been declining in the Arctic, it has been increasing slightly in the Antarctic. However, the global average sea ice extent during the 1979 to 2013 period is downward, meaning that the Antarctic sea ice growth — which may be temporary — is not balancing out the ice losses in the Far North.

According to a recent study, the annual average trend is minus 13,500 square miles per year, or about a drop of 1.5% per decade.