Antarctic sea ice dips to record-low extent for early January

By Bob Henson 
16 January 2019

(Weather Underground) – Just two years after shrinking to its lowest extent ever measured, Antarctic sea ice may challenge that record a few weeks from now. This depletion comes just as scientists reported a harrowing sixfold increase in the loss of Antarctic land ice over the last 40 years. Unlike land ice, the loss of sea ice doesn’t contribute to sea level rise in itself, but it could help make some of Antarctica’s land ice more vulnerable (see below).

The extent of ice cover encircling the Antarctic coast began taking a nosedive in December, dropping even more quickly than usual for the time of year (late spring in the Southern Hemisphere). Since December 25, Antarctic ice extent has set calendar-day record lows every day for more than three solid weeks. Satellite-based records from the National Snow and Ice Data Center go back to 1979.

Typically, Antarctic ice reaches its minimum for the year in late February or early March (late summer). As of Monday, January 14, the extent was 3.979 million sq km, which is well below the value of 4.154 million sq km observed on that date in 2017. We still have a few weeks to go before 2019’s extent can challenge the lowest value measured at any time of year: 2.110 million square kilometers, observed on March 3, 2017.

A new all-time record-low extent isn’t yet a slam dunk, according to polar climate expert Cecilia Bitz (University of Washington). “The minimum won’t happen for another 40 days or so, and the weather between now and the minimum could shrink or grow the margin that exists today,” Bitz said in an email. […]

As the planet warms, the trajectories of northern and southern sea ice have unfolded in starkly differing ways. The Arctic’s storehouse of multiyear ice has been raided by warming in recent years (see Figure 2). Overall, the Arctic’s sea ice loss has been sadly consistent with the projections from climate models. Years of dramatic loss (such as 2007 and 2012) have been interspersed with periods of little change, but the overall downward trend line is clear. Arctic ice loss is also one of the factors behind Arctic amplification, in which warming trends become sharper at high northern latitudes than in more temperate zones.

According to NOAA’s 2018 Arctic Report Card, this past year brought the Arctic’s second-warmest air temperatures ever recorded; the second-lowest overall sea-ice coverage; the lowest recorded winter ice in the Bering Sea; and earlier plankton blooms due to early melting of sea ice in the Bering Sea. […]

Whatever its causes, the unexpectedly resilient Antarctic sea ice certainly wasn’t enough to make up for the myriad effects of planetary warming elsewhere. As Jeff Masters once put it: “Calling attention to Antarctic sea ice gain is like telling someone to ignore the fire smoldering in the attic, and instead go appreciate the coolness of the basement, because there is no fire there.”

Years of extra-abundant Antarctic sea ice came to a halt in mid-2015, when ice extent began dropping below average. The melt season of 2016-17 brought even more dramatic losses, including the record low extent noted above. The sea ice was only slightly more abundant in 2017-18.

“We’ve always suspected that the expansion of Antarctic sea ice which occurred through 2014 or so was a trend destined to reverse itself in a warming climate,” David Schneider (National Center for Atmospheric Research) said in an email. [more]

Antarctic Sea Ice Dips to Record-Low Extent for Early January