Antarctic sea ice retreat could set stage for ice shelf collapses
Staff ReportMonths of above-average temperatures in the Arctic slowed the growth of sea ice formation to a crawl during the second half of October, the National Snow and Ice Data Center reported in its latest monthly update.The ice scientists said that, starting Oct. 20, Arctic sea ice started setting daily record lows for extent. After mid-October, ice growth returned to near-average rates, but extent remained at record low levels through late October. Both sea surface and air temperatures have remained unusually high, extending from the surface high up into the atmosphere.
Specifically, Arctic sea ice extent averaged 2.5 million square miles, the lowest that’s been measured for October during the satellite era.
The season started with an early freeze up in late September, but the slowed considerably. From October 1 to 15, ice extent increased only 146,000 square miles, less than a third of the 1981 to 2010 average gain for that period. By October 31, Arctic sea ice extent stood at 2.73 million square miles, the lowest extent in the satellite record for that date. Through 2016, the linear rate of decline for October is 25,600 square miles per year, or 7.4 percent per decade.
In a forecast of what is to come in the Arctic in years ahead, the NSIDC explained that, in the southern parts of the Arctic, the the sea ice retreated far earlier in the season than previously, with the darker-colored ocean water absorbing the sun’s heat. That warmth inhibited sea ice growth in the autumn. Even as late as October 25, sea surface temperatures were above average in these areas.
Shifts in atmospheric pressure patterns over the Arctic were also factors, with warm southerly winds blowing over the East Siberian and Barents Seas, contributing to high air temperatures in these regions. Unusually low pressure on the Pacific side centered roughly over the western Bering Sea brought also brought southerly winds over the Beaufort and Chukchi Seas.
Antarctic sea ice extent levels have been at second lowest in the satellite record since October 20. Ice extent is particularly low on both sides of the Antarctic Peninsula. The rapid early reduction in sea ice cover in this region may create favorable conditions for the break up of the eastern Peninsula ice shelves at the end of austral summer.
Similar sea ice trends and weather conditions were present during the spring seasons preceding past ice shelf retreats (e.g., 2001 to 2002). Extensive open water, created by the downsloping fosters warmer air and surface melting, and allows longer-period ocean waves to reach the ice front of the ice shelves.