End of year heat wave slowed expansion
Arctic sea ice extent in December ended up as the fourth-lowest on record, and is still hovering near a record low in mid-January, according to the latest monthly update from the National Snow and Ice Data Center.
Through 2015, the linear rate of decline for December sea ice extent is 3.4 percent per decade (about 17,000 miles) per year.
For the month, the sea ice extent averaged 4.74 million square miles, about 301,000 square miles below the 1981 to 2010 average for the month. The rate of sea ice growth slowed slightly throughout December and nearly stopped early in January, federal ice trackers said, suspecting that a period of unusually warm temperatures in the Arctic caused the slowdown.
As always, there are regional variations, with well below average sea ice in the Bering, Okhotsk, and Barents seas, partly balanced by slightly above average extent in Baffin Bay.
According to the NSIDC, 2015 brought the lowest Arctic maximum in the satellite record, the fourth lowest Arctic minimum in the satellite record, and a return to average levels for Antarctic sea ice extent after more than two years of record and near-record highs.
The continued low numbers for Arctic sea ice extent can be at least partially explained by an increasingly young and thin ice cover. Scientists now have a 37 year record of passive satellite microwave data, showing clear downward trends in Arctic sea ice extent and concentration in all months.
A look at the geographic distribution of trends for the seasonal maximum and minimum periods provides insight into how the polar regions are changing. During the Arctic maximum, declines in extent and concentration are pronounced in the Barents Sea and Sea of Okhotsk, but ice cover has increased slightly in the Bering Sea. During the Arctic summer minimum, all areas show negative trends.
The picture is not as clear in Antarctica, where ice cover is increasing around much of the coastline from the Weddell Sea eastward to the western Ross Sea during summer but is declining sharply in the eastern Ross, Amundsen, and southern Bellingshausen seas. Winter ice cover in Antarctica is characterized by increases in the northern Ross Sea and the Indian Ocean sectors, and decreases in the northwestern Weddell Sea and the region south of Australia.
The NSIDC upate explains that Antarctic sea ice was at record or near-record daily extents from February 2013 through June 2015. But during this year’s austral mid-winter period, Antarctic sea ice growth slowed. Since then, extent in the Southern Hemisphere has generally been slightly above average.
Around the North Pole, a combination of weather systems, including a hurricane-force storm near Iceland, led to an unusual heat wave with surface air temperatures up to 23 degrees Celsius (50 degrees Fahrenheit) above average in the far north. A temperature of +0.7 degrees Celsius was briefly recorded by a buoy weather station near the North Pole on December 30, 2015.
The storms brought a strong, deep inflow of warm, moist air into the Arctic Ocean’s high latitudes. “While the event was remarkable and may account for the slow ice growth during the first few days of January 2016, it was short lived and is unlikely to have any long-term effects on the sea ice cover,” the NSIDC ice researchers concluded.
Read the full sea ice post here: http://nsidc.org/arcticseaicenews/