Ice extent shrinking about 18,000 square miles per year
By Summit Voice
FRISCO — December sea ice in the Arctic remained well below average, with the average extent ending up as the fourth-lowest on record — 270,300 square miles below the 1981 to 2010 average — according to the monthly update from the National Snow and Ice Data Center.
Low-ice conditions prevailed in the Barents Sea and along the entire northwest Pacific coast, including the Bering Sea and the Sea of Okhotsk. In the Greenland Sea and Baffin Bay, sea ice extent was near average.
The early part of December was dominated by a positive Arctic Oscillation pattern, but this shifted to near-neutral conditions by the end of the month. The Icelandic low, covering much of the northern North Atlantic Ocean, was stronger than average, and pressures were higher than average over the Bering Sea and Alaska.
Air temperatures at the 925 hPa level (about 3,000 feet above the surface) were above average for the month over most of the Arctic Ocean; unusual warmth was most notable over far eastern Siberia, where temperatures soared to 11 degrees Fahrenheit above average.
Over the central Arctic Ocean, temperatures 4 to 9 degrees Fahrenheit above average. By sharp contrast, relatively cool conditions prevailed over northern North America. Temperatures in areas such as the Yukon Territory were 10 degrees Fahrenheit or more below average.
Overall, Arctic sea ice extent in December has been declining by about 3.5 percent per decade, shrinking by about 18,000 square miles each year.
Summarizing 2013, NSIDC scientists said overall sea ice extent was the sixth-lowest during the era of satellite observations, with low-ice conditions focused across the northern Atlantic. The fraction of the Arctic sea ice cover comprised of old ice continued to decline.
Meanwhile, Antarctic sea ice extent has been at or above historic record high levels for the past few years. According to the NSIDC, the trends in Antarctic sea ice extent remain small (1 to 4 percent) and are statistically significant relative to inter-annual variation only for the late autumn, winter, and early spring months.
Early satellite records (the Nimbus satellite series in 1964, 1966, and 1969) provide further evidence that Antarctic sea ice extent is highly variable; the three years covered by Nimbus show September extents that were both higher and lower than seen in the modern continuous, calibrated satellite record.