Figure 4. Air temperatures were higher than normal over Baffin Island, Hudson Bay, and eastern Siberia for the month of December, which was associated with low sea ice extent in those areas. The temperature pattern resulted from a negative phase of the Arctic Oscillation.



Negative phase of the Arctic Oscillation

As in December 2009, a strongly negative phase of the Arctic Oscillation dominated the middle and high latitudes of the Northern Hemisphere in December 2010, bringing higher-than-normal pressures to the Arctic region, with lower-than-normal pressures in middle latitudes. However, unlike 2009, when higher-than normal pressures centered near the central Arctic , in December 2010 higher pressures centered near Iceland and the eastern tip of the Aleutians in the Pacific, and yielded a different pattern of winds. As a result, different areas experienced warm anomalies in 2010, and a different pattern of ice extent emerged.

Our January 5, 2010 post discussed the connection between very warm temperatures over much of the high Arctic in December 2009 and a strongly negative phase of the Arctic Oscillation.



Figure 5. This full-year graph puts 2010 sea ice extent in context. The gray line shows the 1979 to 2000 climatology, thick blue-gray indicates the 1979 to 2008 (30-year) climatology, dashed green shows 2007, and 2009 is shown in sky blue. Sea Ice Index data —Credit: National Snow and Ice Data Center

High-resolution image



2010 year in review

Despite a late date of the maximum in winter sea ice extent, the minimum sea ice extent for September 2010 was third lowest in the 1979 to 2010 satellite record, above only 2007 (the record low) and 2008. The late summer of 2010 saw an open Northwest Passage: this year, the deep water channel (the northern route) from M’Clure Strait to Lancaster Sound was navigable. The Northern Sea Route along the Siberian coast also became briefly navigable.

2010 started out with a highly negative phase of the Arctic Oscillation, an atmospheric pattern that in the past has favored the survival of old ice through the winter, and more ice at the end of this summer. But this tendency seems to be changing. A recent study led by Julienne Strove of NSIDC showed that while wind patterns linked with the strongly negative Arctic Oscillation winter of 2009-2010 transported much old ice into the southern Beaufort and Chukchi Seas, most of this ice later melted. It may be that with a warmer Arctic, old rules regarding links between the atmospheric pressure patterns and sea ice extent no longer hold. So far the winter of 2010-2011 has also had a strongly negative Arctic Oscillation, but it is not yet clear how this pattern will affect summer sea ice.