NSIDC: Arctic sea ice extent falls below 2005 minimum, now third lowest on record

The National Snow and Ice Data Center reports:

Atmospheric circulation patterns in August helped spread out sea ice, slowing ice loss in most regions of the Arctic. NSIDC scientists expect to see the minimum ice extent for the year in the next few weeks. While this year’s minimum ice extent will probably not reach the record low of 2007, it remains well below normal: average ice extent for August 2009 was the third-lowest in the satellite record. Ice extent has now fallen below the 2005 minimum, previously the third-lowest extent in the satellite record.

Not a big surprise — see “NSIDC: Record low Arctic ice extent unlikely in 2009.” Since the 2009 arctic extent AREA is no longer that close to 2008 levels, which set the record for minimum ice VOLUME, it seem unlikely 2009 will set a volume record (see “Will we see record low Arctic ice VOLUME this year?”).

The long-term trend remains the same (see “Human-caused Arctic warming overtakes 2,000 years of natural cooling, ‘seminal’ study finds”) and hence the medium-term also remains the same (see North Pole poised to be largely ice-free by 2020: “It’s like the Arctic is covered with an egg shell and the egg shell is now just cracking completely”).


NSIDC has some good analysis of the summer 2009 melt seasons to put this in some context:

Conditions in context

In the beginning of August, the rate of ice loss was fairly slow. In the middle of the month, the loss rate sped up, and then slowed again. On average, the decline rate was close to the 1978 to 2000 average for past Augusts. Ice extent declined by 55,000 square kilometers (21,000 square miles) per day during August, compared to 66,000 square kilometers (25,000 square miles) per day in August 2007 and 79,000 square kilometers (31,000 square miles) per day in August 2008. But because of the higher-than-average rate of ice loss in July, average ice extent for August 2009 was still far below the 1978 to 2000 average extent for the month.

On September 2, Arctic sea ice extent dropped below the minimum extent for 2005. This year is now the third-lowest ice extent in the satellite record, with one to two weeks left in the melt season.

The minimum ice extent for the year will probably occur in the next two weeks. NSIDC scientists are closely monitoring conditions and will report the minimum when it occurs.

August 2009 compared to past years

Arctic sea ice extent for August 2009 was the third lowest August since 1978, continuing the downward trend observed over the last three decades. Only 2007 and 2008 had lower ice extent during August. The long-term trend indicates a decline of 8.7% per decade in August ice extent since 1979….

Winds spread ice, enhance melt

The pattern of high pressure over the Beaufort Sea that had characterized much of the summer broke down in early August. The August atmospheric pattern was dominated by low pressure over the Beaufort and Chukchi seas, and high pressure over Greenland and the Atlantic side of the Arctic. This pattern led to winds blowing from the south and southwest into the Beaufort Sea, contributing to melt and poleward ice motion in this area. By contrast, winds from the north favored a drift of ice towards the Siberian coast.

Studies by Mark Serreze, Masayo Ogi, and other researchers have shown that low-pressure patterns promote spreading of the ice pack, a process known as divergence. While ice divergence increases extent, it can also accelerate melt because there are more dark, open-water areas between the floes to absorb the sun’s energy, promoting melt on all sides of the floes.