Arctic Sea Ice Decline Accelerates, Amundsen’s Northwest Passage Opens

12 August 2008

Just several weeks ago it seemed as though the loss of Arctic sea ice would not be as extreme as last year’s, which shattered previous records. (Earlier post.) However, the rate of sea ice loss has accelerated during the past ten days, triggered by a series of strong storms that broke up thin ice in the Beaufort and Chukchi Seas and brought warm southerly winds into the region, according to the National Snow and Ice Data Center (NSIDC).

Daily sea ice extent; the blue line indicates 2008; the gray line indicates extent from 1979 to 2000; the dotted green line shows extent for 2007. Click to enlarge. Source: NSIDC

Amundsen’s historic Northwest Passage is once again opening up; the wider and deeper route through Parry Channel is currently still clogged with ice. This route opened in mid-August last year; it may still open up before the end of this year’s melt season, according to NSIDC.

Arctic sea ice extent on 10 August was 6.54 million square kilometers (2.52 million square miles), according to NSIDC data, a decline of 1 million square kilometers (390,000 square miles) since the beginning of the month. Extent is now within 780,000 square kilometers (300,000 square miles) of last year’s value on the same date and is 1.50 million square kilometers (580,000 square miles) below the 1979 to 2000 average.

Ice extent has begun to decline sharply. The decline rate surged to -113,000 square kilometers per day on August 7 and as of August 10 was -103,000 square kilometers per day. This compares to the long-term average decline of -76,000 square kilometers per day for this time of year. Normally, the peak decline rate is in early July.

Many of the areas now seeing a rapid retreat saw an early melt onset (see July 2, 2008); this helped set the stage for rapid retreat (July 17 and April 7). However, the more fundamental issue is that these regions started the melt season covered with thin first-year ice, which is especially vulnerable to melting out completely. Thin ice is also vulnerable to breakup by winds; the last ten days have seen a windy, stormy pattern that has accelerated the ice loss.

—NSIDC