Here is a long post: I have taken a selection of extracts from the NSIDC press releases, going back to early August, to provide an overview of the season so far.
More remarkable, perhaps, is the figure from CT, regarding the number of days below 7 Mkm2 ice area this year; nearly twice the long-term average, and nearly three times the number compared to 1980.
NSIDC, 10th August:
July 2007 showed the most extreme ice-loss anomaly ever seen since the satellite record began in 1979, with a monthly average extent of only 8.1 million square kilometers (3.13 million square miles).
The absolute minimum usually occurs during the second week in September, but as of only August 9, sea ice has already sunk below that mile-marker. In fact, the daily extent fell below the long-term average absolute minimum back in mid-July.
NSIDC, 17th August:
Yesterday and today, Arctic sea ice surpassed the previous single-day (absolute minimum) record for the lowest extent ever measured by satellite. Sea ice extent has fallen below the 2005 record low absolute minimum and is still melting. Sea ice extent is currently tracking at 5.26 million square kilometers (2.02 million square miles), just below the 2005 record absolute minimum of 5.32 million square kilometers (2.05 million square miles).
NSIDC, 4th September:
August in review
The low ice extent for August 2007 stands out sharply compared to all previous Augusts. The August 2007 monthly average extent was 5.32 million square kilometers (2.05 million square miles), falling well below August 2005 extent, which was 6.30 million square kilometers (2.42 million square miles). Additionally, August 2007 ice extent is 31% below the long-term average of 7.67 million square kilometers (2.95 million square miles).
Even more stunning is that the August 2007 monthly average is the lowest extent in the satellite record for any month, including any previous September, which is typically the lowest month each year. September 2005, the previous record, had a monthly mean extent of 5.56 million square kilometers (2.14 million square miles).
Current Sea Ice Conditions: September 9, 2007
Figure 1 provides the updated map of sea ice extent for September 9, 2007. Sea ice extent now stands at 4.24 million square kilometers (1.63 million square miles). The magenta line shows the median September monthly extent based on data from 1979 to 2000.
The Northwest Passage is still open. The Northeast Passage, along the coast of Siberia, is still closed by a narrow band of sea ice.
Sea ice is still declining, although the rate is very slow at present. Sea ice extent at this time of year can vary from day to day, as regions within the Arctic have small episodes of melt, freeze, or wind movement of the ice, just before the strong autumn cooling. As of September 16, sea ice extent was 4.14 million square kilometers (1.59 million square miles), surpassing the previous one-day record of September 20–21, 2005, by more than 1.2 million square kilometers (461,000 square miles).
The long-term average minimum, based on averaging data from 1979 to 2000, is 6.74 million square kilometers (2.60 million square miles) and occurs on September 12. Compared to this average, five-day mean ice extent for September 16, 2007, was lower by 2.61 million square kilometers (one million square miles), an area approximately equal to the size of Alaska and Texas combined, or the size of ten United Kingdoms.
The minimum for 2007 shatters the previous five-day minimum set on September 20–21, 2005, by 1.19 million square kilometers (460,000 square miles), roughly the size of Texas and California combined, or nearly five United Kingdoms.
Current sea ice conditions: October 17, 2007
Figure 1 provides an updated map of sea ice extent for October 16, 2007; the magenta line shows the median October monthly extent based on data from 1979 to 2000. Sea ice extent is 5.65 million square kilometers (2.18 million square miles), an increase of 1.52 million square kilometers (590,000 square miles) since we reached the minimum extent of 4.13 million square kilometers (1.59 million square miles) on September 16.
While sea ice is again growing, we didn’t actually get above the previous absolute minimum record extent, set on September 20–21, 2005, until October 14 of this year.
An astonishing figure from Cryosphere Today:
The number of days with sea ice area below 7 Million Km2 was 42 in 1980, and as low as 39 as recently as 1996. 2006 saw a record 89 days below 7.0 Mkm2. So far in 2007, (my estimate), we have had 110 days below this figure. We can expect another 30 days, give or take, perhaps 140 days.
The current areal anomaly is close to -3 Mkm2. The most recent figure (from Walt Meier) for extent anomaly was ‘close to’ -3 Mkm2, slightly up from the absolute limit around October 14th.