|Updated map of sea ice extent for September 3, 2007; the magenta line shows the median September extent based on data from 1979 to 2000. Click to enlarge. Source: National Snow and Ice Data Center
The Arctic sea ice extent continues to decline, and is now at a record low of 4.42 million square kilometers (1.70 million square miles), according to the National Snow and Ice Data Center. This puts the sea ice extent yet further below the record absolute minimum of 5.32 million square kilometers (2.05 million square miles) that occurred on September 20–21, 2005.
Between the NSIDC report on 3 September and 28 August, the date of the prior report, the Arctic lost an additional 360,000 square kilometers (138,000 square miles) of ice, an area larger than the size of the state of New Mexico. In the report of 28 August, the NSIDC noted that the daily rate of ice loss was starting to slow; the loss rate has since accelerated again. (See chart below.)
|Data derived from Sea Ice Index data set. Click to enlarge. Source: National Snow and Ice Data Center
The August 2007 monthly average extent of 5.32 million square kilometers (2.05 million square miles) is sharply lower than all previous Augusts, and was 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).—NSIDC
|August sea ice extent. Click to enlarge. Source: national SNow and Ice Data Center
Another notable aspect of August was the opening of the Northwest Passage, which was “the most navigable that people have see since monitoring began,” according to the center. Although the Northeast Passage is still blocked by fairly heavy ice conditions north of the Taymyr Peninsula, the NSIDC suggests that passage might open as well during the next few weeks.
Reduced sea ice during the summer—when more solar energy reaches the surface than during the winter—has a big impact on the Arctic’s overall energy balance, according to the NSIDC. Whereas sea ice reflects much of the sun’s radiation back into space, dark ice-free ocean water absorbs more of the sun’s energy.
In its analysis of the 2005 record minimum, NSIDC noted that lower minimum extents affect the comeback in the following winter. The lack of recovery means that the sea ice is not building back up to prior levels after a summer of melting—leaving it even more susceptible to warmer summer temperatures.
Feedbacks in the system are starting to take hold. Right now, our projections for the future use a steady linear decline, but when feedbacks are involved the decline is not necessarily steady—it could pick up speed.—NSIDC Lead Scientist Ted Scambos, 2005