Sea ice volume in 2011 (blue line) relative to 2007 and the long-term mean. (University of Washington)

Arctic sea ice continues a long-term melting trend, setting new record lows for both volume and extent.

The University of Washington (UW) estimates August sea ice volume was 62% below the 1979-2010 average. And data indicate the volume bottomed out at a record low (as also documented on the excellent Arctic sea ice blog). The UW model for estimating sea volume incorporates data from satellites, Navy submarines, moorings, and field measurements as well as atmospheric information.

News of the “unofficial” 2011 record for minimum Arctic sea ice voume follows acceptance of an article in the Journal of Geophysical Research which demonstrates the 2010 minimum sea ice volume was lower than 2007, the previous recordholder.

The sea ice volume metric is important because, unlike extent, it provides information on ice thickness and, thus, offers a more complete picture of what’s happening to the ice.

As for sea ice extent, the University of Bremen (in Germany) reports it reached a new historic minimum of 4.24 million square kilometers on September 8. In a press release it stated:

It seems to be clear that this is a further consequence of the man-made global warming with global consequences.

An alternative estimate from the National Snow and Ice Data Center (NSIDC) indicates that Arctic sea ice extent is currently at the second-lowest levels in the satellite record - very slightly higher than 2007.

NSIDC provides the following reasoning for the difference between its ranking and University of Bremen’s:

... data from the University of Bremen indicate that sea ice extent from their algorithm fell below the 2007 minimum. They employ an algorithm that uses high resolution information from the JAXA AMSR-E sensor on the NASA Aqua satellite. This resolution allows small ice and open water features to be detected that are not observed by other products. This year the ice cover is more dispersed than 2007 with many of these small open water areas within the ice pack.

Irrespective of whether the extent this year is lower than 2007 or not, NSIDC states: “...all of the data agree that Arctic sea ice is continuing its long-term decline.”

While the minimum sea ice extent and sea ice volume in August and September is an interesting indicator of climate change, the blog Real Climate recently posted a commentary emphasizing the importance of sea ice trends earlier in the melt season:

This importance of sea-ice evolution during the early summer months is directly related to the role of sea ice as an efficient cooling machine: Because of its high albedo (reflectivity), sea ice reflects most of the incoming sunlight and helps to keep the Arctic cold throughout summer. The relative importance of this cooling is largest when days are long and the input of solar radiation is at its maximum, which happens at the beginning of summer. If, like this year, sea-ice extent becomes very low already at that time, solar radiation is efficiently absorbed throughout all summer by the unusually large areas of open water within the Arctic Ocean.

Our has a succinct explanation for the implications of the declining sea ice:

Receding sea-ice cover can disrupt indigenous people’s way of life and threaten animals like polar bears and walruses. The loss of the “refrigerator” on top of the world can alter weather patterns elsewhere in the world. And once ice is lost it becomes more difficult to replace because light can then reach the ocean, which absorbs it and warms.

A well-documented potential beneficial impact of melting ice is the opening of new navigation routes throughout the Arctic.