Arctic sea ice extent in 2011 (blue line) relative to 2007 and 1979-2000 average (National Snow and Ice Data Center)

NSIDC reported: “Arctic sea ice extent averaged for July 2011 reached the lowest level for the month in the 1979 to 2011 satellite record, even though the pace of ice loss slowed substantially during the last two weeks of July.”

Arctic sea ice typically begins declining in March or April, and bottoms out in September before mounting a recovery. Its lowest extent on record occurred in September 2007. Will the depleted extent in September 2011 rival that year?

Walt Meier, a scientist at NSIDC, told Bloomberg: “It will be another low year, very likely one of the five lowest. One year doesn’t say too much in and of itself, but the long-term downward trend and the series of very low years is indicative of a thinner ice cover and warming temperatures.”

Temperatures were, in fact, very warm in the Arctic for at least part of July. Wunderground meteorologist Angela Fritz wrote: “In the first two weeks of July, air temperature over the North Pole was 11 to 14 degrees Fahrenheit above average. During the last two weeks of July, low pressure took over and brought cooler temperatures, although it appears this also acted to push the ice around, which resulted in a larger but thinner area of ice.”

Indeed, while extent provides an idea of the sea ice coverage over the surface of the Arctic, the volume metric provides information on ice thickness as well - offering a more complete picture of what’s happening to the ice. It is not measured directly, but estimated by a model (from the Polar Science Center out of the University of Washington) that assimilates data from a variety of different measurements (taken at different times/locations) from satellites, Navy submarines, mooring and field observations

Arctic sea ice volume in 2011 relative to 2007 and 1979-2010 mean volume (Polar Science Center)

From the image above, it’s clear the sea ice volume is on track to be the lowest on record.

The ice retreat opens up new navigation opportunities for ships. According to NSIDC: “Over the past few weeks, the sea ice edge has retreated from the shores of Siberia and Eurasia, potentially opening up much of the Northern Sea Route, the shipping lane that runs along the Eurasian Arctic coast from Murmansk on the Barents Sea, along Siberia, and through the Bering Strait.”

We’ll have additional updates when new data become available in September and October.

For much more on this topic, see Andrew Freedman’s comprehensive discussion of sea ice trends back in June.