Last week, National Snow and Ice Data Center (NSIDC) director Mark Serreze said, “Every bit of evidence we have says the ice is thinning.” Monday, NSIDC scientist Julienne Stroeve sent me this figure from a forthcoming article using data provided by J. Maslanik and C. Fowler (click to enlarge):
This is the end-of-winter sea ice extent in the Arctic Basin, broken down by age. Stroeve explains:
This figure would support thinning of the icepack over the last couple of decades since older ice tends to be thicker than younger ice. You can see in this figure how little of the really old, and thick ice there is left in the Arctic Basin.
In fact, the figure shows ice 5 years or older dropping from 800,000 sq-km in 2008 to 400,000 in 2009 to only 320,000 sq-km. Spring 2010 also saw a record low in the amount of ice 4 years or older.
Now you can see that we just about hit the same Arctic sea ice area that we did in 2008:
Given that the ice is almost certainly thinner now than in 2008, we are very likely to have witnessed a lower total ice volume.
Remember, 2008 had substantially less ice volume than 2007, even though it had more area. Last year, some of the leading cryoscientists at JPL, the Polar Science Center at the University of Washington, and NASA published a major peer-reviewed article, “Thinning and volume loss of the Arctic Ocean sea ice cover: 2003–2008” (subs. req’d).
You can find a basic discussion of their findings here on NASA’s website, which points out, “Arctic sea ice thinned dramatically between the winters of 2004 and 2008, with thin seasonal ice replacing thick older ice as the dominant type for the first time on record.” That link has some excellent figures, like this one:
Today, PSC’s Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) has determined that “September Ice Volume was lowest in 2009 at 5,800 km^3 or 67% below its 1979 maximum” and that “Total Arctic Ice Volume for March 2010 is 20,300 km^3, the lowest over the 1979–2010 period.”
So although it may be a while before we have a definitive statement, the likelihood seems high that we just set the record low Arctic sea ice volume — possibly for several thousand years (see Major analysis finds “less ice covers the Arctic today than at any time in recent geologic history”).