For the long view on the 2008 Arctic sea ice melt, see today’s commentary on Nature Reports Climate Change by two National Snow and Ice Data Center researchers. Mark Serreze and Julienne Stroeve recap the results:

The seasonal minimum for 2008, occurring on 14 September, entered the books as the second-lowest of the satellite era, probably the second-lowest of at least a century, and just behind the standing record set in 2007.

Barely second-lowest still came as a shock, given the cooler weather this year. Said Stroeve in an NISDC press release, “I find it incredible that we came so close to beating the 2007 record — without the especially warm and clear conditions we saw last summer. I hate to think what 2008 might have looked like if weather patterns had set up in a more extreme way. ”

August 2008 saw the fastest melt ever recorded, according to NASA. And ice volume, a bellwether for the future, probably was at its lowest this year – an observation that hasn’t reached the broadsheets (but see Climate Progress and Stoat).

NSIDC scientist Walt Meier explains, “Warm ocean waters helped contribute to ice losses this year, pushing the already thin ice pack over the edge. In fact, preliminary data indicates that 2008 probably represents the lowest volume of Arctic sea ice on record, partly because less multiyear ice is surviving now, and the remaining ice is so thin.”



Yes, unlike you or me, Arctic sea ice is getting younger and thinner as the years pass. Old, thick ice that has survived through multiple summers – which two decades ago grew fast enough to roughly match the loss of Arctic ice into the North Atlantic – is giving way to flimsy young stuff that readily melts into open water during the warm months. The endpoint of this trajectory would be all-new ice in winter and no ice in summer. Serreze and Stroeve:

With sharply rising atmospheric greenhouse gas concentrations, the change to a seasonally ice-free Arctic Ocean seems inevitable. The only question is how fast we get there. The emerging view is that if we’re still waiting for the rapid slide towards this ice-free state, we won’t be waiting much longer.

Looking back at recent changes, the authors talk triggers. Models suggest that thinning Arctic sea ice is “vulnerable to a ‘kick’ from natural variability that sets the feedback process into high gear,” they note, resulting in “abrupt transition” to ice-free summers. The warmth of 2007, caused by an unusual atmospheric circulation pattern, is one of the candidates for a recent kick – and though this year brought a slight recovery of ice extent, signs point to more losses coming up.

Anna Barnett

Image: Sea ice on 14 September 2008, the date of the minimum. Courtesy of National Snow and Ice Data Center.