Arctic sea ice III: it’s not through melting

NSIDC arctic sea ice extent graph for September 18, 2010

NSIDC Arctic sea ice extent graph for September 18, 2010

On September 15 the US National Snow and Ice Data Center (NSIDC) announced a provisional Arctic sea ice minimum extent of 4.76 million square kilometers, for September 10, based on the five-day-average calculation it uses for that purpose.   However it appears that while sea ice is beginning to grow in the East Siberian Sea, just about everywhere else the ice is still melting or consolidating.  This has led to a “double dip” in the past few days, which is currently visible in the NSIDC’s chart.

At this point we don’t know what will happen to the sea ice extent. Of course it’s bound to grow back rapidly pretty soon because so much of it melted during the summer season and there’s nothing much left that is likely to melt or consolidate. This is bringing the 2010 melt season to an interesting close.

Arctic sea ice I

I’m on a sea ice binge, and here’s what I’ve found.  I’ll probably follow this up at least once as the melt season closes and the figures are added up, so I’ve named it “Arctic sea ice I”.

Joe Romm is crowing over the collapse of yet more Watts/Goddard nonsense about the “rebound” of arctic sea ice and even says

My big $1000 bet with James Annan, William Connolley, and Brian Schmidt still looks pretty good, which is to say I would definitely not switch sides.

Bold, considering what he’s betting against:

“At no time between now and the end of the year 2020 will the minimum total Arctic Sea ice extent be less than 10% of the 1979-2000 average minimum annual Arctic Sea ice extent, as measured by NSIDC data or any other measurement mutually agreed-upon; provided, however, that if two or more volcanic eruptions with the energy level equal to or greater than the 1991 Mount Pinatubo shall occur between now and the end of 2020, then all bets are voided.”

As Joe Romm is quick to admit, William M. Connolley and James Annan are published climate scientists (Connolley was, I should say.  He now works in software engineering.)  Joe is betting against some pretty clever money.

Joe Romm in a December, 2007 posting makes it plain that he’s betting on accelerating sea ice summer melt rates. Intuitively I’d say that seems reasonable, though Joe’s timescale still seems implausibly ambitious. Of course, unlike William Connolley, I haven’t done any modeling, and I certainly don’t have a sophisticated understanding of arctic sea ice dynamics. At best my hunches (and that’s all they are) are simplistic extrapolations of what happens when I defrost my freezer. When the surface area to volume ratio increases the ice melts faster. This is true whether the overall volume decreases or the volume remains the same and I smash the ice up into smaller pieces. A lot more is going on in the arctic during the melt season, of course.

By way of data, NSIDC gives the following figures for September average sea ice extent in millions of square kilometres. Links are to the standard NSIDC sea ice minimum press release for each year.

Or you can see them all collected together in a table where they are also conveniently expressed as sea ice anomaly (baseline 1979-2000). The table also shows the quite noticeable apparent acceleration in the annual and decadal trend that has taken place in the past seven or eight years.  At  -7.3 million square kilometres per decade in 2002, it has risen year on year and after the 2009 season it stood at -11.2.  I’ll be interested to see if the trend drops back in the next few years; that’s to be expected if 2007 was simply an outlier on a linear trend.