did anyone expect this? Arctic sea ice extent has hit record low for November

17 11 2009

I’d stopped looking at the Arctic sea ice extent since it became pretty clear that September — the summer melt peak — was coming in third place and not breaking the previous low of 2007 (or 2008). But thanks to David Spratt, I’ve just seen that November has hit a new record minimum. That is, in the autumn/fall period where ice extent should again be seasonally increasing, that increase has been less than was the case during the 2007 recovery. I wish I knew more on this to be confident, but I’d hazard a guess to say this indicates that localised autumn temperature increases have affected ice regrowth, at least for 2009. This cannot be a good thing, no matter how you look at it…

The NSIDC extent is linked below (this image changes daily).

Daily updated Arctic sea ice extent

And similar data from the US-Japan IJIS: although harder to see, you can make out that the 2009 (red) line is indeed the minimum point recorded for November.

IJIS Arctice sea ice extent

So why does this matter? I have to be careful and state that in itself this new minimum means little; variability around the long term mean is expected. But of course the clear trend is a significant decline in that mean value. To my mind this is disconcerting because it must surely imply that Arctic sea ice recovery in the autumn (and winter?) is being impeded by the dramatic temperature increases being witnessed in that region. The more pronounced this becomes the greater the reinforcing positive feedback: less ice means less albedo (reflection) and more exposed dark ocean, which absorbs more incoming solar energy, which increase local temperatures, which melts more ice, and so on.

I’m not in the least qualified to write anything substantial about this; I only wanted to point it out because it struck me as significant, but yet I haven’t even seen it mentioned anywhere other than by David Spratt.

[UPDATE, Nov 17 @ 15:50 WST]

I found an NSIDC news release from November 3rd which discusses the slowing in recovery for October. That slowing was caused by a combination of strong Siberian winds impeding ice formation near the Siberian coast, and warmer winds around the Beaufort Sea blowing over that exposed water. To give a little more context to the yearly sea ice extent, NSIDC produced this image based on the normal daily updates: the grey band shows two standard deviations from the 1979-2000 long term mean. The September minima for 2005, 2009, 2008, and 2007 are quite clearly well below that range; 2005 and 2007 were below in November, but at the time this was produced one would largely have expected 2009 to continue above the 2007 extent, and quite possibly back into the grey band. Well not any more (see above graph). I would say that NSIDC will update this analysis once we get into December.

NSIDC Arctic sea ice extent in context

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