Sea ice: and the winner is… no-one!

Hurrah. That saves lots of effort paying :-). Not long ago it was looking bad for the good guys (i.e., me) with a “douple dip” recession of sea ice. But a strong perforcance from the boys up north in the mushy white stuff stakes saw a sharp rebound at the end of the month, leading to a monthly average for september of 4.90 (thanks for C for vigilance). As a reminder, recent years have been:

2000  9      Goddard      N   6.32   4.31
2001  9      Goddard      N   6.75   4.55
2002  9      Goddard      N   5.96   3.98
2003  9      Goddard      N   6.15   4.01
2004  9      Goddard      N   6.05   4.35
2005  9      Goddard      N   5.57   4.03
2006  9      Goddard      N   5.92   3.97
2007  9      Goddard      N   4.30   2.78
2008  9       PRELIM      N   4.68   2.93
2009  9      NRTSI-G      N   5.36   3.42
2010  9      NRTSI-G      N   4.90   3.02

Or so says ftp://sidads.colorado.edu/DATASETS/NOAA/G02135/Sep/N_09_area.txt. Other datasets will give you slightly different answers, of course. Note taht 2010 gets the coveted number 3 spot in terms of both September average and absolute minimum.

AMSRE_Sea_Ice_Extent-2010-10-02

The bet for this year was (from Three views of sea ice).

That the september mean ice *extent* be below 4.835; but with a “buffer” where we call it a draw: between 4.735 and 4.935, no one wins. I’m taking the “high” side of this; anyone interested in the “low” side let me know. For my part, 4.835 is arrived at as the 1979-2009 trend extrapolated, minus 0.5 which is the SD. It seems to have become tradiational for people to bet small amounts, which is fair enough if we’re just playing. But this was intended to flush out the “the sea ice is in catastrophic decline” people. OTOH, if there are any “the sea ice will certainly recover this year” people then you can get odds on trend-plus-SD, i.e. ice being above 5.835 if you like (note that those are all spuriously precise but never mind)]

So, if we’d played for just-the-number (without the buffer) I’d have won; but I agree, it is better to include the buffer. Assuming I (or ws it C?) did the calcs right, the trend line was for 5.335, and we’re clearly below that, but by less than the SD, so it doesn’t matter.

Refs

* Three views of sea ice – defn of this years contest.
* 2009
* 2008
* Lab Lemming’s pool (I think I’m the very broad green line)
* Tamino got lucky

Update: pressed by C in the comments, I’ve now calculated the trend for myself, and so I’ve added this pic:

seaice-plus-trends

which shows the extents, the trend-to-2010 calculated using all previous years, the trend-to-year using all previous years, and the trend-to-2010 only using 10 previous years. I make the baseline prediction for next year 5.235, which agrees with NB, so all is well.