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.

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.

Comments

  1. #1 cthulhu
    2010/10/02

    at least there’s the BP share price

    [440. yes, I definitely win :-). I’ll buy you all a beer -W]

  2. #2 crandles
    2010/10/02

    >”Assuming I (or ws it C?) did the calcs right, the trend line was for 5.335″

    Err no. You have actually been told several times that I worked out the 4.835 figure as being half way between the trend figure of 5.37m km^2 (assuming I calculated it correctly) and the lowest ever extent of 4.3m km^2.

    [You can’t possibly expect me to remember anything. Anyway, I quote myself as saying “For my part, 4.835 is arrived at as the 1979-2009 trend extrapolated, minus 0.5 which is the SD” -are you saying that is wrong? It appear to produce about the right answer for the trend, ie 5.335, which hardly differs from 5.37. Perhaps I should just do my own dirty work some time -W]

    Over at lab lemming the figures are IJIS/JAXA so it looks like you came 4th, I came 3rd and JA came 2nd. However, James also came second at Lab Lemming last year so I think he is way ahead of us.

    2009 guess 5050 sigma 100 actual 5250 error 200
    2010 guess 4750 sigma 80 actual 4813 error 63

    average error of 132 is not much more than JA very tight sigmas, very impressive!

    So I think we should just give up and listen to James ;o)

  3. #3 Matt Andrews
    2010/10/03

    Tamino has an interestingly curvaceous (quadratic) trend which happened to coincide with this year’s result.

  4. #4 crandles
    2010/10/03

    >” -are you saying that is wrong?”

    I should have put in more smilies. But on the linked three views thread, I explained what I did in comment 8 and this was also quoted in comment 14. After you posted your update two people told you your update wasn’t quite correct in comments 20 and 23. You replied to both comments 20 and 23 but if you see fit to ignore what people are telling you and not correct your update why shouldn’t I (continue to) tease you about it? :P

    Why not get carried away with it and add that IIRC the 0.5m wasn’t the standard deviation but the standard error of some of the first models reported by SEARCH that did indicate their expected range. ;o)

    [OK, having now checked myself the trend is 5.373. The 0.5 came from RMG I thought. I’ve updated the post with another pic -W]

  5. #5 Nick Barnes
    2010/10/03

    Let’s go again, for 2011. NSIDC September extent means. Linear fit says 5.235. Standard error is about 0.15. Bring it on.

  6. #6 Adam
    2010/10/03

    As Cryosat2 should be(?) active then, maybe the bet should be on volume or average thickness for 2011?

  7. #7 Nick Barnes
    2010/10/04

    That’s the linear fit and standard error for 1979-2010 NSIDC numbers, by my own calculation.

  8. #8 Neven
    2010/10/05

    Bwah, in July and the first half of Agust the Beaufort Gyre stalled completely, low-pressure areas were bringing clouds and low temperatures to the Arctic during the most important period of the melting season (peak insolation) when average daily melt can reach 100K (like it did in July 2007). This year’s July daily average was 60K, IJIS extent.

    You got infinitely more lucky than Tamino, WC. :-p

  9. #9 GoRight
    2010/10/05

    Off Topic: Hey, I’d like to hear your reaction to this video.

    [I’ve already commented at http://watchingthedeniers.wordpress.com/2010/10/03/own-goal-10-10-no-pressure-video-a-disaster/ but you probably don’t watch there -W]

    Do you think it was well conceived and executed, or was it a doomed concept from the start?

    [It is poorly conceived and badly executed and was doomed from the start -W]

    How do you feel in general about the premise of the piece (i.e. that skeptics should be blown up)?

    [Apparently it was an attempt at humour but is so obviously unfunny that it is not possible for me to understand what they were thinking. Even had they managed to make it funny it would still have been a really stupid idea -W]

    Do you see any upside to this video? If so, what?

    [The only upside – and it is a very weak one – is that the absurd over reaction and synthetic outrage of some of the septics makes them look even madder than the video, hard though that is to believe. Delingpole leads the way in this though WUWT isn’t far behind -W]

    Finally, do you, in general, favor or discourage the type of activism we see here?

    [Don’t understand the question I’m afraid -W]

  10. #10 Marco
    2010/10/05

    GoRight: if you believe the premise of the piece is blowing skeptics up, you obviously already made up your mind.

    Wm, I suggest you do not waste time on this one.

    [It is probably some kind of loyalty oath thing. As it happens, I’ve already commented elsewhere, so it does no harm to comment again. However, any further comments on this will be deleted; there really isn’t anything more to say -W]

  11. #11 GoRight
    2010/10/05

    Sorry, here’s a working (for now) link to the actual video. It has been pulled from the original links for the obvious reasons.

  12. #12 GoRight
    2010/10/05

    GoRight: if you believe the premise of the piece is blowing skeptics up, you obviously already made up your mind.

    I thought I was clear, I wish to hear WMC’s reaction. I obviously already know my own reaction.

    My question is not in regards to the need to reduce carbon emissions, which I assume WMC would support and I certainly do not oppose as a general principle, but rather the more controversial aspect of the video which was the premise that skeptics should be blown up … or at least that is what I interpret the video to be saying.

    What message do you think the blowing up of skeptics in the video was meant to convey?

  13. #13 blueshift
    2010/10/05

    Back on topic:
    Has anyone compared the linear trend used here to Tamino’s quadratic? I’m curious when there would be a stat. sig. difference between the two.

    Also, did anyone suggest a multi-year contest? That is, look at extent over the next 3 years or so to eliminate some of the variability. Not sure of the proper way to do that, but it doesn’t seem too hard.

    [We’re impatient people. 3 years is just too long. As for the trends: my feeling is that to fit a quadratic you need some justification – a model of the process – that explains why; not just “well it looks right”. That said, I think my new pic is slightly changing my mind: in that the actual extent has consistently been below what you’d predict from the trend (green line) for the past 10 years.

    But paying too much attention to the line fitting is a bad idea. What you really need is a physical model of what is going on -W]

  14. #14 David B. Benson
    2010/10/05

    No winners; just losers.

    We all lose.

  15. #15 crandles
    2010/10/05

    Blueshift, Yes I think I have suggested a 3 year contest. Just because William is too impatient ( ;-) ) doesn’t necessarily mean everyone else is also too impatient but I haven’t seen people jumping at it so he may be right.

    Could always try the last 3/4/5… years to see if a statistically significant improvement could be found. I may try that sometime. Maybe play guess the Goddard expectation and see if that (can be/when likely to be) seen to be statisically significantly inferior.

  16. #16 Hank Roberts
    2010/10/05

    > some justification — a model

    How about this, from back before the 2007 sea ice low-so-far event?

    http://www.realclimate.org/index.php/archives/2007/01/arctic-sea-ice-decline-in-the-21st-century/

    “… we examined the September Arctic sea ice cover in the 20th and 21st centuries in climate models, and found occasional decades of very rapid retreat …”

    The authors have continued to publish. For purposes of justifying a gamble, if for nothing more serious, their work could be worth a look (by someone competent, not I, to assess whether there’s some basis to allow a curve.

  17. #17 T'other Chris R
    2010/10/06

    Leaving aside the wingnuts’ stance – “Nothing unusual here sea-ice recovering soon” – as detached from reality. And the opposite but equally bizarre – “sea-ice free by 2015″.

    From my reading nobody really knows what the future will bring: From Bitz’s “2007 outlier- followed by resumption of trend” to the various people saying it’ll be a rapid transition to seasonally ice free. Although the residuals from a linear, ’79 to present, trend suggest a dropping away, I’d still not dismiss Bitz’s position on the future of Arctic sea-ice.

    I’ll go with Dr Connelly’s predictions from a linear trend until perhaps 2015 when we should know if 2007 was an outlier or the start of a rapid acceleration in loss.

  18. #18 Phil Hays
    2010/10/07

    Any comments:

    http://geosci.uchicago.edu/~abbot/PAPERS/abbot-tziperman-08a.pdf

    Did your modelling of sea ice free Arctic show signs of strong winter convection?

    If not, is that reasonable?

  19. #19 Tony Sidaway
    2010/10/07

    I’ve watched enough Arctic sea ice to be certain of one thing: anything I said about what may happen in the future would look flat-headed and uninformed (it surely is the latter) in five years time.

    I’ll continue to watch very closely.

  20. #20 Deep Climate
    2010/10/12

    How about next year betting above/below the mid-point between the linear trend (Stoat’s method), and the quadratic trend (Tamino’s method).

    When each year is at or below the pre-existing linear trend (as it has been for the last several years), you have to wonder if the trend is accelerating. According to Tamino, that acceleration is statistically significant. It sounds like W. is starting to come to the same conclusion.

    As far as physical interpretation goes, don’t most sea ice models show an S-curve (i.e. at some point sea ice loss accelerates and then decelerates again as ice-free conditions are approached)?

    The published models (in the IPCC AR4) simply underestimated the rate of Arctic warming. By compressing the smoothed curves of the model projections to ice-free conditions by mid-century, you’d probably get a reasonable fit with current trends. But my intuition is that the quadratic method comes reasonably close at least for the next few years.

  21. #21 crandles
    2010/10/16

    Just checking your attention has been drawn to
    http://hot-topic.co.nz/five-years-threnody-for-arctic-sea-ice/

    (and the first comment).

  22. #22 blueshift
    2010/10/21

    Thank you WMC, crandles, and Hank Roberts for the replies and RC link.

    What about an ongoing, weighted bet with periodic payouts? I’m thinking of Nate Silver’s challenge as a model:

    http://www.fivethirtyeight.com/2009/07/challenge-to-climate-change-skeptics.html

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