I am a Dragon. I emerge from my Egg. The summary of betting on sea ice refers. If you look in my comments, you'll find any number of well intentioned people advising me that its time to close up the bets before I take a bath. But I haven't. Anyone wanting to pile in is still welcome (if you can't be bothered to look up the previous post the bet is simple: will this years Arctic sea ice extent minimum, as measured by the satellites, be less than last year? I say no).
The May 5th version of "Arctic sea ice news and analysis" provides some more fodder. I've ripped off a pic from them which I like. To me, it rather suggests no record this year. They somehow convince themselves that it does suggest a min. Hey ho, we'll find out in a few months. Their section on "Estimating September extent based on past conditions" is cute. I like it; its a nice idea. Totally lacking, of course, is how would this idae have fared if applied last year, or the year before, or...
My personal opinion remains that we simply can't forecast year-to-year variations with any degree of reliability. The long-term trend is clearly downwards, and there will be a new record sometime. But based purely on the behaviour of the sea-ice extent timeseries I still consider that new record this year is less than 50% likely. I also wonder if people aren't in some danger of getting a teensy bit carried away publishing these "forecasts" which they don't really believe. They are speculative prognosticaions, no more.
Andy Revkin (its him again!) covers this. In the comments, Bill Chapman is reported to say "I say the odds favor a new NH record minimum - put my money there." I've replied (#40) but haven't heard from him... I must give him an email.
Comments
While I agree with everything you say, I also know that the system has a lot of hysteresis, meaning that starting from a new minimum means that there is a lot less multi-year ice. You are basically saying all other things being equal, which is true of a random walk, and even in that case there is a 50% chance of a new minimum. All other things are not equal.
[I don't have the data to had right now, but my recollection is that it doesn't support the idea of strong auto-correlation. I'm sure there is some. Maybe someone with the right software could calculate the lag-correlations... -W]
Posted by: Eli Rabett | May 8, 2008 9:54 PM
Hi William,
ok, I put £20 that this year sea ice extent minimum will surpass that of the last year. If I loose, you can give the money to NSIDC to do a better research ;-)
Posted by: Alexander Ač | May 9, 2008 2:38 AM
I'll see your NSIDC extent, and raise you the current area from Bill Chapman which, at the time of writing (9/5) was at exactly the same anomaly as this time last year (-1m km^2).
Posted by: Gareth | May 9, 2008 5:15 AM
NSIDC came up with this interesting (and IMHO compelling)angle:
"To avoid beating the September 2007 record low, more than 50% of this year's first-year ice would have to survive; this has only happened once in the last 25 years, in 1996."
[Yes, I read that. So explain why they haven't used this novel prediction method to post-dict previous years extent? -W]
Posted by: Steve Bloom | May 9, 2008 2:17 PM
The current arctic sea ice area (cryosphere today) is the same as last year as referenced by Gareth, and the extent is greater (NSIDC). This implies that there is the same surface area for ice chunks as at this time last year but that they are more spread out than last year. With more edges it might melt faster.
Posted by: Don Fontaine | May 9, 2008 3:47 PM
I'm probably wrong (I often am), but I think a lot hinges on the weather in July and August.
In 2006 the ice melt was rather more pronounced than 2005 in the earlier months, but a "cool" August saved us from seeing a new record.
In 2007 the ice extent was somewhat higher than 2006 up until the middle of July. But we had an unusually warm August in the Arctic, and the ice extent just kept on falling.
I think it's fair to assume that the melting rate in the next couple of months will probably be higher than we've seen recently, based on the thickness of the ice. But whether or not we break the record depends on Arctic temperatures in late summer, and we don't yet know what they will be.
Posted by: S2 | May 9, 2008 4:03 PM
Looking at the accompanying NSIDC bar graph, it doesn't look as if the first-year ice survival stats would have been very interesting prior to the very recent large increase in the proportion of first-year ice. Am I missing something?
Posted by: Steve Bloom | May 9, 2008 10:21 PM
Hi William,
It all looks pretty close to my. You figure a less-than-50% probability of a new record this year; CCAR give 59%. I'd have thought that S2 (above) is right in saying that when it's this close, it's pretty much weather-dependent... Still: I'll go a small bet of, say, EUR 40 (settlement via PayPal?) if you like. (You already have details on who I am etc. for our bet on sea ice melting by 2020, I think it was...)
Cheers,
Outeast
[OK, taken -W]
Posted by: outeast | May 12, 2008 9:39 AM