4.0 Conditions look similar to last year, and I still don't really trust the volume estimates.

OT, really, but on the subject of ice movement, I see from recent MODIS that the ice is moving away from the NW archipelago coast in a really striking way.

Off-topic: I looked at the mosaic today for the first time in weeks and stuff is happening all over. The Bering Strait is flushing out, there's some quite dramatic break-up happening north of Franz Josef Land, up to at least 86 degrees and possibly all the way to the pole, and (less easy to discern) the western end of the NWP, north of Banks Island, seems to be breaking up. This all seems very early to me.

I can't find anything by Semiletov in the AGU program. But the search tool there is terrible. Can anyone find some actual data?

That ice is fast ice: sea ice attached to the shore. Not an ice shelf. Please don't call it an ice shelf. An ice shelf (like the Ward Hunt ice shelf, for instance) is a different animal. I'm not aware of a study showing the age of this particular fast ice. Does anyone have a cite?

Re areas of zones, sectors, boxes, etc: Archimedes' hatbox theorem tells us that the area of a latitudinal zone (i.e. all the area between latitudes A and B) is 2.pi.R^2.(sin(B) - sin(A)). The earth's polar radius is approximately 6360km, so the constant part there is 254e6 km^2, and I'm being overgenerous by giving three sig fig. The sine table looks like this: 75 0.965925826289 80 0.984807753012 85 0.996194698092 90 1.0 So the 75-80 zone is 4.8e6 km^2. The 80-85 zone is 2.9e6 km^2. The 85-90 zone is 0.97e6 km^2. To get 15-degree chunks of these, obviously divide by 24 (i.e. 200e3, 120e3, 40e3, near enough). I've shown the working so readers can do any related computations themselves.

These recent comments by Ned Ward and Peter Ellis are really excellent: aside from the light-hearted banter, this is the kind of thing that makes the comment threads here worthwhile.

I'm back from my work trip to NYC (First International Workshop on Climate Informatics, very interesting), where I sat out the hurricane in a friend's apartment. Catching up here, and a bit boggled by the last week of IJIS numbers. I haven't much to say, yet. However I *will* mention a book which I took on my travels, and which Everyone Should Read, or everyone interested in sea ice, anyway. It's even on-topic with these ice-breaking discussions. "South", by Ernest Shackleton, his own memoir of the Endurance expedition. I knew the story already (who doesn't) but to have it told in his own words, and illustrated by Hurley's famous photographs, is fantastic. My only caveat would be: see if you can find an edition with maps. I have a feeling that the text may be in the public domain (one reason for this suspicion is that there's no copyright statement on the imprints page), so any of you who like reading books on screens can probably find it for free online.

(by the way, I'm travelling from now until Tuesday; I might be able to get online, but if I can't then I'll have to re-assess this once I'm back).

Paul, our esteemed host has asked for us to have a neutral zone, for which neither of us win. http://neven1.typepad.com/blog/2011/08/sie-2011-update-17-unfulfilled-potential.html?cid=6a0133f03a1e37970b015390f724c4970b#comment-6a0133f03a1e37970b015390f724c4970b Put such a zone symmetrically around your 4.47 number and you have a bet.

Added to which, where did you get a sigma of 0.25?

Paul, you should assess whether or not to accept a bet based entirely on your own expectations, not on those of the other party to the bet. If my expectations differ from yours, you think my expectations are incorrect. Why would you base your bets on incorrect expectations? It makes no sense at all. You're saying that you believe P(minimum extent less than 4.425) is something like 0.36. But you won't take an even-odds bet? That's leaving money on the table.

I only make and take even-odds bets. Let us split the difference between your expected value (4.25) and mine (4.6): 4.425. If the IJIS daily extent minimum is below 4.425 million square kilometres, I will pay you fifty euros. If the IJIS daily extent minimum is above 4.425 million square kilometres, you pay me fifty euros. Result to be decided on 2011-10-01. Do you accept this bet?

Do you have any scientific reasons why the 30 year trend is likely to reverse itself in the near future? D, assuming your comments are aimed at Ned, he is very clear that he bases his opinions on the trends. His criticism is of those who make speculative leaps beyond the trends.

I suggest by looking at the special causes, that breaking 4.6 million is over 90% certain, and the odds of taking out the 4.25 million low extent record set in 2007 is greater than 50%, and there is a significant change (over 20%) that we end up with less than 4.1 million (if the right weather combo hits, which looks to be at least a one-in-five chance). Paul, I'll bet you 50 euros, at even odds, that the IJIS extent minimum will be above 4.3 million square kilometres.

FWIW, I'm with Ned, more-or-less (although I'd note that 2003, 2005, and 2009 are a statistical tie with 2011 for the same loss rate over the previous month, and only 2004 and 2008 were very much faster). And anyone suggesting we've never seen ice conditions like this has a short memory. Consider the terrifying state of the ice this time last year, all around the eastern longitudes, all the way up to the pole. http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?mosaic=Arctic.2010236.terra.4km As for volume: yes, volume is a key number, but we really don't have a good handle on it.

What a lot of egg on my face. I'll keep going, though. Predicted IJIS extent for August 23rd: 5,140,000.

I'm tempted to build a voting widget so everyone can enter their estimated IJIS extent delta for the next day. I think the hyperbole in this echo chamber sometimes gets a bit much, and some sort of tool to score our predictions, and to show each person's track-record, might calm people down a little. Maybe next year. For the record, today I predict an IJIS extent delta of 40,000 (that is, the corrected number for August 22 will be 5,236,719).

Sorry, Neven, I'm sick in bed tonight and can't spend long on this. Agreed that MODIS today is interesting. It's all in the weather; my forecast is still ~4.7.

It's completely obvious, using a Mk I eyeball on the IJIS extent chart, that 2011 and 2007 have broken away from the pack. It would be very surprising if 2011 doesn't break 7M ahead of 2007. Whether it can keep with the breakaway down to 6M is less clear: 2007 did that million in 12 days. I have to say, these races remind me more of the Tour de France than of snooker.

Kevin, the topology also applies to a ring of points close to the south pole, but there are no bears there. For that matter, there are no bears at the north pole, but too many facts spoil any riddle.

No IJIS number yet today....

Werther, maybe I should clarify my position. I think that arctic sea-ice loss is the canary in our coal mine: it provides simple, unambiguous, and highly mediagenic evidence of climate disruption, and over the next couple of decades it will do so with increasing drama and, I hope, increasing political effect. Basically, future ice-free Septembers will provoke our collective governments into actually doing something to address the crisis. In this way, arctic amplification might save civilisation. However, I don't see it this year. It's just a gut feeling: I could easily be wrong - the Beaufort Sea is already looking like a beer cooler.

Neven, that's my recollection based on looking at the orbit swath images at the time. Looking at them now, there's a lot of cloud: http://lance-modis.eosdis.nasa.gov/cgi-bin/imagery/single.cgi?image=crefl1_143.A2007192190000-2007192190500.1km.jpg but I expect a bit of poking around could find a clearer one.

Looking at the MODIS mosaic today, it's a beautiful view of almost the whole central pack. Hardly a lead in sight. This is what I meant by the pack seeming more solid than last year or 2007. http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?mosaic=Arctic.2011191.terra.1km