3.7 million square km. (+/- 1 million square km). I'm guesstimating that it'll be about the same as last year based on current PIOMAS volume, NSIDC extent and Cryosphere area being about the same this year as last year, and based on general drivers not changing that much year-to-year. Put me down as an optimist, I suppose.

@Bosbas, Crandles, Thank you for your responses. If the lower average monthly ice extent for past years is indeed because ice has been more mobile in 2012, and thus seemed more extensive over the course of a month, then it would indeed seem to explain it. And if that is the explanation, then personally, I think it makes sense to place more emphasis on the daily figures, representing the extent of sea covered by ice at any one time, rather than on the monthly figures which would instead seem to represent the extent of where the ice has been. But that may just be my bias talking...

@P-maker, I am indeed pretty dubious of the metric in question - it seems to have been seized upon by some sceptics simply because it is a "last hold-out", as it were. But if it looks like it'll fall soon enough, it's one more bit of debating ground they'll have to abandon. @crandles, One thing I don't get from the nsidc data in the latest bit of Arctic Sea Ice News. Based on Figure 2, November ice extent seems to track lowest in 2012 for most of the month, and 2012 seems to clearly be the lowest in average overall, but in Figure 3 it's only the third lowest November on average. Do you know if there's some difference in how the extent figures are calculated across the two different graphs? (I noticed something similar in the previous installment, but it wasn't quite so stark a contrast as in this month's).

Further record speculation (probably not this year): how long before we see a new record low 365-day Arctic average? That's about the only unbroken Arctic ice record which I've seen sceptics still holding onto; the 2007 record remains the lowest yet, due to the fairly high peak 2012 extent and low peak 2007 extent. But with the average for the last six months of 2012 having been considerably less than the 2007 average for that period, I'd expect this record too might well be broken some time in the next six months. (Although it's far too early yet to speculate on where peak 2013 extent might fall). See this graph for a rough illustration of this metric: http://www.climate4you.com/SeaIce.htm#IRAC%20JAXA%20recent%20Arctic%20sea%20ice%20extent

On the record high shipping: I'd very much expect a new record next year, even without a new low in sea ice area or extent (not that those are unlikely either). There's an increased interest in building ships designed for the arctic, now that the business model's been established and the advantages have been made clear.

@Chris, I hadn't yet leapt so far as to suggest more dams as a deliberate measure to hold back warming, more wondering what the effect of the current trend towards more dams (for other reasons) might be. TBH, I'd be a little surprised if we're creating enough new water cover to seriously alter the climate very much, but I was really wondering if anyone here had some idea of the numbers. To answer your question as best I can, though: I believe that most such projects use freshwater, due to the dual utility value for irrigation and for hydroelectricity (you don't get a lot of salt water flowing downhill to harness for hydroelectric power). But some applications, particularly the creation of a power reservoir from an irregular power supply (e.g. wind) by pumping water uphill, could conceivably use seawater.

I'm interested by this talk of the benefit of making new reservoirs through dam-building in ameliorating sea level rise. Does anyone know the effect on warming and cooling (thinking particularly of albedo, convection-driven cooling, and possibly cloud formation) of trading land for water?

"As for the tail of the Gompertz projection: Gompertz is a logistic function that has a sigmoid form. So a tail is to be expected. Exponential crashes to zero. Projections using either function tell us nothing about the real physical processes." This. Also, the ice following such a projection at one stage in its decline does not mean it will continue such a projection in future stages in its decline when conditions are altered by the absence of ice.

A guess at what record 13 might be: http://barentsobserver.com/en/arctic/towards-cargo-record-northern-sea-route-10-09 In other speculation: given that we're starting the freeze this year with 19% less ice by volume than we did last year, and that extent seems to be shrinking in a non-linear fashion, what are the odds that 2013 will have an even lower extent than 2012?

I'm no expert on glacial movements, but would the fact that, underneath the ice, Greenland is basically bowl-shaped (http://maptd.com/wp-content/uploads/2011/02/Topographic_map_of_Greenland_bedrock.jpg) perhaps reduce the risk of catastrophic glacial flow?

Karl, 1m sq km more winter Antarctic sea ice is less important than 4m sq km less Arctic summer sea ice, for the following reasons: 1) 4m vs 1m 2) Winter sea ice doesn't affect the Earth's albedo the way Summer sea ice does 3) The rising Antarctic sea ice trend is taking place along a declining Antarctic land ice trend, producing a rather confused total effect in the Antarctic, whereas the declining Arctic sea ice trend is taking place alongside a declining Arctic land ice trend, showing a clear total decline in the Arctic. As for next year: it will indeed be interesting, as I said earlier. We've several reasons to think it'll be another low sea ice extent in the Arctic, however: 1) Warming trend 2) Positive feedback loops (lower albedo; increased methane and CO2 release; perhaps also increased shipping and drilling) 3) Little ice left, and what there is is thin, so not much to build from over this winter Set against that, there isn't much except the possibility of interannual stochastic variation. Which can be fairly considerable - I wouldn't be at all surprised if 2013 proves to have a higher sea ice extent than 2012's new record (the same happened the year after the last big drop - see 2007-2008 data here http://nsidc.org/images/arcticseaicenews/20111004_Figure3.png). I would, however, be pretty surprised if it proves to have a higher sea ice extent than 2011, and very surpised indeed if it's higher than 2009.

I was thinking that next year might be even more important than this year to the debate. Right now, the anti-anthropogenic argument seems to have crystalised around the claim that "it's just fluke weather this year", since this is the first individual year that's gone below the 2007 extent. If next year bounces back a little bit, like 2008 did, they may just get away with that argument for a while. If, on the other hand, the 2013 extent is even lower than this year, they'll probably have to abandon that line and move back to the tried and tested "Things are getting warmer, but it couldn't possibly be anything to do with emissions, and we reject any suggestion that this ice melt could be a bad thing anyway". The question is: what extent is likely in 2013? With no model having accurately predicted the current fall that I'm aware of, I've really no idea. But which side of the 2012 extent it ends up, and how far to either side, would seem to be pretty key to both how fast the future ice collapse is likely to go, and how the debate is likely to go this time in 2013.

The NSIDC data for the 23rd looks so close to the minimum for last year that I'd be quite surprised if their data for the 24th or 25th doesn't also show a new low for sea ice extent (http://nsidc.org/arcticseaicenews/). Does anyone know why the IMS data is so different to the others? (Apologies if this is a newbie question).