Just put me in for 3.5, since the data necessary for me to analyse further (as I explained in my previous post) won't be around until after the deadline.

With no buoy data AT ALL on the Siberian side of the Arctic Ocean, it's hard to know just how thin the ice over there has become. Buoys in other areas are returning first year ice thicknesses in the range of ~140 cm at max. If the ice in those areas is really only 140 cm thick, then virtually the entire Siberian sector up to 83-85 degrees North is destined to disappear by September. Given that the Alaska side in the last 3 years has pretty consistently melted up to 80 degrees North or so and the Atlantic side up to 82 or 83, I think it will do at least that this year. So I'm going to shoot (tentatively) for just a hair below 2012, near 3.5 M km^2 for NSIDC September monthly extent. My guess has the potential for revision on the basis of the timing of melt onset in June. If the snow is all gone before June 16 as seen on MODIS, reduce my guess to 3.0 M km^2. If the Siberian sector still has a good snow cover on June 20, increase my guess to 4.0 M km^2 as the area might survive the summer. And if it makes it June 25, I'm going to go for 4.5 but I doubt that will happen.

PIOMAS has updated.

Andy Celsius himself set 0ºC as the boiling point of tap water and 100ºC as the freezing point. Other way 'round my friend, other way 'round.

Crandles said: The price of carbon once stood at 32 euros per tonne.” That article has now been extended. Where now? Doubt the committee will propose a carbon tax instead. The EU central banks perhaps ought to buy (and subsequently destroy) carbon permits on the open market in order to target a certain price level, which would be increased slowly, over time. If it works for bond prices, why wouldn't it also work for carbon permit prices?

R. Gates, Have you not read the P. Rampal et al. paper "IPCC climate models do not capture Arctic sea ice drift acceleration : Consequences in terms of projected sea ice thinning and decline " ? I think it is the increased drift speeds of ice as it thins that accounts for the vast majority of model failure, not an increase in ocean heat advection from lower latitudes. The rest of the discrepancy can be (maybe?) accounted for by the snow albedo feedback, given that the models also seriously underestimate NH snow cover retreat in May and June. (or even multiyearice-albedo feedback???)

Chris, As a large part of the volume loss of 2010 was the loss of thick MYI driven into the Siberian sector I don't think a re-run will occur. I don't think this is right. In the spring of 2008, a whole lot more MYI had been advected into the southern part of the Beaufort Gyre than in 2010, and yet the volume loss that spring and summer was much lower, if we believe PIOMAS. Something else must be invoked in order to explain the loss of 2010. I suspect it had to do with large April temperature anomalies across the Arctic Ocean in 2010, but without the ability to "tweak" the weather and re-run PIOMAS to see the effect, I cannot say for sure.

Doomcomessoon, In recent years, any openings forming after the middle of May do not refreeze again. Openings forming earlier than mid-May often do freeze back over, but if this happens very late in the season, the ice will be thin and nearly transparent, so will melt very quickly once the season gets going. The cracks we had opening up in February and earlier this month have plenty of time and plenty of cold temperatures to freeze over, so expect them to act more or less like any other first-year ice would this season.

http://www7320.nrlssc.navy.mil/hycomARC/navo/arcticicespddrf/nowcast/icespddrf2013031718_2013032500_035_arcticicespddrf.001.gif Are you ready for the big one ?

Bob, Now, let's compare easy (cheap) oil to electricity for transportation. An EV uses about 0.3 kWh/mile. Average US electricity prices are $0.12/kWh. So $0.04/mile. To drive for four cents in a 50 MPG gasmobile you'd need to find $2 gallon fuel. Except that you are ignoring the effects of wear and tear in both cases, the more miles you drive the sooner the car will need servicing, and the sooner it will need to be replaced. Gasoline cars usually cost at least twice as much per mile as you would think if you only look at fuel cost. I am not as familiar with electric cars...

Is there a good reason to think the volume gain cannot simply be a result of the ice going out Fram Strait now being so much FYI and thus less volume export than normal?

http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Arctic_r05c02.2013068.terra The "crack" ice still doesn't have a snow cover...

Espen, 'melting' would mean the ice is turning into water. This is distinct from breaking into smaller pieces of ice.

I still don't expect to see the ice start melting until late May in this region.

There is NO 2nd year ice AT ALL in Barents, Kara, Laptev, East Siberian, Chukchi Sea, or the western Beaufort Sea now. It is 100% FYI: http://saf.met.no/p/ice/nh/type/imgs/OSI_HL_SAF_201303031200_pal.jpg http://www.aari.ru/odata/_d0015.php?lang=1&mod=0&yy=2013 The second year and older ice has retreated more than half way from the Siberian Coast to Greenland and the CAA in all areas, no exceptions...

Lanevn, This would only take an added ~15 ppm of CO2 , in contrast to the current amount which is ~110 ppm above the natural level (390 vs 280). Even the 315 ppm of the late 1950s was ~35 ppm over natural values and thus overkill! We would be MUCH better off all things considered if 85% of human emissions did not occur.

Apocalypse4Real, I wasn't discussing the issue of breakup, rather the age of the main intact floes in a given area. Although it would be interesting to compare the "meltability" of broken-up multi-year ice to first year ice...

Why do you think it will be so hard to keep going as usual ANYWHERE? I understand your point as far as some climates are concerned, but surely somewhere on the earth will still be livable in a way recognizable to us, perhaps with a bit of innovation in biofuel, fast plant growth, and agriculture. Our species has survived through a supervolcano 70,000 years ago, and many of their technologies were not lost. If we could make it through that, why not human-made climate change?

I don't want to get into a philosophy or supernatural belief discussion here except to say that I disagree with James Cobban in his claim that Western civilization is "founded on" one of any two particular worldviews. We have a much more diverse set of views than that, and many of us are proud to embrace this diversity, though some are not. I'm not going to make comments on Apocalypse4Real 's long attempt to discuss stewardship theology. I wanted to point out that if you look at http://saf.met.no/p/ice/nh/type/imgs/OSI_HL_SAF_201302091200_pal.jpg it looks like the North Pole is now covered with first-year ice!!!

Not so fast, Jim. Maybe things will be unpleasant and there will be famines and climate refugees, and the world population in the 22nd century will be reduced to 3 or 4 billion and then stabilize as we adapt, without a singularity occurring. You must first rule out the more mundane possibilities before asserting something extraordinary will occur!

@ Aaron Lewis: Isn't it clear that the diffusion/mixing time-scale of relevance for the methane feedback(s) is that of the layers of atmosphere in which methane would contribute to the maximum marginal greenhouse effect? Or perhaps all layers, weighted by a function representing greenhouse contribution? Chemical reactions and diffusion probably have to be simulated, I would not put my faith in any claims that any reasonably representative set of coupled whole-atmosphere concentration equations can be solved analytically!!!

Peter Ellis said: Steven Goddard has been obsessively following this and touting it as a "recovery" of multi-year ice depite the fact that it's the only cohort of ice to show any improvement. All other brackets are down dramatically. Not to mention just how scary it is when you compare ftp://ccar.colorado.edu/pub/tschudi/iceage/gifs/age1982_52.gif to ftp://ccar.colorado.edu/pub/tschudi/iceage/gifs/age2006_52.gif and ftp://ccar.colorado.edu/pub/tschudi/iceage/gifs/age2012_52.gif

Chris Reynolds said: Comparison of week 52 for years of this century shows that while there has been an increase of oldest category the overall extent is the lowest for any year, except possibly 2007 itself Do you mean area of second year and older ice?

PIOMAS has updated !!!

Aaron Lewis said: The bottom line is that the videos where folks light off methane from bubbles shows that the concentration of methane in those bubbles is greater than 50,000,0000 [sic] ppmbv. Shouldn't that be 50,000,000 ppbbv ?