It would be interesting to know how much the remaining ice is being melted from below. I'm seeing data indicating that a lot of ocean heat is coming in from the Pacific side...

There's a part of me that is ready (and even hoping) for the kind of outcome that we may be seeing this year. It's looking pretty unequivocal, in terms of the impact of increased CO2 levels. But a ringside seat at the end of the world only gives you a better view...

AJBT, I do image to image comparisons looking for colour change - generally gives a reasonable, if broad, indication.

All that open water from the Bering to the CAA, plus clear skies, will certainly mean a lot of heat going into the water at this time of year. We can watch for melt ponds above, but we really need better data on the "melt ponds below".

The relationship between the low sea ice extent and the temperature patterns is interesting. It seems possible that ocean temperatures are driving this process, but I don't have relevant data...

gkoehler. I think that the issue is that the stochastic elements outweigh any ability to predict "ice free" status based on a curve. I expect that within 5 - 10 years we will be in a place where any single year in which all the right (wrong) factors come together could be "ice free".

Looks like the hottest spot in Canada today is northwest of Hudson's Bay, almost on the shores of the Arctic Ocean. That's somewhat anomalous, and if that heat starts getting sucked north it'll certainly accelerate the melting in the CAA, which would likely have knock-on effects.

Wayne: I know the radarsat product... but the $ are the problem...

Wayne: Do you have access to any 1m remote sensing products for that area? I could certainly run open water detection on specified areas (doing the whole arctic would need more computer power than I can dedicate to it), but the best imagery I can get is 10m multispectral.

Melt ponds appear to be developing pretty quickly in the Beaufort over the past few days.

And continuing on the slightly off topic vein, just a detail on the emissions from cement manufacturing. About half of those emissions are recaptured within 50 years by the cement through carbonization... so we have some built in uptake there as well.

Makes sense, Wayne. So the variables in the sublimation equation will be temperature, wind speed, and probably snow compaction/cementation (i.e. snow doesn't blow as much because it is cemented). Temperature will have both + and - impacts, since internal sublimation and recrystalization, resulting in more cemented snow layers, will occur faster at higher temperatures up to some temperature. Growing up in Saskatchewan I've certainly seen that effect at work! It'd be interesting to know how this theoretical equation would interact with the expected impacts of global warming in the arctic.

Sorry, the reference should be https://www.igsoc.org/annals/49/a49a050.pdf

One effect of increased (but still below freezing) Arctic temperatures that I hadn't considered before was the amount of sublimation from snow. A good study of these effects (https://www.igsoc.org/annals/49/a49a050.pdf) shows that there is a significant increase in sublimation rates with increased temperature, as well as with increased wind. These effects will both result in snow mass loss, but also in crystal structure change within the snow, which will interact with the snow ice formation process discussed above. I don't know how much models like PIOMAS take sublimation into account.

Looks to me like the extent maximum may be in. As you say, Neven, the game now is all about snow cover and melt season dynamics. Going to be interesting.

Great summary of the ongoing adventure into the unprecedented and unknown.

Sam: You've given a very thoughtful analysis of the issues. As someone with a strong background in adaptation/restoration/economics, my focus turns toward the relevant adaptive opportunities under the scenarios you have outlined. I tend to think that we can adapt significantly, albeit at pretty great human cost.

Sam: That's a great summary. I do wonder, though, what other inputs beyond raw temperature change might influence the outcome. For instance, do warmer temperatures on top of the greenland ice cap and changed circulation patterns mean more snow there, as seems to be happening in some parts of antarctica, thereby delaying or denying completely movement to phase 5. I can imagine effects like this stalling the progression around 3.5, with some Arctic ice appearing each winter and disappearing in the summer, driven by your lopsided, Greenland driven system.

At a purely anecdotal level, over the past couple of years I'm noticing what looks like a move of the pole of cold from the Siberian side of the AO to the CAA/Greenland. This may be related to some of the other patterns we're seeing that are impacting the ice. I'll have to do some data analysis once spring is really here...

Sam: I think your analysis of the chain of events is essentially correct, although I'm not as bleak about the future of human existence within this new, equable normal. But we certainly appear to be seeing another "warm" winter over the arctic ocean, with impacts on both extent and volume of arctic sea ice, and if this becomes a pattern the results will be dramatic over the medium term, unless the corollary turns out to be cool summers with less melt...

A good article about the wider impacts of changes in the Beaufort gyre http://e360.yale.edu/features/how-a-wayward-arctic-current-could-cool-the-climate-in-europe Thoughts on the differences in ice formation rates as a result of an increasing fresh water cap?

Great work! Given the info that's coming out on 2017 precipitation in the L.A. area - one of the causes of the current fire outbreak - the ridging system/California drought link seems to be somewhat intact, I'm afraid.

Great work, Neven!

Over the next few days it looks likely that a huge plume of wildfire smoke will be pulled out across the ice north of the CAA. It'll be interesting to see if an albedo effect shows up next year as the melt season progresses in that area.

I'm starting to consider the buttressing effect, similar to that found with the Antarctic glaciers, for the arctic ocean ice. My theory is that the peripheral ice buttresses the core, slowing its drift, and more the peripheral ice melts out, the easier it is for storms and normal circulation effects to start to move the core ice north of Ellesmere and Greenland. If that ice gets moved out of that area over the summer (and I think we're already seeing some of this happening), the result may even be a short term increase in extent, due to drifting MYI flows, but this area now becomes likely to melt out each year, which would accelerate the arctic toward ice free...