There appears to have been an extraordinary algae bloom happening north of the Laptev Sea over the past few days. I don't know what this indicates in terms of water temperatures, but given the height of the sun in the sky in that area at this time of year, it's an interesting event.

Doc Snow: I've been observing some signs of decompaction. That's the essential problem with extent as a measure of total ice. 2012, with the GAC, was a compaction event, which exaggerated the ice loss when measured using extent.

javimozo: See for instance https://worldview.earthdata.nasa.gov - set the view to arctic and, depending on the time of day, step back a day for a full view

The plume of Siberian wildfire smoke being sucked out across the ice is truly impressive today. Lots of heat with it, too. Meanwhile the Northwest Passage is within days of opening unless there's major ice movement south. We could have close to a month with both the Northwest and Northeast passages open. Circumnavigation opportunity if anyone is positioned...

I've never been completely convinced by the PIOMAS volume loss associated with 2012's GAC. It was such a dramatic compaction event that it may have pushed the model outside of its range of accuracy. On the other hand, the extent loss truly was dramatic. Whether or not 2019 breaks 2012's record, it will be close enough, and looks like a function of the "new normal", where-as 2012 was a unique event. That in itself is reasonably scary. Looks like there may be some ice export down the east coast of Greenland over the next week. Winds have been keeping that area reasonably compact, so decompaction in this area will impact the extent numbers, although also dooming the exported ice.

AJbT: Great enough to cause some pretty intense melt in Greenland and the Arctic north of Greenland over the past few days...

Personally I am virtually certain that we will see significant ecological and cultural impacts from GHG emissions, although we may be able to avoid the worst of them. There is a part of me that, regarding them as inevitable, wants to see them sooner rather than later, not only because it may stimulate people to avoid the worst, but also unfortunately because I'm scientifically curious about how it all will play out. While I'm already seeing significant ecological change locally, I wish I could see what the coming state will look like. Given how dire this may be for many people, I know that my curiosity is rather ghoulish, but the science is fascinating! In the meantime, this year continues to demonstrate the old adage that there are many ways to arrive at the same end. Great Arctic Cyclone versus Great European Heatwave...

AJbT: There appears to have been a state change in ice conditions - significant (>10 km in longest axis) coherent floes are less frequent - the ice is more composed of broken bits, which give more edge and water openings between them - more opportunities for melt.

The striking thing to me about the 2012-2019 comparison is the reduction in larger floes within the ice. 2012 had more open water in many areas, but within that open water were large relatively strong floes of multi-year ice. But 2012 and the following years have gradually reduced that component of the ice. Now even in areas with relatively continuous ice, it seems to be largely "rubble", except where recent releases of fast ice have occurred.

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.