quote author=Daniel B. link=topic=1834.msg123175#msg123175 date=1501605264]
The long-term trend will of course be sublinear because you can't get negative extent, and it gets harder and harder to melt the remaining ice. But in the satellite era it appears pretty close to linear.
I keep seeing it said that "it gets harder and harder to melt the remaining ice," or words with that meaning, but I cannot remember ever seeing an explanation why that might be so. Seems to me that just like in a margarita, the last of the ice would go quickest. By then you have run out of cold.
Dharma,
The first ice to go was that furthest from the Arctic land masses, in the North Atlantic and the Bering straits. This was in closest proximity to the [relatively] warmer waters of the North Atlantci and Pacific. This has been followed by the ice in the open Arctic. The warmer waters can inflowing can melt this ice from all sides, similar to the ice in your margarita. The ice abutting the colder Artic archipelago and Greenland does not experience this same physical condition, as the warmer waters approach from one side only. That is why this ice will be harder to melt.
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TLDR Summary: We don't really have a clue what the arctic looks like at say 1.0 or 2.0m total extent ice (god knows that volume looks like at that extent) Maybe the ice is in very different places than we're expecting in that case, since as fragmentation increases weather has a much larger effect.
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Regarding this I'm a little skeptical that say 1.0 m to 0.0 ice in some theoretical summer some year in the future, be it 1 or 20 is going to be the hardest. Certainly in the case of the ice sitting on the north pole shrinking into a smaller and smaller cap each each with the ice at the north pole at the highest latitude the last go makes some sense.
However based on the fragmentation at the north pole in 2012, and the possible fragmentation this year due to the state of the ice. (BTW I'm in the ICE is total shit camp, and the only reason we're not going to hit a new record that includes a dramatic free fall is that the weather has been very tender).
Anyway I have strong doubts that it will stay a continuous lump of ice that sits there, and as that central pack fragments earlier and earlier, the weather is going to have a stronger and stronger effect on it, it doesn't seem unlikely that a storm could make some crazy shapes and end up in warmer waters if it hits at the wrong time. At some point an export from a pole region to the general basin is going to eat ice as fast as an export to the Atlantic as sea temps keep climbing.
In regard to the landmass argument, I think going forward to assume that it will be cold there.. might be premature . Irrc the only reason England is a "nice" place to live is an Gulf steam, and to assume that with the extra albedo heat and the general extra heat in the ocean, coupled with less and less ice in the arctic ice is going to leave the ocean currents / circulation unaffected seems unlikely...
My theory is that there's some barrier point, for a while there's that middle cap that is going to stay solid and be slower to melt, but at some point it's going to fragment at the same time as unhelpful weather system, this all becomes extra extra unstable (as opposed to the regular kind instability we've been observing since 1950. But I think that's closer to the 2-3 million extent, and once the pack get pushed through that point, it'll free fall rapidly.
Now noes anyone know if anyone has done any studies / modeling from the opposite direction? take a warm climate with no summer ice, and look at how much the the climate has to cool off to start forming an arctic ice pack again? And then compare that to the global temperature range that can simply sustain an existing Cap but not grow / shrink it on average, compared to the global temp required to create one? (they could be the same I suppose, but I have doubts). Looking at how an artic ice cap forms might give just insight in what to look for when it might be disintegrating.
Liam
*P.S. Three other things I want to get my two cents in on while I'm writing a book. I debated separate poses for these, but the first two do really apply to this melting season.
1. Piomas and 2017 vs crappy satellite volume metrics. I think the science behind Piomas is SOLID, and all the measurements that have cross checked the model over the years bear it out, and I've watched it over the last couple years and I consider it the gold standard for volume. But lately I'm getting nervous, the largest problem with this model is that you have underlying assumptions, and some point the underlying assumptions that govern the Piomas model are going to fall out of wack with the reality of our warming planet. Hopefully it'll cause a small error, or maybe a large one. I also have a feeling that it (like most climate models seem to in an effort not to cry wolf) errs towards being conservative, and I've wonder if it's a bit out of sync with the current Year due to the weird freeze up last year, etc.
2.
Something that comes up a lot, and that might be be worth melt pondering on, everyone uses the GAC of 2012 as that ultimate disaster, implying it was almost like that "100 year storm", and it does seem like it was a perfect storm in the right(wrong?) place at the right(wrong?) time. Maybe it was, but I have a hard time imagining that, I saw a link somewhere about how a meteorologist said systems similar to the GAC setup every 4-5 years on average. It still has to be in the right place at the right time, but if the GAC setup is the 5 year storm... what's everyone's theory of an actual 100 even looks? if the 2012 GAC is only the bad dream, what's everyone's nightmare specifically as it applies to this melting season.
3.
This forum feels a bit more acrimonious than previous years. I do wonder if the waiting is getting to us a bit?... humans are not made to be patient in terms of a single melting season let alone year to year, and every year we're all thinking is this the one? is the sudden drop theory correct? or does the system stabilize for a decade or two due to negative feed backs such as the increased snowfall / cloudiness of a arctic that's not always a desert (I was pretty convinced it was going to be a record shattering year based on the slow freeze up until those started popping up, and I'm not convinced they're a one off).... Anyway... I think it might be worth remembering, we're all on the same side here... I'm pretty sure based on the comments on the forum that in regard to the climate we pretty much all of us think that instead of just crying about the that lone wolf snacking on the odd sheep, we should be using a megaphone to scream about the goddam fucking zombie horde of genetically altered super wolfs at the gate... even if we disagree how it might come about. I work as an Engineering, and when we're doing group designs with no obvious solution, and trying to decide what leads to use resources on, tempers can get heated... so we have a policy/philosophy that we ask everyone to hold on to and try and remember.... if you're feeling picked on and start to substitute anger and derision instead of reasoned debate.....remember this isn't art class, this is fucking grade A science, it has a right answer and wrong one (a over simplification perhaps but generally true), and the best part about that is that you don't need to yell, if you're convinced you're right but get veto/out voted, get your piece on the record in a reasonable matter, and if everyone disagree's and we don't go that way, just know that if you are right, someday you'll get to send an email (I guess in this case post) "I was right and you'll where wrong" (You're even allowed to use all caps, a huge font and and bold if you want)...Anyway if you made it this far, thanks for reading! cheers!
<I'll let this stand because it's your 3rd post, but next time be more on-topic and be shorter, or I will have to get my scissors; N.>