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When will the Arctic Extent dip below 1,000,000 Km^2

2018-2019
12 (17.9%)
2020-2025
21 (31.3%)
2026-2030
13 (19.4%)
2031-2040
15 (22.4%)
2041-2060
2 (3%)
2061-2080
0 (0%)
2081-2099
1 (1.5%)
2100-beyond
3 (4.5%)

Total Members Voted: 64

Voting closed: July 27, 2018, 07:46:32 AM

Author Topic: When will the Arctic Go Ice Free?  (Read 139766 times)

binntho

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Re: When will the Arctic Go Ice Free?
« Reply #1400 on: November 21, 2019, 10:57:19 AM »
A possible mechanism for correlation of bathy with summer ice edge from Svalbard to FJL and possibly to SZ.

Strangely enough, I had some difficulty seeing the correlation (talk about confirmation bias!), but I guess you are talking about where the ice edge is a fairly straight line at the beginning, north of Svalbard, Franz Josef Land and the "Communist Archipelago".

But looking closer, I wonder why the ice edge that is seemingly following the shelf edge is actually either op to 100 km south of, or 50 km north of, the edge. There is almost never any exact match, or anything where you could say that the two are correlated with a shift of one against the other.

I am still not convinced that this seeming correlation is a temporary artifact - the shelf is aligned east to west, the minimum summer ice edge is also aligned east to west, and for some years the two will therefore invariably seem to follow each other.

Quote
The east spitsbergen current is probably not in doubt on this thread. It's effects can be seen on the surface clearly at times during the animation and, in my view, also beneath the ice as leads or lower concentration up until the line where the 'warm water waterfall' falls into the Nansen basin.
You mean the West Spitzbergen Current? The one that flows up the Fram strait to the west of Svalbard? That is admittedly most likely closely linked to the bathymetry, but then again, that's only a tiny area of the Arctic.
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binntho

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Re: When will the Arctic Go Ice Free?
« Reply #1401 on: November 21, 2019, 11:02:43 AM »
binntho, I think where I most differ with you is that you give the impression your only considering surface and near surface waters.
Not at all. But the ice is obviously only on the surface, and for bathymetry to have an effect there has to be a mechanism for different depths to affect the surface.

Quote
For me there is no resident water in the Norwegian sea, it's constantly being renewed by 'gulf stream/nad' waters from further south, so that water occupies the whole depth. Moving north/east it splits into energetic fractions the densest flowing north along the steep contours of the Barents shelf towards and around Svalbard then east along the shelfs contours and here the turbulence it creates in the waters coming off the shelf causes weak ice to melt.

Much as gerontocrat pointed out. And it's very probably right to say that bathymetry has an effect on the West Spitzbergen Current which again has an effect on the ice edge north of Svalbar. But that's still only a very small part of the supposed ice edge / continental shelf correlation.
Quote
The energetic potential of the lightest fraction [recently at 60degN, @500mph surface speed now 68degN, @370mph] rounding Norway loses some of it's kinetic energy to heat but never enough to allow it to return by the same route, thus there's a constant but variable flow off the shelf into Nansen.
 Enough images here
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binntho

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Re: When will the Arctic Go Ice Free?
« Reply #1402 on: November 21, 2019, 11:47:08 AM »
johnm33 kindly posted a link to images on Google,  and it is certainly worth having a look if for no other reason than to refresh our memory of how the currents are shown on the various maps.

But they did make me wonder: We all know that the warm currents flowing northwards are surface currents. What is it that makes the incoming water sink, even to such dephts that they start following the continental slope?

There are two possible mechanisms:
  • The warm water cools and sinks. This is one of the main drivers behind the AMOC.
  • The warm(ish) water, being salty, will dip below the freshwater lens found under the ice.

Neither of the two has anything obvious to do with bathymetry. The first one indicates that as the air (and ocean) warms up, the sinking areas will move northwards. No bathymetric requirements here.

The second indicates that the warm water will sink when it meets the ice - the fresh water lens is under the ice, as the warm current meets the ice it is pushed downwards. But at the same time, it will be warming up the edges of the fresh water lense, and if the waters are getting warmer then the balancing line will shift northwards. No bathymetric requirements here.

Waters that sink because of 1) will obviously follow bathymetric contours after it sinks. But not before, and since the ice is at the surface, I find it difficult to see any correlation.

Waters that sink because of 2) should just slip under the fresh water lens, however if the ocean depth is close to the thickness of the lens then obviously something has to give. So a potential correlation here - the warm waters want to sink, but the fresh-water lens is obstructing them in shallower waters. Once the barrier meets deeper water, there is suddenly room for the warm water to slip under the freshwater lense, releasing a lot of pressure.

So perhaps the mechanism has been found after all? Seems to me a bit too easy given how many people have been claiming correlation but unable to spell out the causality. And anyway this only applies to  the Atlantic side - there is very little correlation north of the Alaskan coast, and the Siberian coast seems to be more complicated (fairly good correlation, but then there's the Laptev bite ... but it wouldn't surprise me if there was a good bathymetric explanation for that too).
because a thing is eloquently expressed it should not be taken to be as necessarily true
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oren

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Re: When will the Arctic Go Ice Free?
« Reply #1403 on: November 21, 2019, 12:04:11 PM »
Waters that sink because of 2) should just slip under the fresh water lens, however if the ocean depth is close to the thickness of the lens then obviously something has to give. So a potential correlation here - the warm waters want to sink, but the fresh-water lens is obstructing them in shallower waters. Once the barrier meets deeper water, there is suddenly room for the warm water to slip under the freshwater lense, releasing a lot of pressure.

So perhaps the mechanism has been found after all? Seems to me a bit too easy given how many people have been claiming correlation but unable to spell out the causality. And anyway this only applies to  the Atlantic side - there is very little correlation north of the Alaskan coast, and the Siberian coast seems to be more complicated (fairly good correlation, but then there's the Laptev bite ... but it wouldn't surprise me if there was a good bathymetric explanation for that too).
Binntho, this is what people here have been saying all along - the correlation is mostly on the Atlantic side, and it has a good physical reason that you have just outlined. People did spell it out. A-Team even discussed this back in 2016 if I am not mistaken.
Currently the battleground is along the shelf break and is weather dependent, some years the fresh water lens is more advanced due to constant export, and some years it is driven back, which is why the correlation is not totally "on the line". But it's certainly there.
In other regions of the Arctic the story is different and there that correlation is typically missing.

johnm33

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Re: When will the Arctic Go Ice Free?
« Reply #1404 on: November 21, 2019, 12:17:03 PM »
" We all know that the warm currents flowing northwards are surface currents."
This is where we differ, in the image below the current splits where it meets the Barents shelf close to Norway, the shelf contour here is 500m implying that that acts as a barrier suggesting the current is below that level, and i suspect flowing across the contours at much greater depths, it may even be forced up by denser waters when it rounds SV. and heads towards SZ and Laptev, thus washing up and down the shelf as it moves east still driven by the inertia it aquired further south.

binntho

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Re: When will the Arctic Go Ice Free?
« Reply #1405 on: November 21, 2019, 01:01:01 PM »
Binntho, this is what people here have been saying all along - the correlation is mostly on the Atlantic side, and it has a good physical reason that you have just outlined. People did spell it out. A-Team even discussed this back in 2016 if I am not mistaken.

Well, recently they've been saying it very quietly. I myself didn't remember what A-Team actually said about any causality, but I remember him pointing out the correlation. And I've seen people making all sorts of wild claims about warm waters plummeting down into the abys and whatnot. So a refresher into the actual physics of the thing is surely a good thing?

Perhaps what's bugging me is that people make claims, and then when you ask "why" they become all defensive instead of simply explaining. Perhaps because they don't know the explanation?
because a thing is eloquently expressed it should not be taken to be as necessarily true
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binntho

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Re: When will the Arctic Go Ice Free?
« Reply #1406 on: November 21, 2019, 01:02:41 PM »
" We all know that the warm currents flowing northwards are surface currents."
This is where we differ, in the image below the current splits where it meets the Barents shelf close to Norway, the shelf contour here is 500m implying that that acts as a barrier suggesting the current is below that level, and i suspect flowing across the contours at much greater depths, it may even be forced up by denser waters when it rounds SV. and heads towards SZ and Laptev, thus washing up and down the shelf as it moves east still driven by the inertia it aquired further south.


Up to the point where the current starts sinking, it is most definitely flowing along the surface. And I think I did say something about the continental slope and the current having sunk enough to actually follow that slope. But not before it sinks!
because a thing is eloquently expressed it should not be taken to be as necessarily true
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gerontocrat

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Re: When will the Arctic Go Ice Free?
« Reply #1407 on: November 21, 2019, 02:36:09 PM »
When will the Arctic Go Ice Free? - when the Arctic gets too warm.

https://productiongap.org/2019report/
Quote
Governments are planning to produce about 50% more fossil fuels by 2030 than would be consistent with limiting warming to 2°C and 120% more than would be consistent with limiting warming to 1.5°C.
I made a longer post on "Paris 2015 & Beyond"
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uniquorn

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Re: When will the Arctic Go Ice Free?
« Reply #1408 on: November 21, 2019, 03:26:19 PM »
A possible mechanism for correlation of bathy with summer ice edge from Svalbard to FJL and possibly to SZ.
Strangely enough, I had some difficulty seeing the correlation (talk about confirmation bias!),
Wow. A possible mechanism to confirmation bias in one line.

El Cid

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Re: When will the Arctic Go Ice Free?
« Reply #1409 on: November 21, 2019, 03:28:09 PM »
"But I presume that you have no idea as to any mechanism behind why there should be any correlation between the edge of the continental shelf and the summer ice edge"

Well, people did not know for a long time the mechanisms behind why some herbs are useful, or eg. why winters are colder than summers. But they realized the pattern and without knowing the exact mechanisms, used these...

gerontocrat

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Re: When will the Arctic Go Ice Free?
« Reply #1410 on: November 23, 2019, 12:26:34 PM »
This quote is from an article about something completely different, but maybe it applies to the issues discussed in many threads on the ASIF, including this thread......

Quote
Things go along much as before, until – seemingly abruptly, but not really – they don’t. What now for it all? I can’t help thinking of that great bit of Hemingway dialogue from The Sun Also Rises. “How did you go bankrupt?” “Two ways,” comes the reply. “Gradually and then suddenly.”
https://www.theguardian.com/commentisfree/2019/nov/22/prince-andrew-duke-of-york-sacked
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johnm33

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Re: When will the Arctic Go Ice Free?
« Reply #1411 on: November 23, 2019, 10:37:52 PM »
"Up to the point where the current starts sinking, it is most definitely flowing along the surface. And I think I did say something about the continental slope and the current having sunk enough to actually follow that slope. But not before it sinks!"
I've said elsewhere that I've convinced myself that current are the residuals of tidal movements. Here there's a tidal surge flowing north between Iceland and the Hebrides it passes in the west over a shelf about 500m deep and east of the Faroes over a shelf about 1500m deep, that is how deep the current could be, but flowing south over the same shelves are some Arctic waters that have been led by bathymetry away from Denmark strait where the bulk of Arctic waters flow south, but on the western side of the mid atlantic ridge. My guess would be that the inflow here exceeds the outflow so allow maybe max depth of 800m for the northbound current. Some part of it diverts around the Voring plateau which lies below 1000m suggesting it's saline enough to drop below 800m. It's moving north and east so outpacing the Earths rotation and has to shed about 15mph. per deg. as it moves north, that kinetic energy adds to the temp. of the current. The deeper parts of the currents are never going to make the climb, in competition with the top 500m of flow, onto the Barents shelf and are forced almost due north towards SV. and again become warmer. Some fraction also makes it onto the shelf as it traverses the slope the rest piles up near the persistent anomoly before it moves either around SV to head east, across the north Greenland shelf to Nares/CAA or flows south joining the Arctic waters. Each of the flows is variable according to tidal forcings and mslps even as far as Bering. 
Someone [?] linked to a paper that found evidence that the Arctic ice cap once rested on Lomonosov, so 1km+ thick, I suspect that this was coincident with the breakdown in the thermohaline circulation in the north Atlantic. If the ice was 1km in the central arctic then it's not a stretch to think that Barents too was icebound and that tidally driven currents have very slowly Atlantified the Norwegian, Greenland and now Barents seas. The tides remain consistent but the currents are slowly increasing and penetrating ever further so very slowly then all at once seems about right.
Tangential speed
Given their rounded shape both the Voring plateau and the Barents shelf north of Norway could be ancient landslides?

KiwiGriff

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Re: When will the Arctic Go Ice Free?
« Reply #1412 on: December 03, 2019, 06:40:13 AM »
Tamino has done a analyse of the sea ice extent trend .
here
https://tamino.wordpress.com/2019/12/02/the-thermometer-is-melting/

binntho

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Re: When will the Arctic Go Ice Free?
« Reply #1413 on: December 03, 2019, 07:57:01 AM »
Tamino has done a analyse of the sea ice extent trend .
here
https://tamino.wordpress.com/2019/12/02/the-thermometer-is-melting/

Extremely interesting! And I note that there are no signs of any stall in Tamino's analysis. There are two graphs that caught my attention. The first is this one along with Tamino's explanation:



Quote from: Tamino
The interesting result is that there have been three “episodes” of Arctice sea ice loss. The first extends to about October of the year 2001, with sea ice declining at about 35,000 km^2/yr. During the second episode, up to around February 2007, it declined faster at about 155,000 km^2/yr. Since then it has returned to very near its previous rate of decline at 46,000 km^2/yr (faster loss than the first episode, but the difference is not “statistically significant.”)

The second graph is perhaps the most interesting, showing changes in the rate of sea ice loss. The lowess is showing a remarkably steady rate of loss that starts dropping precipitously just before 2000, ending in a deep through in 2004, only to jump back up to a peak in 2012 (the rate of loss was actually at it's lowest in 2012, matched only by 1995).

So the plateau of 1979 to 1998 ends in a steep sided canyon, and on the other side is a local peak. But then things start going downhill at a steady rate. Ever since 2012 the rate of loss has increased (did someone mention a stall?).

Steady rate of loss the first 20 years interrupted by a very rapidly increasing rate of loss between 1998 and 2004, a rebound of rapidly decreasing rate of loss ending in 2012, with a steadily increasing rate of loss since then.

And it's the increasing rate of loss since 2012 that really got my attention. As mentioned before, there is no stall visible, but more importantly, the ice seems to be having an ever easier time melting year from year.



Quote from: Tamino
I can even plot the rate of sea ice loss over time, according to both models (PLF and lowess). The PLF actually estimates the average rate during each episode, while lowess can estimate the instantaneous rate. Here they are, lowess in red, PLF in blue, with pink shading for the lowess uncertainty range and blue dashed lines marking the PLF uncertainty range

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KiwiGriff

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Re: When will the Arctic Go Ice Free?
« Reply #1414 on: December 03, 2019, 08:04:43 AM »
Has anyone proposed a mechanism for the sudden acceleration then return to prior trend ?

 


 

binntho

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Re: When will the Arctic Go Ice Free?
« Reply #1415 on: December 03, 2019, 08:29:43 AM »
Has anyone proposed a mechanism for the sudden acceleration then return to prior trend ?

As far as I know, nobody has come up with a good explanation for the big dip, nor for the slippery slope. Which perhaps tells us how little we know about what's going on up there!
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KiwiGriff

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Re: When will the Arctic Go Ice Free?
« Reply #1416 on: December 03, 2019, 09:13:56 AM »
Certainly puts a dent in the pauseites case for a slow down.

I don't see the dip as the effect of an  influence like a cyclic weather pattern. To my ignorant eyes it looks like a permanent state change had a large but limited effect that once saturated reverted to the  steadily increasing prior trend.
if that makes sense  :-\

« Last Edit: December 03, 2019, 09:27:41 AM by KiwiGriff »

Sam

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Re: When will the Arctic Go Ice Free?
« Reply #1417 on: December 03, 2019, 09:26:42 AM »
Has anyone proposed a mechanism for the sudden acceleration then return to prior trend ?

As far as I know, nobody has come up with a good explanation for the big dip, nor for the slippery slope. Which perhaps tells us how little we know about what's going on up there!

Binntho,

I haven’t marshaled the plots and data to show it, so take this as my guesstimate as to cause rather than as a rigorous argument.

I think several factors are involved.

First, extent as it is defined is a crude tool ill suited to assessing the ice condition as we enter the terminal phase of the meltout of the Arctic Ocean. It’s original intent was to smooth the edge measures of the melting sheet. The difference in using a wide array of assumptions about the area of ice in a measured surface area to count as 100% ice wasn’t particularly impactful or important. Now that the central arctic is breaking up each year that no longer holds true.

Second, beginning about 2004 the annual melting of the arctic ice began to seriously involve the central arctic. By 2007 it was basin wide.

Third, as the melt has progressed, the sheet has progressively thinned. This exposes more and more ice area to breakup into smaller chunks with more ocean between them.

Fourth, fifth, sixth, seventh ... the mixing of the near ice sea under the ice became greater exposing the ice to warmer more saline waters; the fluxes of fresh water driving the great oceanic current began to collapse which greatly shifted the oceanic movements; the atmosphere began to destabilize introducing several new wrinkles into the ice dynamics; masking effects of ponding declined as the unit areas of intact ice segments became smaller  ...

I suspect that several key factors came into play. The ice area (not extent) became more volatile annually as the initial area subject to melt declined, and with it the annual minimum areas. This exposed the ice to greater variability in ice area subject to all of the melt processes. That then allowed a shattering of the sheet. It is/was almost inevitable that at some point the 15% ice cover definition for extent would be breached over large areas of shattered ice sheet. This would give the false impression of a sudden decline in extent, not matched by a sudden decline in area. In truth what it reveals is the inadequacy of extent being used as a surrogate for ice condition.

Ice area suffers a similar flaw. The ice has thickness. When the ice thickness falls below a critical threshold, the ice area may likewise suffer great variation and sudden drops. We seem to be seeing the first of these in the past decade. I wonder how much longer we have until the second shows up.

I suspect that we shall soon have answers to those questions. And that when we do that they will be meaningless, as the September minimum will have seemingly suddenly reached near zero.

Sam

KiwiGriff

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Re: When will the Arctic Go Ice Free?
« Reply #1418 on: December 03, 2019, 09:35:34 AM »
Sam have a look at Taminos full post you will find more interesting detail on the seasonal cycle.
https://tamino.wordpress.com/2019/12/02/the-thermometer-is-melting/
I left a comment trying to entice him into looking at the volume as well.

crandles

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Re: When will the Arctic Go Ice Free?
« Reply #1419 on: December 03, 2019, 02:25:28 PM »
Has anyone proposed a mechanism for the sudden acceleration then return to prior trend ?

As far as I know, nobody has come up with a good explanation for the big dip, nor for the slippery slope. Which perhaps tells us how little we know about what's going on up there!

There is perhaps partial explanation in beaufort gyre flywheel failure: MYI used to make it around the Beaufort gyre which gave it time allowing it to thicken by compression in the safer parts of the gyre. When Beaufort, Chukchi, East Siberian seas started melting the MYI was mainly melting rather than mainly making it around gyre. This caused rapid drop in old ice coverage so Beaufort, Chukchi, East Siberian were able to consistently melt out and make it hard for MYI to make it around gyre.

see
http://dosbat.blogspot.com/2012/05/transition-complete.html
and the references given

Bintho has indicated his opinion is that the timing is wrong for this to be the explanation. The dip looks more v shaped than u shaped which widens the timing.

.

The downward slope at the end is interesting and perhaps shows a new behaviour such that gompertz shape may need to evolve. A word of warning about this seems in order, the uncertainty range at the end is very large. We may need to see how this develops. (Or maybe I am just too attached to gompertz shape that the models seem to show.)

kassy

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Re: When will the Arctic Go Ice Free?
« Reply #1420 on: December 03, 2019, 05:03:05 PM »
On the dosbat link you see the perennial extent dive down at the same time. I think it is a good match.

Other areas used to freeze and melt then they got cleared so did not protect the rest anymore.
This affected all the outer Arctic seas and the gyre and got us to here.

The future ice is harder to melt by location but it easier to melt because it is thinner and more mobile and the background forcing increases year over year.

The remaining area is also not really sticking to Greenland for safety as we had hoped for a long time so what is left might get really floaty at some point. Or just disintegrate and die in place.

I would love to know how Remaining ice at max for every year is composed by Ice Grown Locally (in the 80N circle or whatever the metric is) vs Imported ice over the previous year.
But we don´t.

I bet it would make for a cleaner fit.
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dnem

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Re: When will the Arctic Go Ice Free?
« Reply #1421 on: December 03, 2019, 05:10:37 PM »

The remaining area is also not really sticking to Greenland for safety as we had hoped for a long time so what is left might get really floaty at some point. Or just disintegrate and die in place.

A-Team used to say "we could have a total late summer blow out any year now". (I'm paraphrasing).  I agree.  One summer, any summer, the remaining ice will be thin and fragile enough to become a completely shattered, mobile mess by season's end.

binntho

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Re: When will the Arctic Go Ice Free?
« Reply #1422 on: December 04, 2019, 03:13:39 AM »
There is perhaps partial explanation in beaufort gyre flywheel failure: MYI used to make it around the Beaufort gyre which gave it time allowing it to thicken by compression in the safer parts of the gyre. When Beaufort, Chukchi, East Siberian seas started melting the MYI was mainly melting rather than mainly making it around gyre. This caused rapid drop in old ice coverage so Beaufort, Chukchi, East Siberian were able to consistently melt out and make it hard for MYI to make it around gyre.

see
http://dosbat.blogspot.com/2012/05/transition-complete.html
and the references given

Bintho has indicated his opinion is that the timing is wrong for this to be the explanation. The dip looks more v shaped than u shaped which widens the timing.

Even if old, that blogspot article gives as good an explanation as any of why the ice should be melting ever faster, as seen in the slippery slope. Loss of multi-year ice and the collapse of the Beafort gyre, the increase in open-water potential etc.

As far as the timing goes, I do find it interesting that the big changes in the rate of change (the red lowess line) seem to happen in 1998, in 2004/5 and in 2011, which were not remarkable as far as ice extent goes. Perhaps an El Nino effect? Seems difficult to pinpoint, except for the fact that 1998 was the big one by far, a mega El Nino and a significant anomaly.
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gerontocrat

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Re: When will the Arctic Go Ice Free?
« Reply #1423 on: December 04, 2019, 11:52:31 AM »
Looks like the CAA's ability to block ice export from the Arctic Ocean is reducing. Maybe one of those small things with large consequences?

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GL085116?af=R
The Dynamic Response of Sea Ice to Warming in the Canadian Arctic Archipelago
Quote


Ice arches in the Canadian Arctic Archipelago (CAA) block the inflow of Arctic Ocean ice for the majority of the year.

Plain Language Summary

Satellite observations are used to understand the effect of warmer temperatures on how much sea ice is transferred between the Canadian Arctic Archipelago (CAA) and the Arctic Ocean. Larger sea ice area flux values are associated with (i) longer flow duration, (ii) faster moving ice, and (iii) more open water leeway from the CAA's long‐term transition to a younger and thinner ice regime.

These factors have contributed to a significant increase in the amount of sea ice entering the northern regions of the CAA from 1997 to 2018. Remarkably, the amount of Arctic Ocean ice entering the CAA in 2016 was 7 times larger the 1997–2018 average and almost double that of the amount of ice transported through Nares Strait in 2007.

Overall, with continued warming the CAA could be larger pathway for the loss of sea ice in the Arctic Ocean.

1. Introduction

Canada's Changing Climate Report indicates that annual average air temperature in northern Canadian regions have increased 2.3 °C over the period of 1948–2016 and relative to 1986–2005 are projected to increase 7.8 °C by 2081–2100 (Zhang et al., 2019).
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crandles

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Re: When will the Arctic Go Ice Free?
« Reply #1424 on: December 04, 2019, 12:45:13 PM »
There is perhaps partial explanation in beaufort gyre flywheel failure: MYI used to make it around the Beaufort gyre which gave it time allowing it to thicken by compression in the safer parts of the gyre. When Beaufort, Chukchi, East Siberian seas started melting the MYI was mainly melting rather than mainly making it around gyre. This caused rapid drop in old ice coverage so Beaufort, Chukchi, East Siberian were able to consistently melt out and make it hard for MYI to make it around gyre.

see
http://dosbat.blogspot.com/2012/05/transition-complete.html
and the references given

Bintho has indicated his opinion is that the timing is wrong for this to be the explanation. The dip looks more v shaped than u shaped which widens the timing.

Even if old, that blogspot article gives as good an explanation as any of why the ice should be melting ever faster, as seen in the slippery slope. Loss of multi-year ice and the collapse of the Beafort gyre, the increase in open-water potential etc.


By 'slippery slope', I assume you are referring to the increasing rate of loss at the end of the graph?

I don't see why you aren't seeing it as a reason for high rate of loss while the MYI is disappearing rapidly, then when the MYI is down to the new lower level then things return to around the normal rate.

Does the following image help show a high MYI level then a low level?



http://nsidc.org/arcticseaicenews/files/1999/11/Figure5-1-350x443.png

The 2-3 year ice is pretty steady til 2002, then downwards every year til 2008, then pretty horizontal after that. Other ages show similar pattern. That seems pretty close to the timing of the extent loss rapid change. Correlation does not prove causation but this is in the scientific literature at the appropriate time for the temporary rapid  rate of loss. (Not for the slippery slope if I am interpreting that term correctly.)
« Last Edit: December 04, 2019, 12:56:14 PM by crandles »

binntho

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Re: When will the Arctic Go Ice Free?
« Reply #1425 on: December 04, 2019, 01:38:46 PM »
You interpret the "slippery slope" correctly! But other than that I'm not really catching your argument. If the slippery slope is real (and remember that the error margins get very big towards the end), then the sudden drop in MYI could very well be part of the explanation. I'm not sure if you think so as well, and think that I don't, or you don't and think that I do ...

Lack of MYI presumably means more open water potential which seems to me to be a good setup for increased positive feedback from albedo, all of which should increase the rate of melt.

But how to explain the big dip (aka the uncanny valley or the curious canyon)?
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crandles

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Re: When will the Arctic Go Ice Free?
« Reply #1426 on: December 04, 2019, 02:48:59 PM »
But other than that I'm not really catching your argument.

My interpretation, if it helps, is that:

The beaufort gyre flywheel argument only affects part of the Arctic basin. As area and volume of MYI is rapidly reduced, this causes rapid retreat of extent. This does not continue indefinitely, once the flywheel is broken then it is broken, and MYI begins an irreversible rapid decline. This doesn't result in no MYI, it changes the system to a lower level of MYI. In part this is because it only affects the part of the arctic involved with Beaufort gyre not all of the Arctic. Once the transition to low level of MYI is complete then the rapid reductions in MYI cease but some MYI persists at lower levels (away from affected area) with little trend.

When there is little trend in MYI, (and/because no MYI arriving in the affected area can survive) then the reason for rapid extent reduction has disappeared. So extent retreat returns to a more normal level.

I have tried explaining this to you before, but you seem unable to see/accept it. I am not sure I can find a way to say it any more clearly, it just seems to get longer with more repetition.




crandles

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Re: When will the Arctic Go Ice Free?
« Reply #1427 on: December 04, 2019, 02:58:25 PM »
Lack of MYI presumably means more open water potential which seems to me to be a good setup for increased positive feedback from albedo, all of which should increase the rate of melt.

It is a change to a lower level of MYI that causes an increased rate of melt.

A low level of MYI eg 0.5m km^2 not changing but remaining at a low level of 0.5m km^2 is clearly not a reason for an increased rate of melt.

Glen Koehler

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Re: When will the Arctic Go Ice Free?
« Reply #1428 on: December 05, 2019, 02:18:38 AM »
1.
Does the following image help show a high MYI level then a low level?

http://nsidc.org/arcticseaicenews/files/1999/11/Figure5-1-350x443.png

Crandles' theory makes sense to me.  But I would change "The 2-3 year ice is pretty steady til 2002, then downwards every year til 2008.... etc." to "The 2+ year old ice...". 
     It is the combination of decline in the 2-3, , 3-4 and 4+ age categories (esp. the 4+ year ice) that causes the steep slope ca. 2001-2007. 

     The transition of the Beaufort gyre from a nursery to a melting zone seems to fit as a qualitative transitional event that gave rise to the observed trends. 

2.
Looks like the CAA's ability to block ice export from the Arctic Ocean is reducing. Maybe one of those small things with large consequences?
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GL085116?af=R
The Dynamic Response of Sea Ice to Warming in the Canadian Arctic Archipelago

This seems like another qualitative change that could accelerate the end game for late summer ASI decline.  Adding another doorway for ice export can't be good for retaining ice.


3.
    The remaining area is also not really sticking to Greenland for safety as we had hoped for a long time so what is left might get really floaty at some point. Or just disintegrate and die in place.
 
A-Team used to say "we could have a total late summer blow out any year now". (I'm paraphrasing).  I agree.  One summer, any summer, the remaining ice will be thin and fragile enough to become a completely shattered, mobile mess by season's end.

See ice thickness on gerontocrat's last graph over in the PIOMAS thread at https://forum.arctic-sea-ice.net/index.php/topic,119.msg239492.html#msg239492

Not sure where I saw it, but somebody (Notz and Strove 2018?)  suggested that once thickness gets below 0.5 to 0.8m, flash melt under the right conditions becomes possible.  Looking at the thickness trend, the combination of trend + high melt conditions could bring Sept. Extent below 1M km2 as early as mid 2020s. 

4.  Independent of above, Notz and Strove 2018 article gives info to correlate Sept. Extent with Global avg. temperature.  That points to cumulative probability of the 1st Sept with < 1M km2 exceeding 50% by 2035, and regularly (each individual year chance >50%) by 2037. 
(My dates, not theirs, details later.)

   N&S 2018 correlation of ASI Extent with cumulative CO2 emissions puts the cumulative chance of 1st Aug. and Sept. as 'largely ice free' (which from my guesswork seems to line up with ca. < 2M km2 Extent, details later) at >50% chance by 2033, and regularly (individual year chance > 50%) by 2036.

   Finally, N&S 2018 give correlation of CO2 with July - October being "largely ice free" (which as above, I interpret as ca. < 2M km2 Extent).  For that I used observed emissions through 2019, and Intl Energy Agency emissions trend forecast of 1.1% continued emissions growth out to 2040, then reducing subsequent global emissions as per the observed US and EU combined downward trend since their recent peak.  With those CO2 assumptions, the cumulative 50% chance for a 1st July-Oct  that is "largely ice free" is by 2045, and regularly (individual year chance > 50%) by 2048. 

 

« Last Edit: December 05, 2019, 06:05:34 PM by Glen Koehler »

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Re: When will the Arctic Go Ice Free?
« Reply #1429 on: December 05, 2019, 03:07:48 AM »
    With Arctic albedo already increasing radiative forcing by about 25% of the GHG influence (forget the source, could look it up if somebody really needs it), consider how much MORE albedo impact would arise from July being "largely ice free".  Remember, if July (a high solar gain month in it's own right) has hugely reduced Extent by 2048, then June must also have much lower Extent than at present. Wide expanses of open Arctic Ocean in June and July = Albedo nightmare.

    That makes 2050 look like end of the line for a planet any of us would recognize.  If Jennifer Francis et al. are even half-right about weather impacts of Arctic warming and ASI decline at 2010-2019 levels, the effects by 2040-50 would be off the charts.

    I believe that with collective human ingenuity just about anything is possible.  But the performance to date for human wisdom with regard to climate management does not make for an optimistic outlook.  By the ASI situation alone (ignoring the many other vectors), it looks like human civilization could be in dire straits by, or well before, 2050 unless things start changing radically and soon.  So let's stop using 2100 as the benchmark and focus on how humans can get past 2050.
« Last Edit: December 05, 2019, 06:13:37 PM by Glen Koehler »

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Re: When will the Arctic Go Ice Free?
« Reply #1430 on: December 05, 2019, 05:15:29 AM »
    With Arctic albedo already increasing radiative forcing by about 25% of the GHG influence (forget the source, could look it up if somebody really needs it), consider how much MORE albedo impact would arise from July being "largely ice free".  Remember, if July (a high solar gain month in it's own right) has hugely reduced Extent by 2048, then June must also have much lower Extent than at present. Wide expanses of open Arctic Ocean in June and July = Albedo nightmare.

    That makes 2050 look like end of the line for a planet any of us would recognize.  If Jennifer Francis et al. are even half-right about weather impacts of Arctic warming and ASI decline at 2010-2019 levels, the effects by 2040-50 would be off the charts.

    I believe that with collective humanity ingenuity just about anything is possible.  But the performance to date for human wisdom with regard to climate management does not make for an optimistic outlook.  By the ASI situation alone (ignoring the many other vectors), it looks like human civilization could be in dire straits by, or well before, 2050 unless things start changing radically and soon.  So let's stop using 2100 as the benchmark and focus on how humans can get past 2050.

2020 30 year bonds mature in 2050.
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binntho

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Re: When will the Arctic Go Ice Free?
« Reply #1431 on: December 05, 2019, 07:53:00 AM »
But other than that I'm not really catching your argument.

My interpretation, if it helps, is that:

The beaufort gyre flywheel argument only affects part of the Arctic basin. As area and volume of MYI is rapidly reduced, this causes rapid retreat of extent. This does not continue indefinitely, once the flywheel is broken then it is broken, and MYI begins an irreversible rapid decline. This doesn't result in no MYI, it changes the system to a lower level of MYI. In part this is because it only affects the part of the arctic involved with Beaufort gyre not all of the Arctic. Once the transition to low level of MYI is complete then the rapid reductions in MYI cease but some MYI persists at lower levels (away from affected area) with little trend.

When there is little trend in MYI, (and/because no MYI arriving in the affected area can survive) then the reason for rapid extent reduction has disappeared. So extent retreat returns to a more normal level.

I have tried explaining this to you before, but you seem unable to see/accept it. I am not sure I can find a way to say it any more clearly, it just seems to get longer with more repetition.

Well, with thick heads you just have to keep hammerin'

If I understand you correctly, you are saying that the break-down of the Beaufort gyre and the resulting rapid loss in MYI explains the downard slope into the big dip, and once the amount of MYI levels off, then the rate of melt slows down as well, explaining the upwards slope of the big dip?

As seen in your graphs, there is a big drop in MYI in 2007, temporally it looks like a single year event and is strongly matched by a very large drop in FYI.

We've seen from Tamino's blog that there was no stall, but there was a period of faster melt. The linear piecewise change starts 2002 and ends 2006. In the smoothed lowess the big dip starts around 1998 and reaches bottom around 2004/5, and is back up again 2011. So the timing doesn't match very well with the MYI drop in 2007.

So I'm probably still as unconvinced as I was then. There have been changes, yes, the Beaufort gyre stopped, the MYI is vanishing rapidly etc. etc. But how important is that to the overall picture? How much of a difference does it make to the annual meltout? In my view, the strongest signal by far is the steadily rising temperatures. Everything else is just nibbling at the heels.

So my take on the Big Dip is that the big jump in temperatures around 1998 led to the 00's starting out a lot warmer than previous decades, but then come pretty close to stalling, leading to oft-repeated claims of a global warming hiatus and whatnot. So a good kick downwards from c.a. 1998 but then the speed peters out towards the end of the decade.

Since the early teens, temperatures have been rising and although the verdict is not in yet, the rate of temperature rise may well have increased. The attached graph shows global temperatures, and the red boxes mark the three period I am interested in, the two halves of the Big Dip and then the Slippery Slope.

As usual, I come to the conclusion that by far the best explanation of the behaviour of arctic ice, when it melts and how fast it melts, is found by looking at the changes in temperature and not hypothesising about MYI or the Beafort gyre.
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crandles

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Re: When will the Arctic Go Ice Free?
« Reply #1432 on: December 05, 2019, 12:58:45 PM »

Crandles' theory makes sense to me.  But I would change "The 2-3 year ice is pretty steady til 2002, then downwards every year til 2008.... etc." to "The 2+ year old ice...". 
     It is the combination of decline in the 2-3, , 3-4 and 4+ age categories (esp. the 4+ year ice) that causes the steep slope ca. 2001-2007. 

Correct, of course.

binntho

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Re: When will the Arctic Go Ice Free?
« Reply #1433 on: December 05, 2019, 01:02:22 PM »

Crandles' theory makes sense to me.  But I would change "The 2-3 year ice is pretty steady til 2002, then downwards every year til 2008.... etc." to "The 2+ year old ice...". 
     It is the combination of decline in the 2-3, , 3-4 and 4+ age categories (esp. the 4+ year ice) that causes the steep slope ca. 2001-2007. 

Correct, of course.

Really? And what then caused the steep slope between 1998 and 2004? And the steep slope between 2011 and ongoing? And what caused the steep rise between 2005 and 2010?
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crandles

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Re: When will the Arctic Go Ice Free?
« Reply #1434 on: December 05, 2019, 01:19:47 PM »


As seen in your graphs, there is a big drop in MYI in 2007, temporally it looks like a single year event and is strongly matched by a very large drop in FYI.

...

So I'm probably still as unconvinced as I was then. There have been changes, yes, the Beaufort gyre stopped, the MYI is vanishing rapidly etc. etc. But how important is that to the overall picture? How much of a difference does it make to the annual meltout? In my view, the strongest signal by far is the steadily rising temperatures. Everything else is just nibbling at the heels.


2007 was a big melt out year, I am not denying that.  But there appears to be a new trend in 2+ year ice starting ~2001/2 and continuing until ~2008. I am not sure why you would see this trend as a one year event. Surely it is more a process that became particularly visible in 2007?

Do these images work or do you have to be logged in?

Early March 2001


Early March 2008

crandles

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Re: When will the Arctic Go Ice Free?
« Reply #1435 on: December 05, 2019, 01:34:56 PM »

Crandles' theory makes sense to me.  But I would change "The 2-3 year ice is pretty steady til 2002, then downwards every year til 2008.... etc." to "The 2+ year old ice...". 
     It is the combination of decline in the 2-3, , 3-4 and 4+ age categories (esp. the 4+ year ice) that causes the steep slope ca. 2001-2007. 

Correct, of course.

Really? And what then caused the steep slope between 1998 and 2004? And the steep slope between 2011 and ongoing? And what caused the steep rise between 2005 and 2010?


Correct of course was me admitting I got the 2/3 year description wrong it should be 2+ year.

The new trend in 2+ year ice starts by 2002. This continues to ~2008. So this explains steep ice loss ~2002-2008. Not a perfect match for your 1998 to 2004 but I think those date are a little early and the precise times of the changes in slope are not very clear. There is also a possibility that the process is more likely to start with a larger than normal loss of extent eating into Chukchi so the explanation can have earlier extent loss than the ice age area losses. It is a pretty good match and is in the scientific literature as an explanation.

Once we have got down to the new lower level of MYI the the reason for the rapid extent losses has ceased so the rate of loss goes back up to a more normal level.

>And the steep slope between 2011 and ongoing?
I am not attempting an explanation of that, just the big dip and return to normal.


nanning

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Re: When will the Arctic Go Ice Free?
« Reply #1436 on: December 05, 2019, 05:05:19 PM »
A live stream of COP25
"special event: Special report on the Ocean and Cryosphere in a Changing Climate (SROCC)"

https://unfccc-cop25.streamworld.de/webcast/joint-sbsta-ipcc-special-event-special-report-on-t

edit: this live stream is finished but the link to COP25 is valid.
I have watched and my conclusion is: ESLD (erring on the side of least drama)
« Last Edit: December 05, 2019, 06:59:00 PM by nanning »
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Glen Koehler

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Re: When will the Arctic Go Ice Free?
« Reply #1437 on: December 06, 2019, 12:31:56 AM »
Correction
   N&S 2018 correlation of ASI Extent with cumulative CO2 emissions puts the cumulative chance of 1st Aug. and Sept. as 'largely ice free' (which from my guesswork seems to line up with ca. < 2M km2 Extent, details later) at >50% chance by 2033, and regularly (individual year chance > 50%) by 2036.
     Finally, N&S 2018 give correlation of CO2 with July - October being "largely ice free" (which as above, I interpret as ca. < 2M km2 Extent).  For that I used observed emissions through 2019, and Intl Energy Agency emissions trend forecast of 1.1% continued emissions growth out to 2040, then reducing subsequent global emissions as per the observed US and EU combined downward trend since their recent peak.  With those CO2 assumptions, the cumulative 50% chance for a 1st July-Oct  that is "largely ice free" is by 2045, and regularly (individual year chance > 50%) by 2048. 
   -- Rereading Strove and Notz 2018 (which is a 19-page textbook on Arctic sea ice situation as of Sept. 2018, and serves as a background info for the more applied Notz and Stroeve 2018 companion article), I find this statement:
"Extrapolating the linear relationships into the future, we find that the Arctic Ocean completely loses its ice cover (emphasis mine) throughout August and September for an additional roughly 800 ± 300 Gt of anthropogenic CO2 emissions. For an additional 1400 ± 300 Gt of anthropogenic CO2 emissions, we estimate the Arctic to become sea-ice free from July throughout October ..."

    Those are the CO2-ASI correlations I used for that prior post, and it seems I was far too lukewarmist in my interpretation of what was meant by "largely ice free" in the companion Notz and Stroeve article.  Thus, instead of those projected dates being when Aug-Sept, or July-Oct could get below 2M km2 Extent, they may actually be estimates for when those months can have virtually Zero Extent.   Ouch.  I keep thinking climate projections can't get worse, then they do.

     But just to keep things confusing, I settled on the meaning of Aug-Sept being "largely ice free" as < 2M km2 Extent because the extrapolated dates for N&S Aug-Sept "largely ice free" almost match the N&S extrapolated dates for Sept. <1M km2, and the fact that Aug Extent runs about 0.8M km2 higher than Sept Extent.  So my original interpretation still makes more sense to me, but hard to argue against statement by same two authors writing about the same topic at the same time.  So take your pick, and 'Caveat emptor'.  Either way, it doesn't give the Arctic sea ice much time.

   What remains the same is that the timing depends upon the future emissions trend.  The CO2 regime I used assumes that global emissions do not peak until 2040 (as per 2019 IEA estimate).  Unfortunately, that seems to be a plausible scenario.  As suggested by S&N and N&S papers, that emission scenario obliterates ASI in Aug-Sept by the mid 2030s, and for July-Oct by the late 2040s.  That is not a good prospect for human civilization.  But it does not have to be that way.
 
« Last Edit: December 06, 2019, 05:42:43 PM by Glen Koehler »

Glen Koehler

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Re: When will the Arctic Go Ice Free?
« Reply #1438 on: December 06, 2019, 12:38:18 AM »
       Mining S&N 2018 again - these excerpts about the timing of Atlantification line up well with the discussion of possible mechanisms the 2001-2007 steep slope decline:

    "Another large pulse of warm water occurred in the 2000s, peaking in 2007..."
 
     "This ocean warming largely explains the observed Barents Sea winter ice variability and provides a useful predictor for the annual mean sea-ice cover in the Barents Sea.  The Barents Sea region has also been identified as key for explaining model differences between oceanic and atmospheric pathways of energy transfer to the central Arctic Ocean…” 

    "The Atlantification of the eastern Eurasian Basin may therefore provide an additional factor
behind sea ice reductions in that region, perhaps on the same order of magnitude as atmospheric thermodynamic forcing."
(citations removed)

-------------------
      And relevant to Crandles' invocation of the role of Beaufort Gyre decline in the 2001-2007 steep slope episode:

    "Over the last two decades, the amount of freshwater in the Arctic has increased. This is particularly evident in the Beaufort Gyre, which has accumulated an extra 5000 km3 of freshwater in the 2000s compared to the 1980s and 1990s..."

   "The large Eurasian and North American rivers input warm freshwater (on average 15 °C)..."

   "Peak discharge occurs in June and this water is immediately available to melt ice, helping to break up the fast ice. River discharge also adds a large amount of chromophoric dissolved organic matter, which absorbs sunlight at short wavelengths, further warming the surface layers of the ocean and increasing ice melt. On the other hand, increased ice melt and freshwater input increases summer stratification, allowing for more heat to be trapped in the upper ocean, which in turn delays ice formation in autumn."  (citations removed)
« Last Edit: December 06, 2019, 05:40:20 PM by Glen Koehler »

Tom_Mazanec

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Re: When will the Arctic Go Ice Free?
« Reply #1439 on: December 06, 2019, 01:02:22 AM »
Remember, all those MTs of CO2 are actually CO2e. We may emit that much sooner than you might think.
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Glen Koehler

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Re: When will the Arctic Go Ice Free?
« Reply #1440 on: December 06, 2019, 01:03:08 AM »
As usual, I come to the conclusion that by far the best explanation of the behaviour of arctic ice, when it melts and how fast it melts, is found by looking at the changes in temperature ... etc."

Moving on to Notz and Stroeve 2018, it says
    "The sensitivity of Arctic sea ice as described by the linear relationship between global-mean temperature and Arctic sea-ice coverage has been found to remain constant in model simulations across a wide spectrum of temperature trajectories.  In particular, the linearity holds in all CMIP5 models until summer sea ice vanishes in individual simulations. Hence, the observed sensitivity can be extrapolated to directly estimate the response of the Arctic sea-ice cover to future warming."

After describing some complications, they go on to say:
     "Despite these uncertainties, the different estimates result in a relatively narrow range of additional warming above present that is required to obtain a near-ice free Arctic Ocean during summer, defined as the total sea-ice coverage dropping below 1 million km2."

Then they discuss specific temperatures, and variation around those, from which I derived a median estimate of 1.68 +/- 0.25C (95% CI) above the (inferred) 1850-1900 NASA GISS global average land and ocean surface temperature.  (inferred because GISSTemp doesn't start until 1880. Details to translate to 1850-1900 equivalent are trivial and don't affect the stated value).
And for those of you keeping score at home --- as of 2019 the running 5-year average GISSTemp is at +1.15 C.  In earlier post, I used observed recent GISSTemp trends compared to the 1.68 +/- 0.25C to make the year estimates for when Sept gets below 1M km2 Extent.

The 1.7C estimate fits with their statement:
     "As soon as the global-mean temperature has risen by slightly below 2 ◦C, the Arctic Ocean is expected to be on average nearly ice-free during September."

and slightly out of context, but still relevant:
     "A possible modification of these estimates might be caused by the future evolution of anthropogenic aerosols, as they are expected to become less abundant over the next few
decades. "   

     "... in climate-model simulations the expected aerosol reduction causes additional ice loss..."

    "This would imply that the estimates given here are too conservative."

And finally, they remind us that:
     "While the observed linear relationship between sea-ice coverage and global-mean temperature allows one to estimate the long-term average future evolution of the pan-Arctic ice cover, the evolution of the real ice cover will show substantial year-to-year variability because of internal variability."

-----------------
So it seems to me that binntho and crandles are both right!
« Last Edit: December 06, 2019, 01:24:25 AM by Glen Koehler »

Glen Koehler

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Re: When will the Arctic Go Ice Free?
« Reply #1441 on: December 06, 2019, 01:10:47 AM »
Remember, all those MTs of CO2 are actually CO2e. We may emit that much sooner than you might think.
Agreed Tom. Though I am often not sure if people actually mean CO2e when they throw out cumulative emissions values.  But unless they specify CO2e one has to assume they mean what they say, i.e. CO2. 

Thus, as you point out, the real situation with CO2e increasing even faster makes the siutation... more worser?  Climate change trajectories are so bad they require new language. 

jai mitchell

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Re: When will the Arctic Go Ice Free?
« Reply #1442 on: December 06, 2019, 02:34:17 AM »
As usual, I come to the conclusion that by far the best explanation of the behaviour of arctic ice, when it melts and how fast it melts, is found by looking at the changes in temperature ... etc."

Moving on to Notz and Stroeve 2018, it says
    "The sensitivity of Arctic sea ice as described by the linear relationship between global-mean temperature and Arctic sea-ice coverage has been found to remain constant in model simulations across a wide spectrum of temperature trajectories.  In particular, the linearity holds in all CMIP5 models until summer sea ice vanishes in individual simulations. Hence, the observed sensitivity can be extrapolated to directly estimate the response of the Arctic sea-ice cover to future warming."

After describing some complications, they go on to say:
     "Despite these uncertainties, the different estimates result in a relatively narrow range of additional warming above present that is required to obtain a near-ice free Arctic Ocean during summer, defined as the total sea-ice coverage dropping below 1 million km2."

Then they discuss specific temperatures, and variation around those, from which I derived a median estimate of 1.68 +/- 0.25C (95% CI) above the (inferred) 1850-1900 NASA GISS global average land and ocean surface temperature.  (inferred because GISSTemp doesn't start until 1880. Details to translate to 1850-1900 equivalent are trivial and don't affect the stated value).
And for those of you keeping score at home --- as of 2019 the running 5-year average GISSTemp is at +1.15 C.  In earlier post, I used observed recent GISSTemp trends compared to the 1.68 +/- 0.25C to make the year estimates for when Sept gets below 1M km2 Extent.

The 1.7C estimate fits with their statement:
     "As soon as the global-mean temperature has risen by slightly below 2 ◦C, the Arctic Ocean is expected to be on average nearly ice-free during September."

and slightly out of context, but still relevant:
     "A possible modification of these estimates might be caused by the future evolution of anthropogenic aerosols, as they are expected to become less abundant over the next few
decades. "   

     "... in climate-model simulations the expected aerosol reduction causes additional ice loss..."

    "This would imply that the estimates given here are too conservative."

And finally, they remind us that:
     "While the observed linear relationship between sea-ice coverage and global-mean temperature allows one to estimate the long-term average future evolution of the pan-Arctic ice cover, the evolution of the real ice cover will show substantial year-to-year variability because of internal variability."

-----------------
So it seems to me that binntho and crandles are both right!

https://forum.arctic-sea-ice.net/index.php/topic,1384.msg149174.html#msg149174

The Arctic is highly sensitive to aerosols:

Q. Coopman  T. J. Garrett  D. P. Finch  J. Riedi (2017), "High Sensitivity of Arctic Liquid Clouds to Long‐Range Anthropogenic Aerosol Transport", Geophysical Research Letters,  https://doi.org/10.1002/2017GL075795

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2017GL075795

Abstract: "The rate of warming in the Arctic depends upon the response of low‐level microphysical and radiative cloud properties to aerosols advected from distant anthropogenic and biomass‐burning sources. Cloud droplet cross‐section density increases with higher concentrations of cloud condensation nuclei, leading to an increase of cloud droplet absorption and scattering radiative cross sections. The challenge of assessing the magnitude of the effect has been decoupling the aerosol impacts on clouds from how clouds change solely due to natural meteorological variability. Here we address this issue with large, multi‐year satellite, meteorological, and tracer transport model data sets to show that the response of low‐level clouds in the Arctic to anthropogenic aerosols lies close to a theoretical maximum and is between 2 and 8 times higher than has been observed elsewhere. However, a previously described response of arctic clouds to biomass‐burning plumes appears to be overstated because the interactions are rare and modification of cloud radiative properties appears better explained by coincident changes in temperature, humidity, and atmospheric stability."
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+3C today

kassy

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Re: When will the Arctic Go Ice Free?
« Reply #1443 on: December 06, 2019, 02:18:01 PM »
Glen nice series of posts.

"... in climate-model simulations the expected aerosol reduction causes additional ice loss..."

The change in shipping fuel rules should cause a drop from next year so we might not have to wait that long to see the extra effects of that one in the real world?
Þetta minnismerki er til vitnis um að við vitum hvað er að gerast og hvað þarf að gera. Aðeins þú veist hvort við gerðum eitthvað.

Tom_Mazanec

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Re: When will the Arctic Go Ice Free?
« Reply #1444 on: December 06, 2019, 02:28:27 PM »
I posted on another thread about Sam Carana’s estimate about that, and was contradicted.
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Shared Humanity

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Re: When will the Arctic Go Ice Free?
« Reply #1445 on: December 06, 2019, 05:02:02 PM »
There have been changes, yes, the Beaufort gyre stopped, the MYI is vanishing rapidly etc. etc.

The Beaufort gyre hasn't stopped. Ice, FYI and MYI, is still being transported from the central CAB and north of the CAA into the Beaufort and continues along this path into the Chukchi and ultimately the ESS. In the past, this movement of some of the thickest MYI served to preserve it, resulting in the very thick slabs of ice found throughout the Arctic Ocean.

...by far the best explanation of the behaviour of arctic ice, when it melts and how fast it melts, is found by looking at the changes in temperature and not hypothesising about MYI or the Beafort gyre.

Yes, rising temperatures are the best explanation for the behavior of the arctic ice, when it melts and how fast it melts, but the local temperatures in the arctic are what is driving melt and needs to be understood. The science calls this amplification and falling albedo is a significant factor in this amplification.

Arguing that a global surface temperature measure is the best explanation for the seasonal behavior of the arctic ice is a lot like following the S&P 500 as the best way of evaluating the fortunes of a single company. I would not make any forecast on that company's future nor would I buy its stock based on the movement of the S&P 500.

If we try to understand arctic amplification, what is driving temperature anomalies in the arctic and the resultant sea ice loss, we necessarily need to look at what is happening in the Arctic, how are things changing?

Others here have said it far better than me but the increasingly lengthy ice free conditions of the Beaufort, Chukchi and ESS have turned the still very healthy Beaufort gyre into an ice killing machine.

https://sites.google.com/site/arctischepinguin/home/amsr2/grf/amsr2-area-regional.png?attredirects=0

MYI is now melting out instead of being preserved. This explains the dramatic drop in the thickest MYI. The changing role of the Beaufort gyre and its impact on MYI is certainly something to watch and has far more impact on the ice from season to season than a small uptick in the global temperature.
« Last Edit: December 08, 2019, 04:38:17 AM by Shared Humanity »

wdmn

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Re: When will the Arctic Go Ice Free?
« Reply #1446 on: December 08, 2019, 07:09:51 AM »
This could be a stupid question...

Has anyone looked at the annual extent data by arctic region, found the lowest year's number, and calculated what the overall extent would be if all of the seas reached that lowest number simultaneously?

I'm not sure it would have any merit as an exercise, but it strikes me that once a sea has reached a minimum we have to accept the possibility of its reoccurring soon. Might give a kind of glimpse into what sort of abrupt declines might be possible...

Also, would have just done this myself, but can't find the relevant regional data.

Stephan

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Re: When will the Arctic Go Ice Free?
« Reply #1447 on: December 08, 2019, 08:09:11 AM »
Here are the regional data:
ftp://sidads.colorado.edu/DATASETS/NOAA/G02135/seaice_analysis/
click on "Regional monthly (or daily) data".
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El Cid

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Re: When will the Arctic Go Ice Free?
« Reply #1448 on: December 08, 2019, 08:09:41 AM »
You just take the 2012 minimum and you are almost done :) except for the Bering-facing part around the NP which was more open in 2007 and 16

crandles

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Re: When will the Arctic Go Ice Free?
« Reply #1449 on: December 08, 2019, 01:10:39 PM »
I'm not sure it would have any merit as an exercise, but it strikes me that once a sea has reached a minimum we have to accept the possibility of its reoccurring soon. Might give a kind of glimpse into what sort of abrupt declines might be possible...

Some years are low on Pacific side and some years low on Atlantic side, possibly depending on winds.

So you want to look at the possibility that winds are blowing in the wrong direction in every location. Does this strike you as rather unlikely and confirm little merit as a exercise?