When will the Arctic Go Ice Free?

[The Walrus]

You can not just use extent or volume or area, you must check how they dance together.

If you look at those long term Arctic ice movies you see a sort of skeleton and all the ice goes towards Greenland. As volume declines and most of it is near Greenland anyway we might run out of  ice in the CAB/Siberia CAB/Atlantic area early which would open up the areas for mixing up bottom heat. Mix up enough and you can make it through the winter.

I am convinced that this is the mechanism which explains the quick (within a decade) climate flips in the HCO so we will see something similar happen but with more heat buried below and much more heat from the rest of the system. I think the bet is rather safe.

Just aside

And as the ice concentrates near the Greenland coast (and CAA), the volume may not change considerably, but extent would continue declining.  Extent would become the more critical factor, leading to more open water in the central basin.

[Glen Koehler]

From Oren at https://forum.arctic-sea-ice.net/index.php/topic,2348.msg299564.html#msg299564


      If the system was truly stable, i.e. not changing, then with 40 years of data, for each of those 40 years for each category there would be a random chance of 365/40 = ~9 days in that category.  That is not what we see at all.  Early years have no days with record lows, and the more recent years have much more than 9 days in each category.

      If that is too mathematical, here is simpler evidence.  Look at the Wipneus annual minimum PIOMAS volume graph or the monthly average volume graphs. 
      Yes, you can cherry-pick the most recent few years to see a flat trend.  But in context with the complete range of years the arbitrary bias of selecting out only the most recent years is obvious.

[The Walrus]

      If the system was truly stable, i.e. not changing, then with 40 years of data, for each of those 40 years for each category there would be a random chance of 365/40 = ~9 days in that category.  That is not what we see at all.  Early years have no days with recods lows, and far greater than 9 days in each category for the more recent years.

      If that is too mathematical, here is simpler evidence.  Look at the Wipneus annual minimum PIOMAS volume graph or the monthly average volume graphs. 
Yes, you can cherry pick the most recent few years to see a flat trend.  But in context with the other years the arbitrariness of selecting those years is obvious.

No one is arguing that the system has been unchanged for 40 years.  Every piece of data points to declining sea ice.  The question is whether Tamino’s graph of two relatively stable system with a sharp intermediate decline is supported.  Your data suggests that it is.  What he did is not cherry picking.  Rather, he is showing that the data supports a two-tiered system better than a straight line decline.  Basic statistics.  Whether this holds in the future is uncertain (due to the relatively short time frame), but denying the trend exists in the data is poor science.

[Glen Koehler]

Yikes...
"Arctic Sea Ice Could Be Gone by 2035, According to Earth's Climate History"
https://www.sciencealert.com/the-arctic-could-be-free-of-sea-ice-next-decade-if-it-warms-the-same-as-last-time
      LIG = Last Interglacial period, ca. 125,000 years ago.
      Their smoking gun is melt ponds.  So Neven has been right all along!

     "A new and improved model, based on the last warm period in Earth's history, now suggests shallow pools of rain and melt water could bring about the end of summer sea ice considerably sooner than we thought."

     "Their model suggests the Arctic was very likely to have been ice-free during the summers of the last interglacial period, and this was enhanced by the presence of melt ponds - even more so than clouds or ocean currents, which have historically been given more weight in the warming Arctic."

     "The ability of the [new] model to realistically simulate the very warm LIG Arctic climate provides independent support for predictions of ice-free conditions by summer 2035," the authors conclude.

     "This should be of huge concern to Arctic communities and climate scientists."
(snarky edit - and about 7.49 billion other people too.)

From the journal article
Guarino, MV., Sime, L.C., Schröeder, D. et al. Sea-ice-free Arctic during the Last Interglacial supports fast future loss. Nat. Clim. Chang. 10, 928–932 (2020).   Not open access.

  HadCM3 is the older version (CMIP3) of the UK Met global climate model.
  HadGEM2-ES is the CMIP5 version (generation of models used for IPCC reports in 2013-2014).
  HadGEM3 is the new version (one of the new CMIP6 generation being developed for next IPCC report).
     
(slightly edited to remove references and extraneous text, and formatted for clarity)
-- Partial abstract
     "Here, we show that the latest version of the fully coupled UK Hadley Center climate model (HadGEM3) simulates a more accurate Arctic LIG climate, including elevated temperatures. Improved model physics, including a sophisticated sea-ice melt-pond scheme, result in a complete simulated loss of Arctic sea ice in summer during the LIG, which has yet to be simulated in past generations of models. This ice-free Arctic yields a compelling solution to the long-standing puzzle of what drove LIG Arctic warmth and supports a fast retreat of future Arctic summer sea ice."

from Conclusions
(comparing the UK Met model vs. larger suite of CMIP models for each generation):
     "We compare standard scenarios where no additional efforts are made to constrain GHG emissions.  The predicted year of disappearance of September sea ice under high-emissions
scenarios is
     2086 for HadCM3 (CMIP3/5),
     2048 for HadGEM2-ES (CMIP5)
     and 2035 for HadGEM3 (CMIP6).

     More broadly, multimodel CMIP3–6 mean predictions (and ranges) for a summer sea-ice-free Arctic are as follows:
     CMIP3, 2062 (2040–2086);
     CMIP5, 2048 (2020–2081);
     and CMIP6, 2046 (2029–2066).

     We note that the latest year of sea-ice disappearance for CMIP6 models is 2066 and that 50% of the models predict sea-ice-free conditions between ~2030 and 2040.  From this we can see that HadGEM3 is not a particular outlier, in terms of its ECS or projected ice-free year."

[oren]

      If the system was truly stable, i.e. not changing, then with 40 years of data, for each of those 40 years for each category there would be a random chance of 365/40 = ~9 days in that category.  That is not what we see at all.  Early years have no days with recods lows, and far greater than 9 days in each category for the more recent years.

      If that is too mathematical, here is simpler evidence.  Look at the Wipneus annual minimum PIOMAS volume graph or the monthly average volume graphs. 
Yes, you can cherry pick the most recent few years to see a flat trend.  But in context with the other years the arbitrariness of selecting those years is obvious.

No one is arguing that the system has been unchanged for 40 years.  Every piece of data points to declining sea ice.  The question is whether Tamino’s graph of two relatively stable system with a sharp intermediate decline is supported.  Your data suggests that it is.  What he did is not cherry picking.  Rather, he is showing that the data supports a two-tiered system better than a straight line decline.  Basic statistics.  Whether this holds in the future is uncertain (due to the relatively short time frame), but denying the trend exists in the data is poor science.

The chart of daily records does NOT support a stable system since 2007, 2010, 2011 or 2012. It barely supports a stable system since 2016.

[kassy]

Yikes...
"Arctic Sea Ice Could Be Gone by 2035, According to Earth's Climate History"

Cute isn´t it?

Too bad it is paywalled but at least they start from a very relevant mechanism.

 Still, most CMIP6 models fail to simulate at the same time a plausible evolution of sea‐ice area and of global mean surface temperature. In the vast majority of the available CMIP6 simulations, the Arctic Ocean becomes practically sea‐ice free (sea‐ice area <1 × 106 km2) in September for the first time before the Year 2050 in each of the four emission scenarios SSP1‐1.9, SSP1‐2.6, SSP2‐4.5, and SSP5‐8.5 examined here.

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GL086749

The quote above also show another problem with models. Since they show trouble in a relative short time range we might want to have some models that produce relevant output on a much shorter time scale but we don´t have those because we ´forgot´ to invest into that research decades ago.

[kassy]

Scoring in the same range (taken broadly) does not hint at a stable system either.
It´s record lows which each have their physical repercussions.
Looks transitory to me.

How can clustered lows be stable?

[crandles]

Yikes...
"Arctic Sea Ice Could Be Gone by 2035, According to Earth's Climate History"

Cute isn´t it?

Too bad it is paywalled but at least they start from a very relevant mechanism.

 Still, most CMIP6 models fail to simulate at the same time a plausible evolution of sea‐ice area and of global mean surface temperature. In the vast majority of the available CMIP6 simulations, the Arctic Ocean becomes practically sea‐ice free (sea‐ice area <1 × 106 km2) in September for the first time before the Year 2050 in each of the four emission scenarios SSP1‐1.9, SSP1‐2.6, SSP2‐4.5, and SSP5‐8.5 examined here.

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GL086749

The quote above also show another problem with models. Since they show trouble in a relative short time range we might want to have some models that produce relevant output on a much shorter time scale but we don´t have those because we ´forgot´ to invest into that research decades ago.

Or maybe we have too many of those?

High climate sensitivity in CMIP6 model not supported by paleoclimate
https://www.nature.com/articles/s41558-020-0764-6

Equilibrium climate sensitivity (ECS) is the long-term response of global mean surface temperature (GMST) to a doubling of atmospheric CO2 concentrations. It is poorly constrained with a ‘likely’ range of 1.5–4.5 °C, which has remained nearly unchanged since the Charney report 40 years ago1. Ten in twenty-seven of the available climate models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6) have an ECS higher than the upper end of this range, in contrast to two in twenty-eight CMIP5 models2,3. For example, the ECS in the Community Earth System Model version 2 (CESM2)4 — a CMIP6 model — is 5.3 °C (ref. 5). Determining whether this high ECS is realistic is paramount for estimating future climate and crafting effective policies and adaptation plans.

...

With 3× piCO2, at the low end of the proxy CO2 range, modelled GMST is 37.5 °C, 5.5 °C greater than the upper end of proxy temperature estimates (Fig. 1a). Moreover, modelled tropical land temperature exceeds 55 °C, which is much higher than the temperature tolerance of plant photosynthesis10 and is inconsistent with fossil evidence of an Eocene Neotropical rainforest11.

[Glen Koehler]

No one is arguing that the system has been unchanged for 40 years.  Every piece of data points to declining sea ice.  The question is whether Tamino’s graph of two relatively stable system with a sharp intermediate decline is supported.  Your data suggests that it is.  What he did is not cherry picking.  Rather, he is showing that the data supports a two-tiered system better than a straight line decline.  Basic statistics.  Whether this holds in the future is uncertain (due to the relatively short time frame), but denying the trend exists in the data is poor science.

     I did not interpret your earlier post to say that the system has been unchanged for 40 years.  What I did hear you saying is that current evidence indicates that for now at least the ASI appears to be in a period of equilibrium.

     My point in repeating oren's data (not mine, I just updated the re-post of oren's chart to give proper attribution) was to show that the recent number of record low days does NOT support the idea of a system in even a temporary state of equilibrium.  Oren just made that same point in a post today.

     I think you are misinterpreting the great Tamino (long may he live).  He did not say that the slower rate of decline in annual ASI minima after a period of accelerated decline indicated a new stable state.

     I agree with you that "Whether this holds in the future is uncertain (due to the relatively short time frame),".  I disagree with your inaccurate representation of what I said, or that what I said was an example "poor science".  (I also do not appreciate the personal attack, but I'm not interested in one of those tedious ASIF dogfights, so let's stick to the data and interpretations and leave personal attributes out of it). 

     If you meant that I was denying the appearance of a new trend of stability since the end of the 2003-2007 acceleration, you are correct.  I deny that the data since 2007 indicate a period of stability in the ASI.  And so did Tamino.  In fact, that was the whole point of his analysis at https://tamino.wordpress.com/2018/10/16/arctic-sea-ice-more-than-just-the-minimum/

    Tamino (in October 2018):
   "We have data for each day over nearly 40 years, we have annual averages for 39 years, and both yearly maxima and minima for 40 years. But for some reason, some people (as in, most climate deniers) only want to talk about 12 minima. Why do you think that is?"

    "Since 2000, the situation didn’t get better.  It got worse.  Yet climate deniers only like to talk about the minimum values since 2007, and they love to declare a “recovery!” "

    "There’s definitely no improvement since 2000."

     "Here are the yearly average values:   (Tamino chart shown below)
     "Again, no improvement, no recovery. The two lowest values are in the last two years, the three lowest values in the last three years. It’s not better than it would have been if it had followed the pre-existing trend; it’s worse."

      I wish I could agree with you the ASI data suggests a possible stabilization.  But that isn't how it looks to me.  And it didn't look that way to Tamino in October 2018.  And oren's histogram of low record days per year does not show evidence of stabilization. 

      My interpretation of oren's chart is that the number of new record low Extent values is higher in 2016-2020 than in 2004-2015.  And that the rate of decline (as measured categorically by the number of days with new record and near-record lows) has been fairly stable since 2016.  Saying that the rate of new record lows being acquired is stable is not the same as saying that the ASI is in a state of stable equilibrium.

[crandles]

If I were to talk about arctic sea ice being a stable system, then I would want to point out that in my mind the level of ice that is the equilibrium level of sea ice in this 'stable system' can be (and is) declining over time.

I don't think the amount of ice is levelling off in the way my 4 parameter fits suggest. The rate of decline in the equilibrium level seems fairly low and, to extent we can tell appears to be getting slower. (ie can't tell over 5 years but over something like 15+ years we probably can tell.) I don't believe zero decline. While it seems a slow decline in ice levels at the moment, to me, that isn't relevant to what is, to my mind, a stable system - it would be quite possible to consider the system stable during a period of rapid decline like 2000-2008.

If it equilibrium level is declining what do I mean by a stable system? This refers to what happens if you perturb the system. eg remove sea all sea ice and models suggest it pretty much recovers to the trend in a couple of years or so. That is an extreme perturbation and maybe some don't believe what the models show. However, milder perturbations can be seen in the record like 2007 and 2012 lows - did the next couple of years tend to bounce back towards trends or did it produce even more extreme lows. If your answer is that it bounces back from perturbations then it is a stable system. If the system bounces back from small perturbations but not from larger perturbations then the system may well just be locally stable.

Just thought people might be talking past each other because they may not understand what the other person means by a stable system.

Can we stick with this meaning of stable system and if you want to refer to a horizontal tend in sea ice then call it flatlining or something?

[binntho]

In short tamino points out in a later post there is...
No hiatus in ice loss unless you only focus on just one metric the yearly minimum.

In my view.
It is a faux pause like the one from 1998 in global temperatures.
Looking at a few outlaying data points like the extreme lows in 2007 and 2012  is looking at the  noise in yearly weather not the long term trend that is  climate change.
Global Warming is ongoing.
Sooner or later the minimum loss will again reflect the ongoing ice loss year around.

Which is the correct and obvious conclusion, and the same we reach every time this is discussed. There is no hiatus, melting is ongoing and probably speeding up rather than slowing down.

[crandles]

In short tamino points out in a later post there is...
No hiatus in ice loss unless you only focus on just one metric the yearly minimum.

In my view.
It is a faux pause like the one from 1998 in global temperatures.
Looking at a few outlaying data points like the extreme lows in 2007 and 2012  is looking at the  noise in yearly weather not the long term trend that is  climate change.
Global Warming is ongoing.
Sooner or later the minimum loss will again reflect the ongoing ice loss year around.

Which is the correct and obvious conclusion, and the same we reach every time this is discussed. There is no hiatus, melting is ongoing and probably speeding up rather than slowing down.

The slowing down after a period of fast decline is statistically significant as shown by Tamino.

Sometimes statistical significance is not enough - it is only 95% certain so sometimes this will be broken. Picking 1998 as start point for hiatus is cherrypicking and makes the stats required for statistical significance harder to achieve. Even if statistical significance was reached that was likely to be a false positive - CO2 levels increasing and science of this being a GHG is very solid and there is no science suggesting a significant change in the rate in the short term while GHGs and other forcings change steadily. Also lots of noise from ENSO. Remove the cherrypicking and ENSO effects and there is no temperature hiatus. With temperature, statistical significance, if this was reached, was then such that a false positive was likely.

So I suggest the science is relevant to deciding if a false positive is likely. With sea ice the science is certainly not all pointing toward it being a false positive and accelerating decline in sea ice. The summer melting is increasing but this means less insulation so the winter freezing is also increasing. It is logical for the balance to change to a slower net rate once a lot of thick MYI has been reduced to a much lower level. Also there are many models showing a slow down in rate of decline as lower levels of ice are reached.

So let me fix up your comment for you:

The Arctic sea ice catastrophists (yeah I am overdoing this term ) reach the same conclusion every time this is discussed as do deniers and realists but each group's conclusion is different. The realists conclude

1. Melting is trending towards increasing amounts.
2. This effect of lower sea ice at end of summer on insulation in winter means freezing is also increasing.
3. Since around 2005 the net difference is still declining but has slowed down in a statistically significant manner. This statistical significance is much less likely to be a false positive than with the temperature hiatus following 1998.
4. This slowing trend may change in future but there is no evidence for that presently. The trend is unlikely to level off completely and extremely unlikely to start to increase in the near term (in absence of extreme unexpected changes).
 

[crandles]

Melt and freeze look fairly flat for last 10 years but I believe the trend continues to be of increases because there is no reason for them not to continue increasing while GHG levels and other forcings like imported water temps are continuing to increase.

That logic does not apply to annual changes - with this there is reason to believe trend rate in ice loss is slowing down and the change to slower rate of decline is statistically significant.

Can you see the difference? The declining rate of annual change is supported by the science. A hiatus in increasing melt is not supported by the science.

[gerontocrat]

To add to the confusion here are 3 graphs of the yearly average daily data from Jan 1to Dec 31 for

- JAXA extent data. 2020 lowest in the satellite record,
- NSIDC Area data. 2020 2nd lowest in the satellite record,
- PIOMA Volume data. 2020 3rd lowest in the satellite record.

This average is useful as it gives some idea whether sea ice is reducing. The linear trend R2 value is pretty good for all the graphs.The time to panic is when a number of years in a row are so out of step as to count as outliers. One or two years, e.g. volume 2011&2012, 2016&2017, don't signify in my extremely unhumble opinion..

[The Walrus]

No one is arguing that the system has been unchanged for 40 years.  Every piece of data points to declining sea ice.  The question is whether Tamino’s graph of two relatively stable system with a sharp intermediate decline is supported.  Your data suggests that it is.  What he did is not cherry picking.  Rather, he is showing that the data supports a two-tiered system better than a straight line decline.  Basic statistics.  Whether this holds in the future is uncertain (due to the relatively short time frame), but denying the trend exists in the data is poor science.

     I did not interpret your earlier post to say that the system has been unchanged for 40 years.  What I did hear you saying is that current evidence indicates that for now at least the ASI appears to be in a period of equilibrium.

     My point in repeating oren's data (not mine, I just updated the re-post of oren's chart to give proper attribution) was to show that the recent number of record low days does NOT support the idea of a system in even a temporary state of equilibrium.  Oren just made that same point in a post today.

     I think you are misinterpreting the great Tamino (long may he live).  He did not say that the slower rate of decline in annual ASI minima after a period of accelerated decline indicated a new stable state.

     I agree with you that "Whether this holds in the future is uncertain (due to the relatively short time frame),".  I disagree with your inaccurate representation of what I said, or that what I said was an example "poor science".  (I also do not appreciate the personal attack, but I'm not interested in one of those tedious ASIF dogfights, so let's stick to the data and interpretations and leave personal attributes out of it). 

     If you meant that I was denying the appearance of a new trend of stability since the end of the 2003-2007 acceleration, you are correct.  I deny that the data since 2007 indicate a period of stability in the ASI.  And so did Tamino.  In fact, that was the whole point of his analysis at https://tamino.wordpress.com/2018/10/16/arctic-sea-ice-more-than-just-the-minimum/

    Tamino (in October 2018):
   "We have data for each day over nearly 40 years, we have annual averages for 39 years, and both yearly maxima and minima for 40 years. But for some reason, some people (as in, most climate deniers) only want to talk about 12 minima. Why do you think that is?"

    "Since 2000, the situation didn’t get better.  It got worse.  Yet climate deniers only like to talk about the minimum values since 2007, and they love to declare a “recovery!” "

    "There’s definitely no improvement since 2000."

     "Here are the yearly average values:   (Tamino chart shown below)
     "Again, no improvement, no recovery. The two lowest values are in the last two years, the three lowest values in the last three years. It’s not better than it would have been if it had followed the pre-existing trend; it’s worse."

      I wish I could agree with you the ASI data suggests a possible stabilization.  But that isn't how it looks to me.  And it didn't look that way to Tamino in October 2018.  And oren's histogram of low record days per year does not show evidence of stabilization. 

      My interpretation of oren's chart is that the number of new record low Extent values is higher in 2016-2020 than in 2004-2015.  And that the rate of decline (as measured categorically by the number of days with new record and near-record lows) has been fairly stable since 2016.  Saying that the rate of new record lows being acquired is stable is not the same as saying that the ASI is in a state of stable equilibrium.

First off, let me apologize for what was taken as a "personal attack."  It was not intended as such.  Sorry.

Secondly, it appears that such terms as "stable" and "equilibrium" have drawn the ire of some posters here.  I never said that it was in a state of equilibrium, rather that perhaps we are approaching such a state.  Crandles plots do indicate that is occurring, although neither of us are convinced of that.  Perhaps simply a new "system" or "regime" would suffice.  Whatever we choose to call, I think we can agree that recent years (timeframe is somewhat dependent on the dataset chosen) have differed from the immediately preceding ones in that the rate of decline as diminished. 

I will make one last statement concerning oren's graph in an attempt to illustrated my point.  The graph of daily new lows supports either a system in decline or a system in equilibrium [after a steady decline].  Any year prior to the last year of decline is much less likely to reach as many daily new lows, simply due to the declining nature of the system.  That is precisely why the last five years have more new lows than the preceding years.  Additionally, the data would support a system in decline better if the highest number of daily new lows was in the most recent year (2020) and not the earliest year (2016).  The data supports either, but as I mentioned previously, the timeframe is too short to make any definitive claims (to which you agreed). 

I have never stated that the situation has "improved."  Arctic sea ice is not increasing.  However, the situation is not as dire as it was a few years ago.  Looking at gerontocrat's data over on the sea ice threads, both area and extent were only 10th lowest at the end of January, and higher than the average over the past decade.  Of course it is lower than the preceding decade, but that was the decade of largest decline.  Perhaps you prefer the term "decelerating."  All of this is just an exercise in semantics.  Regardless, it took three decades of rapid sea ice loss for the minimum extent to decline from 7 M sq. km to 4.  The current rate of decline is less than that, so I suspect that the time required to decline a similar 3 M sq km (the threshold definition for ice-free) would be longer. 

All the graphs of arctic sea ice point to a period of relative stability (or flatness) following by accelerated ice sea, and now a deceleration in that loss.  The data supports, and I agree, that the ice loss is not a linear function.  Gerontocrat's most recent graphs point that out.  His volume graph (and extent and area are not much different) shows that the first years fall far below the linear trend.  For the ensuing 20 years, all but one year falls above the trend line.  This is indicative of a system with accelerating losses.  The inflection point appears to be around 2007, as the next period shows eight years without a single point above the trend line.  The last eight years are fairly evenly distributed.  This again supports a Tamino-line two-tiered system of losses.

[kassy]

Actually that is just a lot of denialism veiled in lots of words.

Whatever we choose to call, I think we can agree that recent years (timeframe is somewhat dependent on the dataset chosen) have differed from the immediately preceding ones in that the rate of decline as diminished.

This is a longwinded way of saying hey i see a hiatus.

Behind the statistics there is also a changing physical world. The arctic now is quite unlike the arctic 10 years ago.

The key metric is volume and ice grows from ice. Prolonged open water is what will allow mixing up heat from below at some point. You can go by spreadsheets or think about the physical processes going on.

[The Walrus]

Actually that is just a lot of denialism veiled in lots of words.

Whatever we choose to call, I think we can agree that recent years (timeframe is somewhat dependent on the dataset chosen) have differed from the immediately preceding ones in that the rate of decline as diminished.

This is a longwinded way of saying hey i see a hiatus.

Behind the statistics there is also a changing physical world. The arctic now is quite unlike the arctic 10 years ago.

The key metric is volume and ice grows from ice. Prolonged open water is what will allow mixing up heat from below at some point. You can go by spreadsheets or think about the physical processes going on.

I see now.  You either do not understand or do not wish to understand.  Hence, you call it denialism and hiatus.  There is no hiatus.  Hiatus is temporary.  The arctic ice is not. 

You contradict yourself in your last paragraph.  If open water is the so important, then the two-dimension metric is the key, as it is the better measure of open water.  That is the physical process occurring.  Volume is only important in how it may affect the extent of open water.

Yes, it is different today than ten years.  Just as it was different then from ten years prior.  During that period, conditions were ripe for a large decline in sea ice.  Now that regime is finished.  Many scientists and posters here recognize that.  There is no need to cling to antiquated theories.

<I am getting tired of reading the same arguments. "Now that regime is finished", you would do well to use less certainty in your terminology, else I will start editing/removing. Or you could simply let the thread breathe little until new information comes in. O>

[binntho]

In short tamino points out in a later post there is...
No hiatus in ice loss unless you only focus on just one metric the yearly minimum.

In my view.
It is a faux pause like the one from 1998 in global temperatures.
Looking at a few outlaying data points like the extreme lows in 2007 and 2012  is looking at the  noise in yearly weather not the long term trend that is  climate change.
Global Warming is ongoing.
Sooner or later the minimum loss will again reflect the ongoing ice loss year around.

Which is the correct and obvious conclusion, and the same we reach every time this is discussed. There is no hiatus, melting is ongoing and probably speeding up rather than slowing down.

The slowing down after a period of fast decline is statistically significant as shown by Tamino.

Indeed. But just to be clear: I am not sayting that there wasnt a period of rapid decline during the 2000's and that this rapid spurt didn't slow down. What I am arguing against is talk of a "hiatus" since then. It is the before-and-after periods, the rate of decline before the rapid drop compared to the rate of decline after the rapid drop that I'm talking about.

Tamino's graph as shown in Crandle's post above, only reached to 2015 and as you point out, statistical significance is not the same as truth or reality.

And if you extend Tamino's graph another another few years things look somewhat different. Here is one he himself posted two years ago (February 24 2019), this time with another three years up to 2018.

The middle period of rapid decline stands out clearly, but is followed by a period of decline faster than the one that went before. Which of course shows that all talk of "hiatus" is nonsense.

[KiwiGriff]

Some time around 2004 there was a significant phase change in some system in the arctic seas effecting the ice minimum.
I would guess it was the Atlantification  of some of the surrounding seas.
This produced the rapid decline in sea ice  we see in the record .
This effect was caused by global warming but is not the long term declining trend  due to warming we see in the record.
 As to the the Ice presently being in a stable state
Without being able to quantify my impression  generated by mark one eyeball it seems to me recent years have been more unstable with a greater spread between extremes than prior to my suggested phase change. 

[binntho]

To continue from above: I made my own version of Tamino's graph adding the last two years, but having severely stunted statistical brain centers, I' restricted my self to using Excel and straight trend lines in the first version a second order polynomial in the second version and a third order in the third.

I must admit that the "rapid period of decline" that Tamino found above seems to be disappearing into the background noise

EDIT: I see that I forgot to specify that this is Extent.

[binntho]

Some time around 2004 there was a significant phase change in some system in the arctic seas effecting the ice minimum.
I would guess ...

Says it all. A lot of people want to claim that there was some major underlying change in the Arctic system, but not one person can explain what that change was. Guesswork is the best anybody can do. The more years we add to the graphs, and the more graphs we study, the less significant this "phase change" seems to be.

[uniquorn]

Thanks everyone. The discussion around yearly averages has been a real eye opener (for me).

[crandles]

>more and more open water in summer
>atmosphere over cracked up ice ... some day we are going to get a steady drizzle

What make you think these are not gradual processes slowly encroaching further into the Arctic applying throughout the period of record and into the future, and instead are going to pick up in importance in some future period to cause a noticeable acceleration in ice loss?

One is physics.

Open water. If a large stretch of water opens up earlier in the year it will soak up more heat during the summer which will make it harder to freeze when next winter comes. Then there is also a chance of storms mixing up heat from below which increases with the time we have open water during summer.

This is an accelerating process because it further hinders the overall growth of ice and in the HCO it it is the most plausible mechanism for the quick climate flips.

We can also turn the argument around.

Why would you expect this current system to be stable? If we just went through an event which flushed out the big ice then why on earth would that same process fail to flush out much thinner ice in the long term?

The key metric is volume and ice grows from ice. Prolonged open water is what will allow mixing up heat from below at some point. You can go by spreadsheets or think about the physical processes going on.

>If a large stretch of water opens up earlier in the year
This of course has been going throughout last 20 years.

>make it harder to freeze when next winter comes
Heat does build up when there is open water. But come winter open water loses heat much faster. Extent is possibly delayed by a month over last 40 year but winter is longer than a month and given the much faster rate of heat loss through no or thin ice there is quite a bit of time to mostly catch up. Of course this has also been going on throughout last 20 years.

>a chance of storms mixing up heat from below which increases with the time we have open water during summer.
A lot of open water for a long time does seem to offer much more chance for storms to stir up heat. So I think I should admit there is possibility of accelerating effect here. I did wonder whether to argue that we are already giving extra chance of stirring up heat around the edges so this effect is already built into the slow rates of decline before and after the naughties. Perhaps not fully built in and unfortunately I am not sure of the size of this effect - does a storm stir it up everywhere or is it fairly limited to ekman pumping only near the centre of rotation? How significant will this be?


>If we just went through an event which flushed out the big ice then why on earth would that same process fail to flush out much thinner ice in the long term?

I explained that the thick multi year ice if thinned does not regrow in winter. Thin ice if melted out does largely regrow in winter. This is quite different from 'flushing out'.

Since you mention flushing out, have you looked at what happens to remaining MYI from one year to the next? There are big losses in the naughties. Since then one year it may look like it is nearly at point of being flushed out the fram, next year it bounced bach to being more abundant nearer Beaufort. Another year it look like beaufort gyre is about to flush it into Beaufort sea but the next year it bounces back to being more abundant nearer Greenland, another year it may look like the 5 year old MYI is down to a tiny thin strip so perhaps the oldest MYI is going but then it bounces back to a much thicker strip.

This bouncing back makes it quite clear that the MYI is down to a new much lower equilibrium level compared to before 2000. So any losses of this MYI is now slow and the FYI largely grows back each winter.

There are still losses but these are at a slow rate compared to the fast rate when we were losing thick MYI.

[Shared Humanity]

Whatever we choose to call, I think we can agree that recent years (timeframe is somewhat dependent on the dataset chosen) have differed from the immediately preceding ones in that the rate of decline as diminished. 

I will not try to characterize your comments here but I am always on the lookout for commenters who try to speak for others with comments like...

"I think we can all agree that..."

There are a lot of bright, highly informed individuals who comment here. All of us are free to express our viewpoints, backed up by data and/or research. None of us should attempt to speak for others which then requires others to chime in with a denial that agreement exists.

I've been visiting here for years and it is my observation that rampant, informed and usually friendly disagreement is the norm. 

[Shared Humanity]

Yes, it is different today than ten years.  Just as it was different then from ten years prior.  During that period, conditions were ripe for a large decline in sea ice.  Now that regime is finished.  Many scientists and posters here recognize that.  There is no need to cling to antiquated theories.

Again with the rhetorical technique to suggest others support your position without any data or links to those many scientists who "recognize" this.

[Glen Koehler]

<snip>
 A lot of people want to claim that there was some major underlying change in the Arctic system, but not one person can explain what that change was. Guesswork is the best anybody can do. The more years we add to the graphs, and the more graphs we study, the less significant this "phase change" seems to be.

       
     I think the explanation by Crandles about the so-called Beaufort Gyre, that used to retain ice for multiple years for MYI increase, losing that function as the Chukchi and Laptev seas became summer melting zones is a good candidate for that major underlying change.  Once that systemic change happens and much of the MYI is lost, it doesn't keep happening.  That explanation is consistent with the acceleration of losses followed by a slow down in losses because once the MYI is lost, there is less MYI to lose.  There are probably other factors involved, but as a first-order approximation I find the "Beaufort Gyre MYI nursery is no more" scenario plausible.  Comparing the 2002-2012 period of accelerated decline in September minimum Volume with the decline in percentage of MYI shows the two as happening at about the same time.  (charts attached below).

     I also think Crandles correctly called us out for talking past each other in the discussion about whether ASI losses have stabilized in recent years  When Walrus mentions a possible temporary stabilization point, those of us with allergic reactivity to climate change denialism are prone to seeing it as a claim that all is well in the Arctic.  Which we know is NOT true.  But he wasn't saying that.  I don't agree that the Arctic has stabilized (and I expect losses no matter how you measure them, to accelerate again within 5 years), but what Walrus proposed is not impossible. 

     Part of the difference in interpretations could be caused by focusing on September minimum Extent as the true measure of the health of the ASI.  The September minimum is just one day, and even the Sept. average is just one month, out of the whole year.  The annual minimum does not accurately represent the whole year.  Either annual average, or an index based on multiple values such annual max, min, and average etc. would be a better focal point.  Alas, we all like the drama and can relate to the melt season progression to the annual minimum, so that focus probably won't change.

     A second source of distorted interpretation is our fixation on Extent, which is not a great way to precisely measure the health of the ASI.  A grid cell counts the same for Extent whether is covered by 16% sparse slush or 100% thick MYI.  We only get Thickness and Volume updates intermittently, so those don't meet our need for a dailiy data fix.  But we do get Area estimates every day just like Extent, so it would seem better to focus on Area.  But I guess the greater calculation error in estimating Area argues against that.  So that probably won't change either!

     Our focus on annual minimum Extent is exemplified by crowning 2012 as the reference year.
While 2012 was indeed a big melt year, a good portion of the 2012 Extent losses were due to the GAC, which tossed around the ice and temporarily applied subsurface heat to make the minimum Extent even more of an extreme outlier.  But the temporary nature of that outburst was subsequently revealed.  When viewed as annual average (vs. minimum) Extent, or as annual average Volume, 2012 is a much less impressive outlier.

     I hope we can continue to discuss these observations and interpretations productively.  Knowing the import of what's going on with climate change while seeing most of society not apparently giving it sufficient attention and concern can cause a slightly fevered passion.  It is useful (for me at least) to remember that the black and white sterility and lack of nuance in email and forum posts makes oof-the-cuff  (typo not corrected because the misspelling looks better than corrected version) reactive text messaging a difficult medium for keeping respectful debate from becoming personalized arguments.  I'm grateful that ASIF has had less of those in the past year, no doubt thanks to the hovering benevolent guidance of Oren to turn down the heat when the pot starts boiling.

[Glen Koehler]

    My personal fixation is on Thickness.  I think that non-linear melt sensitivity kicks in once thickness gets below 1 meter, and especially below 0.8 meter.  That increased melt sensitivity would be due to synergisms between
1) less mechanical resistance to fracture,
2) greater mobility and Fram/Nares export
3) greater Nares export with weakening of Nares ice arches and duration of period when they do not block export (shortening by 1 week per year!)
4) higher % of younger more saline ice that begins to melt at a lower  temperature, and
5) greater % of ice volume exposed to top and bottom surface melt.

    I think gerontocrat nailed it with his extrapolation of the multiplicative effect of Thickness x Area trend to get Volume trend.  (chart observations end with 2019, this is the most recent version I have, is there a 2020 update?)

[binntho]

<snip>
 A lot of people want to claim that there was some major underlying change in the Arctic system, but not one person can explain what that change was. Guesswork is the best anybody can do. The more years we add to the graphs, and the more graphs we study, the less significant this "phase change" seems to be.

       
     I think the explanation by Crandles about the so-called Beaufort Gyre, that used to retain ice for multiple years for MYI increase, losing that function as the Chukchi and Laptev seas became summer melting zones is a good candidate for that major underlying change. 

Much as I enjoy your posts, Glen, I must disagree with you here. My point is that there never was a "phase change", and looking for one is a fools errand. And the more I see people speculate as to what this putative "phase change" might have been, the less likely it seems.

My graph above (repeated below), showing average extent from 1979 to 2020, does not really support any "phase change". Perhaps there was one in the noughties, but since nobody can conclusively figure out the physics there is not much point in chasing one.

This is not to say that the Arctic is always without "phase changes". But after various members of this forum having spent a decade looking for an explanation for what might just as well be a statisical fluke, or something totally different, and not finding anything conclusive, perhaps it is time to reconsider?

As for statistical flukes as well as other ways of looking at the graphs - the most interesting aspect of the average extent graph (as well as most of the other graphs floating around) is the apparent stability of the Artctic in the 9 year period from 1999 1996-2004. In the satellite era one can see six clear "punches" of major losses marked with thick red lines, with a cyclus of 4-6 years between "punches". The "stable 9", on the other hand, seem to have missed their punch.

The "stable 9" were followed by the "rapid 4a" (with 2004 belonging to both ... don't ask me why!). But the "rapidity" of the early noughties loss is easily matched by the "rapid 4b" of 2013-2016.

Looking at it like this, there doesn't seem to be any particularly rapid loss in the noughties, so no phase change. There is no speed up or slow down other than the "punches" and the "recoveries" inbetween, with one of the "punches" simply missing (perhaps we can spend the next 10 year trying to figure out why?)

But perhaps the right-hand end is where we should be focusing our attention. Here things truly seem to be behaving differently. The post-punch recovery is missing, and we are due another "punch" either 2021 or 2022. So perhaps there really is a "phase change" underway?

[binntho]

After having messed up Gero's 365 day area trailing average graph as well, the same main features emerge: The stable period is shorter, the punches are 7 and not 6, but he cycle period between them is still from 4 - 6 years.

The "rapid 3a" is where everybody thinks they see a phase change, but it is easily matched by the "rapid 3b" - the real anomaly is still the "missing punch" at the beinning of the century, during Gero's "stable 7" and my "stable 9".

The right hand tail is not so conspicously flat as in my graph, but a "punch" is very clearly due this summer. So let's lean back and see what happens!

And before anybody asks - no I've no idea what causes the "punches" but my guess is that cyclical interlocking climate systems are the main culprit, a bit like the Milankovich cycles for ice ages, and just like with the Milankovich solar maxima, not every cycle produces a punch (or ends an ice age).

[binntho]

Not being one to let go of an idea that easily, I've been messing about with some more numbers and graphs. Below is my previous graph from a few posts earlier, combined with a graph showing, for each year, the average AO index of the previous year. Thus the point for 2020 is the average AO index for 2019 etc.

The red "punchlines" (pun nearly intended) are extented downwards, and show a fairly clear predilection for high AO index (for the previous year remember) while the green "stable" period is easily discernible.

So my hunch from yesterday has moved today from wild guess to a preliminary hypothesis: The AO index is one of the cyclical "punchers" with a fairly strong signal. There was no "phase change" in the ice, all the graphs can be explained by "business as usual" overlaying a steady (and presumably accelerating) decline.

Given how lacklustre the final data point is (the AO index for 2019 is decidedly not that sprightly), the next punch is probably more likely to land in 2022 rather than 2021. Anybody who cares to place a bet here and now that after 2 years I will be able to extend these graphs with a new and clearly defined "punch" in 2022?

EDIT: I forgot that of course we do have the AO index for 2020 - and it's an humdinger! Which of course means that the next punch is going to be 2021 as I've suggested earlier. I've added a graph of AO index annual average, with 2020 rearing it's randy head.

The offer of a bet still stands, but now we only have to wait half a year to the end of the year to see who wins.

[oren]

Interesting chart, though my reading of it tells me the predictiveness is not quite as high as you might think. If you run some mathematical analysis - correlation, tentative prediction for each year compared to actual, or some such - it could help explain my intuition.
For example 2010-20111 happened after negative AO, and 1993 should had positive AO but no punch at all.
It depends if you define it as absolute negative AO, or lower AO than the year before, but it requires further examination in any case.

[binntho]

Interesting chart, though my reading of it tells me the predictiveness is not quite as high as you might think. If you run some mathematical analysis - correlation, tentative prediction for each year compared to actual, or some such - it could help explain my intuition.
For example 2010-20111 happened after negative AO, and 1993 should had positive AO but no punch at all.
It depends if you define it as absolute negative AO, or lower AO than the year before, but it requires further examination in any case.

Well, it's more fun than anything else. I postulate that a large positive AO index in the previous year is one of the major predictors (but not the only one!) of a very low average extent in a given year.

But my main point is really to point out the fallacy of the "hiatus" and "phase change" discussion. There are lots of other explanations and hypothesis that can be built out of the existing data, and this fixation on "phase change" is only clouding the issue.

The shape of the graphs be explained by an unusually quiet period at the beginning of the century followed by "back to normal" variability. There is no hiatus, no stepwise acceleration and deceleration, no phase change.

And I am ready, purely in the interest of some light entertainment, to place a couple of thousand ETB bet on my "punch + AO index" hypothesis - I predict a "punch" in 2021 based on the very positive AO index of 2020 and the regular cycle of "punches" (not withstanding the one that went missing). And a "punch" is defined as a significantly lower annual extent average than the preciding years. By "significantly" I mean lower than the last "punch" in 2016.

[oren]

But my main point is really to point out the fallacy of the "hiatus" and "phase change" discussion. There are lots of other explanations and hypothesis that can be built out of the existing data, and this fixation on "phase change" is only clouding the issue.

The shape of the graphs be explained by an unusually quiet period at the beginning of the century followed by "back to normal" variability. There is no hiatus, no stepwise acceleration and deceleration, no phase change.

I tend to agree when analyzing extent and especially 365-day average extent. When looking at volume things are cloudier, and there might be some rate of change slowdown, though certainly no hiatus. This can be largely explained by the big loss of MYI, now that MYI is mostly gone the rate of change cannot be as high, as FYI regrows every year. Largely, the "slow transition" theory with some caveats (slowly declining instead of relatively stable).
OTOH, the images from the North Pole this year hint that "when will the Arctic go ice free?" may be a moot question, and sooner or later the larger metrics will reflect the visible catastrophe.

[binntho]

Volume is indeed the only "real" measure!. So let's see how it measures up to my previous graphs. I've added PIOMAS annual average volume to the one with Extent at the top, and AO index (previous year) in the middle.

The punclines are extended and again they fit surprisingly well - and the green "stable" period is also discernible. I've added a punchline at the very beginning, which brings these graphs into line with the 365 day area average graph.

So again, everything seems to point to:

• Arctic sea ice is undergoing a steady decline.
• The decline may be accelerating but definitely not slowing down.
• There was never a "hiatus" nor a "phase change"
• The AO index is a strong but not entirely trustworthy indicator of years with low extent/area/volume, i.e. a high positive index strongly predicts a low average the following year on all measures.
• A curiously quiescent AO index around and following the turn of the century seems to explain much of what has been confusing the forum until now.

[crandles]

<snip>
 A lot of people want to claim that there was some major underlying change in the Arctic system, but not one person can explain what that change was. Guesswork is the best anybody can do. The more years we add to the graphs, and the more graphs we study, the less significant this "phase change" seems to be.

       
     I think the explanation by Crandles about the so-called Beaufort Gyre, that used to retain ice for multiple years for MYI increase, losing that function as the Chukchi and Laptev seas became summer melting zones is a good candidate for that major underlying change. 

Much as I enjoy your posts, Glen, I must disagree with you here. My point is that there never was a "phase change", and looking for one is a fools errand. And the more I see people speculate as to what this putative "phase change" might have been, the less likely it seems.

I should do better at providing my sources - it is not really *my* explanation:

quote from Armour et al 2010:

Given the strong thickness–growth feedback of sea ice (Bitz and Roe 2004), where in a warming climate we can expect the thicker MY (multi year) ice to thin at a greater rate than the thinner FY (first year) ice, and the fact that the ratio of MY to FY ice entering into the MY ice category each year is decreasing, it is likely that the difference between FY and MY ice survival ratios will decrease in a warming climate. If this occurs, the Arctic sea ice system would move toward a regime of decreased memory and decreased sensitivity to climate forcing...

http://dosbat.blogspot.com/2015/01/the-slow-transition-mono-modal-spike.html

it is from the scientific literature like Bitz and Roe 2004 and Armour et al 2010.

(Maybe that casts a different light on whether it is a fools errand.)

[binntho]

(Maybe that casts a different light on whether it is a fools errand.)

Not really - scientists can be fools just like the rest of us. But thinking about things and coming up with various hypotheses is never a "fools errand" - while reading too much into squiggles in graphs easily can be.

[Richard Rathbone]

>make it harder to freeze when next winter comes
Heat does build up when there is open water. But come winter open water loses heat much faster. Extent is possibly delayed by a month over last 40 year but winter is longer than a month and given the much faster rate of heat loss through no or thin ice there is quite a bit of time to mostly catch up. Of course this has also been going on throughout last 20 years.

>a chance of storms mixing up heat from below which increases with the time we have open water during summer.
A lot of open water for a long time does seem to offer much more chance for storms to stir up heat. So I think I should admit there is possibility of accelerating effect here. I did wonder whether to argue that we are already giving extra chance of stirring up heat around the edges so this effect is already built into the slow rates of decline before and after the naughties. Perhaps not fully built in and unfortunately I am not sure of the size of this effect - does a storm stir it up everywhere or is it fairly limited to ekman pumping only near the centre of rotation? How significant will this be?

Heat is being mixed down, not up. The Arctic is warming at depth as not all the radiation that is soaked up by open water in the summer gets radiated back to space in the autumn. Some of it gets mixed down and this shows up as a gradual increase in heat content. If storms were pulling excess heat to the surface, the ocean heat content would be dropping, but its increasing which shows that net effect of removing ice is for increased transfer of heat down from the surface.

Ice acts as an insulator, and this applies in winter as well as in summer, and the winter effect dominates the summer one. Long term the trend is simply that more insulation from CO2 in the atmosphere is balanced by less insulation from coverage of ice.

A GAC is not just a great cyclone, its in August, and August is when the open water is hot. The long term effect is to heat the depths, not the surface.

[Glen Koehler]

 

But my main point is really to point out the fallacy of the "hiatus" and "phase change" discussion. There are lots of other explanations and hypothesis that can be built out of the existing data, and this fixation on "phase change" is only clouding the issue.

The shape of the graphs be explained by an unusually quiet period at the beginning of the century followed by "back to normal" variability. There is no hiatus, no stepwise acceleration and deceleration, no phase change.

   
     
Halló binntho - They are not exclusive possibilities, i.e. both AO effect and Beaufort Gyre no longer supporting MYI ice growth could be driving factors for ASI Extent/Area/Thickness/Volume changes across years.

      RE: Was there a period of accelerated losses?  The fact that Tamino found a statistically significant change in rate of annual average Extent decline followed by return to a less steep slope is where that idea came from.  I don't think we can dismiss that as a non-entity.  Of course, Extent is a flukey thing, so even if that rate change is real, that by itself is not a compelling statement about the condition or trends of the ASI.  I agree with you that Volume is a better measure.  A quick search of the Tamino site for a change-point analysis on rate of ASI Volume decline came up empty.

      As oren alluded to, as we analyze the numbers it is important to remember what the North Pole looked like last summer.  Maybe a picture is worth 1000 numbers in addition to 1000 words.  Here is the Polarstern at the North Pole on August 16, 2020, and the NSIDC Extent map for one day later. Looks to me like you might have sunk into the ocean if you tried to walk across that slop, but it showed up as 100% solid white Extent.  Numbers, especially ASI Extent, can be deceptive. 

     Good that MOSAIC was there to capture the moment.  Or has the North Pole been this degraded in many years? (I'm thinking of that swimming hole at the NP picture from 2016 that Jim Hunt posted showing that open water at the NP is not news).  Are satellite images too low resolution to provide photo evidence of ice condition at a specific location?

[kassy]

Our North Pole photos thread:
https://forum.arctic-sea-ice.net/index.php/topic,3280.0.html

Number 5 is August 2019.

[kassy]

But perhaps the right-hand end is where we should be focusing our attention. Here things truly seem to be behaving differently. The post-punch recovery is missing, and we are due another "punch" either 2021 or 2022. So perhaps there really is a "phase change" underway?

Interesting stuff and i also like the really short time scale on which it should show.

[Glen Koehler]

From Students on Ice https://studentsonice.com/north-pole-looks-like-today/
Oden at N 89° 59,998´ W 046° 40,558´ on August 22, 2016.


From Jim Hunt Great White Con blogpost about the 2016 NP swimming hole
https://greatwhitecon.info/2016/09/santa-extends-his-secret-summer-swimming-pool/

NASA Worldview “true-color” image of the North Pole on September 8th 2016, derived from the MODIS sensor on the Terra satellite

Below: 
NSIDC Extent map on Aug 14, 2016
NSIDC Extent map on Sept 10, 2016

[Glen Koehler]

FWIW - some model views and metrics North Pole on same dates of the 2016 Oden photos and NASA Worldview image.

HYCOM Concentration for Aug 22, 2016


HYCOM Concentration for Sep 8, 2016


Images posted at ASIF PIOMAS thread
AMSR Concentration Aug 31


JAXA concentration for Sept. 1, 2016


Attached below:  AMSR concentration for Sep 5 2016  from NSIDC (click on it twice to enlarge for a close up view).

[Glen Koehler]

HYCOM - CICE thickness Aug 22, 2016


HYCOM - CICE Thickness Sep 8, 2016



WIPNEUS PIOMAS thickness animations from ASIF PIOMAS thread in 2016.
August 2016 (click to activate).


September 2016 (click to activate).

[Glen Koehler]

Sorry if I'm overposting.... but this NSIDC chart turned up while searching for 2016 photo-comparisons.  From https://nsidc.org/arcticseaicenews/2015/10/
   
       My interpretation is that it provides support for the hypothesis that a loss of Arctic MYI due to Beaufort Gyre transition into a summer melt zone resulted in a rapid acceleration in Volume loss in the years 2002-2007.  If I understand it correctly, it shows a gradual decline in summer survival until a big event in 2007.  Then after 2007, continuing with survival % still lower than before 2007 in 2008-20012.

      The change in summer survival rate before and after 2007 does not look that different, but remember that the absolute value for the baseline is also declining.  For example, the higher survival in 2013 is the portion of the much-diminished volume of MYI that was still around by then, i.e. much of the MYI had been lost over the previous decade, so while the 2013 proportion looks relatively high, it is the portion of a lower absolute baseline amount of MYI than used for the proportion measurement indicated for years prior to 2007.  And remember, most of the Volume is/was in the MYI. 
   
      Thus the rather modest downward slope in the graph is showing a declining survival % for a starting pool of ice that is also declining across years.  The multiplicative effect for all three age classes on the chart is that not only is the amount of ice heading into melt season declining through time, but the portion of it surviving the melt season is also declining as the years progress.  Smaller starting amount x Smaller summer survival % = Much smaller end of melt season amount X Repeat cycle.  As usual, caveat emptor, this is complete guesswork and very possibly a misinterpretation.  And if were fully true, it seems that Volume numbers in recent years would have declined more than they have.

       As for FYI, a simple separation into Early and Late years shows a reduction in average survival rate from about 55% to about 40%.  Sustained over time, that indicates a functionally different system and an ASI death spiral. 

       This chart is one more piece of evidence pointing to 2007 as the "Year the Arctic Sea Ice Changed."  2012 was dramatic, but really just an aftershock of a more fundamental change that occurred in 2007, and from which the ASI has never recovered. 

       It would be interesting to see a 2016-2020 update for this chart.  If anybody knows of such, please post.  The second image below from October 2020 NSIDC update indicates that MYI has been pretty stable since 2015.     

[binntho]

But my main point is really to point out the fallacy of the "hiatus" and "phase change" discussion. There are lots of other explanations and hypothesis that can be built out of the existing data, and this fixation on "phase change" is only clouding the issue.

The shape of the graphs be explained by an unusually quiet period at the beginning of the century followed by "back to normal" variability. There is no hiatus, no stepwise acceleration and deceleration, no phase change.

   
     
Halló binntho - They are not exclusive possibilities, i.e. both AO effect and Beaufort Gyre no longer supporting MYI ice growth could be driving factors for ASI Extent/Area/Thickness/Volume changes across years.

      RE: Was there a period of accelerated losses?   ...

Hi Glen I've been fairly "snowed under" (or rather "sanded under")  these last few days trying to find why an officially signed SAML Assertion signature woudldn't load in C# (hint: They had "id" instead of "Id") and now I'm waiting to see if the sandstorm thins enough so that we can fly to  Addis for a dental appointment. But I am planning to combine the content of my posts from earlier in the week into a more coherent whole, and perhaps starting a "is the AO index of 2020 a predictor of record low averages in 2021" thread or something similar.

[Stephan]

It is time for the monthly update of my extrapolation when the extent [Ausdehnung], volume [Volumen], thickness [Dicke] and area [Fläche] will reach zero. The extrapolation occured linearly and by a logarithmic function; the latter one almost constantly resulting in earlier times (valid for volume and thickness, not for extent and area in the winter months). The January value now includes 2021.

Position of January 2021 towards the long-term trend lines
Thickness and area lie slightly below the long term linear trend, volume is at the trend line, extent is above the trend line.

Trend of the trends
The "BOE numbers" did not change (thickness) and increased by 1 year (volume), 2 years (area) and by 5 years (extent) compared to January 2020.
So there is a divergence between the "late values" (area, extent) and the "early values" (volume, thickness) which seems to be usual as I already posted for the "high winter months".
The order (earlier → later BOE) generally is volume < thickness < area < extent.

Please note that this is not a forecast but a trend!
See attached table, now widened to see the linear function value (y-AA) at t = 0. Stg = slope.

Click to enlarge it.

[Stephan]

It is time for the monthly update of my extrapolation when the extent [Ausdehnung], volume [Volumen], thickness [Dicke] and area [Fläche] will reach zero. The extrapolation occured linearly and by a logarithmic function; the latter one almost constantly resulting in earlier times (valid for volume and thickness, not for extent and area in the winter months). The February value now includes 2021.

Position of February 2021 towards the long-term trend lines
Thickness lies slightly above the long term linear trend, volume, extent and area are well above the trend line.

Trend of the trends
The "BOE numbers" did not change (thickness) and increased by 1 year (volume), by 15 (!) years (area) and by 6 years (extent) compared to February 2020.
So there is a divergence between the "late values" (area, extent) and the "early values" (volume, thickness) which seems to be usual as I already posted for the "high winter months".
The order (earlier → later BOE) generally is volume < thickness < area < extent.

Please note that this is not a forecast but a trend!
See attached table, now widened to see the linear function value (y-AA) at t = 0. Stg = slope.

Click to enlarge it.

[Glen Koehler]

An analogy with river valleys to describe the gradual destruction of the Arctic Ocean sea ice.. continued

Very well done, gerontocrat, indeed.
Just imagine how the world will look like if the shape of the ice area in the CAB in 20XX (some decades ahead!) looks like the Barents' shape these days...

      The Wipneus straight-line volume trend chart at https://sites.google.com/site/arctischepinguin/home/piomas suggests that the average September will reach BOE by 2030 (using < 1M km3 Volume as a pretty good proxy for the "official" BOE definition of < 1M km2 Extent).  The monthly Wipneus chart on the same page indicates that August and October trail September by only about 3 years.  I can't come up with a simple Y-axis scale conversion to make the Barents Sea volume chart fit a near-future CAB, but the shape (multi-month, near-zero flat bottom with crumbling side slopes) seems like a good guess at how the CAB (or entire Arctic) ice volume chart could look by 2035. 
     
      I'm too far behind at work to mess around with it anytime soon, but an enterprising soul could find the straight-line CAB trends for the other months to create a projected 2035 version for Gerontocrat's CAB volume chart.  A visual representation of the future year-round CAB/Arctic volume would be more holistically informative than speculation on which exact year first reaches BOE. 

      Is it correct to assume that when it gets to the point that CAB is going BOE, that also means the Arctic as a whole has reached BOE?  Other than a few inlets in the CAA, my guess is that when the CAB is going below 1M km3, all the other Arctic seas will be at essentially zero, so it really does come down to the CAB and Arctic volumes being almost the same number.

[JNap]

Here's a link to the specific Wipneus' straight-line volume trend chart that Glen mentions.
https://14adebb0-a-62cb3a1a-s-sites.googlegroups.com/site/arctischepinguin/home/piomas/grf/piomas-trnd7.png?attachauth=ANoY7crBmD7HEkJJAeetXJCa21KQ6Tx0QN-9c8FooJlFBOsarHKB_RPthWJjG4gRKmEXJ5uwMlc41i-8NXgulYpae1isSDl5fRn64IFGm8E0DeT83o5bydA5UvQ0s8oxkz4qe7yDnctPrjlU0lThgGUqDOeBy4AINaC1zoVbwhR-VX2cKXPFpDf6CVYB1KchtmZu6nWDjgbHQrWm8u94WPRuWmJCdMDoYN9D2VK_9awqPifpJIq4lh44NejgXNpwV_SmrDfQLeFo&attredirects=0

That straight line trend shows that the likelihood for a BOE will be in the late 2020s or early 2030s.

The most interesting data point for me to see is when we break the 2012 lows.   It will help to be a good validation point that we are continuing along that trajectory.

[Tom_Mazanec]

The most interesting data point for me to see is when we break the 2012 lows.   It will help to be a good validation point that we are continuing along that trajectory.

Yes. Since it is likely that the 2012 low had weather effects in theNorth Temperate Zone (particularly Hurricane Sandy) it will be interesting to see if there are any more effects when it happens again.