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Tor Bejnar

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Re: How soon could we go ice free?
« Reply #100 on: June 15, 2018, 04:59:13 PM »
I particularly appreciate Jim Pettit's graphs, available through the ASI Long-term Graphs  page, specifically (in this thread's context) the graph reproduced below.

Any year that maintains the low recent ice volume maximum that is coupled with the already experienced greatest ice loss year will achieve a record low of about 1,000 km^3 of ice. 

I have argued that the less ice there is to start with may decrease the possibility of 'maximum already experienced ice loss' [there is 'harder to melt ice' areas], but the history of actual Arctic-wide ice loss doesn't strongly support this.

I don't expect 'ice free' happening this year, but I see the potential for it happening any year now.  We've experience 'near perfect low ice freezing years' and 'near perfect high ice melting years'; they just haven't happened together, yet.


« Last Edit: June 15, 2018, 05:20:41 PM by Tor Bejnar »
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crandles

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Re: How soon could we go ice free?
« Reply #101 on: June 15, 2018, 05:03:54 PM »
These three graphs from Arctische Penguin really say it all. Linear trend shows 0 volume in 2033, exponential in 2023 while gomperz curve seems to trend to the mid thirties. So a ballpark guess of 2025-2035 ?

But why those three? There are any number of curves that fit the data and then do different things.

A 4 parameter gompertz fit is shown below and goes flat pretty much immediately and never gets down to 1000km^3 let alone 0. I don't believe it should or will go flat, as GW continues. But clearly 3 parameter gompertz hitting 1000 km^3 in 2025 is not the most conservative possibility so your 3 graphs don't show the full range of possibilities.

jai mitchell

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Re: How soon could we go ice free?
« Reply #102 on: June 15, 2018, 05:06:53 PM »

I don't see the number "66" or the word "confidence" anywhere in the paper, nor the year "2020" anywhere except in a minor note about the changing forcing from black carbon.

Ned,

Model Ensemble range is the range of model outputs without uncertainty estimates.  Go to the Supplemental information and you will find that the green shading in the graphic I posted is the confidence interval of the RCP 2.6 range of all model outputs.  The green shading shows potential ice free conditions under 66% confidence as early as 2020.
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jai mitchell

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Re: How soon could we go ice free?
« Reply #103 on: June 15, 2018, 05:11:03 PM »
These three graphs from Arctische Penguin really say it all. Linear trend shows 0 volume in 2033, exponential in 2023 while gomperz curve seems to trend to the mid thirties. So a ballpark guess of 2025-2035 ?

But why those three? There are any number of curves that fit the data and then do different things.

A 4 parameter gompertz fit is shown below and goes flat pretty much immediately and never gets down to 1000km^3 let alone 0. I don't believe it should or will go flat, as GW continues. But clearly 3 parameter gompertz hitting 1000 km^3 in 2025 is not the most conservative possibility so your 3 graphs don't show the full range of possibilities.

Crandles,

Every time I see your 4 parameter gompertz fit curve it gives me a chuckle until I realize that you actually seem to believe that this is a potential reality going forward.

I see this assertion of future ice conditions without model or even realistic physical mechanism as a kind of magical thinking.  It would be akin to claiming that butterfly wings in the Amazon are driving sea ice variability and creating a curve to fit this idea.

Then I just figure you are trying to make a point about uncertainty and are just being contrary.
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crandles

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Re: How soon could we go ice free?
« Reply #104 on: June 15, 2018, 05:45:38 PM »

Every time I see your 4 parameter gompertz fit curve it gives me a chuckle until I realize that you actually seem to believe that this is a potential reality going forward.

I see this assertion of future ice conditions without model or even realistic physical mechanism as a kind of magical thinking.  It would be akin to claiming that butterfly wings in the Amazon are driving sea ice variability and creating a curve to fit this idea.

Then I just figure you are trying to make a point about uncertainty and are just being contrary.

I do try to say every time that I don't literally believe the completely horizontal path extrapolation. I do believe in a continuing downwards path but rate of decline could well be getting a less steep as practically all the models show

>"without model or even realistic physical mechanism"

I see lots of people here doing this (i.e. ignoring models and not considering some physical mechanisms which I believe are realistic) whereas I believe I have considered the major physics involved regarding the slow transition that MYI doesn't get replaced quickly but FYI does essentially get almost completely replaced each year. I don't believe I can prove this is highly significant nor that it is insignificant from basic reasoning of the physics. But discussion of it is in the scientific literature suggesting it is likely to be significant and the data of the last 5 to 12 years seems to be coming down on the side of a slowdown in the rate of decline.

If the models show a slowdown in the rate of decline as zero ice is approached and also the data is tending to show this recently, then assuming the rate will be steady or increase needs some substantial explanation. Without such substantial explanation, the default assumption should be of a declining rate of decline.

I see lots of people here just not wanting to see this.

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Re: How soon could we go ice free?
« Reply #105 on: June 15, 2018, 05:55:54 PM »

I don't see the number "66" or the word "confidence" anywhere in the paper, nor the year "2020" anywhere except in a minor note about the changing forcing from black carbon.

Ned,

Model Ensemble range is the range of model outputs without uncertainty estimates.  Go to the Supplemental information and you will find that the green shading in the graphic I posted is the confidence interval of the RCP 2.6 range of all model outputs.  The green shading shows potential ice free conditions under 66% confidence as early as 2020.

Thanks for the reply, but:

(1) When I follow your link, the "Supporting Information" contains only two files, labeled Figure S1 and Figure S2.  They are EPS documents with figures that don't directly relate to the figure you posted, and have no explanatory text. 

(2) I do note that in Figure 3 from the paper itself, the caption states that "The shading shows the 5–95% range of uncertainty in the mean from each ensemble of simulations."

So it seems likely to me that the shading in Figure 4 also shows the 90% confidence interval, not the 66% confidence interval you claimed.  I still have no idea where you got that from.

If that's in fact the case, then the best explanation of this would be:

The model ensemble predicts the development of an ice-free Arctic in 2042 to 2075, with a mean of 2048.  The 90% confidence interval extends from approximately 2021 to some unknown year later than 2075.
« Last Edit: June 15, 2018, 06:25:17 PM by Ned W »

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Re: How soon could we go ice free?
« Reply #106 on: June 15, 2018, 06:00:53 PM »
Ken Feldman your assumptions are not correct.

 First you should use volume, not extent. Volume hits 0 much sooner than extent, but they must hit 0 at the same time. That means a poof.
...

Just because extent and volume must hit zero does not mean there has to be a poof. It is quite possible for both extent and volume to slow down their rate of decline so they both reach zero at the same time which is well after the linear trends.

Yes, I agree with crandles.  Currently, some ways of extrapolating the past data show volume reaching zero before extent reaches zero.  There are three possible implications of that:

(1) Extent loss could speed up to match volume
(2) Volume loss could slow down to match extent
(3) Both extent and volume could change to reach zero at some other point

For some reason, a lot of people around here simply assume that (1) is the only possible outcome.  That's wrong. 

Daniel B.

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Re: How soon could we go ice free?
« Reply #107 on: June 15, 2018, 06:29:14 PM »
Ken Feldman your assumptions are not correct.

 First you should use volume, not extent. Volume hits 0 much sooner than extent, but they must hit 0 at the same time. That means a poof.
...

Just because extent and volume must hit zero does not mean there has to be a poof. It is quite possible for both extent and volume to slow down their rate of decline so they both reach zero at the same time which is well after the linear trends.

Yes, I agree with crandles.  Currently, some ways of extrapolating the past data show volume reaching zero before extent reaches zero.  There are three possible implications of that:

(1) Extent loss could speed up to match volume
(2) Volume loss could slow down to match extent
(3) Both extent and volume could change to reach zero at some other point

For some reason, a lot of people around here simply assume that (1) is the only possible outcome.  That's wrong.

I agree.  In any three-dimensional object, volume will always change faster than area (or extent in the case of sea ice) initially.  This is simple mathematics; three dimensions changing, compared to two.  A linear change in area, will result in an exponential change in volume (unless the third dimension is somehow held constant.  With the sea ice, the volume has changed faster initially, but will slow as the overall volume decreases.  There is simply less ice to melt.  The most likely scenario is (2), that the extent (or area) will continue on its trend, and volume will adjust.  This is especially true with respect to the sea ice, which has two very large dimensions, and one extremely small dimension (thickness).

Does this preclude other possibilities?  No.  There could be another 2012, with significant wave action to decimate another large chuck of the total sea ice, such that ice-free occurs in a year or so, or it could resemble that gompertz fit, as negative feedbacks dominate, resulting in a higher, minimum sea ice level.  Hard to say, as so many factor influence the annual changes.

Archimid

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Re: How soon could we go ice free?
« Reply #108 on: June 15, 2018, 06:52:52 PM »

Just an observation: you attack others for their assumptions being incorrect, then immediately draw a wrong conclusion and use your own big iffy assumptions.

I didn't attack anyone. I merely stated the fact that using extent to determine the first year of 0 ice is wrong because volume hits 0 much sooner. No attack on Ken Feldman. He has been a gentleman so far and his points are backed up by good arguments.  I'm merely pointing at the flaw of his argument.

Quote
Just because extent and volume must hit zero does not mean there has to be a poof. It is quite possible for both extent and volume to slow down their rate of decline so they both reach zero at the same time which is well after the linear trends.

The linear trends clearly point to a poof. Using the minimum, extent hits 0 a few decades after volume. That will be perceived as a poof.

Quote
I can follow what you are saying as an explanation of what you think is the situation but with big iffy assumptions, that doesn't make it correct.

I'm not making any assumption, I'm only looking at the linear trends and that's what they show. Mathematically the most basic assumption one can make, a pair of linear trends clearly points to a poof.


(1) Extent loss could speed up to match volume
(2) Volume loss could slow down to match extent
(3) Both extent and volume could change to reach zero at some other point

For some reason, a lot of people around here simply assume that (1) is the only possible outcome.  That's wrong. 

No one is assuming that is the only possible outcome. That is merely the outcome the basic data points to. Also if you take ice melting mechanisms into account a poof is also quite likely.

Now the really bad news. Most if not all of these models you are talking about use extent (a very crude version of it) to calculate the first ice free Arctic.  That's why they match the extent calculation but not the volume calculation.
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Daniel B.

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Re: How soon could we go ice free?
« Reply #109 on: June 15, 2018, 08:16:25 PM »
Have you looked at the annual change in ice?  The net change in ice extent (growth-melt) is slightly positive over the past decade.  Half the time, there has been a net loss over a full season, and the other half has seen a net gain.  That is a change from the previous decade, which witnessed much more losses than gains.

Ken Feldman

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Re: How soon could we go ice free?
« Reply #110 on: June 15, 2018, 09:33:48 PM »
Most methods used to predict an ice-free Arctic within the next decade are based on linear projections of current trends, with no consideration of feedbacks.  If any feedback is considered, it's usually to over estimate the ice-albedo feedback, which leads to more melt.

There are other feedbacks that impact sea ice, and there is a good summary of them in this study:

http://pubman.mpdl.mpg.de/pubman/item/escidoc:2461121/component/escidoc:2461125/PAGESmagazine_2017_14-19_Notz.pdf

Here's an explanation of the negative feedback, which lead to sea ice retention:

Quote
Annual variability: The importance of negative feedbacks

In addition to seasonal forecasts on time scales of a few months, also forecasts on time scales of a few years have made some headlines over the past decade. These headlines were usually related to claims that the Arctic would lose its remaining summer sea ice within just a few years. The underlying reasoning of such claims was often related to a discussion of a possible ’tipping point’ that is related to the ice-albedo feedback. Given the substantial loss of Arctic sea ice in the past few years, the ocean could potentially absorb enough heat to rapidly melt the remainder of the sea ice cover.

However, our current understanding of the Arctic climate system strongly suggests that this reasoning is unrealistic. A first indication for this finding derived from model experiments in which all Arctic sea ice was synthetically removed from the Arctic Ocean at the onset of summer, thus maximising the possible ice-albedo feedback (Tietsche et al., 2011). Despite such maximised feedback, the ice cover recovered in these experiments within just a few years. This is because on annual time scales, negative feedbacks dominate the evolution of the Arctic sea ice cover. Three negative feedbacks are particularly important: First, the open ocean very effectively releases its heat to the atmosphere during winter, causing a rapid loss of much of the heat that was accumulated in the icefree water during summer. Second, the thin ice that forms during winter can grow much more rapidly than ice that survived the summer, because heat can more effectively be transported from the ocean to the atmosphere when the ice cover is thin (Bitz and Roe, 2004). Third, as ice forms later in the season, it will carry a thinner insolating snow cover as any snow fall occurring before ice formation simply falls into the open ocean (Notz, 2009).

The effectiveness of these negative feedbacks on an annual time scale is not only apparent in our model simulations; the observed time series of Arctic summer sea ice also carries a clear signature of such mechanisms. A year with a strong drop in ice coverage during September is usually followed by an increase in September ice coverage in the following year. More formally, the time series shows significant negative autocorrelation (Notz and Marotzke, 2012). If indeed the ice albedo feedback was as effective on annual time scales as implied by statements supporting the entire loss of Arctic summer sea ice within this decade, one would certainly expect that any year with a strong drop in ice coverage would be followed by a year with yet another drop. This is found neither in the observational record, nor in model simulation. This underpins the dominance of negative feedbacks, which stabilize the Arctic ice cover and prevent a possible “tipping point”.

johnm33

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Re: How soon could we go ice free?
« Reply #111 on: June 16, 2018, 02:36:28 AM »
I'm looking at ice dynamics, there are 3 main factors afaics, the main one being the expansion/dispersion of ice with every weather change. That is that as the ice moves creating gaps these are rapidly filled with new ice, the cumulative effect is to push the ice south away from the centre of the ice mass, generally south. As the ice moves south to maintain station it has to accelerate by about 24kph per deg, it doesn't, hence it appears to rotate c/w,  there are pinch points and the ice builds up against the coast, where?   well as far south as Prince Patrick island on the american side, and after the freedom of Beaufort from the NSI through NZ-FJ to Svalbard on the Russian side.
The next factor is the entry of Atlantic water, previously the ice in Barents suppressed the tides, I think ocean currents are residuals of tidal movements, the tides are no longer suppressed and new currents are forming, these currents help to keep Barents free of ice, being free of ice gives the wind free reign, so over the continental shelf the waves thrash the ice, it melts and no longer rotates to accumulate on the american side.     
The third factor is an ice free Amundsen gulf, every tide there can shift a significant fraction of 20,0002km of seawater/ice westward across southern Beaufort, and conversely suck in a similar amount from further north in Beaufort.
Nothing to do with ice but one has to bear in mind that Atlantic/Pacific waters entering the arctic tend to rotate ccw.
If the growing currents coming in from the Atlantic can weaken the ice over the ESAS in concert with weather systems bringing heat from the south, and persistent winds from E/W then the Siberian shelf will also become a killing field for ice. Which gives the possibility of no ice to rotate into the islands, no ice to rotate back towards Amundsen, whats next?
 Well given that systems tend to hold on beyond any reasonable expectation and then suddenly collapse, it's remotely possible that it happens this year, but I don't think we've passed beyond reasonable expectation yet we're close.

Dharma Rupa

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Re: How soon could we go ice free?
« Reply #112 on: June 16, 2018, 02:49:57 AM »
If the models show a slowdown in the rate of decline as zero ice is approached and also the data is tending to show this recently, then assuming the rate will be steady or increase needs some substantial explanation. Without such substantial explanation, the default assumption should be of a declining rate of decline.

Given the currently demonstrated skill of the global models, the default assumption ought to be "we don't know."

Any other assumption is pure hubris.

Archimid

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Re: How soon could we go ice free?
« Reply #113 on: June 16, 2018, 03:09:55 AM »
Quote
(Tietsche et al., 2011)

That study is dated. Some of their results are already exceeded by real life events like winter temperature anomalies. Winters are getting significantly warmer, very fast. Their assumptions are now incorrect even before the first BOE.
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DavidR

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Re: How soon could we go ice free?
« Reply #114 on: June 16, 2018, 03:34:10 AM »

I don't expect 'ice free' happening this year, but I see the potential for it happening any year now.  We've experience 'near perfect low ice freezing years' and 'near perfect high ice melting years'; they just haven't happened together, yet.
I  agree.  We have never seen a volume loss greater than 20K km^3 however the trend is clearly that we will be starting below that figure by 2025. On average each year we are seeing the loss in volume from the previous year increasing.

The loss from May  31st ranges from ~16.2K km^3 to  ~13.5K km^3 over the past  40 years but the trend value is a steady ~15.  However loss of volume does not equate directly  to loss of extent.  2015 lost  15.82K Km^3 after 31 May compared to  2012's 15.92, however 2012 lost more than 1.6 M km^2 more extent than 2015.  Even the volume loss from August  1st  was very  similar.  2012 lost  2.87K Km^3 whereas 2015 lost 2.80K Km^3.

Another example is that 2016 lost about 10% more volume and extent than 2012 after August 1st, despite not having a GAC. Basically confidence in any prediction from now should be low. But a minimum below 4K Km^3 in 2018 seems highly improbable.
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Re: How soon could we go ice free?
« Reply #115 on: June 16, 2018, 04:01:14 AM »
Study: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/grl.50316

" Time horizons for a nearly sea ice‐free summer for these three approaches are roughly 2020 or earlier, 2030 ± 10 years, and 2040 or later."
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Re: How soon could we go ice free?
« Reply #116 on: June 16, 2018, 06:07:27 AM »
How soon could we...? Within a week or so, if we really wanted to.
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Re: How soon could we go ice free?
« Reply #117 on: June 16, 2018, 06:11:27 AM »
... If the models show a slowdown in the rate of decline as zero ice is approached and also the data is tending to show this recently...

Which models are you referring to? I've never seen a physics-based model with good predictive ability on this trend. True, there are models that don't work well, e.g. for the IPCC studies. If the model can't find the recent trend then it's not much use for predicting future trends.

Why do you say the data is showing a slowdown recently? If I look back at the linear fit of #97 then the residuals are all over the place and I don't see that trend. Based on the second plot, I suspect a quadratic fit would also curve downwards rather than upwards.


  If we're looking for a physical reason for a slowdown then I would point to the existence of a 'sanctuary region' against the North side of the CAA and Greenland where the ice hasn't melted out in any year.

  The prevailing combination of winds and current tends to push the ice against the coast - it has every single season we've been observing. It's deep water so the warm salty Atlantic waters can't get to it - their higher salinity makes them denser so they dive down instead.

   That's where the remaining multi-year ice is, so that also makes it harder to melt through.

   It might even be that it's cloudier there in the Summer than over the rest of the Arctic basin, so it sees less sun? (True or false? I have that impression but may be wrong.)
 
   So the first year below 1 million square kilometres should be the first year where the ice sanctuary is no longer effective, for whatever reason. The ice gets pushed away from there and/or melts in situ.


   When will that happen? I don't know. But the presence of an identifiable ice sanctuary region provides an arguable physical reason for a potential future slowdown in the rate of the year-to-year decline in minimum sea ice extent.

crandles

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Re: How soon could we go ice free?
« Reply #118 on: June 16, 2018, 01:40:11 PM »
I didn't attack anyone.

Sorry if the word attack came across as implying acrimonious discussion.


I'm not making any assumption, I'm only looking at the linear trends and that's what they show.

I think the observation stands.

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Re: How soon could we go ice free?
« Reply #119 on: June 16, 2018, 02:43:01 PM »
What observation? That the basic data clearly indicates a poof? That's not iffy. That must be the base assumption. In my opinion, the "iffy" assumption is to use a 2 dimensional, enthalpy ignoring mechanism to determine the first ice free Arctic. Any model that uses a "slab of ice" to analyse the past and make projections for the future is missing the big picture.
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Re: How soon could we go ice free?
« Reply #120 on: June 16, 2018, 03:10:37 PM »
What observation? That the basic data clearly indicates a poof? That's not iffy. That must be the base assumption. In my opinion, the "iffy" assumption is to use a 2 dimensional, enthalpy ignoring mechanism to determine the first ice free Arctic. Any model that uses a "slab of ice" to analyse the past and make projections for the future is missing the big picture.



I'm not making any assumption, I'm only looking at the linear trends and that's what they show.

"I'm only looking at the linear trends" is just another way of saying 'if the linear trend continues' and that is an assumption you are making even if you want to try and say you are not making any assumption. FWIW I think you are making yourself sound ridiculous by clearly contradicting yourself.

As Ned W said

Yes, I agree with crandles.  Currently, some ways of extrapolating the past data show volume reaching zero before extent reaches zero.  There are three possible implications of that:

(1) Extent loss could speed up to match volume
(2) Volume loss could slow down to match extent
(3) Both extent and volume could change to reach zero at some other point

For some reason, a lot of people around here simply assume that (1) is the only possible outcome.  That's wrong. 

We both think the other is making big iffy assumptions. I think I have made the point and attempted clarification enough times, time to agree to disagree.

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Re: How soon could we go ice free?
« Reply #121 on: June 16, 2018, 04:00:09 PM »
... If the models show a slowdown in the rate of decline as zero ice is approached and also the data is tending to show this recently...

Which models are you referring to? I've never seen a physics-based model with good predictive ability on this trend. True, there are models that don't work well, e.g. for the IPCC studies. If the model can't find the recent trend then it's not much use for predicting future trends.

Why do you say the data is showing a slowdown recently? If I look back at the linear fit of #97 then the residuals are all over the place and I don't see that trend. Based on the second plot, I suspect a quadratic fit would also curve downwards rather than upwards.

Lots of models. There are lots of graphs like attached below, some with many more model runs on them.

>" good predictive ability on this trend."

Clearly not they are all over the place on level of ice and also the trend. While some don't have enough data to see, all the model runs where you can see the change in trend where ice approaches zero is for the trend to get less steep as zero ice is approached.

Do we throw out all evidence because they are all over the place wrt level and trend? Or, do we say yes not much good for level or trend, but it looks like they all agree on trend in slope as zero ice is approached? So don't use them where they are bad but do use them for what they are good at, ie suggesting the change in trend as zero ice is approached declines.

>"Why do you say the data is showing a slowdown recently?"

The 4 parameter gompertz fit has a single inflection point. Whether I use Sept or April, that inflection point occurs in 2005. We have 12 years data since that inflection point. If there was only ~6 or fewer years data since the inflection point, I would be inclined to the opinion that 4 parameters might be too many parameters and I was overfitting. So just random residuals in last few years was allowing a better fit by using too many parameters. However with 12 years data past the infection point, that is too much data led and seems to me to be indicative that the data is showing a decline in the rate of decline.

See 4 parameter gompertz fit at top of this page.

>"If we're looking for a physical reason for a slowdown then I would point to the existence of a 'sanctuary region' against the North side of the CAA and Greenland where the ice hasn't melted out in any year."

Certainly wouldn't disagree with that being one physical reason, but I think there are lots of others.

I would tend to add in albedo feedback to this explanation (as well as deep water). In areas where ice moves out of the area, melting and ice movement allows albedo to drop and more sunlight energy be absorbed and this obviously helps additional melting. In contrast where ice piles up against Greenland & CAA, ice tend to move into area. So rather than melting and movement of ice causing extra area to open up, movement tend to close up areas opened by melting so it is much harder to get albedo drops to assist the melting.


If the ice retreats to a smaller area, that relevant area receives less sunlight energy so less volume melts seems quite possible. I guess this is complicated by winds bringing warmer temperature air so it isn't clear whether this accelerates or decelerates the volume of melt so maybe we need to look to the data and/or models?

Then there is oft discussed failure of MYI to make it around Beaufort gyre leading to rapid collapse of MYI to much lower proportion of the ice over a few years, but once we are down to these lower levels there is more FYI which almost completely recoveres itself each winter.

Are the people on these forums thinking through these reasonings and rejecting them because they don't believe they are significant compared to positive feedbacks they believe in? Or are they just rejecting the reasonings because it is just not exciting or they want to see catastrophic decline in sea ice or .... ?


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Re: How soon could we go ice free?
« Reply #122 on: June 16, 2018, 05:04:01 PM »
Quote
"I'm only looking at the linear trends" is just another way of saying 'if the linear trend continues' and that is an assumption you are making even if you want to try and say you are not making any assumption.

The good thing about linear trends is that they have no human introduced bias. When you all go on fantastical trips with gompertz curves or exponential fits all you are doing is adding your bias to the projection. Sure, your bias might be informed by smart speculation but it is also affected by your errors and incomplete knowledge.

Quote
FWIW I think you are making yourself sound ridiculous by clearly contradicting yourself.

I think you do not understand the power of simplicity and the risk of complexity. A linear trend has no human bias. It is the simplest operation that can be be used to fit a line to data. As such, it is what it is. Any projections made with it assumes the past will repeat. Assuming the past will repeat is not iffy, it's a pilar of science.

Quote
We both think the other is making big iffy assumptions. I think I have made the point and attempted clarification enough times, time to agree to disagree.

Nope. You are objectively making iffy assumptions.

1. Extent vs volume. Volume is a 3D measure and a measure that's directly related to the enthalpy of the ice. Extent is 2D abstraction with no information about enthalpy.

2. Projections made only using the Minimum. The minimum alone is a much a weaker measure to determine the future of the arctic. I used both, the Maximum directly and the Minimum represented as anual loss. I used the most basic representation I could think to keep my bias out. The only bias I used is the selection of  2007-2017 as the years to compute the loss average and I think the data justifies it as well as the physics.

3. Models that use a slab of ice are using a very iffy simplification.
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Dharma Rupa

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Re: How soon could we go ice free?
« Reply #123 on: June 16, 2018, 06:37:14 PM »
Do we throw out all evidence because they are all over the place wrt level and trend? Or, do we say yes not much good for level or trend, but it looks like they all agree on trend in slope as zero ice is approached? So don't use them where they are bad but do use them for what they are good at, ie suggesting the change in trend as zero ice is approached declines.

I'm trying to remember the correct name for this fallacy, but it is basically a combination of following the herd and appeal to authority.

Is there any evidence of skill in any of these projections?  If you could show that any of them have in the past been skillful in projecting a decrease in the slope as the ice approaches zero, but since that is impossible to demonstrate...



Dharma Rupa

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Re: How soon could we go ice free?
« Reply #124 on: June 16, 2018, 06:48:57 PM »
The most common pattern in general systems dynamics is slow change until an inflection point is reached, followed by a sudden a dramatic change to a new state.  In the mathematics, these sudden changes at inflection points in the potential surface are called catastrophes.  This is where the potential surface no longer supports the current situation and the system has to fall to a new meta-stable state where the potential surface once again supports slow change.

The important thing to note is that we do not have the information required to determine the slope of the potential surface, and therefore cannot have a clue when there will be a catastrophe.




magnamentis

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Re: How soon could we go ice free?
« Reply #125 on: June 16, 2018, 07:17:16 PM »
interesting page thus far, keep going LOL

thing is that there is a lot of knowledge provided in such disputes and this is good for
neutral observers to learn.

just one thing caught my eyes, i'm an analyst not a scientist but that said:

if there is a given amount of ice volume, we can loose a certain percentage per years (average)
and that makes a certain amount of ice volume.

since the volume shrinks either the same loss in percent is less absolute volume lost
or the same absolute volume lost would be a higher percentage.

this thought to the last year of the process it we shall loose 100% of the ice in one single year as compared to last year, while the amount of volume lost that year will be much smaller than the volume we lost i.e. in the year 2012.

this is why i like to look at the big picture and keep it simple but if i say "I like" or "I prefer" that does not mean to keep others from trying to be more accurate but at a higher risk to err. ;)

thing is that the knowledge gathered in the process of finding different ways is good and useful
for everyone who joins the club later in time. this is how we develop.

« Last Edit: June 16, 2018, 10:20:54 PM by magnamentis »

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Re: How soon could we go ice free?
« Reply #126 on: June 16, 2018, 07:31:46 PM »
The most common pattern in general systems dynamics is slow change until an inflection point is reached, followed by a sudden a dramatic change to a new state.  In the mathematics, these sudden changes at inflection points in the potential surface are called catastrophes.  This is where the potential surface no longer supports the current situation and the system has to fall to a new meta-stable state where the potential surface once again supports slow change.

The important thing to note is that we do not have the information required to determine the slope of the potential surface, and therefore cannot have a clue when there will be a catastrophe.
And I think one of those inflection points was 2012. 

Folding in points crandles makes about a system with mostly FYI vs MYI, 2012 and the following years have made exactly that transition.

As a result, a major, MAJOR variable in the dynamic has been taken out of play - something like 95% of the 3+ Meter MYI that used to exist for thousands of years in the Arctic is gone, and it happened in an eyeblink.

The over-all volatility of the system vis-a-vis extent, area and (albeit at a significantly lower level) volume has increased immensely.

With this volatility, statistically it may be we want to look more closely for modal points, rather than median or mean.  I think that will be more reflective of the actual state of the system - as governed by total heat content as affected by seasonal inputs/losses caused by weather and ocean currents.
[edit]
With the loss of MYI, particularly the thicker, 3+M 3+year old ice, the Arctic has lost its "long term memory".  As such the year over year relevance of a previous season's starting and ending states has diminished dramatically.  With out that "information" being carried over, each year is a completely new dice roll, increasingly independent of past ice states.
« Last Edit: June 16, 2018, 07:36:51 PM by jdallen »
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Re: How soon could we go ice free?
« Reply #127 on: June 16, 2018, 07:37:52 PM »
magnamentis, I think the attached graph illustrates what you are saying. It shows the total volume lost from Maximum to Minimum divided by the volume at Maximum. I haven't fully digested that graph yet but any insight would be appreciated.
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Re: How soon could we go ice free?
« Reply #128 on: June 16, 2018, 07:41:02 PM »
How soon could we...? Within a week or so, if we really wanted to.

I gave up Ice for Lent. It was real heavy, man. Cold Turkey stinks.

Meanwhile - a little "reductio ad adsurdum" spreadsheet I did last year when the same discussion happened. This extremely crude effort does show that using the linear fit as in PIOMAS volume and NSIDC extent graphs to project the future must eventually crash against reality.

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Re: How soon could we go ice free?
« Reply #129 on: June 16, 2018, 07:45:42 PM »
magnamentis, I think the attached graph illustrates what you are saying. It shows the total volume lost from Maximum to Minimum divided by the volume at Maximum. I haven't fully digested that graph yet but any insight would be appreciated.
And that, is a measure of increasing volatility.
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Re: How soon could we go ice free?
« Reply #130 on: June 16, 2018, 07:47:58 PM »
I see better quantifying three factors and how they are changing over time will improve our skillfulness in determining when the ice will drop under 1 million KM2.

(1) Total Arctic ocean heat content
(2) Annual variations in oceanic heat transport into the Arctic
(3) Variations in the annual Arctic heat budget as modified by weather
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Re: How soon could we go ice free?
« Reply #131 on: June 16, 2018, 08:00:55 PM »
Quote
"I'm only looking at the linear trends" is just another way of saying 'if the linear trend continues' and that is an assumption you are making even if you want to try and say you are not making any assumption.

The good thing about linear trends is that they have no human introduced bias. When you all go on fantastical trips with gompertz curves or exponential fits all you are doing is adding your bias to the projection. Sure, your bias might be informed by smart speculation but it is also affected by your errors and incomplete knowledge.

Quote
FWIW I think you are making yourself sound ridiculous by clearly contradicting yourself.

I think you do not understand the power of simplicity and the risk of complexity. A linear trend has no human bias. It is the simplest operation that can be be used to fit a line to data. As such, it is what it is. Any projections made with it assumes the past will repeat. Assuming the past will repeat is not iffy, it's a pilar of science.

Quote
We both think the other is making big iffy assumptions. I think I have made the point and attempted clarification enough times, time to agree to disagree.

Nope. You are objectively making iffy assumptions.

1. Extent vs volume. Volume is a 3D measure and a measure that's directly related to the enthalpy of the ice. Extent is 2D abstraction with no information about enthalpy.

2. Projections made only using the Minimum. The minimum alone is a much a weaker measure to determine the future of the arctic. I used both, the Maximum directly and the Minimum represented as anual loss. I used the most basic representation I could think to keep my bias out. The only bias I used is the selection of  2007-2017 as the years to compute the loss average and I think the data justifies it as well as the physics.

3. Models that use a slab of ice are using a very iffy simplification.

Choosing a linear trend is just as biased as choosing any other.  There is no mathematical reason that the sea ice should follow any mathematical expression.  Choosing the trend that gives your preferred answer is in itself subjective.  Past data does not follow a linear trend, why should future changes?  The Arctic is a complex environment.  Why would you think it can be represented by a simple expression?  We are all making assumptions.  You should not delude yourself by believing that your analysis is above that.

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Re: How soon could we go ice free?
« Reply #132 on: June 16, 2018, 08:57:37 PM »
Quote
"I'm only looking at the linear trends" is just another way of saying 'if the linear trend continues' and that is an assumption you are making even if you want to try and say you are not making any assumption.

The good thing about linear trends is that they have no human introduced bias. When you all go on fantastical trips with gompertz curves or exponential fits all you are doing is adding your bias to the projection. Sure, your bias might be informed by smart speculation but it is also affected by your errors and incomplete knowledge.

Quote
FWIW I think you are making yourself sound ridiculous by clearly contradicting yourself.

I think you do not understand the power of simplicity and the risk of complexity. A linear trend has no human bias. It is the simplest operation that can be be used to fit a line to data. As such, it is what it is. Any projections made with it assumes the past will repeat. Assuming the past will repeat is not iffy, it's a pilar of science.

Quote
We both think the other is making big iffy assumptions. I think I have made the point and attempted clarification enough times, time to agree to disagree.

Nope. You are objectively making iffy assumptions.

1. Extent vs volume. Volume is a 3D measure and a measure that's directly related to the enthalpy of the ice. Extent is 2D abstraction with no information about enthalpy.

2. Projections made only using the Minimum. The minimum alone is a much a weaker measure to determine the future of the arctic. I used both, the Maximum directly and the Minimum represented as anual loss. I used the most basic representation I could think to keep my bias out. The only bias I used is the selection of  2007-2017 as the years to compute the loss average and I think the data justifies it as well as the physics.

3. Models that use a slab of ice are using a very iffy simplification.

Choosing a linear trend is just as biased as choosing any other.  There is no mathematical reason that the sea ice should follow any mathematical expression.  Choosing the trend that gives your preferred answer is in itself subjective.  Past data does not follow a linear trend, why should future changes?  The Arctic is a complex environment.  Why would you think it can be represented by a simple expression?  We are all making assumptions.  You should not delude yourself by believing that your analysis is above that.

The Arctic is changing rapidly. The ice is going away. How ever you think the data will go, the ice is gonna go away
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Re: How soon could we go ice free?
« Reply #133 on: June 16, 2018, 10:31:34 PM »
magnamentis, I think the attached graph illustrates what you are saying. It shows the total volume lost from Maximum to Minimum divided by the volume at Maximum. I haven't fully digested that graph yet but any insight would be appreciated.

yeah something along this line i meant, thanks.

you IMO there are many experts/scientists around here and on the other side there are the, let's call them "phiolosphers"

experts are often narrow minded but have gathered a huge knowledge in their specific field
while philosophers (thinkers translated from greek) often have the bigger picture in mind but lack specific and detailed knowledge in all the fields the ponder about.

only way to overcoe this gap is to overcome the personal bias and ego to join forces.

one of the greater difficulties is that people with a great mind often have great energy reserves and those are not easy to hold in check, which is probably one of the main reasons why genuinely wise men/women are usually of a certain advanced age. the good old council of the wise has most often if not always been the council of the elder.

so since this is more or less a given thing, the only thing we can do is to approach everything and any discussion with a huge amount of goodwill (good intention)  this will ultimately soften things and keep the animal like hormone driven macho behaviour in check LOL

( this is a general statement, no-one specific in mind except perhaps myself LOL)

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Re: How soon could we go ice free?
« Reply #134 on: June 16, 2018, 10:57:41 PM »

Choosing a linear trend is just as biased as choosing any other.  There is no mathematical reason that the sea ice should follow any mathematical expression.  Choosing the trend that gives your preferred answer is in itself subjective.  Past data does not follow a linear trend, why should future changes?  The Arctic is a complex environment.  Why would you think it can be represented by a simple expression?  We are all making assumptions.  You should not delude yourself by believing that your analysis is above that.

Noise is normally higher frequency than signal, which means linear tends to fit the signal compared to higher order functions tending to fit the noise, which generally leads to much wider margins of error than when extrapolating a linear fit.

magnamentis

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Re: How soon could we go ice free?
« Reply #135 on: June 16, 2018, 11:29:25 PM »
linearity even though it does not necessarily predict the future correctly is an honest, hence NOT biased effort based on facts of the past while any algorithm contains an idea for the future development with a certain claim to do it better than others which is exactly the reason for
at times unpleasant discussions, it's a form of competition while linearity does not claim anything, it' simply draws a line based on the past and provides a rough visual where we're heading.

again, don't get me wrong, both are valid approaches, it just depends a bit on the motives. if the motives are some kind of profiling and elevate oneself over the rest it's of lesser value than if the motives are a kind of exchange and brainstorming.

it's similar to religions, if the motives are to make people behave ethical it's ok, if the motives are to get rich, recognized, renown etc. or to claim to be the only one who knows the truth it's not.


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Re: How soon could we go ice free?
« Reply #136 on: June 17, 2018, 12:01:29 AM »
And I think one of those inflection points was 2012. 

I am rather unclear on 2012....there is a difference between the point of inflection and the point where the system has to fall away from the potential surface in order to reorganize.

It is, however, clear to me that in late December 2015 the Arctic climate became disconnected from its prior meta-stable state.

It could very well be true that the inflection was reached sometime in 2012 and it took 3 years to start into freefall.

[ed: Note: I am assuming a continuous potential surface.  There is no real known reason to assume that, but it has seemed to work in the past.]
« Last Edit: June 17, 2018, 12:36:44 AM by Dharma Rupa »

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Re: How soon could we go ice free?
« Reply #137 on: June 17, 2018, 12:41:13 AM »
Comment by new member further upthread that I had to release first:

The problem I see with applying linear trends to estimate the "ice-free" date is that it doesn't make sense to me that the arctic will continue being able to melt xxx km3 of ice each year.

I assume that as the ice volume reduces it will retreat into the CAB, where it will be more resistant to melt (shorter melting season etc).

Currently the melting season starts first in the peripheral seas.  As warming continues in winter and max volume reduces, presumably comparatively more of the reduction in winter volume will be in the periphery than in the CAB, so it won't be there to be easily melted at the beginning of the melt season.

I'm sure this will make the ice in the CAB easier to melt, but not by enough to make up for the overall volume reduction.

In summary, I think that as the winter max volume reduces the volume of ice melted each year will decline, and there will be a slowing of the rate-of-change in volume reduction (a long-tail decline)

Having posted all this obviously I should point out that I'm just making stuff up based on opinions from this forum  :)  I also think that the system is incredibly complex and trying to predict the future is a fools errand.
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magnamentis

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Re: How soon could we go ice free?
« Reply #138 on: June 17, 2018, 01:03:55 AM »
The problem I see with applying linear trends to estimate the "ice-free" date is that it doesn't make sense to me that the arctic will continue being able to melt xxx km3 of ice each year.

I assume that as the ice volume reduces it will retreat into the CAB, where it will be more resistant to melt (shorter melting season etc).

a) i agree with what you're saying about a slow down due to where the ice will be mainly located in the future while we don't know for sure what the impact on much more surrounding open water much earlier and with much lower albedo will have on melt-out and before that on general temperature level in the high arctic.

it may well be that positive feedbacks will even accelerate the death stroke to the reminder, after all the ice above 80N is not very thick and the north pole at times is already now showing larger areas of open water.

what i disagree with is the word "estimate"

a linear curve can very well provide a clue as to about when, +/- a few years, we shall reach zero ice while if you had used the word "predict" i'd fully agree because a prediction is stronger, claims more than an rough estimate, but that's a detail, i think i understand you general direction of thinking and the main content of your post and it's a valid possibility, even though, as explained above, not totally certain as well (IMHO)

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Re: How soon could we go ice free?
« Reply #139 on: June 17, 2018, 01:05:04 AM »
And I think one of those inflection points was 2012. 

I am rather unclear on 2012....there is a difference between the point of inflection and the point where the system has to fall away from the potential surface in order to reorganize.

It is, however, clear to me that in late December 2015 the Arctic climate became disconnected from its prior meta-stable state.

It could very well be true that the inflection was reached sometime in 2012 and it took 3 years to start into freefall.

[ed: Note: I am assuming a continuous potential surface.  There is no real known reason to assume that, but it has seemed to work in the past.]
You may be right about 2015. 

My assumption was based around the disappearance of MYI it represented.  But then, both 2011 and 2010 were very hard on MYI as well. 

Perhaps we should look at it as a range instead - 2010-2015 - where the catastrophe took place, and the system tumbled into a new state sufficiently disconnected from the previous regime that we can't recover to it without serious changes elsewhere in the system.
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Re: How soon could we go ice free?
« Reply #140 on: June 17, 2018, 02:31:05 AM »
And I think one of those inflection points was 2012. 

I am rather unclear on 2012....there is a difference between the point of inflection and the point where the system has to fall away from the potential surface in order to reorganize.

It is, however, clear to me that in late December 2015 the Arctic climate became disconnected from its prior meta-stable state.

It could very well be true that the inflection was reached sometime in 2012 and it took 3 years to start into freefall.

[ed: Note: I am assuming a continuous potential surface.  There is no real known reason to assume that, but it has seemed to work in the past.]
You may be right about 2015. 

My assumption was based around the disappearance of MYI it represented.  But then, both 2011 and 2010 were very hard on MYI as well. 

Perhaps we should look at it as a range instead - 2010-2015 - where the catastrophe took place, and the system tumbled into a new state sufficiently disconnected from the previous regime that we can't recover to it without serious changes elsewhere in the system.

I can buy into that.  The loss of MYI leads to the open water, leads to higher humidity -- leads to warmer winters, but not much warmer summers.  Basically, everything you would expect in a warming climate.  In that viewpoint the state of the ice is sort of a side-show.

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Re: How soon could we go ice free?
« Reply #141 on: June 17, 2018, 02:50:36 AM »
And I think one of those inflection points was 2012. 
<snippage>
It is, however, clear to me that in late December 2015 the Arctic climate became disconnected from its prior meta-stable state.
<snippage>
You may be right about 2015. 
<snippage>
I can buy into that.  The loss of MYI leads to the open water, leads to higher humidity -- leads to warmer winters, but not much warmer summers.  Basically, everything you would expect in a warming climate.  In that viewpoint the state of the ice is sort of a side-show.
Precisely!

It does have some causal effect on changing conditions, but in and of itself, is more of an effect than a cause.

I was thinking that a blue water Arctic would be the next inflection point, but the more I think about it, it's not preventable.  We are already in the chute. Namely current changes which have already taken place cannot be undone quickly enough to prevent it, nor is it likely that  that even if some systems stabilized, the momentum of the system could be prevented from still carrying us over the edge.
« Last Edit: June 17, 2018, 03:00:09 AM by jdallen »
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Re: How soon could we go ice free?
« Reply #142 on: June 17, 2018, 03:14:41 AM »
I was thinking that a blue water Arctic would be the next inflection point, but the more I think about it, it's not preventable.  We are already in the chute. Namely current changes which have already taken place cannot be undone quickly enough to prevent it, nor is it likely that  that even if some systems stabilized, the momentum of the system could be prevented from still carrying us over the edge.

Since I am of the opinion that the Industrial Revolution sealed our fate about 200 years ago I don't worry too much about current affairs.  (We shall see, but the demonstrated skill of the global models isn't any better than my guess.)

I am just here watching the show while I am still alive.  (A 65-year-old lung cancer survivor with one lung.)

We can at least take heart that current measurements of the system state are not too bad.

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Re: How soon could we go ice free?
« Reply #143 on: June 17, 2018, 03:29:40 AM »
The problem I see with applying linear trends to estimate the "ice-free" date is that it doesn't make sense to me that the arctic will continue being able to melt xxx km3 of ice each year.

I assume that as the ice volume reduces it will retreat into the CAB, where it will be more resistant to melt (shorter melting season etc).

Currently the melting season starts first in the peripheral seas.  As warming continues in winter and max volume reduces, presumably comparatively more of the reduction in winter volume will be in the periphery than in the CAB, so it won't be there to be easily melted at the beginning of the melt season.

I'm sure this will make the ice in the CAB easier to melt, but not by enough to make up for the overall volume reduction.

In summary, I think that as the winter max volume reduces the volume of ice melted each year will decline, and there will be a slowing of the rate-of-change in volume reduction (a long-tail decline)

Having posted all this obviously I should point out that I'm just making stuff up based on opinions from this forum  :)  I also think that the system is incredibly complex and trying to predict the future is a fools errand.
The ice is not really retreating into the CAB but into the sheltered coast north of Greenland and Canada.  We can see from the behavior of Okhotsk, Kara and the Canadian Archipelago  that protected waters shelter the ice.  These areas retain ice long after open ocean and similar latitudes.  Summer Ice is already  melting  out very  close to the North Pole on the Russian side which gets the bulk of the heat from the south.  Both the currents and the geography point to  greater warmth on that  side of the Arctic. 

Warmer water, which is the primary driver of the increasing volume melt  continues to  flow into the Arctic via the Atlantic current and to a  lesser extent the Bering  strait, driving colder water out through Fram and the Canadian Archipelago.

The fact that both ocean and air temperatures are increasing means that the Arctic will continue to absorb increasing levels of warmth. According to GISS the last two years in the Arctic have been warmest on record and a step upwards from the previous 10 years.    https://data.giss.nasa.gov/gistemp/tabledata_v3/ZonAnn.Ts+dSST.csv.

As you  can see from the attached graph arctic temperature anomalies were fairly steady  from 2005 to 2015 but then leapt  significantly in 2016, 2017 beat every year prior to 2016 and 2018 is shaping up  to be warmer than 2017 according to NOAA particularly in the high Arctic. 

I can't see any reason for this heat transport into the Arctic to weaken, or for the current increasing annual decline in volume to slow in any way. The peripheral seas that retain summer extent can not maintain a million km ^2 in area or 1000 km^3 in volume. One year soon we will see a small increase in volume combined with a large decline the following year and the CAB will  be essentially blue all over.  Following that a blue arctic will become normal in summer very  quickly. By 2030 we could be seeing three months a year of open water in the Arctic. 
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Re: How soon could we go ice free?
« Reply #144 on: June 17, 2018, 07:50:05 AM »
How soon could we...? Within a week or so, if we really wanted to.

I gave up Ice for Lent. It was real heavy, man. Cold Turkey stinks.

Meanwhile - a little "reductio ad adsurdum" spreadsheet I did last year when the same discussion happened. This extremely crude effort does show that using the linear fit as in PIOMAS volume and NSIDC extent graphs to project the future must eventually crash against reality.
Crash against reality they will. 2030's seems most likely right now.
The somewhat amusing part for me was that this topic started on May 28 2017 with this question; "could we be ice free by the end of June?"


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Re: How soon could we go ice free?
« Reply #145 on: June 17, 2018, 12:25:37 PM »
To me, the residuals look fairly random and have no obvious particular trend in residual size.

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Re: How soon could we go ice free?
« Reply #146 on: June 17, 2018, 12:57:26 PM »
Can we stick to 2005 as the point of inflection.

For piecewise linear fits there may well be discontinuities in the rate of decline at around 2000 and 2012. Can we call these turning points?

Then there is catastrophe theory and its state changes.

Catastrophe theory is discussed in the literature so shouldn't be dismissed. I admit the possibility but it doesn't seem very likely. Even if it is likely, is it useful? Or do we just end up concluding well something might happen at some time?

Is it likely? Weather is chaotic but generally climate is stable. Arctic sea ice seems to be showing slow steady changes. Do we have any evidence of chaotic / catastrophic behaviour?

So wrong to conclude there won't be catastrophic change but if no such evidence is it reasonable to conclude it is unlikely in the near term?

Maybe we don't need much possibility to judge we need more action on cc, but for the purpose of predicting what will happen in next few years to decades is low probability and low usefulness a reasonable conclusion?

dnem

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Re: How soon could we go ice free?
« Reply #147 on: June 17, 2018, 01:31:07 PM »
Personally, I think the analogy of the spinning top is relevant.  As the top begins to slow, its overall motion is predictable: the rotational speed slows and the movement about the axis is tightly constrained.  As it continues to lose speed, the wobbles about the axis increase in amplitude and become more chaotic.  In the final revolutions before it topples over, the motions are chaotic and unpredictable.

I think most here believe the top WILL topple over: the arctic will go functionally seasonally ice free with enormous implications for global climate.  There will likely be a refuge along the CAA and Greenland for quite some time, and whether it is + or - 1 M km2 is almost irrelevant. 

I do not believe that ANY curve fitting exercise is useful in predicting when the next big inflection point will come.  There is ample evidence that the metrics (especially SIE) are becoming more variable and more difficult to interpret.  Volume is straightforward to interpret but difficult to measure (and model).

My guess would be that sometime before 2025 the 2012 minimum will be obliterated and we will be left with a highly mobile jumble of ice that is functionally entirely different than the previous coherent pack.  There will be no 2013/2014 recovery the next time.  Albedo will not recover and knock on impacts will be huge.

I would not be the least bit surprised if this happened during a seemingly "normal" season where the ASIF community is having its annual debate about slow vs fast transition, the reliability of the metrics, the likelihood of a new record and so on. 

I would be surprised but not flabbergasted if 2018 was the year.  I will be entirely shocked if it does not happen before 2025.

gerontocrat

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Re: How soon could we go ice free?
« Reply #148 on: June 17, 2018, 04:03:43 PM »
"This is my speculation and it belongs to me""

A good many posts ago, A-Team suggested that it was of more use to consider how even now there are climatic effects as individual seas such as the Barents become emptier of ice.

Others have commented on when there is less ice, the less ice there is to melt.

As I have NSIDC area graphs for each sea sitting in my laptop I thought - let us have a look. This first post looks at the melting behaviour of seas that melt out early, late or never.

The first observation is that the S-Curve applies in all cases, i.e. independently of the time of year melt out is finished or minimum is reached. (Yes, individual years have lots of wobbles due to the weather and other local conditions, but that is noise disguising the underlying characteristic.)

I attach graphs of -
- The St Lawrence, melts out May to June,
- The Barents Sea, melted out by 1st August,
- The Kara Sea - minimum late September (well below 5% of 1980's average maximum).
- Canadian Archipelago - mid-September minimum.
To repeat, loss of ice declines late in the melting no matter the time of year.
 
Thinks about what might happen to individual seas ice-free days as warmth (ocean and atmosphere) pushes north, in fits and starts, in the years to come.

They are going to be knocked off one by one, until surely the only two left with significant summer ice, but less of it, will be the Central Arctic and the Canadian Archipelago. But as A-Team might agree, as the years go by, the number of ice-free days in the other seas must increase and with increasing feed-backs on the climate.

But that requires more thought. It is Sunday, I is tired and my brain hurts. Ta ra
"Para a Causa do Povo a Luta Continua!"
"And that's all I'm going to say about that". Forrest Gump
"Damn, I wanted to see what happened next" (Epitaph)

oren

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Re: How soon could we go ice free?
« Reply #149 on: June 18, 2018, 03:47:47 AM »
Hullo gerontocrat, your post inspired me to look at the same data from my favorite perspective - that of the transition of regional seas to a seasonally ice-free state. While trying to extrapolate the arctic ocean to the future, people have used linear fits, gompertz and other curves.
Looking at the Chukchi, which has already completed its transition, shows how linear turned out to make good predictions, and how the first "BOE" happened before the linear extrapolation hit zero because of the inherent volatility of the data.
Notes: I am using a 5-yr average of the annual extent minimum as it gives a better approximation of the variability of the whole arctic data. I've marked the BOE threshold at 7% of max extent.
The same analysis can be made for other seas, and is especially interesting for those that started the data-set as ice-covered at minimum, but have transitioned to seasonally ice-free, or are advanced in the transition.

Note: of course, the Chukchi is not a true approximation of the behavior of the whole arctic, due to many varied reasons (ice export and import, one region instead of amalgamation, different MYI distribution over time, etc.). I still found the result interesting.

Edit: Another such chart for the Laptev. Very interesting IMHO.
« Last Edit: June 18, 2018, 04:44:26 AM by oren »