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jai mitchell

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Re: How soon could we go ice free?
« Reply #150 on: June 18, 2018, 04:53:21 AM »
Can we stick to 2005 as the point of inflection.



98 is more significant I think
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Peter Ellis

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Re: How soon could we go ice free?
« Reply #151 on: June 18, 2018, 12:25:28 PM »
I think Figure 1 from Tietsche et al 2011 is important.
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2010GL045698

This shows two things - firstly, the general shape of the (modelled) decline in Arctic ice over the coming decades, and secondly the time taken to recover from extreme events such as the summers of 2007 and 2012.

For the latter, the conclusion is quite simple - the Arctic has a "memory" of about two years, and so any major excursion will bounce back to the long-term trendline within a couple of years.  They only modelled downward excursions, but my guess is that it holds the other way too - even if by chance we have a particularly good year for ice retention, it'll be gone in another couple of years.  The paper discusses the mechanisms for this, but fundamentally it's quite simple - if you have a massive loss of ice one autumn, that means a correspondingly massive extra heat loss in the following winter.  By the end of spring, first year ice has grown back. A low summer minimum has very little effect on the following maximum.  This is believable, and we've seen it after every major loss year for more than a decade now.

For the longer term decline, look at the shape of the curve.  Note how it's staggered and stepped.  This reflects the shape of the Arctic ice basin. There are shallow seas around the edge, and a deep central portion that covers about 5 million square km. So, as ice loss progresses, there's an initial period of rapid decline that plateaus at around 4.5 to 5 million until about 2020.  That's exactly where we are now, in that plateau, where the summer minimum roughly covers the deep parts of the Arctic Ocean but the peripheral seas melt out each summer. Subsequently, there's another period of rapid decline that plateaus again at 1.5-2 million.  This is the "remnant above Greenland" stage.  The final collapse comes after that.

The shape looks entirely plausible to me, all that we need to work out is the scaling on the X axis, and to be honest I'd be surprised if they're far off. Right now we're on the verge of the second period of decline - but it'll plateau again in another couple of decades, probably before hitting the "ice free" threshold of 1 million.

It may be we need to squash the X axis up by 10% or so to fit reality - someone with more time than I can probably make an overlay - but it's really not far off.

gerontocrat

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Re: How soon could we go ice free?
« Reply #152 on: June 18, 2018, 01:10:35 PM »
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.

Is not the next stage to consider the length of time that each sea has been, is and will be ice free? The longer the time the ice is not there the greater the climatic effects.  You may remember an exercise I did looking at the history of the number of days each sea was 95% ice-free, 85% ice free and 50% ice free..

but perhaps off-topic for this thread.

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crandles

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Re: How soon could we go ice free?
« Reply #153 on: June 18, 2018, 01:16:15 PM »
Can we stick to 2005 as the point of inflection.

98 is more significant I think

With data to 2017, 1998 may well be a more significant turning point than the 2012 turning point. (There is only 5 years data after 2012 which might not be enough. Maybe with more data which one of these turning points is more significant might change.)

There is only one point of inflection which is 2005.

I am trying to say, please get the nomenclature right. Only 2005 (+/- a year or 2) is a point of inflection. Getting nomenclature right helps avoid talking at cross purposes.

Quote
noun: point of inflection
1. MATHEMATICS
a point of a curve at which a change in the direction of curvature occurs.

https://en.wikipedia.org/wiki/Inflection_point#/media/File:X_cubed_plot.svg

You might find two turning points at circa x=-1 and +1 but the curve only changes direction of curvature once ie there is only one inflection point at x=0

(Turning point probably isn't strictly correct term but discontinuity in rate of decline seems a bit of a mouthful.)
« Last Edit: June 18, 2018, 01:52:05 PM by crandles »

Dharma Rupa

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Re: How soon could we go ice free?
« Reply #154 on: June 18, 2018, 02:05:35 PM »
(Turning point probably isn't strictly correct term but discontinuity in rate of decline seems a bit of a mouthful.)

Are you referring to the jerk?

(speed is rate of change in distance over time.  Acceleration is rate of change in Speed. Jerk is rate of change in acceleration.  By analogy the same terms have been used for other basic derivatives.)

crandles

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Re: How soon could we go ice free?
« Reply #155 on: June 18, 2018, 02:36:17 PM »
(Turning point probably isn't strictly correct term but discontinuity in rate of decline seems a bit of a mouthful.)

Are you referring to the jerk?

(speed is rate of change in distance over time.  Acceleration is rate of change in Speed. Jerk is rate of change in acceleration.  By analogy the same terms have been used for other basic derivatives.)

Jerk is nice and short rather than a mouthful. Is it a non smooth change in speed rather than a "rate of change in acceleration"?

Might work OK as long as not misinterpreted as a name calling insult. 'kink' in the graph may have different interpretation issue.

Archimid

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Re: How soon could we go ice free?
« Reply #156 on: June 18, 2018, 02:53:54 PM »
The observations in that  Tietsche et al 2011 are obsolete and nonsensical. Maybe in 2011 made sense when they thought winter temperatures will remain close to average for a few more decades.

From Tietsche et al 2011
Quote
The SST anomaly only lasts until November; by then sufficient heat has been extracted from the surface water to cool it to the freezing temperature. Sea ice then forms from open water very rapidly, and partly recovers. In the next summer the sea‐ice cover is still below normal, and larger shortwave absorption leads to a second positive SST anomaly. However, after the second year the SST anomalies are not larger than the natural variability of the reference run.

According to this model freezing doesn't start until November.  The study argues that rapid refreeze will commence then even tho air temperature will be highly anomalously warm.  Last year Chukchi Sea growth disproves this point. After a warm year, sea ice growth is slowed down to a crawl by higher temperatures.


Quote
[18] For SAT a large positive anomaly occurs between October and February after the initial perturbation, with a peak of almost 11 K in November (Figure 2). After February, there are no further SAT anomalies stronger than natural variability. The warming is mainly restricted to the lower troposphere (see auxiliary material), which is a result that has also been found in GCM studies that prescribed permanent ice‐free conditions in the Arctic Ocean [Royer et al., 1990; Winton, 2008] and in observations of recent Arctic climate change [Screen and Simmonds, 2010]. The peak of the SAT anomaly occurs about four months later than the SST anomaly; the reason for this becomes clear when considering the energy budget

This is already false, and we haven't even had a BOE in June as the study pretends to simulate. Winter temps are already surpassing the anomalies they expect after the year of the first BOE.  Heat anomalies do not end in February, they continue until the end of the freezing season. This assumption does not match observations.

As bad as this assumptions are, the model as a whole is worse. What this model is doing is assuming a one time black swan event that makes the Arctic disappear followed by perfectly normal years. That's ridiculous.
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Daniel B.

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Re: How soon could we go ice free?
« Reply #157 on: June 18, 2018, 02:55:05 PM »
(Turning point probably isn't strictly correct term but discontinuity in rate of decline seems a bit of a mouthful.)

Are you referring to the jerk?

(speed is rate of change in distance over time.  Acceleration is rate of change in Speed. Jerk is rate of change in acceleration.  By analogy the same terms have been used for other basic derivatives.)

Jerk is nice and short rather than a mouthful. Is it a non smooth change in speed rather than a "rate of change in acceleration"?

Might work OK as long as not misinterpreted as a name calling insult. 'kink' in the graph may have different interpretation issue.

Agreed.  That is roughly the year that the annual ice loss shifted from accelerating to decelerating. 

With regards to terminology, remember that all turning points have a corresponding jerk, but not all jerks have a corresponding turning point.

Dharma Rupa

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Re: How soon could we go ice free?
« Reply #158 on: June 18, 2018, 04:11:26 PM »
(Turning point probably isn't strictly correct term but discontinuity in rate of decline seems a bit of a mouthful.)

Are you referring to the jerk?

(speed is rate of change in distance over time.  Acceleration is rate of change in Speed. Jerk is rate of change in acceleration.  By analogy the same terms have been used for other basic derivatives.)

Jerk is nice and short rather than a mouthful. Is it a non smooth change in speed rather than a "rate of change in acceleration"?

Might work OK as long as not misinterpreted as a name calling insult. 'kink' in the graph may have different interpretation issue.

Agreed.  That is roughly the year that the annual ice loss shifted from accelerating to decelerating. 

With regards to terminology, remember that all turning points have a corresponding jerk, but not all jerks have a corresponding turning point.

Heheh.

The way jerk was pointed out to me by a physics professor when I was a kid, was to ask what the rate of change of acceleration was, and when I couldn't answer he said: "Jerk, jerk."  (He was a physics prof, but to me he was a climbing companion.)

Obviously, there are big jerks, and there are little jerks.



Dharma Rupa

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Re: How soon could we go ice free?
« Reply #159 on: June 18, 2018, 04:27:46 PM »
Jerk is nice and short rather than a mouthful. Is it a non smooth change in speed rather than a "rate of change in acceleration"?
If the jerk is 0 then you are smoothly accelerating.  If the jerk is high then your rate of acceleration is changing rapidly.

For example:  If you are tied to the end of a slack rope and fall you start with almost no jerk and it is like being in outer space, but when you reach the end of the rope and it stops you then the large jerk is extremely painful.


jai mitchell

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Re: How soon could we go ice free?
« Reply #160 on: June 18, 2018, 04:41:25 PM »
The observations in that  Tietsche et al 2011 are obsolete and nonsensical. Maybe in 2011 made sense when they thought winter temperatures will remain close to average for a few more decades.

From Tietsche et al 2011
Quote
The SST anomaly only lasts until November; by then sufficient heat has been extracted from the surface water to cool it to the freezing temperature. Sea ice then forms from open water very rapidly, and partly recovers. In the next summer the sea‐ice cover is still below normal, and larger shortwave absorption leads to a second positive SST anomaly. However, after the second year the SST anomalies are not larger than the natural variability of the reference run.

According to this model freezing doesn't start until November.  The study argues that rapid refreeze will commence then even tho air temperature will be highly anomalously warm.  Last year Chukchi Sea growth disproves this point. After a warm year, sea ice growth is slowed down to a crawl by higher temperatures.

Here is my bit on Tietsche et. al. from 2014

https://forum.arctic-sea-ice.net/index.php/topic,1017.msg38135.html#msg38135

Quote
Re: Arctic Summer Sea Ice transition
« Reply #2 on: October 12, 2014, 10:34:15 PM »

3.  Slow vs. fast transition.

I told you that I do not believe that tietsche correctly modeled atmospheric feedbacks in the paper.  you responded by saying that they used a GCM for the arctic.  That is good that they did, I would expect that they did.  However, I do not believe that they included the regional land and extreme ocean surface warming that a June 1 ice free state would bring.  I have seen the enthalphy increase curves for 2007 near shore ESAS and they are MASSIVE, having an ice-free state on June 1st is a scenario that has not been properly modeled.  The primary near term effect is high humidity and residual heat preventing surface air temperatures to drop far below zero for a significant period. 

The second is that the high temperature body of water below the halocline will continue to produce under ice melt.

Finally, relying on those models as a projection of future warming is not realistic because. . .

4.  DURACK et al.

You said that the information doesn't change the 1.5 to 6 C ECS value, are you sure you are not still a climate denier? (being tongue-in-cheek here)

I said that the cumulative energy gain over the last 30 years has been underestimated by between 10 and 30%.  And that the models appeared to fit the northern hemisphere.  Which likely means that the effect of northern hemisphere aerosols has also been severely understated.

These two factors indicate then that the lower range of the ECS is no possible so instead of a 1.5C it is closer to 2.5C as an unlikely minimum.  The fat tail of ECS is now fatter and the most likely value of 3C is now 3.6 to 4 C with a high end range of 8C for a doubling of CO2. 

If long and slow feedbacks are also included (i.e. albedo changes,  ice free arctic, carbon cycle responses) we are already looking to push global temperatures past 4C at CURRENT CO2 abundance levels.
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Richard Rathbone

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Re: How soon could we go ice free?
« Reply #161 on: June 19, 2018, 02:39:54 PM »
The observations in that  Tietsche et al 2011 are obsolete and nonsensical. Maybe in 2011 made sense when they thought winter temperatures will remain close to average for a few more decades.

From Tietsche et al 2011
Quote
The SST anomaly only lasts until November; by then sufficient heat has been extracted from the surface water to cool it to the freezing temperature. Sea ice then forms from open water very rapidly, and partly recovers. In the next summer the sea‐ice cover is still below normal, and larger shortwave absorption leads to a second positive SST anomaly. However, after the second year the SST anomalies are not larger than the natural variability of the reference run.

According to this model freezing doesn't start until November.  The study argues that rapid refreeze will commence then even tho air temperature will be highly anomalously warm.  Last year Chukchi Sea growth disproves this point. After a warm year, sea ice growth is slowed down to a crawl by higher temperatures.


You are misrepresenting the paper here. You are quoting from a discussion of what happens if all ice is removed from the Arctic July 1st not what happens in a typical year.

Archimid

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Re: How soon could we go ice free?
« Reply #162 on: June 19, 2018, 03:15:30 PM »
Quote
You are misrepresenting the paper here. You are quoting from a discussion of what happens if all ice is removed from the Arctic July 1st not what happens in a typical year.

Read the context. He posted that paper out of context since we are talking about the first ice free arctic, not the year after the first ice free arctic, which is the context of the paper. But if he posted thinking that there is value in examining the boundary cases then I agree with him. My reply was meant to show that even worst case scenarios like the ones examined by that 2011 paper are already proving not to be worst case at all.
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Daniel B.

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Re: How soon could we go ice free?
« Reply #163 on: June 19, 2018, 04:50:52 PM »
Are you saying that the worst case scenarios are not so, because we have not come close to experiencing them?

crandles

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Re: How soon could we go ice free?
« Reply #164 on: June 19, 2018, 05:34:40 PM »
Are you saying that the worst case scenarios are not so, because we have not come close to experiencing them?

I think he is saying

'the worst case scenarios are not so, because we have already come close to experiencing worse.'

Quote
For SAT a large positive anomaly occurs between October and February after the initial perturbation, with a peak of almost 11 K in November (Figure 2). After February, there are no further SAT anomalies stronger than natural variability.


doesn't seem to get to 11C but perhaps

does on some days in November.

This is comparing 2016 to 1958-2002 average whereas paper is presumably comparing year with ice removed to nearby years without ice removal.

Hmm. not exactly apples to apples comparison? Since both are large differences we shouldn't be surprised both show large anomalies, is partly my reaction.

Still at least there is some substance to the arguments rather than just saying Tietsche et al is 'dated'. Schroeder and Connolley reached similar conclusions to Tietsche et al.

Just saying Tietsche at al is rubbish isn't very robust/sufficiently complete, where are the rebuttal papers or where is something better?

Archimid

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Re: How soon could we go ice free?
« Reply #165 on: June 19, 2018, 06:09:08 PM »
Quote
I think he is saying

'the worst case scenarios are not so, because we have already come close to experiencing worse.'

Correct.

Quote
Just saying Tietsche at al is rubbish isn't very robust/sufficiently complete, where are the rebuttal papers or where is something better?

I don't think it is rubbish. To the contrary, I think it is a good paper, well written and provides a lot of insight. That said, I think observations make it obsolete.  The Arctic  before 2011 was a different beast from today, specially during the Arctic night.

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Re: How soon could we go ice free?
« Reply #166 on: June 19, 2018, 06:44:56 PM »
The observations in that  Tietsche et al 2011 are obsolete and nonsensical. Maybe in 2011 made sense when they thought winter temperatures will remain close to average for a few more decades.

From Tietsche et al 2011
Quote
The SST anomaly only lasts until November; by then sufficient heat has been extracted from the surface water to cool it to the freezing temperature. Sea ice then forms from open water very rapidly, and partly recovers. In the next summer the sea‐ice cover is still below normal, and larger shortwave absorption leads to a second positive SST anomaly. However, after the second year the SST anomalies are not larger than the natural variability of the reference run.

According to this model freezing doesn't start until November.  The study argues that rapid refreeze will commence then even tho air temperature will be highly anomalously warm.  Last year Chukchi Sea growth disproves this point. After a warm year, sea ice growth is slowed down to a crawl by higher temperatures.


Quote
[18] For SAT a large positive anomaly occurs between October and February after the initial perturbation, with a peak of almost 11 K in November (Figure 2). After February, there are no further SAT anomalies stronger than natural variability. The warming is mainly restricted to the lower troposphere (see auxiliary material), which is a result that has also been found in GCM studies that prescribed permanent ice‐free conditions in the Arctic Ocean [Royer et al., 1990; Winton, 2008] and in observations of recent Arctic climate change [Screen and Simmonds, 2010]. The peak of the SAT anomaly occurs about four months later than the SST anomaly; the reason for this becomes clear when considering the energy budget

This is already false, and we haven't even had a BOE in June as the study pretends to simulate. Winter temps are already surpassing the anomalies they expect after the year of the first BOE.  Heat anomalies do not end in February, they continue until the end of the freezing season. This assumption does not match observations.

As bad as this assumptions are, the model as a whole is worse. What this model is doing is assuming a one time black swan event that makes the Arctic disappear followed by perfectly normal years. That's ridiculous.

I think you misunderstand the Tietsche et al 2011.  It showing that the known feedbacks in the climate system mitigate against a tipping point where one extreme melt year leads to a perennial ice-free Arctic, at least until the greenhouse gases reach a level where the excess heat absorbed during the summer can't be released in the winter.  (BTW, those higher winter temperatures you like to talk about are evidence that the excess heat is being released.  As long as those temps are below freezing, new ice is forming.)

I entered Tietsche et al 2011 into Google Scholar and found that it has been cited 148 times since it's publication.  I can't find any of those cites that refute the findings in the paper.

Here's a 2015 paper that cites Tietsche et al 2011 and examines the trends in Arctic sea ice declines (including 2012's extreme season):

http://rsta.royalsocietypublishing.org/content/373/2045/20140159

A few excerpts from that study:

Quote
September Arctic sea ice extent over the period of satellite observations has a strong downward trend, accompanied by pronounced interannual variability with a detrended 1 year lag autocorrelation of essentially zero. We argue that through a combination of thinning and associated processes related to a warming climate (a stronger albedo feedback, a longer melt season, the lack of especially cold winters) the downward trend itself is steepening. The lack of autocorrelation manifests both the inherent large variability in summer atmospheric circulation patterns and that oceanic heat loss in winter acts as a negative (stabilizing) feedback, albeit insufficient to counter the steepening trend. These findings have implications for seasonal ice forecasting. In particular, while advances in observing sea ice thickness and assimilating thickness into coupled forecast systems have improved forecast skill, there remains an inherent limit to predictability owing to the largely chaotic nature of atmospheric variability.

Quote
The other key driver of sea ice variability, reflected in the lack of autocorrelation in the detrended September sea ice extent (and modest autocorrelation with volume), is that autumn and winter heat loss acts as a strong negative (stabilizing) feedback [5,8]. If anomalous atmospheric forcing leads to a large negative anomaly in September ice extent, there will also be large oceanic heat losses in autumn and winter from open water areas that in turn foster a large production of new ice. One manifestation of this ocean heat loss is that autumns following large negative anomalies in extent are attended by large positive anomalies in surface and lower tropospheric air temperatures. Indeed, the downward trend in September ice extent is one of the major drivers of Arctic amplification—the observed outsized rise in surface and lower tropospheric temperatures in the Arctic relative to the hemispheric average [28,29]. It follows that, unless a September with a large negative sea ice anomaly is followed by another summer with weather conditions favouring ice loss such as the DA pattern, extent will tend to climb back towards the trend line.

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Re: How soon could we go ice free?
« Reply #167 on: June 19, 2018, 08:15:08 PM »
Read the context. He posted that paper out of context since we are talking about the first ice free arctic, not the year after the first ice free arctic, which is the context of the paper.

No, you missed the two points I was making.

1)  In their model, when you perturb the system - even a perturbation as massive as removing all ice - it returns to the long-term trendline within two years.

This means that it's important for us not to get misled by single extraordinary years, but instead concentrate on the shape of that long term trendline and how it declines towards zero. The claimed two-year "memory" of the Arctic for extraordinary shocks is consistent with what we see in the real world, where there was a short-term "rebound" after both 2007 and 2012, but in each case the "rebound" only took us back up to the long-term downward trendline. 


2)  Leaving aside any of the artificial non-physical perturbations, the SHAPE of the approach to zero is not linear, not quadratic, not exponential, and not a sudden "poof" to zero.

The prediction is for a "stepped" decline with plateaus at ~5 million and ~1.5 million km^2. These plateaus are dictated by the overall geography of the Arctic and the bathymetry of the Arctic ocean. In my view regardless of whether their precise predicted timetable for the fall towards zero is accurate or not, these plateaus make physical sense, and so we should expect a similar "stepped" decline to play out in the real world.



As it happens, the real world progression of September extents seems to be reasonably close to their model, which predicts a plateau until ~2020 and then a comparatively rapid collapse to about ~1.5 million.  I would hazard a guess that we're on the verge of that transition.

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Re: How soon could we go ice free?
« Reply #168 on: June 19, 2018, 08:46:41 PM »
Quote
I think you misunderstand the Tietsche et al 2011

Ditto. A model is an abstraction of reality, some of them can be useful. In the reality created by Tietsche et al 2011 Arctic sea ice extent does not reach 0 until 2070. That goes against observations and many models, particularly more recent models.  In that universe where Arctic extent decay is so slow that it won't disappear until 2070, the arctic recovers after a BOE.

If you show me a model that predicts an ice free Arctic anywhere from now to 2040 (as the adjusted consensus indicates)and then run the same simulation we can talk.

From a few comments up thread:

Quote
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.

If you run the same experiment on a model that predicts an earlier BOE the results will be very different.
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Re: How soon could we go ice free?
« Reply #169 on: June 19, 2018, 09:11:39 PM »
Quote
I think you misunderstand the Tietsche et al 2011

Ditto. A model is an abstraction of reality, some of them can be useful. In the reality created by Tietsche et al 2011 Arctic sea ice extent does not reach 0 until 2070. That goes against observations

No it doesn't. Arctic ice has not reached zero yet, nor has the year reached 2070.


...and many models, particularly more recent models. 

This would be more believable if you linked to the models and publications derived therefrom.

In that universe where Arctic extent decay is so slow that it won't disappear until 2070, the arctic recovers after a BOE.

I wish I hadn't mentioned the BOE aspect.  The point I was making was not about what happens in the event of a BOE, it was to discuss the shape of the way the long term trend approaches zero, i.e. a stepped decline.  The Tietsche model is not really "so slow" - it predicts that the current slight plateau is temporary, that the trendline is about to accelerate sharply downwards, that there will be a rapid collapse over about a decade or so to leave a rump of about 1.5 million square km hanging out above Greenland.  Their error bars show a dip below 1 million square km (i.e. the generally accepted "ice free" threshold for the Arctic) as early as 2035.

If even that isn't alarmist enough for you, I honestly don't know what to say.

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Re: How soon could we go ice free?
« Reply #170 on: June 19, 2018, 09:18:40 PM »
Seriously - ignore the blue bits on this and just look at the black line and dotted surround, i.e. the long term trend and the variability around that trend.

The variability goes below 1 million square km from 2035 onwards, i.e. it's predicting that from 2035 onwards, a "bad year" for the Arctic will count as ice-free for the entire month of September, not just a day or so.  From ~2055 on, the UPPER bound is below 1 million, meaning that EVERY year is ice-free for the entire month of September, even the good years.

This paper, and that graph are SCARY AS FUCK.  They say we are on the edge of a precipitate decline (the trend from ~2020-2035 is 2.5x the trend from 1985 to 2010) to a "remnant rump" state with a residual amount of ice hanging around northern Greenland.
« Last Edit: June 19, 2018, 09:24:44 PM by Peter Ellis »

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Re: How soon could we go ice free?
« Reply #171 on: June 19, 2018, 09:44:34 PM »
I see a lot of discussion of "models" but I still have never seen any good analysis for demonstrated skill of same.

A good weather model does well three days out.  Please show me a global model that does a good job three years out.

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Re: How soon could we go ice free?
« Reply #172 on: June 19, 2018, 10:28:08 PM »
You can't compare weather and GCM models like that. They do different things. It is actually a climate risk denier talking point.

A GCM can't tell you what whether it will be on August 7th 2021. It can, however, give you an idea of how much warmer it will be globally on average in 2100, given various conditions.

There are hundreds of examples of climate models accurately predicting things, because they rely on physics. That doesn't mean they're perfect. No tool is perfect.
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Dharma Rupa

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Re: How soon could we go ice free?
« Reply #173 on: June 20, 2018, 01:09:10 AM »
A GCM can't tell you what whether it will be on August 7th 2021. It can, however, give you an idea of how much warmer it will be globally on average in 2100, given various conditions.

I personally think our fate was sealed by the Industrial Revolution 200 years ago.

Archimid

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Re: How soon could we go ice free?
« Reply #174 on: June 20, 2018, 03:03:22 AM »
Quote
Seriously - ignore the blue bits on this and just look at the black line and dotted surround, i.e. the long term trend and the variability around that trend.


Let me try again. In a model where ice hits 0 in 2070, ice will not return after 2070. In this model ice hits 0 in 2070 and it doesn't return afterwards. If the model predicted 0 ice by 2030, then Ice probably wouldn't return afterwards.  All this "perturbations" are artificially induced.
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Archimid

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Re: How soon could we go ice free?
« Reply #175 on: June 20, 2018, 03:40:04 AM »

No it doesn't. Arctic ice has not reached zero yet, nor has the year reached 2070.

Ok. I'll rephrase. The model observations for the period after an ice free Arctic do not match recent winter warming observations

Quote
This would be more believable if you linked to the models and publications derived therefrom.


As I said, I got those numbers from a paper posted a few comments ago in this thread. Look it up.

Quote

I wish I hadn't mentioned the BOE aspect.  The point I was making was not about what happens in the event of a BOE, it was to discuss the shape of the way the long term trend approaches zero, i.e. a stepped decline.  The Tietsche model is not really "so slow" - it predicts that the current slight plateau is temporary, that the trendline is about to accelerate sharply downwards, that there will be a rapid collapse over about a decade or so to leave a rump of about 1.5 million square km hanging out above Greenland.  Their error bars show a dip below 1 million square km (i.e. the generally accepted "ice free" threshold for the Arctic) as early as 2035. [/quote

If even that isn't alarmist enough for you, I honestly don't know what to say.

It is not alarmist enough. Even if that model was the best model our physics were capable of showing, it is still a model with tons of uncertainties. A bad freeze year followed by a 2012 like melt year is probably enough for the Arctic to go ice free any year now.   
 
Policy makers need to know this risk. They can't go in thinking "there is no chance for this to happen in less than 20 years" or something like that. They need to know there is imminent danger ahead and could happen sooner than expected.
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bbr2314

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Re: How soon could we go ice free?
« Reply #176 on: June 20, 2018, 03:48:26 AM »
You can't compare weather and GCM models like that. They do different things. It is actually a climate risk denier talking point.

A GCM can't tell you what whether it will be on August 7th 2021. It can, however, give you an idea of how much warmer it will be globally on average in 2100, given various conditions.

There are hundreds of examples of climate models accurately predicting things, because they rely on physics. That doesn't mean they're perfect. No tool is perfect.
I think the albedo situation this spring has disproven the climate models. It may not yet be apparent but as we see repeats / worsening of this year's event as we head deeper into the 2020s, it is going to be obvious. It is actually a far worse scenario than current projections but because it doesn't follow a line directly upwards the negative impacts are incomprehensible to most of the apes.

In any case I don't take give models beyond the simulations of Hansen et. al any dose of credibility. They are literally so wrong as to be absurd.

bbr2314

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Re: How soon could we go ice free?
« Reply #177 on: June 20, 2018, 03:53:14 AM »
The models show blanket red etc. Patently absurd. 2018 is proving we are at an inflection point / entering hysteresis in transition to colder continents + growing ice sheets, and the switch could accelerate exceedingly quickly.

By the 2030s I think the current scientific thought will be derided on a scale worse than the 70s projections for cooling, that is, if we haven't blown up the planet due to crop failures etc by then.


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Re: How soon could we go ice free?
« Reply #178 on: June 20, 2018, 02:18:07 PM »
You can't compare weather and GCM models like that. They do different things. It is actually a climate risk denier talking point.

A GCM can't tell you what whether it will be on August 7th 2021. It can, however, give you an idea of how much warmer it will be globally on average in 2100, given various conditions.

There are hundreds of examples of climate models accurately predicting things, because they rely on physics. That doesn't mean they're perfect. No tool is perfect.
I think the albedo situation this spring has disproven the climate models. It may not yet be apparent but as we see repeats / worsening of this year's event as we head deeper into the 2020s, it is going to be obvious. It is actually a far worse scenario than current projections but because it doesn't follow a line directly upwards the negative impacts are incomprehensible to most of the apes.

In any case I don't take give models beyond the simulations of Hansen et. al any dose of credibility. They are literally so wrong as to be absurd.

Yes, but I believe that is because the models do not know how to handle many of the heat transfer effects.  Open water will absorb more heat in summer, but lose more in winter.  How do these compare?  Clouds are having a much greater effect than anticipated, as evidenced by cooler summer temperatures.  Increased snowfall in areas is having a large albedo effect.  Obviously, the models predicted an ice-free Arctic several years ago were wrong, but what about those predicting ice-free in the 2020s, 2060s, never?

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Re: How soon could we go ice free?
« Reply #179 on: June 20, 2018, 02:59:52 PM »
Obviously, the models predicted an ice-free Arctic several years ago were wrong, but what about those predicting ice-free in the 2020s, 2060s, never?

What models? Only extrapolations produced results like in 2020s or 2016 +/-3 years

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Re: How soon could we go ice free?
« Reply #180 on: June 20, 2018, 03:46:19 PM »
Obviously, the models predicted an ice-free Arctic several years ago were wrong, but what about those predicting ice-free in the 2020s, 2060s, never?

What models? Only extrapolations produced results like in 2020s or 2016 +/-3 years

Is not an extrapolation just a continuation of a model outside of the data range?

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Re: How soon could we go ice free?
« Reply #181 on: June 20, 2018, 04:05:29 PM »
Obviously, the models predicted an ice-free Arctic several years ago were wrong, but what about those predicting ice-free in the 2020s, 2060s, never?

What models? Only extrapolations produced results like in 2020s or 2016 +/-3 years

Is not an extrapolation just a continuation of a model outside of the data range?

crandles is right.  No well-known models projected an ice-free Arctic earlier than 2016+/-3.  Unlike the people using the models, I don't think the people making the models really believe them yet.


crandles

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Re: How soon could we go ice free?
« Reply #182 on: June 20, 2018, 04:57:46 PM »
What models? Only extrapolations produced results like in 2020s or 2016 +/-3 years
Is not an extrapolation just a continuation of a model outside of the data range?

That is talking about extrapolating a model but the data extrapolations use actual data not model output.

It may well be possible to claim a data extrapolation is a model but it is a very simple naive model whereas a GCM type model has lots of physics built into it. Very different things even if you want to claim the term model can be applied to both.

crandles

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Re: How soon could we go ice free?
« Reply #183 on: June 20, 2018, 05:11:57 PM »
Maybe there are some but not many. If they are outliers perhaps we shouldn't pay too much attention to such outliers.

Overland and Wang 2013 paper "When will the summer Arctic be nearly sea ice free?" abstract includes

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/grl.50316

Quote
Three recent approaches to predictions in the scientific literature are as follows: (1) extrapolation of sea ice volume data, (2) assuming several more rapid loss events such as 2007 and 2012, and (3) climate model projections. 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.

Graph from paper:

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Re: How soon could we go ice free?
« Reply #184 on: June 20, 2018, 05:37:45 PM »
Yes, that graph is from 89 ensemble runs under RCP8.5 emission scenario.  The mean value is still above 1.0 M km2 by 2100.  The large variability is due to how much weight is placed on various factors, such as albedo, clouds, radiation losses, and observational data. 

jai mitchell

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Re: How soon could we go ice free?
« Reply #185 on: June 20, 2018, 05:56:29 PM »
Yes, that graph is from 89 ensemble runs under RCP8.5 emission scenario.  The mean value is still above 1.0 M km2 by 2100.  The large variability is due to how much weight is placed on various factors, such as albedo, clouds, radiation losses, and observational data.

The test of whether a model is good or not is performed by seeing how it has been able to replicate historic conditions.  If it is good at that then it is a pretty good bet that it will do well going forward.

There is no good models in that squiggly bunch of lines that I can see.

the best  and most recent assessment on climate science says the following:

https://science2017.globalchange.gov/chapter/15/

Quote
Another surprise has come from arctic sea ice. While the potential for powerful positive ice-albedo feedbacks has been understood since the late 19th century, climate models have struggled to capture the magnitude of these feedbacks and to include all the relevant dynamics that affect sea ice extent. As of 2007, the observed decline in arctic sea ice from the start of the satellite era in 1979 outpaced the declines projected by almost all the models used by the Intergovernmental Panel on Climate Change’s Fourth Assessment Report (AR4), and it was not until AR4 that the IPCC first raised the prospect of an ice-free summer Arctic during this century. More recent studies are more consistent with observations and have moved the date of an ice-free summer Arctic up to approximately mid-century (see Ch. 11: Arctic Changes). But continued rapid declines—2016 featured the lowest annually averaged arctic sea ice extent on record, and the 2017 winter maximum was also the lowest on record—suggest that climate models may still be underestimating or missing relevant feedback processes. These processes could include, for example, effects of melt ponds, changes in storminess and ocean wave impacts, and warming of near surface waters. , ,

and

Quote
third potential tipping element is arctic sea ice, which may exhibit abrupt state shifts into summer ice-free or year-round ice-free states. , As discussed above, climate models have historically underestimated the rate of arctic sea ice loss. This is likely due to insufficient representation of critical positive feedbacks in models. Such feedbacks could include: greater high-latitude storminess and ocean wave penetration as sea ice declines; more northerly incursions of warm air and water; melting associated with increasing water vapor; loss of multiyear ice; and albedo decreases on the sea ice surface (e.g., Schröder et al. 2014; Asplin et al. 2012; Perovich et al. 2008 ). At the same time, however, the point at which the threshold for an abrupt shift would be crossed also depends on the role of natural variability in a changing system; the relative importance of potential stabilizing negative feedbacks, such as more efficient heat transfer from the ocean to the atmosphere in fall and winter as sea declines; and how sea ice in other seasons, as well as the climate system more generally, responds once the first “ice-free” summer occurs (e.g., Ding et al. 2017 ). It is also possible that summer sea ice may not abruptly collapse, but instead respond in a manner proportional to the increase in temperature. , , , Moreover, an abrupt decrease in winter sea ice may result simply as the gradual warming of Arctic Ocean causes it to cross a critical temperature for ice formation, rather than from self-reinforcing cycles.
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crandles

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Re: How soon could we go ice free?
« Reply #186 on: June 20, 2018, 05:57:15 PM »
The mean value is still above 1.0 M km2 by 2100.

The models keeping mean value above 1m km^2 by 2100, have absurdly high levels of ice at all times, way above what we actually have now. Obviously these models do their own thing and have not been adjusted to observations. If they were adjusted to realistic ice now by moving line up or down to match observation or applying a scaling factor, the projections arrived at would be much more consistent.

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Re: How soon could we go ice free?
« Reply #187 on: June 20, 2018, 06:58:21 PM »
Yes, that graph is from 89 ensemble runs under RCP8.5 emission scenario.  The mean value is still above 1.0 M km2 by 2100.  The large variability is due to how much weight is placed on various factors, such as albedo, clouds, radiation losses, and observational data. 

Due to the non-normal distribution of the models mean should not be counted, median is the correct value to use.  Basically the models in red are ridiculous outliers that are shifting the mean too high.

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Re: How soon could we go ice free?
« Reply #188 on: June 20, 2018, 07:46:46 PM »
The mean value is still above 1.0 M km2 by 2100.

The models keeping mean value above 1m km^2 by 2100, have absurdly high levels of ice at all times, way above what we actually have now. Obviously these models do their own thing and have not been adjusted to observations. If they were adjusted to realistic ice now by moving line up or down to match observation or applying a scaling factor, the projections arrived at would be much more consistent.

Yes.  Those are probably the models giving low weighted value to the observational data.  Hard to say if the observations will ever match those models again.

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Re: How soon could we go ice free?
« Reply #189 on: June 20, 2018, 08:10:45 PM »
Yes, that graph is from 89 ensemble runs under RCP8.5 emission scenario.  The mean value is still above 1.0 M km2 by 2100.  The large variability is due to how much weight is placed on various factors, such as albedo, clouds, radiation losses, and observational data.
The mean is the wrong measure to use when there are significant outliers like the red series of lines.  Try something more robust like the median.  A median which - with five more years of data to include after the plotted values that stop at 2017 - the real world is pretty much bang on.

Of course, do also remember that this isn't a prediction of the FIRST ice free year.  When the median hits 1.0 M km^2 (in around 2045), it means that ~every other year will be ice free.  The first ice-free year could easily come a decade earlier in 2035 or so.

Dharma Rupa

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Re: How soon could we go ice free?
« Reply #190 on: June 20, 2018, 09:10:45 PM »
The test of whether a model is good or not is performed by seeing how it has been able to replicate historic conditions.  If it is good at that then it is a pretty good bet that it will do well going forward.

Actually, I have to disagree with that.  I have never seen any analysis of skill that indicated that hindcast models are better at predicting the future.  They can be better at predicting the past...

crandles

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Re: How soon could we go ice free?
« Reply #191 on: June 21, 2018, 12:48:46 AM »

The models keeping mean value above 1m km^2 by 2100, have absurdly high levels of ice at all times, way above what we actually have now. Obviously these models do their own thing and have not been adjusted to observations. If they were adjusted to realistic ice now by moving line up or down to match observation or applying a scaling factor, the projections arrived at would be much more consistent.

Yes.  Those are probably the models giving low weighted value to the observational data.  Hard to say if the observations will ever match those models again.

No, observational data haven't been given low weight. Observational data just is not a feature of how the model works at all.

crandles

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Re: How soon could we go ice free?
« Reply #192 on: June 21, 2018, 12:55:15 AM »
The test of whether a model is good or not is performed by seeing how it has been able to replicate historic conditions.  If it is good at that then it is a pretty good bet that it will do well going forward.

Actually, I have to disagree with that.  I have never seen any analysis of skill that indicated that hindcast models are better at predicting the future.  They can be better at predicting the past...

I have to disagree with that. Everybody believes models(/parameter sets) that do well in hindcast mode will in general be better in forecast mode. Very little has been done with this because it opens up all sorts of tricky issues. Which data obs do you use to say a model is good? Inevitable you want lots of data not just a single data item to be good but then how do you weight importance of each.

Dharma Rupa

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Re: How soon could we go ice free?
« Reply #193 on: June 21, 2018, 02:50:50 AM »
...believes...

I think that is the operative word there.  I believe lots of things I do not have sufficient data to demonstrate.  Maybe in 100 years we will have enough data about the models to know which ones actually have any skill.


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Re: How soon could we go ice free?
« Reply #194 on: June 22, 2018, 01:28:04 PM »
Since the ice loss will not be linear, arguing which linear function is best is ridiculous.

Quote
The distinction between linear and nonlinear systems in mathematics defines the boundary between the relatively knowable, and the frustratingly elusive. Both types of systems can describe the dynamics of many different processes, such as planets orbiting each other, fluctuations in animal populations, the behavior of electrical circuits, and so on. The difference between linear and nonlinear lies in the details of the equations that govern how these systems interact. For systems that behave linearly, it is relatively easy to find exact solutions that we can use to predict future behavior within the system. For nonlinear systems, we are lucky to find any such solution. Indeed, in nonlinear dynamics, we often have to redefine what we consider to be a solution.

Here is an excellent introduction to Sensitive Dependence, Iteration, Bifurcation and Feigenbaum's Constants.

http://www.learner.org/courses/mathilluminated/units/13/textbook/04.php
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Daniel B.

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Re: How soon could we go ice free?
« Reply #195 on: June 22, 2018, 03:37:32 PM »
Since the ice loss will not be linear, arguing which linear function is best is ridiculous.

Quote
The distinction between linear and nonlinear systems in mathematics defines the boundary between the relatively knowable, and the frustratingly elusive. Both types of systems can describe the dynamics of many different processes, such as planets orbiting each other, fluctuations in animal populations, the behavior of electrical circuits, and so on. The difference between linear and nonlinear lies in the details of the equations that govern how these systems interact. For systems that behave linearly, it is relatively easy to find exact solutions that we can use to predict future behavior within the system. For nonlinear systems, we are lucky to find any such solution. Indeed, in nonlinear dynamics, we often have to redefine what we consider to be a solution.

Here is an excellent introduction to Sensitive Dependence, Iteration, Bifurcation and Feigenbaum's Constants.

http://www.learner.org/courses/mathilluminated/units/13/textbook/04.php

Very nice.  For most systems, there exists a zone of linearity, beyond which a linear function fails.

RoxTheGeologist

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Re: How soon could we go ice free?
« Reply #196 on: June 22, 2018, 06:36:49 PM »
Since the ice loss will not be linear, arguing which linear function is best is ridiculous.

Quote
The distinction between linear and nonlinear systems in mathematics defines the boundary between the relatively knowable, and the frustratingly elusive. Both types of systems can describe the dynamics of many different processes, such as planets orbiting each other, fluctuations in animal populations, the behavior of electrical circuits, and so on. The difference between linear and nonlinear lies in the details of the equations that govern how these systems interact. For systems that behave linearly, it is relatively easy to find exact solutions that we can use to predict future behavior within the system. For nonlinear systems, we are lucky to find any such solution. Indeed, in nonlinear dynamics, we often have to redefine what we consider to be a solution.

Here is an excellent introduction to Sensitive Dependence, Iteration, Bifurcation and Feigenbaum's Constants.

http://www.learner.org/courses/mathilluminated/units/13/textbook/04.php

Very nice.  For most systems, there exists a zone of linearity, beyond which a linear function fails.

e.g. Newtonian and Relativist laws of motion.... Newtonian physics are very linear at small fractions of the speed of light.

litesong

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Re: How soon could we go ice free?
« Reply #197 on: June 23, 2018, 01:49:24 AM »
Average Arctic sea ice VOLUME for June 1, for the period 1980-89, was ~ 29,000 cubic kilometers. Present June 1, 2018 sea ice VOLUME was ~ 20,000 cubic kilometers, ~ 9000 cubic kilometers less than the 1980-89 period for June 1, the equivalent energy needed to melt such...... 28 times the annual energy consumption of the USA.
« Last Edit: June 23, 2018, 02:58:44 AM by litesong »

Cid_Yama

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Re: How soon could we go ice free?
« Reply #198 on: June 23, 2018, 02:14:49 AM »
Since the ice loss will not be linear, arguing which linear function is best is ridiculous.

Quote
The distinction between linear and nonlinear systems in mathematics defines the boundary between the relatively knowable, and the frustratingly elusive. Both types of systems can describe the dynamics of many different processes, such as planets orbiting each other, fluctuations in animal populations, the behavior of electrical circuits, and so on. The difference between linear and nonlinear lies in the details of the equations that govern how these systems interact. For systems that behave linearly, it is relatively easy to find exact solutions that we can use to predict future behavior within the system. For nonlinear systems, we are lucky to find any such solution. Indeed, in nonlinear dynamics, we often have to redefine what we consider to be a solution.

Here is an excellent introduction to Sensitive Dependence, Iteration, Bifurcation and Feigenbaum's Constants.

http://www.learner.org/courses/mathilluminated/units/13/textbook/04.php

Very nice.  For most systems, there exists a zone of linearity, beyond which a linear function fails.

e.g. Newtonian and Relativist laws of motion.... Newtonian physics are very linear at small fractions of the speed of light.

And how does that even come close to applying to the subject at hand?  Either: 1. You do not understand the math.  or 2. That was an attempt to obfuscate.

The article I linked to was designed to allow even a layman to understand.  Give it a try.

Might I suggest starting back a page, or even from the introduction on the link I gave.  Give special attention to Poincare.

http://www.learner.org/courses/mathilluminated/units/13/textbook/03.php
« Last Edit: June 23, 2018, 02:47:40 AM by Cid_Yama »
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gerontocrat

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Re: How soon could we go ice free?
« Reply #199 on: June 30, 2018, 12:33:44 PM »
Nice article at https://www.carbonbrief.org/atlantification-arctic-sea-tipping-towards-new-climate-regime

Specifically on the process of Atlantification of the Barents Sea. It seems that the process that inhibits winter re-freeze is the key. I attach a graph that seems to illustrate that (though 2018 bucked the trend).

And I've added an image from the article.
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