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

2018-2019
12 (17.9%)
2020-2025
21 (31.3%)
2026-2030
13 (19.4%)
2031-2040
15 (22.4%)
2041-2060
2 (3%)
2061-2080
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2081-2099
1 (1.5%)
2100-beyond
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Total Members Voted: 64

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

Author Topic: When will the Arctic Go Ice Free?  (Read 124048 times)

philopek

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Re: When will the Arctic Go Ice Free?
« Reply #1250 on: October 12, 2019, 08:34:19 PM »
All good points philopek, but here is an alternate view:   

Those are valid ways to see things. As we all know it's quite complex system about which it's hard or even impossible to tell exactly what happens and certainly even harder to tell exactly when and in which order.

Therefore it's a good thing to think through things from various angles. The only opinions I have serious issues with is "re-glaciation" or a long term rebound while the rest of the planet including it's oceans is getting warmer and gaining momentum doing so.

I for on am very reluctant to discuss whether we lost and/or are currently loosing ice mass, for me it's a fact that we do, while how fast and touching which way-points in the process some can make educated guesses bordering to calculations, most of us can make educated guesses based on observations and information form places like the ASIF and those who promote outrageous provocations for profiling purposes I try to avoid with intermittent success ;)

Thanks for your contribution, very much appreciated, content and attitude wise.

gerontocrat

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Re: When will the Arctic Go Ice Free?
« Reply #1251 on: October 13, 2019, 08:44:10 PM »
By the way, I still think that endless discussions on what charts that use extent & area are best to predict an ice-free Arctic are a waste of time because:-
- CO2 ppm is increasing at an accelerating rate (looks like will at 3 ppm per year this year)
- There is evidence that the Carbon Sinks are not doing so well, (recent post by AbruptSLR re the Southern Ocean & some work I did on carbon sinks c.f. emissions and CO" increases),
- Global Surface ar temps at record levels in an ENSO neutral year plus scary WMO report on recent trends.

BUT - I read the NSIDC talking about a hiatus in extent loss & I think it is WRONG.. Even though they emphasise caveats & the need to look at longer-term trends, it is God's gift to the denier industry.

So here is a 2nd post about it.
____________________________________________

By why stop with your so-called exaggerated years in one direction only?  If your are going to selectively discard data points, why not toss out the high years of 2000 and 2006 also?

Indeed, why not? So I googled to refresh my hazy memory of a Uni course on Mathematical Statistics to fin the standard methodology for identification of outliers. (That course was so long ago for analysis we did it by hand on mechanical machine Babbage would have recognised.)

It got wider - seems to be a big thing in machine learning (AI ?):-

https://machinelearningmastery.com/how-to-use-statistics-to-identify-outliers-in-data/
Machine Learning Mastery
How to Use Statistics to Identify Outliers in Data

Sometimes a dataset can contain extreme values that are outside the range of what is expected and unlike the other data. These are called outliers and often machine learning modeling and model skill in general can be improved by understanding and even removing these outlier values.

- An outlier is an unlikely observation in a dataset and may have one of many causes.
-Standard deviation can be used to identify outliers in Gaussian or Gaussian-like data.
- The interquartile range can be used to identify outliers in data regardless of the distribution.

I followed the recognised  interquartile range method using absolute deviations from the "expected" value from the linear regression used by NSIDC & me in these graphs

For NSIDC Extent it told me to dump an extra year, the very high extent value in 1996.

I did they same analysis or PIOMAS September volume, and it told me to dump 3 years, all very low values, 1981, 1982, and 2012.

The answers re all the same -
- there is barely any change from the linear regression with or without the "outlier years",
- there is no "hiatus" in the steady loss of Arctic Sea Ice extent as implied on the 3rd October  NSIDC analysis (https://nsidc.org/arcticseaicenews/)

Quote
Within the overall decline, it is notable that the most recent 13 years, from 2007 to 2019, have shown very little decline (Figure 3b). Both 2007 and 2012 were extreme low extent years, and variability has been high in this period. However, an earlier 13 year period, 1999 to 2012, shows a rate of decline that is more than double the overall rate in the satellite record. This illustrates the challenge of extracting a quantitative rate of decline in a highly variable system like sea ice, and the benefits of looking at decadal, and not year-to-year variations.
"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)

philopek

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Re: When will the Arctic Go Ice Free?
« Reply #1252 on: October 13, 2019, 11:29:58 PM »
Extremely well explained @gerontocrat

If there is anything where I'm in agreement with the vast majority, which is rare ;) ;) it's that it's a real pleasure and very enlightening to read through your posts.

gandul

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Re: When will the Arctic Go Ice Free?
« Reply #1253 on: October 13, 2019, 11:59:00 PM »
Still you should leave those years there. Well-intentioned mods as yours can give deniers arguments as much as discussing a hiatus. The statistical tendency backed by almost 40 years is clear without needing tweaks.
No me lo trago

gandul

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Re: When will the Arctic Go Ice Free?
« Reply #1254 on: October 14, 2019, 12:03:25 AM »
Also, outliers are more justified when doing a statistical analysis with samples prone to unfrequent but existing large measurement errors, manufacturing defects caused by a distress in the production line, etc.

September average of NSIDC has an intrinsic range of uncertainty that is already very small, so there’s no reason to discard a year against another years, unless you accept discarding the product of nature itself.
No me lo trago

philopek

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Re: When will the Arctic Go Ice Free?
« Reply #1255 on: October 14, 2019, 01:07:44 AM »
Still you should leave those years there. Well-intentioned mods as yours can give deniers arguments as much as discussing a hiatus. The statistical tendency backed by almost 40 years is clear without needing tweaks.

Also a good and valid point but you know what?

While this will take nothing away from your reasoning (not kidding) one of the ways a denier
is distinguished from a realistic and honest thinker is, that it does not matter what we tell them.
because they DENY facts ;) ;)

In other words, your point is valid and Gero's point is valid, and the results are very close and the tendency is obvious (even without tweaks) but since a denier denies ANY valid point, there is no
point in spending a lot of time and energy to find out which of all the valid points we want to
present to a DENIER to DENY ;)

[half kidding but true nevertheless]

Shared Humanity

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Re: When will the Arctic Go Ice Free?
« Reply #1256 on: October 14, 2019, 02:05:34 AM »
Extremely well explained @gerontocrat

If there is anything where I'm in agreement with the vast majority, which is rare ;) ;) it's that it's a real pleasure and very enlightening to read through your posts.

I agree...great post.

Aporia_filia

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Re: When will the Arctic Go Ice Free?
« Reply #1257 on: October 14, 2019, 11:09:19 AM »
^^^Great post Gero. Great person You.

gerontocrat

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Re: When will the Arctic Go Ice Free?
« Reply #1258 on: October 14, 2019, 09:21:59 PM »
One thing is for sure - the linear trends of PIOMAS volume & NSIDC Area can't go on for many more years.

If they did continue, average September thickness in the year 2030 would be 25 centimetres.

See attached
________________________

In my work on deviations from the average, I came up with the following.

The climate / ice system is complex, but all the processes depend on well-known basic physics. It is the interaction that creates the complexity. And physics imposes limits. E.g. If carbon sinks completely failed, i.e. all CO2 emissions stayed in the atmosphere, the current rate of emissions would produce a maximum annual increase in CO2 ppm of around 5 ppm.

So the deviations from the average trend in a year of extent, area and volume are also limited by the current limits to variations in climate and all the other variables affecting ice loss and gain.

So my speculation that belongs to me is that the maximum variations - both more & less - in the last 40 years are a good guide to the absolute minimum and maximum September minimum possible in the next year.

For Extent that suggests the following ranges....
- a 2020 NSIDC September Average Extent minimum of around 4.3 million km2 +20%/-30%,
- a 2020 PIOMAS  September Average Volume  minimum of around 4.0 thousand KM3 +25%/-40% million WHOOPS.
« Last Edit: October 15, 2019, 06:08:07 PM by gerontocrat »
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Glen Koehler

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Re: When will the Arctic Go Ice Free?
« Reply #1259 on: October 14, 2019, 10:59:29 PM »
     
     Extrapolating any trend line too far beyond the data used to define it is prone to error, but less so for a straight line trend, and much less so for extending a straight line trend by a single data point.  The Wipenus linear Sept. minimum volume trend graph
https://forum.arctic-sea-ice.net/index.php/topic,119.msg232085.html#msg232085
shows the 95% confidence interval for the 2020 ASI September minimum volume as 2.0 to 5.5 million km3.  The +/- 1 standard deviation range shows that the 2020 minimum volume has a 68% chance of being between 3.0 and 4.5 million km3.

     A downward trend at a consistent absolute rate of about 333,000 km3 per year becomes an increasing percentage of the total as the total shrinks.  Back in 1980, losing 0.3M km3 represented less than 2% of the total.  A 0.3M loss between 2019 and 2020 would be a greater than 8% year to year decline.   

     As we approach 3M then 2M annual volume minimums (not that far off according the trendline at 2022 and 2026, respectively), continued declines would become more visually dramatic.  And the ratio of % Extent loss to % Volume loss has to increase as the zero point nears.  The advantage of ASI as a visual marker for global warming will likely become more prominent in media coverage.  Neven may have to start wearing sunglasses in public.   8)

     As Sept. average ice thickness nears 1 meter that suggests (to me at least) that the final phase of September ASI losses may accelerate despite countervailing issues like the final ice being at higher latitude with shorter summer solar input, deeper bathymetry, sparser winter ice allowing more heat loss from ocean to atmosphere etc.  The resistance of sea ice to melt is NOT linear.  It decreases faster than thickness.  1 meter thick ice requires significantly less than 50% of the melting power as 2 meter thick ice. 

      Declining ice quality could be another accelerating factor.   The fortress of hard core MYI ice that used to persist along the northern coast of Greenland and the CAA took a serious hit in 2019, (see https://forum.arctic-sea-ice.net/index.php/topic,2839.msg232342.html#msg232342)
And as far as I know, the CAA garlic press ridging did not really occur in 2019.  The qualitative effect that reduced ice quality will have on the melting pattern in 2020 will be morbidly interesting to watch.

     But that is next year.  Right now the developing story of low refreeze and a possible record low April maximum volume is almost as compelling as summer progression to the September minimum.  So thanks to gerontocrat, Juan C. Garcia and others for continuing to post updates.
« Last Edit: October 14, 2019, 11:39:16 PM by Glen Koehler »

binntho

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Re: When will the Arctic Go Ice Free?
« Reply #1260 on: October 15, 2019, 07:35:38 AM »
As much as I agree with the two eminent posters above, the following sentence intrigued me:

1 meter thick ice requires significantly less than 50% of the melting power as 2 meter thick ice. 

If I understand Glen correctly, he is saying that even if "melting power" (however quantified) increases linearly, the resulting melt does not increase linearly (or, perhaps more precisely, will cease to increase linearly in the near future).

Sounds reasonable, and I'd tend to agree. But it's still unsubstantiated - what is "melting power" and is it quantifiable? I would guess that time would be a factor in "melting power", i.e. the number of days of above-freezing temperatures or with clear skies or with strong wave action would all contribute to increased melt - but at a non-linear rate as Glen indicates? I'm not sure.

Surface area / volume rises non-linearly as volume falls, but is that really a factor when it comes to ASI annual melt?

So what other non-linear factors included in "melting power" could cause 1m thick ice to be significantly easier to melt than 2m thick ice?
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crandles

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Re: When will the Arctic Go Ice Free?
« Reply #1261 on: October 15, 2019, 11:54:09 AM »
1 meter thick ice requires significantly less than 50% of the melting power as 2 meter thick ice. 

If I understand Glen correctly, he is saying that even if "melting power" (however quantified) increases linearly, the resulting melt does not increase linearly (or, perhaps more precisely, will cease to increase linearly in the near future).

...

So what other non-linear factors included in "melting power" could cause 1m thick ice to be significantly easier to melt than 2m thick ice?

A major difference will be albedo, I think. So your "melting power" is incoming solar and LW radiation. More of this is absorbed by thin ice (under .5m ish ?) so takes less than half the time. There are other effects:

2. Ability of waves to break up the ice and increase the surface area relative to volume.

3. Warm water (polyna/open water absorb more radiation) being forced by currents under ice affect melting rate of lets say bottom 1cm. That bottom 1cm is higher proportion of 1m ice than 2m ice.
and probably other effects.

binntho

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Re: When will the Arctic Go Ice Free?
« Reply #1262 on: October 15, 2019, 12:41:13 PM »
1 meter thick ice requires significantly less than 50% of the melting power as 2 meter thick ice. 
So what other non-linear factors included in "melting power" could cause 1m thick ice to be significantly easier to melt than 2m thick ice?

A major difference will be albedo, I think. So your "melting power" is incoming solar and LW radiation. More of this is absorbed by thin ice (under .5m ish ?) so takes less than half the time. There are other effects:

2. Ability of waves to break up the ice and increase the surface area relative to volume.

3. Warm water (polyna/open water absorb more radiation) being forced by currents under ice affect melting rate of lets say bottom 1cm. That bottom 1cm is higher proportion of 1m ice than 2m ice.
and probably other effects.
I agree that as the proportion of open ocean increases, the rest of the ice will have a harder time resisting things like high SST's in the ice-free areas, and increased wave action etc. all of which adds up to "melting power"

But none of that is directly tied to ice thickness. Changes in albedo of the ice itself (or rather, how much radiation makes it through the ice and into the top layer of the underlying ocean) will be related to thickness, and I'd expect that this would be a big effect when comparing say 0.5m with 0.25m. But is it significant when comparing 2m with 1m?
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kassy

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Re: When will the Arctic Go Ice Free?
« Reply #1263 on: October 15, 2019, 01:45:49 PM »
Quote
1 meter thick ice requires significantly less than 50% of the melting power as 2 meter thick ice.


Most of this ice will be really young and thus saltier and easier to melt with the same ´melting power´.

Þetta minnismerki er til vitnis um að við vitum hvað er að gerast og hvað þarf að gera. Aðeins þú veist hvort við gerðum eitthvað.

binntho

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Re: When will the Arctic Go Ice Free?
« Reply #1264 on: October 15, 2019, 01:58:10 PM »
Quote
1 meter thick ice requires significantly less than 50% of the melting power as 2 meter thick ice.


Most of this ice will be really young and thus saltier and easier to melt with the same ´melting power´.
I'm not at all sure that this is correct. Younger and saltier ice is going to be easier to melt, and younger ice will tend to be thinner, but that is not enough to explain why 1m thick ice in general would melt significantly faster than 2m ice given the same "melting power".

At the start of the melting season, a large proportion of the ice is 1m or less, and this ice tends to melt out every year anyway. The remaining ice starts out at being thicker than 1m or even thicker than 2m. Given constant "melting power", does the melt-rate incrase as the ice gets thinner in such a way that there will be a "significant" difference between 2m and 1m ice?
because a thing is eloquently expressed it should not be taken to be as necessarily true
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macid

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Re: When will the Arctic Go Ice Free?
« Reply #1265 on: October 15, 2019, 02:23:36 PM »
When ice melts, where does the cold fresh water go? Above or under the ice? Do you think it will sink because it's cold binntho? If it doesn't sink, what effect does it have on heat transfer from the sunken, warmer salty layers?

crandles

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Re: When will the Arctic Go Ice Free?
« Reply #1266 on: October 15, 2019, 02:27:56 PM »

But none of that is directly tied to ice thickness. Changes in albedo of the ice itself (or rather, how much radiation makes it through the ice and into the top layer of the underlying ocean) will be related to thickness, and I'd expect that this would be a big effect when comparing say 0.5m with 0.25m. But is it significant when comparing 2m with 1m?

Does it matter to the proposition that 1m takes less time than half time to melt of 2m?

1m = 0.75m slowly melted + 0.25m quickly melted.
2m = 1.75m slowly melted + 0.25m quickly melted.

means 1m takes less than half the time of 2m and the proposition is true.


>But none of that is directly tied to ice thickness

Are you disagreeing with idea that the thinner the ice the smaller the pieces it breaks into? If so, why?

binntho

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Re: When will the Arctic Go Ice Free?
« Reply #1267 on: October 15, 2019, 02:41:52 PM »

But none of that is directly tied to ice thickness. Changes in albedo of the ice itself (or rather, how much radiation makes it through the ice and into the top layer of the underlying ocean) will be related to thickness, and I'd expect that this would be a big effect when comparing say 0.5m with 0.25m. But is it significant when comparing 2m with 1m?

Does it matter to the proposition that 1m takes less time than half time to melt of 2m?

1m = 0.75m slowly melted + 0.25m quickly melted.
2m = 1.75m slowly melted + 0.25m quickly melted.

means 1m takes less than half the time of 2m and the proposition is true.

But this does not follow at all from what I said! When I talk about 0.25m thick ice I mean 0.25m thick ice, not some random 0.25m segment of 1m or 2m thick ice.

Besides, what ever physical processes do you foresee would cause what you propose? Or are you perhaps saying "the last 25cm are going to melt really very fast, and 25cm is of course only 1/8 of 2m meters while it's 1/4 of one meter, therefore the last 1m is going to melt faster than the first 1m". But if that is what you are trying to say, then you are saying something quite different from what Glen was saying, i.e. that given constant "melting power", 1m thick ice would melt significantly faster than 2m thick ice.

Besides, there is no evidence that the last 25cm would melt faster than the penultimate 25cm given the same "melting power", and even if it sounds reasonable, why should it be true?

It's like saying that the last 1Million km2 of ice will melt a lot quicker than it took going from 2M to 1M, because the last 250.000 km2 will melt really fast because the final 50.000km2 is going to vanish almost instantly etc. etc.

Quote

>But none of that is directly tied to ice thickness

Are you disagreeing with idea that the thinner the ice the smaller the pieces it breaks into? If so, why?
Am I? I didn't know that. I'll be the first to admit that 1m thick ice breaks into smaller pieces than 2m thick ice. But does it have any "significant" effect on the speed of melt? I doubt that very much. If we were talking about 0.5m vs. 0.25m on the other hand, the effect would be considerably bigger and might even be called "significant" if there was any empirical evidence to back that up (and of course some generally agreed-upon definition of "significant", i.e. as in "being meaningful", "having an easily recognizable effect" or other such).
because a thing is eloquently expressed it should not be taken to be as necessarily true
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crandles

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Re: When will the Arctic Go Ice Free?
« Reply #1268 on: October 15, 2019, 04:27:31 PM »
Glen Wrote
"The resistance of sea ice to melt is NOT linear.  It decreases faster than thickness.  1 meter thick ice requires significantly less than 50% of the melting power as 2 meter thick ice. "

to me this seems consistent with considering what needs to happen to fully melt out and with you saying

Quote
"the last 25cm are going to melt really very fast, and 25cm is of course only 1/8 of 2m meters while it's 1/4 of one meter, therefore the last 1m is going to melt faster than the first 1m"

If you want to interpret it as something different like: the rate of melting at 1m is faster than at 2m thick then please explain why you are insisting on such an interpretation. FWIW, I doubt there is a significant difference, if this is the interpretation you are insisting on.

I'll be the first to admit that 1m thick ice breaks into smaller pieces than 2m thick ice. But does it have any "significant" effect on the speed of melt? I doubt that very much.

This does to some extent depend on circumstances: If there is adequate heat in the water (think middle/end of melt season rather than beginning) surrounding the ice then it is about speed of transfer of the heat to the ice. Here, a high ratio of surface area to volume given by small pieces is very helpful to melting the ice quickly.

However a different situation might be earlier in melt season when the heat is not available in the water and air and you have to wait for sufficient heat to be absorbed. This situation is dominated by albedo so the ice being very thin is more likely to be key.

binntho

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Re: When will the Arctic Go Ice Free?
« Reply #1269 on: October 16, 2019, 07:35:36 AM »
Glen Wrote
"The resistance of sea ice to melt is NOT linear.  It decreases faster than thickness.  1 meter thick ice requires significantly less than 50% of the melting power as 2 meter thick ice. "

to me this seems consistent with considering what needs to happen to fully melt out and with you saying

Well I don't see it as being "consistent" with what "needs to happen" to fully melt out. Linear melting would do just as well.

I understand Glen's statement, "the resistence of sea ice to melt is NOT linear. It decreases faster than thickness" to mean that the resistence of ice to melting decreases as the ice becomes thinner.

For a meaningful discussion, let's assume that "melting" means actual melting, i.e. decrease in volume.

If we were to imagine two bodies of water, identical to each other except for the fact that one starts out with thinner ice than the other, would the same climatological effects cause the volume of the thinner ice to decrease faster than the volume of the thicker ice?

As long as the ice is at 100% extent, I don't see how there could be any difference. But as soon as the ice begins to break up, other factors such as wave action and increased albedo, start to kick in and melting should progress faster. The thinner ice can be assumed to start this process sooner than the thicker, resulting in an overall faster volume drop in the thinner ice if melting reaches the point where the ice starts to break up.

So we could well see significant difference between the two bodies of water is one was covered in 10cm ice and the other in 5cm ice. But would there be any significant difference if one was covered in 2m and the other in 1m? I'm not at all sure that the effect of break up would be sufficient to classify as "significant".

If we take the second part of Glen's statement, "1 meter thick ice requires significantly less than 50% of the melting power as 2 meter thick ice. " at face value, I'm not sure that it holds. That word, "significantly" requires a large effect. And a simplistic (or idealised) comparison of 2m and 1m ice does not automatically lead to a "significant" difference in volume loss given the same climatology.

However, if we understand Glen to be talking about averages, then perhaps it starts to make more sense. This year, the average at maximum was ~1.8m and at minimum just under 1m. The "melting power" of this season has removed 0.8m of average thickness.

So if Glen's idea is correct, then if in some future year, average thickness at maximum is 1m then the same "melting power" as in this year would melt it out totally and with a lot to spare. And the effect should presumably be visible sooner, if we started out at 1.5m then a 2019 "melting power" should result in less than 0.5m.

But looking at Neven's Pijamas chart, every year seems to lose about the same average thickness more or less, around the 0.8 mark, so Glen's idea doesn't really hold up - melting power varies signficantly, loss in average thickness does not vary significantly.
because a thing is eloquently expressed it should not be taken to be as necessarily true
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Tor Bejnar

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Re: When will the Arctic Go Ice Free?
« Reply #1270 on: October 16, 2019, 04:31:46 PM »
From above:
Quote
As long as the ice is at 100% extent, I don't see how there could be any difference.
From the internet (NOAA):
Quote
The underside of the ice cover also responds to the surface melt. Directly underneath melt pools the ice is thinner and is absorbing more incoming radiation. This causes an enhanced rate of bottom melt so that the ice bottom develops a topography of depressions to mirror the melt pool distribution on the top side.
Thinner ice (especially under a melt pond) allows for more warming of the water under the ice, so there is more bottom melt under 1m thick ice than under 2m thick ice (with identical surface conditions).
Arctic ice is healthy for children and other living things.

binntho

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Re: When will the Arctic Go Ice Free?
« Reply #1271 on: October 17, 2019, 07:35:06 AM »
From above:
Quote
As long as the ice is at 100% extent, I don't see how there could be any difference.
From the internet (NOAA):
Quote
The underside of the ice cover also responds to the surface melt. Directly underneath melt pools the ice is thinner and is absorbing more incoming radiation. This causes an enhanced rate of bottom melt so that the ice bottom develops a topography of depressions to mirror the melt pool distribution on the top side.
Thinner ice (especially under a melt pond) allows for more warming of the water under the ice, so there is more bottom melt under 1m thick ice than under 2m thick ice (with identical surface conditions).
Yes I wasn't sure about that one. And I still am not sure - if the sunlight enters through the surface, does it make a difference to the final outcome if it reaches the bottom of the floe or not? At an intermediate state it cleary does, since sunlight reaching the underlying water causes visible bottom melt.

But if the light doesn' reach the underlying water, it must instead go into warming up the ice, causing it to melt quicker towards the end. In fact, I'd assume that more of the sun's energy will go towards final melt if it doesn't reach through the ice, since any energy that hits the water can also be dissipated away from the floe.
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oren

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Re: When will the Arctic Go Ice Free?
« Reply #1272 on: October 17, 2019, 11:33:24 AM »
Not entirely true. I think thicker floes have a somewhat higher albedo.

binntho

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Re: When will the Arctic Go Ice Free?
« Reply #1273 on: October 17, 2019, 12:33:11 PM »
Not entirely true. I think thicker floes have a somewhat higher albedo.
It's obvious when looking at thin ice - the darker water below has a much lower albedo, so thinner ice looks darker when looked at from above.

But I'm still after that elusive "significant" effect where 1m ice is a lot easier to melt than 2m ice. And although I'm reluctant to use such strong language, I'm coming to the conclusion that Glen was talking out of his foundational orifice when he made the following claim:

   The resistance of sea ice to melt is NOT linear.  It decreases faster than thickness.  1 meter thick ice requires significantly less than 50% of the melting power as 2 meter thick ice. 

Which is a pity since I quite liked the rest of his post - the two posts,  Gerontocrat's at #1258 and Glen Koehler's at #1259 were extremely good, but when you make big unsubstantiated claims then the rest of what you are saying becomes somewhat tainted.
because a thing is eloquently expressed it should not be taken to be as necessarily true
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wili

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Re: When will the Arctic Go Ice Free?
« Reply #1274 on: October 17, 2019, 02:41:44 PM »
Wouldn't that depend also on the quality of the ice? How salty or slushy it is, for instance?
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Re: When will the Arctic Go Ice Free?
« Reply #1275 on: October 17, 2019, 06:13:20 PM »
I found this nice study on the thickness and transmittance of solar energy on sea ice.
 
Quote
But the present study suggests that the transmittance through bare, melting ice is also significant, and our calculations suggest that as much as 3% of the incident radiation may penetrate 3 m thick ice while 15% may penetrate 1 m thick ice.

Transmission and absorption of solar radiation by Arctic sea ice during the melt season

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2006JC003977
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Tor Bejnar

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Re: When will the Arctic Go Ice Free?
« Reply #1276 on: October 17, 2019, 09:17:08 PM »
I appreciate your concern, binntho.

I don't know if this helps any, one way or another:
One of the factors affecting ice melt is its temperature profile (or 'average' temperature).  During (let's say a snow-less - to remove one variable) winter, the top of a floe will be something like -40ºC and the bottom ice will be something like -1.8ºC (with the coldest ice at the top surface).  By summer, the top will warm all the way to 0ºC, the bottom will remain  -1.8ºC, and the profile will show the coldest ice somewhere in between.  Even as top melt and bottom melt progress, the coldest ice will be found somewhere in between (until the coldest ice is the -1.8ºC ice at the bottom).

My conjecture: it is likely, but not a requirement, that the coldest mid-ice temperature in 2 m thick ice will be colder than the coldest mid-ice temperature in 1 m thick ice, and therefore the heat required to melt 2 m thick ice will be more than twice that required to melt 1 m thick ice.
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Archimid

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Re: When will the Arctic Go Ice Free?
« Reply #1277 on: October 18, 2019, 11:40:40 AM »
Thin ice melts faster than thick ice.  See this image from the previously linked reference:




Even at 3 m thick ice, 3% of incident radiation on Aug 6th somewhere on the Beaufort Sea makes it to the oceans. At 1 m as much as 15% makes it to the ocean.  The thinner the ice gets from there the more energy the ice lets through.

Then you start taking into account mechanical strength, fractures on the ice and geometry...
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binntho

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Re: When will the Arctic Go Ice Free?
« Reply #1278 on: October 18, 2019, 12:03:43 PM »
Even at 3 m thick ice, 3% of incident radiation on Aug 6th somewhere on the Beaufort Sea makes it to the oceans. At 1 m as much as 15% makes it to the ocean.  The thinner the ice gets from there the more energy the ice lets through.

Then you start taking into account mechanical strength, fractures on the ice and geometry...
I think we can all agree that thin ice melts faster than thick ice under most real world circumstances, particularly due to mechanical effects.

But the original source of my nitpicking was the word "significantly" when comparing 2m ice to 1m ice and I've not seen anybody posting anything supporting that claim. We all seem to have a rather vague feeling that the thinner the ice, the easier it is to get rid off, but on the other hand, nobody seems to be able to quantify this or to give empirical evidence.

As for how much energy makes it through the ice, to me it seems counterintuitive to say that the less energy retained by the ice (i.e. because it is thinner), the faster it will melt. The energy that gets through into the underlying water will contribute to bottom melt, but some if the energy will be dissipated away from the ice.

Glen originally talked about "melting power", so if we imagine that there was some sort of melting power unit (MPU) then his claim is that if it takes 200 MPU to melt a particular area of 2m thick ice, then a same-sized area of 1m thick ice will need "significantly" less than 100 MPU.

And this may be correct, but cannot be explained by difference in Albedo between 1m and 2m thick ice. While the ice is thicker, the energy goes into warming the interior, as the ice gets thinner bottom melt kicks in. Because the 2m thick ice has gone throught the "warming the interor" stage that the 1m thick ice missed out on, the 2m should be ahead on points - but given that thicker ice has more cold interior to warm up, perhaps the net result is nil.

I'm sorry about the endless nit-picking, but Glen's claim was intriguing and bold, and sounded reasonable. But there doesn't seem to be any real evidence to support it.
because a thing is eloquently expressed it should not be taken to be as necessarily true
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oren

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Re: When will the Arctic Go Ice Free?
« Reply #1279 on: October 18, 2019, 12:19:09 PM »
Personally I would not use the word significantly in that context, but bear in mind that 95 or 99 instead of 100 MPU might seem significant to some. It's subjective.
Personally I would also avoid nitpicking this to death and beyond...

binntho

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Re: When will the Arctic Go Ice Free?
« Reply #1280 on: October 18, 2019, 01:50:17 PM »
Personally I would not use the word significantly in that context, but bear in mind that 95 or 99 instead of 100 MPU might seem significant to some. It's subjective.
Personally I would also avoid nitpicking this to death and beyond...
Heard and understood!  :-[
because a thing is eloquently expressed it should not be taken to be as necessarily true
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