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

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

Total Members Voted: 62

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

Author Topic: When will the Arctic Go Ice Free?  (Read 222440 times)

oren

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Re: When will the Arctic Go Ice Free?
« Reply #1800 on: December 02, 2020, 03:37:52 AM »
Quote
Beckwith is not the most accurate or reliable source and his commercializing the catastrophe is offputting.
I agree.

BTW, Paul Beckwith is registered in the ASIF and has made a few posts some years ago, though he's not been seen since.

El Cid

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Re: When will the Arctic Go Ice Free?
« Reply #1801 on: December 02, 2020, 08:38:09 AM »

Quote
Beckwith is not the most accurate or reliable source and his commercializing the catastrophe is offputting.

And that is putting it very mildly...

Tom_Mazanec

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Re: When will the Arctic Go Ice Free?
« Reply #1802 on: December 05, 2020, 03:40:51 PM »
Interestingly, I thought that if the Arctic was not ice free in the Holocene (at least so far) at least it probably was in the Eemian, so it would not be completely novel in "recent" Earth history.
Seems I was wrong:
https://phys.org/news/2012-06-climate-cold-arctic-eemian.html
So AFAIK the Arctic may be about to be ice free for the first time in a couple million years?
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Stephan

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Re: When will the Arctic Go Ice Free?
« Reply #1803 on: December 16, 2020, 05:22:21 PM »
It is time for the monthly update of my extrapolation when the extent [Ausdehnung], volume [Volumen], thickness [Dicke] and area [Fläche] will reach zero. The extrapolation occured linearly and by a logarithmic function; the latter one almost constantly resulting in earlier times (valid for volume and thickness, not for extent and area in the winter months). The November value now includes 2020.
Extent and volume lie slightly below the long term linear trend, thickness is lower than the long term trend line, whereas area dives deeply below it. The "BOE numbers" did not change (volume, thickness) and decreased by 4-5 years (extent, area) compared to November 2019.
So there is a further convergence between the "late values" (area, extent) and the "early value" (volume).
The order (earlier → later BOE) generally is volume < thickness < area < extent.

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

Click to enlarge it.
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Glen Koehler

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Re: When will the Arctic Go Ice Free?
« Reply #1804 on: December 16, 2020, 05:49:57 PM »
    Thanks for tracking the data Stephan. 

    I don't expect the "Great Convergence" between Extent and Volume trends until closer to the endpoint as Volume gets below about 0.8 km3 and when the average thickness is below 0.8 meter.  But you mentioned that the Ext and Vol trends are already converging. 

     Do you have a record over recent years of the difference between the extrapolated zero-year estimates for Extent and Volume trends?  That would be interesting to see, and would correct the mistaken (IMHO) assumption by some who think the Extent trend is an accurate predictor for the first, and then regular, BOE status in Septembers.   

     My view is that Vol. dictates Ext., not vice versa.  And that as Thickness declines there will be an acceleration of Extent decline until it catches up to Volume at zero.  Thus, first <1m km2 Extent BOE around 2030 or earlier, not around 2060 as estimated from extrapolation of the Extent trend.  Multiple other correlated indicators such as global average surface temperature and cumulative atmospheric CO2 ppm also point to BOE status being reached around the same time as the Volume trend estimate. 

     The problem with Extent, as noted in JC Garcia's tagline, is that Extent alone hides about half of the ice losses because it does not account for simultaneous Thickness reduction.
« Last Edit: December 16, 2020, 06:03:12 PM by Glen Koehler »

Stephan

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Re: When will the Arctic Go Ice Free?
« Reply #1805 on: December 16, 2020, 06:31:56 PM »
         Do you have a record over recent years of the difference between the extrapolated zero-year estimates for Extent and Volume trends?  That would be interesting to see, and would correct the mistaken (IMHO) assumption by some who think the Extent trend is an accurate predictor for the first, and then regular, BOE status in Septembers.   
Glen,
unfortunately no. I save the actual screenshot of the values under the same file name. So the only way to look back is to look at my postings in this thread which began roughly two years ago...

kind regards Stephan
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The Walrus

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Re: When will the Arctic Go Ice Free?
« Reply #1806 on: December 16, 2020, 09:08:08 PM »
         Do you have a record over recent years of the difference between the extrapolated zero-year estimates for Extent and Volume trends?  That would be interesting to see, and would correct the mistaken (IMHO) assumption by some who think the Extent trend is an accurate predictor for the first, and then regular, BOE status in Septembers.   
Glen,
unfortunately no. I save the actual screenshot of the values under the same file name. So the only way to look back is to look at my postings in this thread which began roughly two years ago...

kind regards Stephan

If you look at the data over the long term, the trend in extent has stayed relatively constant (actually slow slightly, but not much). Conversely, volume decline has slowed considerably, bringing it closer to extent.  This is not surprising, as volume is three-dimensional, and will decrease faster than either extent (area) or thickness which are two- and one-dimensional.  For this reason partly, and also that volume is an estimated value whereas extent and area are measured, I am one of those that view extent dictates volume.

Glen Koehler

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Re: When will the Arctic Go Ice Free?
« Reply #1807 on: December 16, 2020, 11:13:44 PM »
    Thanks for the reply Stephan.  If/when I get around to addressing what is really just a statistical fetish, it would not be difficult to get the extrapolated BOE dates from regressions of annual values for Ext, Vol, and Thickness for incrementally later sets of years
(e.g. calculate the Ext and Vol/Thickness trends with data for 1978 - 1988, then 1980 - 1990, 82-92, etc., then for each set of years record the difference between estimated BOE year based on Extent trend minus estimated year based on Vol/Thickness trend).
 
    The point of this obsessive number crunching would be to see if the difference between the Extent-based vs. Volume-based BOE estimate is already getting smaller through time, aka the
'Great Convergence".  But since I don't really expect the convergence to emerge until closer to the endpoint, I won't be convinced that my theory is incorrect even if that difference is not yet diminishing.  Which is troubling because it means that in a way I am as situationally immune to math as certain psychiatrically-damaged morally-void politicians who shall remain nameless in order to keep this forum apolitical.

Stephan

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Re: When will the Arctic Go Ice Free?
« Reply #1808 on: December 17, 2020, 05:39:48 PM »
Glen,
I just did a "quick and dirty" experiment with a set of reduced data (1979-2008) versus 1979-2020.
I calculated the "BOE numbers" for the time period 1979-2008 and compared it with the full period (1979-2020). I reduced the evaluation on extent and volume and just performed the linear evaluation. Finally I compared the differences (column Delta) for each month (extent versus volume). If the Delta in extent is larger than the Delta in volume, the "BOE numbers" converge. If it is the other way round, the values develop apart.

Conclusions:
1. The slope of almost all months has grown steeper from 1979-2008 to 1979-2020.
2. This results in earlier "BOE numbers" for most, but not all of the months. The "BOE numbers" for extent increased in Jan, March and April!
3. There is a clear season for convergence: summer and autumn, marked in green. In winter and spring the values go even further apart, marked in pale magenta (column "Delta"). June and Sep are more or less undecided.

See attached table.
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Glen Koehler

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Re: When will the Arctic Go Ice Free?
« Reply #1809 on: December 18, 2020, 10:27:43 PM »
Dear Stephan - Nice work and much appreciated.  I think that this addition to your monthly trend posts really gets to the heart of the issue.

       Everybody else - especially Arctic amateurs like me:  Take enough time to understand what these numbers are saying.  What may appear at first glance may appear to be an innocuous table of numbers, in truth says major and disturbing things about the future of the Arctic, this planet, humanity in general, and the not-very-distant future for each us individually and the people we love.

    1) Lots of talk by IPCC and elsewhere about sea level rise by 2100.  No disagreement with that, it is a huge impactful manifestation of our insane management of the planetary life support system.  But also consider what it means to have ZERO Arctic sea ice volume in June, the month of maximum solar energy injection, by 2067.  Moreover, that the date for that catastrophic milestone gets 20 years earlier when you add 12 years to the straight-line trend to go from 1979-2008 to 1979-2020.  Will adding another 12 years, i.e. 1979-2032 put that date at 2047? 
       A planet without its reflective polar cap in June is a different planet than the one we were born on.

    2)  If 2047-2067 is too far off to get your interest, how about 2032-2035?  And what about 2026?  Is that close enough to get your attention as being real?

        ZERO Arctic Sea in August - October is also a radically different planet. While far below June, there is still considerable solar energy input in August.  And an ice-free Arctic Ocean in October (and with much reduced ice in November) venting heat into the atmosphere is bound to have strong effects on mid-latitude weather patterns. 

        The table highlights the fact that adding 12 years to the dataset used to define the trend pushes the zero volume dates 9-14 years earlier.  2032-2035 is already close at hand, but will those trend endpoints continue to get earlier as each new year is added?  Where will those endpoint dates be in just 6 more years in December 2026?  The "trend of the trends" suggests that the estimated ice-free Sept date by then could be another six years earlier, i.e. 2026.  At risk of piling extrapolations on top of each other, does that suggest that we could already have had a zero-ice September by then?

        One of the problems in conceptualizing climate change is that the perceived impacts are in the future.  People already dealing with wildfires, heat waves, droughts, hurricanes, crop failures etc. will have a more immediate perspective, but for many/most of us, the climate changes that worry us are said to be decades ahead and so bring a bit less visceral fear. 

        The dates shown for zero ice volume are nothing new to me, so I've long had the mental concern.  And perhaps I am misinterpreting and over-reacting to seeing the earlier progression of endpoint dates that result from adding 12 years to the dataset.  But my visceral fear just went up.  My emotional operating principle has been that the proverbial poop could hit the fan if global average surface temperature reaches +1.5C over preindustrial circa 2030.
 
       I keep thinking that my understanding of climate change and Arctic Sea Ice decline has reached a level of stability at which I can at least see the horror for what it is, and at least define the problem.  But the damn problem keeps growing like a cancerous tumor.  Seeing that date migration of the Sept. zero ice year has me wondering if I should recalibrate my gut-level fear threshold and "poop in the fan" date more towards August 2026 - less than 68 months from now. 

       Of course, ranting aside, the "Now" is all that we can change to affect the Future.  I hope your data serves as that one additional piece of alarming evidence that tips the scales to wake up the political and business powers to realize that the money won't do any good if there is not a livable planet on which to spend it.  Sorry for such a bleak message as we head into the traditional western holiday season.  I would highlight the fact that some good things are also underway, but this message is already long.  So yes, there are also some good possibilities emerging.  We MUST make those possibilities real.
« Last Edit: December 19, 2020, 12:25:09 AM by Glen Koehler »

Glen Koehler

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Re: When will the Arctic Go Ice Free?
« Reply #1810 on: December 18, 2020, 11:55:37 PM »
To get back to the Convergence question:
      The hypothesis is that the number of years remaining until the zero ice date estimated by the Extent trend will decrease relative to the date estimated by Volume as we get closer to that date.
The hypothesis says that until they meet when both Volume and Extent trends reach zero, it is the Extent date that will shift to meet the earlier Volume date, not vice versa.

      Here are the relative zero date migrations for 1979-2008 vs. 1979-2020 for each month.
The values for Extent and Volume are the number of years earlier the end date became by adding 2009-2020 to the 1979-2008 dataset.

      By subtracting the Volume shift from the Extent shift, a Positive value means that the Extent estimate moved earlier by a greater amount, which is what the hypothesis predicts.  A negative difference means the opposite, that instead of drawing closer to the Volume-based estimate, the Extent-based estimate is moving away from it. 

Jan: -2 (for Extent) minus 13 (for Volume) = -15 
    The Vol. estimate got 13 years earlier, but Extent est. became later not earlier, and thus farther away from the Vol estimate.  This is the opposite of convergence and NOT what the hypothesis predicts.

Feb:   12 minus 15 =  -3
Mar: -22 minus 15 = -37 
Apr: -45 minus 15 = -60  (Wow, Ext estimate became 45 years LATER).
May:   6 minus 19 = -19
Jun:  21 minus 20 =    1
Jul:   24 minus 15 =    9
Aug: 20 minus 11 =    9
Sep: 13 minus 14 =   -1
Oct:  30 minus 9  =   21
Nov: 27 minus 11 =  18
Dec:   4 minus 10 =  -6 

      As you noted, the winter and spring months are doing the opposite of convergence.  While summer and fall are generally showing convergence.  That makes sense in that we would expect the "thin ice" months to show convergence between Extent and Volume before the "thick ice" months.  It is when thickness reaches a critical low threshold that Extent losses increase causing it to begin to catch up to Volume.

      June being a neutral month with respect to the "Extent trend must bend down to catch Volume trend" hypothesis makes sense because it is the transition between the thick ice and the thin ice months.

      But September is a brain twister.  It seems like it should show a full expression of the 'Extent catches Volume as ice thins' trend.  My guess is that those bays in the CAA and other ice traps that are the reason for setting the BOE definition at 1M km2 of residual Extent instead of zero, are already constraining reduction in September Extent.  Those areas may be superficial thin ice that add to the Sept. Extent value without adding much to the Sept Volume because they are so thin.  As a result, the Sept. Extent value does not decline as much as it "should", but Sept. Volume does not as effectively hide the loss of ice.

      It is also a bit mysterious to see the peak "thick ice" months going the opposite direction, i.e. the Extent-trend zero date is getting farther away not closer to the Volume date.  And for March and April, the zero Extent estimate is getting absolutely later, not just getting earlier at a slower rate than the Volume date. 

      My guess is that happens because once the Arctic Ocean fills up with ice, it is full.  Even in the colder, higher ice volume past, it could not add more Extent because the Arctic Ocean is surrounded by land.   These days, the ice Extent comes from thinner low-volume ice, but that change is not reflected in the Extent value.  It still counts for Extent.  The March and April constraint on Extent in the past means that as the ice declines now, relative to the previous years, March and April don't show much if any Extent loss.  So as more years are added to the dataset, with little change in the constrained monthly Extent values for March and April, the trend towards a Zero Extent date for those months is essentially no trend at all with termination dates over 300 years from now vs. decades for the other months. 

      Actually, that point applies to ALL of the maximum ice months of January through May.  For each of them, the zero Extent year estimate is past 2300, and for Feb-May, in the late 2300s.  Thus the negative trend slope is so minor that there really isn't much trend at all due to the constraint on maximum Extent in earlier years.

      The "land bound Arctic Sea Ice" argument conveniently ignores the potential for additional Extent in the peripheral seas not bound by the coast of the Arctic Ocean.  Are your Extent and Volume data for the entire Arctic, including the peripheral seas, or are they limited to the (mostly land bound) central Arctic Ocean?

      If the data are limited to the central Arctic, then I don't have to explain away that potential for additional Extent.  But if your data also include those peripheral areas (Greenland, Okhotsk, Bering Seas) that the "land bound Arctic Ocean" argument does not address, I won't even attempt to concoct some reason to explain them away as I have already used up my daily allowance for fabricating "evidence".
« Last Edit: December 19, 2020, 03:11:32 AM by Glen Koehler »

Stephan

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Re: When will the Arctic Go Ice Free?
« Reply #1811 on: December 19, 2020, 09:39:17 PM »
Glen,

thank you for your excellent reply and thoughts.
I have performed a second experiment on the data. I only used the first twenty (instead of thirty) years. One of the reasons is to omit the super melting year 2007 which, lying almost at the end of the 1979-2008 series, may have influenced the statistical analysis. And, the years 1997-1998 have been unspectacular, both extent- and volume-wise.

Please find the same evaluation, which has to be taken with a certain grain of salt as only 20 years were used. Especially the April value seems not to be very trustful, but I double-checked the data.
But the general trend is comparable. Please notice that the slopes (column stg) are again much smaller than the slopes 19291979-2008 have been. This results in a massive time shift of the "BOE numbers" compared to what they are calculated today. And who may know whether this tendency goes on like that in the next decade?

Evaluation:
Spring months still develop apart. June is still undecided. Summer, autumn and winter values converge.

Please note that I used the NSIDC data for the whole Arctic including all peripheral seas.

One final note to the "undecided" September from the 1979-2008 evaluation: The slope has been higher than it should have been because Sep 2007 was so low. This resulted in a "BOE number" close to what it is estimated today.

See attached table.
« Last Edit: December 20, 2020, 03:44:18 PM by Stephan »
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kassy

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Re: When will the Arctic Go Ice Free?
« Reply #1812 on: December 20, 2020, 10:38:11 AM »
Please note that I used the NSIDC data for the whole Arctic including all peripheral seas.

Is there a way to do this data but without the 4 B´s (Baffin, Barentz, Bering and (B)Okhotsk?
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The Walrus

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Re: When will the Arctic Go Ice Free?
« Reply #1813 on: December 20, 2020, 02:29:41 PM »
Please note that I used the NSIDC data for the whole Arctic including all peripheral seas.

Is there a way to do this data but without the 4 B´s (Baffin, Barentz, Bering and (B)Okhotsk?

That would be nice, as there is some belief that the trend change was due largely to the melting out of these areas.  If I remember correctly, it was gerontocrat who show a graph of just the central arctic.  Perhaps, he can help.

Stephan

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Re: When will the Arctic Go Ice Free?
« Reply #1814 on: December 20, 2020, 03:43:24 PM »
I do not have the regional data in my PC. Maybe I can download them from somewhere or there is a file that someone could share with me. Then I'd like to do this evaluation.
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kassy

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Re: When will the Arctic Go Ice Free?
« Reply #1815 on: December 20, 2020, 11:30:30 PM »
I went looking back to what Oren used before but NSIDC regional data is extent only so that is not going to help.

Jan: -2 (for Extent) minus 13 (for Volume) = -15
    The Vol. estimate got 13 years earlier, but Extent est. became later not earlier, and thus farther away from the Vol estimate.  This is the opposite of convergence and NOT what the hypothesis predicts.


But it is consistent with melting stuff. Volume is hard to make and extent not so much. Extent chases area chases volume.

On another note there must be some thickness which leads to trouble. What is the average thickness to disappear in a year? At some point all kinds of processes that were not important are going to play a role. The summer ice will become ever more shattered and drift more.

Of the 4 measurements i would totally go with volume as the best predictor.

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Rodius

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Re: When will the Arctic Go Ice Free?
« Reply #1816 on: December 21, 2020, 10:35:56 AM »
I think I located the first one, so I saved it and the latest one for those who want to compare.
The first one was Sept 2018

EDIT: One is 2018 (top)
Two is 2020 (Bottom)

Stephan

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Re: When will the Arctic Go Ice Free?
« Reply #1817 on: December 21, 2020, 02:30:40 PM »
Thank you rodius,
I did the same and wrote down the "BOE numbers" from Feb 2019 (they contain the whole year of 2018) into my spread sheet.
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oren

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Re: When will the Arctic Go Ice Free?
« Reply #1818 on: December 21, 2020, 03:39:36 PM »
The amazing Wipneus has all sorts of regional data on his website, including the regional NSIDC extent and area numbers.
https://sites.google.com/site/arctischepinguin/home/sea-ice-extent-area/data/nsidc_arc_nt_detail.txt

Glen Koehler

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Re: When will the Arctic Go Ice Free?
« Reply #1819 on: December 23, 2020, 02:36:51 AM »
      Here are the relative zero date migrations for each month using Stephan's revised data.  The values for Extent and Volume are the number of years earlier the extrapolated date for reaching zero migrated due to changing the period of years used to define the trend from 1979-1998 (= a midyear of ca. 1989) to  1979-2020 (midyear 1999). 

      By subtracting the amount of change in the projected zero Volume date from the amount of change in the Extent zero date, a Positive value means that the Extent zero date moved earlier by a greater amount, which suggests that Extent losses accelerated to catch up to Volume.  A negative difference means the opposite, that the Extent trend estimate changed at a slower rate than the Volume-based estimate.   

      The original hypothesis was that as ASI declines, eventually the Extent losses will accelerate to catch up to Volume losses, and that Volume is a more reliable predictor for reaching extreme low values such as a BOE (i.e. < 1M km2 Exent and < ca. 0.8M km3 Volume) or the first date with zero ASI.  The mechanism for this happening was attributed to accelerated Extent losses as ice thickness gets below a threshold value at which rapid Extent losses can occur.  That threshold is incremental, but the effect probably becomes noticeable for a given area of ice when its average thickness gets below about 1 meter.  (If I recall correctly, across the Arctic Ocean as a whole, the average thickness during a melt season declines by about 2 meters before ice accumulation and thickness increase begins in late autumn.)

BEGIN THICK ICE MONTHS
Jan: 152 (for Extent) minus 101 (for Volume) = 51    Positive difference.  Extent CONverged 
      The date for zero Extent moved 152 years earlier, while the date for zero Volume moved 101 years earlier.  Thus, Extent advanced 51 years more than the Volume date. 
Feb:   182 minus 119 =   63  Extent CONverged.
Mar:    20 minus 105 =  -85  Extent DIverged, Extent migration was slower than Volume. 
Apr:   -60 minus 93 =  -153  Big DIvergence.  (Ext estimate became 63 years LATER).
May:   11 minus 90 =    -89  Extent DIverged.
END THICK ICE MONTHS
THICK to THIN TRANSITION
Jun:    72 minus 69 =      3  Slight CONvergence, but essentially Ext and Vol had equal change.
BEGIN THIN ICE MONTHS
Jul:     73 minus 46 =   27  Extent CONverged.
Aug:  120 minus 38 =   82   Extent CONverged.
Sep:  123 minus 45 =   78   Extent CONverged.
Oct:   190 minus 55 = 135   Extent CONverged.
Nov:  157 minus 73 =   80   Extent CONverged.
END THIN ICE MONTHS
THIN to THICK TRANSITION
Dec:  243 minus 98 = 145   Big Extent CONvergence.

      The hypothesis that Extent losses during the thin ice months appear to be accelerating to eventually converge with Volume losses seems to hold up.

      In the first comparison (using 1979-2008 vs 1979-2020), the Sept difference between the relative change in extrapolated zero date for Extent and Volume was contrary to the hypothesis.  In this second comparison (1979-1998 vs 1979-2020) the relative Sept change supports the hypothesis.  And this time, the relative changes in Dec, Jan, and Feb Ext vs. Volume zero dates show convergence even though those months were expected (by me at least) to be neutral because the thin ice mechanism expected to drive convergence does not yet exist for those months. 

      More important than the hypothesis is the larger point is that if we want to estimate when ASI losses will reach some extremely low (never seen in human history) level, then the Volume straight-line trend is a more reliable predictor than the Extent trend.  Extrapolating the Volume trend estimates that a first complete or near-complete loss of late-summer ice will occur by 2029-2034.  It is interesting and disturbing to see estimates from the straight-line Volume trend getting even earlier as more years are added to the data. 

      It is too bad we apparently do not still have Tamino available.  This is the kind of stuff he would slice and dice and pull whatever meaning exists from the numbers.  He might say we are sword fighting with shadows, i.e. the net differences are based on too few years of data to make conclusions.  But my guess is that these differences in trend-based estimates would pass statistical muster (my guess being worth exactly nothing, that is why we have statistics - to get past guesswork based on intuitive hunches).

      We may have squeezed this lemon dry, but the patterns are interesting.  If Stephan or somebody else is up for one more round, it would be interesting to see what comes from comparing non-overlapping periods, i.e. 1979 - 1999 vs 2000 - 2020.
« Last Edit: December 24, 2020, 06:56:18 PM by Glen Koehler »

kassy

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Re: When will the Arctic Go Ice Free?
« Reply #1820 on: December 23, 2020, 08:17:47 PM »
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if we want to estimate when ASI losses will reach some extremely low (never seen in human history) level, then the Volume straight-line trend is a more reliable predictor than the Extent trend

But this also just completely follows from physics.

Another problem is that purely looking at ASI you miss part of the data. Of the simple prediction models that used to play in the yearly poll the best one ran of NHEM snow cover. So here we are looking at the reactions of a system (the ASI growing back its extent).
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.

gerontocrat

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Re: When will the Arctic Go Ice Free?
« Reply #1821 on: December 26, 2020, 03:38:27 PM »
https://forum.arctic-sea-ice.net/index.php/topic,2245.msg296662/topicseen.html#msg296662

There is a big lump of ice in the Antarctic called A-68-A. Ok, so it is a lump of ice sitting in a cold ocean and it is melting. But just about everything else is different from the ice and its environment in the Arctic

Nevertheless, in the years since 2017 when it started its voyage, ice extent is down by 54%, ice volume down by 64%.

The two large bits that broke off on 21 Dec were much thinner than the averge, so before that happened volume loss difference from extent loss would have been even higher. Looking at the graph in the post linked above suggests that on Dec 20 the extent loss was about 32% and volume loss about 45%. (Why don't they provide the data in a table?)

So my speculation that belongs to me is that if you put any old lump of  ice into water the volume loss exceeds area loss (until?) It will be fascinating iff we get to see the end of days of this berg and see how long this excess of volume loss over area loss continues.

Is this relationship between volume and area universal simply because
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this also just completely follows from physics.  Kassy
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The Walrus

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Re: When will the Arctic Go Ice Free?
« Reply #1822 on: December 27, 2020, 02:53:07 PM »
Excellent example gerontocrat.  I have been arguing that same point for years.  The example I would use is an ice cube.  If every side melted 30%, any one side would decrease 30% (thickness), while any surface area would decrease 51%, and total volume would decrease 66%.  That real life example is close, and it would be real interesting to follow it to completion to help settle the area/extent vs volume debate.

binntho

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Re: When will the Arctic Go Ice Free?
« Reply #1823 on: December 28, 2020, 08:15:35 AM »
Good idea Gero to use that big floating lump of ice as an experiment in seeing how the extent / volume ratio changes leading up to the inevitable convergence at 0 of both measures.

We should be careful, though, not to draw too many conclusions, the big Antartic lump is not sea ice (it is fresh-water glacial ice that has broken off an ice shelf), and it is very much thicker than normal sea ice will ever be.

I would expect the ice to disappear very quickly once structural integrity breaks down. Due to the excessive thickness, extent might actually increase temporarily, specifically if distances between breakup fractures is less than the thickness at the time (the narrow wedges will simply fall on their sides as they break away).

The rush to convergence will possibly start while the ice is signifcantly thicker than our normal sea ice due to it's location in the middle of an open ocean with the concomitant swells and wave action.
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 #1824 on: December 28, 2020, 02:47:17 PM »
The example I would use is an ice cube.
Sea ice is not a cube, it is very thin compared to its length and width, which is why the analogy and the insights derived from it are irrelevant.

The Walrus

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Re: When will the Arctic Go Ice Free?
« Reply #1825 on: December 28, 2020, 02:54:40 PM »
The example I would use is an ice cube.
Sea ice is not a cube, it is very thin compared to its length and width, which is why the analogy and the insights derived from it are irrelevant.

True, it is a simplistic examples.  In actual sea ice, extent is more relevant than volume, due to the very thin thickness.  Large percentage changes in a very small number can have a profound effect on the volume, while the extent (or area) appears to be little changed.

P-maker

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Re: When will the Arctic Go Ice Free?
« Reply #1826 on: December 28, 2020, 03:07:14 PM »
Oren,

the relative dimensions for individual sea ice-floes are not that different from those of A68-A.

In the Southern open ocean, also swells and currents are stronger than in the Arctic ice-pack during melting.

I guess it is premature to rule out a new learning experience from this ongoing devastation.

oren

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Re: When will the Arctic Go Ice Free?
« Reply #1827 on: December 28, 2020, 04:06:42 PM »
P-Maker, I agree with the A68 analogy and find it interesting, but the ice cube analogy is irrelevant.

Stephan

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Re: When will the Arctic Go Ice Free?
« Reply #1828 on: January 10, 2021, 09:48:17 PM »
It is time for the monthly update of my extrapolation when the extent [Ausdehnung], volume [Volumen], thickness [Dicke] and area [Fläche] will reach zero. The extrapolation occured linearly and by a logarithmic function; the latter one almost constantly resulting in earlier times (valid for volume and thickness, not for extent and area in the winter months). The December value now includes 2020.
Extent and area lie slightly below the long term linear trend, thickness and volume are close to their trend lines. The "BOE numbers" did not change (volume, thickness) and decreased by 5 years (extent, area) compared to December 2019.
So there is a further convergence between the "late values" (area, extent) and the "early values" (volume, thickness).
The order (earlier → later BOE) generally is volume < thickness < area < extent.

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

Click to enlarge it.
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crandles

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Re: When will the Arctic Go Ice Free?
« Reply #1829 on: January 14, 2021, 01:30:14 AM »
https://xkcd.com/2048/



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Logistic: I need to connect these two line but my first idea didn't have enough maths.


Stephan

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Re: When will the Arctic Go Ice Free?
« Reply #1830 on: January 14, 2021, 10:08:55 PM »
Luckily the Arctic Sea Ice graphs look much less scattered and chaotic than the ones in your sketch.
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