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Messages - Glen Koehler

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151
Arctic sea ice / Re: The 2020 melting season
« on: April 20, 2020, 12:12:13 AM »
And I can't recall any source that tracks melt ponding quantitatively, though looking at Worldview shows a telltale bluish color when melt ponding is widespread.
  Neven discussed visual estimates of melt pond prevalence on the ASI blog a few years ago.  It seems like a tool was being developed but never really arrived.

This from: https://neven1.typepad.com/blog/2014/04/more-on-melt-ponds.html#more
-------------------
Neven asks - "How difficult is it to create near real-time melt pond cover fraction data that can be compared to other melting seasons in the 2007-2013 period?"

We may not be that far away. One of the papers currently in discussion at The Cryosphere Discuss is Sea ice melt pond fraction estimation from dual-polarisation C-band SAR – Part 1: In situ observations (R. K. Scharien, J. Landy, and D. G. Barber).
http://www.the-cryosphere-discuss.net/8/805/2014/tcd-8-805-2014.pdf
Posted by: Kevin O'Neill | April 27, 2014 at 01:09
-------------------

And this
https://neven1.typepad.com/blog/2016/07/2016-melting-momentum-part-3.html?cid=6a0133f03a1e37970b01b7c87b7ac1970b#comment-6a0133f03a1e37970b01b7c87b7ac1970b

152
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 19, 2020, 11:28:37 PM »
 Last time I promise...
        ugh, I now realize that I can't use whole-Arctic values for linear regression because as peripheral seas melt out they can no longer contribute to the ice loss rate.  Thus a trend based on earlier years when those seas contributed to year-to-year losses is invalid because doing so contributes fictional negative volumes into the trend.

      The correction is to focus on the CAB trend only.  But even that combines earlier melting of the peripheral CAB areas with the areas where the final 1M km2 ice extent (the consensus threshold for BOE) is likely to occur.  The best approach I can think of is to partially correct for that by ignoring CAB data from 1979-1999 or 1979-2004 to discount the earlier years when the peripheral CAB areas still had September ice, and thus base the trend on losses after those areas were no longer contributing to the year-to-year losses.

      I looked at CAB Sept. average volume linear, polynomial and logarithmic trends for 2000-2019 and 2005-2019.  Starting in 2005 gives a flatter slope, and a lower R2 than starting in 2000.  Defining BOE threshold as 0.8K km3, the estimated date for when there is a 50% cumulative chance for having had a first year of BOE is 3.5 years earlier when using the 2000-2019 data.  The estimate for 95% cumulative chance of BOE is 5.3 years earlier using the 2000-2019 data.  And the date for when each Single year has a 50% chance of being <BOE threshold is 6.2 years earlier when using the 2000-2019 data.

      I also looked at CAA as a potential last refuge area, which was interesting because it brought to my attention the fact that in 2012 the CAA Sept. volume was almost down to zero. But then I found this map of the where the last 1M km2 ASI extent is expected posted by Tor Bejnar at https://forum.arctic-sea-ice.net/index.php/topic,417.msg122285.html#msg122285

     Comparing that "final ice extent map" to the NSIDC Arctic seas boundary lines at https://nsidc.org/data/masie/browse_regions shows that the final ice refuge is almost (perhaps entirely) within the NSIDC defined boundaries of the CAB.  In addition, the CAA trend has it blinking out shockingly soon.  So the estimates below are derived from the 2005-2019 CAB-only volume trend.  The CAB volume data are from PIOMAS, which defines the CAB boundary somewhat differently than NSIDC, but that should not affect the resulting date estimates. 

      I am using 0.8K km3 as the volume threshold proxy for BOE. If you don't like that, we all at least agree that 0 volume means zero extent.  This is the most demanding possible definition for BOE.  Using a 0 volume threshold only delays the 50% and 95% cumulative chance dates, and the 50% Single year date, by 3.0 to 3.3 years.  Thus, whether we define BOE as 0.8K km3 or Zero km3 doesn't make much difference.

      Enough fussbudgetry, here are the numbers for my latest and last attempt to use linear regression to estimate BOE dates.
 
*************************
DATA: PIOMAS Central Arctic Basin (CAB) September average volume estimates based on linear trend from 2005-2019.
Threshold: 0.8K km3  as an arbitrary definition of BOE based on volume.
Values rounded to the nearest whole percent.

Year    Chance of that single year     Chance of at least one year since 2019
            going below 0.8K km3           having gone below 0.8 km3
2020          0%                                        0%
2021          0%                                        1%
2022          1%                                        1%
2023          1%                                        2%
2024         2%                                         4%
2025         3%                                         6%
2026         4%                                       10%
2027         6%                                       15%
2028         8%                                       22%
2029       12%                                       31%
2030       16%                                       42% 
2031       21%                                       55%  First BOE more likely than not by 2031
2032       28%                                       67%
2033       34%                                       78%
2034       42%                                       87%
2035       49%                                       94%
After 2035, each single year has >50% chance of BOE
2036       57%                                       97%
2037       65%                                       99%
2038       72%                                     100%
2039       78%
2040       83%

    Finally, several points that seem worth repeating. 
     1) Some of the difference in intuitive impression for when the ASI will reach BOE status is due to the difference between the cumulative chance of a first year BOE (almost certainly to be followed by subsequent non-BOE years), and when each individual year has >50% of going below a BOE threshold.
   
     2) As experienced ASIF members have commented, melt season weather will determine when the first BOE occurs, and the Arctic may have already reached a state where BOE is within reach of an extremely warm and significant cyclone year.  But the trend analysis shown above estimates that ia first BOE year s unlikely until after 2030.

     3) Scientists who study ASI decline say that any such estimates are subject to +/- 20 years error due to high variability in the ASI!  (In other words "You don't know, and we don't know either!").

     4) BOE is an arbitrary marker, and the world won't end when there is a first BOE.  But it serves as an important observable and easily understood marker with visual impact to communicate climate change progression.  As the late-summer ASI ice decline continues and eats into August (which trails September by only a few years) and into July, the effects on albedo, weather, ecosystems etc., and the consequent impacts on human civilization, will increase.   

153
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 18, 2020, 06:40:24 PM »
FYI - The straight line linear trend used to calculate the probabilities in previous past was derived by regression of all the PIOMAS September average volumes vs. year for 1979-2019.  That trend was then extended into the future to get future estimated Sept. average volume.

     The linear model explains 88.6% (adjusted R2 88.3%) of the variation between individual years.  The standard deviation for the iinear model estimates minus observations was 1.38 K km3.  Probabilites were calclulated by comparing the number of standard deviations between the value estimated for each single year and the respective threshold, and evaluating that number of standard deviations against a normal distribution z score. 

      I did a visual check of residuals to evaluate the assumption of normal distribution.  They looked OK to me, and they were virtually, if not completely, identical to the residuals chart shown on the linear Wipneus Sept. volume graph at https://sites.google.com/site/arctischepinguin/home/piomas .  The pattern of residuals suggest that a curved trend would be a better fit.  I use the straight-line trend because it is more reliable and conservative for making future projections beyond the range of data.  A curved trend would create much earlier estimates for dates when Sept. volume goes below a threshold volume, as shown on the Wipneus exponential chart.  I did not do any formal testing of the residuals or the assumption of normality. 

    I think the trend estimate based solely on volume trend gives dates 5 years earlier than the previous attempt to estimate 1.0M km2 Extent (https://forum.arctic-sea-ice.net/index.php/topic,2348.msg252395.html#msg252395) because the volume trend (being a value based on two multiplicative declining trends) is steeper than thickness trend used for that estimate, so the combination with thickness trend diffused the steep volume trend in the attempt to estimate Extent. But this probably just confusing you and is making my head hurt.

     And I hereby disavow my attempts in posts 1477, 1478 and 1480 to accommodate those who think Extent should be treated as a driving factor.  It just ain't.  As the great Juan C Garcia has as his tagline "Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.  -> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost."
   
    But lest I lead anyone into sin, I must acknowledge that the experts come up with significantly later dates for BOE, e.g. https://interactive.carbonbrief.org/when-will-the-arctic-see-its-first-ice-free-summer/  --- If temperatures rise by 2C, then:  "...the Arctic has a one-in-five chance of seeing its first ice-free summer in 2035, according to the study. The chances of an ice-free summer in any given year rise to one-in-two by 2045."

    Sorry for the longwinded post(s), but there it is, my best number crunching shot at using the good ole, brute force but robust straight-line volume trend to estimate when the ASI will
a) break the 2012 record (proposed answer = soon, good chance in 2020, and almost certainly by 2023), and
b) will have had at least one BOE year with volume <= 0.8K km3 (proposed answer = sometime
 in 2025-2030, sooner than most folks seem to think). 

154
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 18, 2020, 05:56:33 PM »
Can you check the 2012 volume record of 3.79k km3 above? In post #1545, you indicate 3.399k km3 for 2012 and 3.794k km3 for 2019.

Post #1545 was about ice volume in just the CAB - Central Arctic Basin, not the entire Arctic.
     The point being discussed there was that the decline of CAB volume is almost as steep as the Arctic as a whole.  That argues against the CAB being able to resist melting because of high latitude.   Though it is still possible that as peripheral parts of the CAB melt out, continued losses from the CAB will stall when the only remaining ice is at the highest latitudes.  But I don't see evidence for that in the observations so far.
     Post #1574 just above is about volume for all of the Arctic sea ice.
https://forum.arctic-sea-ice.net/index.php/topic,2348.msg260423.html#msg260423


RE GAC 2012 - Agreed, Arctic cyclones are a regular occurrence.  The analysis cited was about the combination of unprecedented intensity and scale of the GAC 2012.  The fact that it hit at the worst possible time for damaging the ice was icing on the cake.


RE Linear trend probabilities for being below the current low volume record for the entire ASI
          The multiplicative effect that generates a cumulative probability for at least one year going below a threshold value makes those probabilities much higher than for any single year.  It is the same math that makes compound interest on savings so powerful over time (or drives up the interest charges on a 30-year mortgage).

    Here are details for the probabilities posted in #1574
Threshold:  Current low record ASI (entire Arctic) September volume of 3.787K km3
    Values rounded to the nearest whole % for display.

Year    Chance of that single year       Chance of at least one year since 2019
          being below 3.787K km3         having gone below 3.787K km3
2020      47%                                    47%
2021      54%                                    76%
2022      61%                                    91%
2023      68%                                    97%
2024      74%                                    99%
2025      80%                                    99.8%
2026      84%                                  100%
2027      88%
2028      91%
2029      94%
2030      96%
2031      97%
2032      98%
2033      99%

*****************************
Threshold:  Using 0.8K km3 as arbitrary definition of BOE based on volume.
Derived from consensus Extent BOE threshold of 1M k2,
and E - V/T. 
    And the observation that linear trends for thickness and volume reach 0.8m and 0.8K km3, respectively, at roughly the same year.  Thus E = 1.0 when V/T = 1.0, which 0.8K km3 / 0.8m fulfills.
    Values rounded to the nearest whole % for display.

Year    Chance of that single year     Chance of at least one year since 2019
          going below 0.8K km3           having gone below 0.8 km3
2020      4%                                       4%
2021      6%                                     10%  because 1 - [(1-0.04) * (1-0.06)]
                                                                = 1 - (96% * 94%) = 1 - 90% = 10%
2022      8%                                     17%   same as above but keep adding multiplier terms
                                                                  e.g 1 - (96%*94%*92%) = 1 - 83% = 17%   
2023    12%                                     27%
2024    15%                                     38%
2025    20%                                     51%
2026    26%                                     63%
2027    32%                                     75%
2028    38%                                     84%
2029    45%                                     92%
2030    52%                                     96% 
Starting in 2030, each single year has >50% chance of BOE
2031    59%                                     98%
2032    66%                                     99%
2033    73%                                     99.8%
2034    78%                                   100%
2035    83%
2036    87%
2037    91%
2038    93%
2039    95%
2040    97%

155
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 18, 2020, 01:43:20 AM »
    1) Good points Oren.  I had forgotten the MYI aspect of the "slow transition" discussion and focused on the "faster early winter heat loss from open water" and the "quick-growing thin recovery ice" aspects.  FWIW (i.e. pure guesswork), I think the lack of MYI export to support the volume loss rate is likely to be compensated for by degradation of the structural integrity of the remaining weaker thinner ice being more vulnerable to shattering by wave action, thus more mobile, and therefore more susceptible to flushing out the FRAM.
   
    2) Just to prove that I am big-hearted, fair-minded guy, I will throw a bone to after-2030 crowd and say that I do not agree with "2012 August GAC was not a fluke."  An analysis of the 2012 GAC found that it truly was an extreme outlier event, "The most extreme August Arctic cyclone (out of a population of 1618)."  The authors did not say so, but I presume that also means it is not likely to be repeated anytime soon. 

      They also noted that in addition to being a meteorological oddity, the GAC 2012 was perfectly timed to wreck ice already weakened by a strong melt season.  (The great Arctic cyclone of August 2012.  Ian Simmonds and Irina Rudeva,  Geophys. Res. Ltr. 39, L23709, 2012.)
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2012GL054259.

    That said, anything that happened once can surely happen again.  Even more so in a rapidly changing Arctic.


    3)  RE Phoenix interest in markers for when to throw in the towel for a 2030 BOE prediction.  The stats around the linear trend allow for estimating a cumulative probability for at least one year having gone below the 2012 volume record (3.79K km3).  Those values are:
2020    47%
2021    75%
2022    90%
2023    97%
   
    Translated to English, that means a new volume record is entirely possible but not expected this year.  But it is expected by Sept. 2021, strongly expected by 2022, and almost certainly by 2023.  If the record has not been broken by 2023 then one who worships regression religion would have to conclude that the reason is very likely due to failure of the linear trend (as stated in 2020), not just annual variability (for which the Arctic sea ice is infamous.) 

   Same reasoning gives a 50% cumulative chance of a first BOE (@ 0.8K km3 volume, 0.8m thickness, and 1M km2 extent) by 2025, and a 95% chance by 2030.  By 2030 each individual year has less than a 50% chance (and declining each year) of avoiding a September BOE.  By 2040 just about every year would have a September BOE.  This is one bet I'd like to lose.

156
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 17, 2020, 06:47:17 PM »
.... on the other hand
   - Simple linear regression has performed better at estimating future ASI volume over the past 10 years than the Earth System models.

   - As far as I can tell, reinforcing "positive" feedback mechanisms (thinning ice with less structural integrity, mobility, and susceptibility to export; longer wind fetch for more wave action; albedo reduction during melt season and higher water vapor (a powerful GHG) from more open water; weakening Arctic isolation from warm air masses and possible increase of cyclone activity from warming waters etc.) either match or exceed the number and impact of suppressive "negative" feedbacks (greater winter heat loss from open water, rapid recovery of thin first-year ice extent).

   - Higher latitude of the remaining September ice does not appear to be a strong protective factor.  The remaining ice is not centered around 90N.  CAB volume has been decreasing almost as fast as the Arctic as a whole.

    What is the argument that simple linear regression of ASI volume is not a reliable predictor?  What mechanism is going to kick in now that September volume has decreased by 75%(!) in just the last 40 years, from 16 down to 4K km3, to interrupt continued progression along this trend until the cumulative Sept. volume loss reaches 95% and BOE at 0.8K km3?

    The X2 polynomial curved regression (labeled "exponential" on the Wipneus graph page  https://sites.google.com/site/arctischepinguin/home/piomas)  shows an accelerating rate of decline that is a statistically better fit to the data than the straight-line trend.  (That said, I don't trust it for future trajectory).

    Global GHG gas emissions not only continue, until 2020 they continued to increase at an increasing rate.  Even if there is an emissions drop because of economic calamity in 2020, that is not a reduction in atmospheric CO2, just a slowing of the rate at which we are adding more CO2 into the air.  Earth system response for global average surface temperature shows signs of acceleration as carbon sinks are weakened and new CO2 sources (e.g. permafrost) activate.  Yada yada.

    It seems ridiculous for me to opine about this when there are expert analyses available. A recent comprehensive review (IPCC, Special Report on Cryosphere, Sept. 2019) is at https://www.ipcc.ch/srocc/chapter/chapter-3-2/  (top section is good, but also scroll down to section 3.2.2.1).

    Here is the key sentence (edited to remove citations):
     "There is a large spread in the timing of when the Arctic may become ice free in the summer, and for how long during the season as a result of natural climate variability, scenario uncertainty, and model uncertainties related to sea ice dynamics and thermodynamics. Internal climate variability results in an uncertainty of approximately 20 years in the timing of seasonally ice-free conditions, but the clear link between summer sea ice extent and cumulative CO2 emissions provides a basis for when consistent ice-free conditions may be expected (high confidence). "

    God bless IPCC, but that report while detailing the driving factors and current status, doesn't stick its neck out to estimate a specific date for first and regular BOE.  The experts don't have a crystal ball either, and the Wipneus linear volume trend looks compelling. 

    If you know of reasons why we should not expect to continue following that path (with the inevitable ups and downs around it due to annual variability of course) please educate me.  I see September ASI as reaching its first BOE (defined as ca. 0.8K km3 volume associated with 1M km2 extent) between [edit 2024 and 2036] 2021-2030, with a best-guess of [2028- 2029] 2025. 

157
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 16, 2020, 09:30:02 PM »
The following statements are excerpts from:
Dirk Notz, 2015.  How well must climate models agree with observations?
Phil. Trans. R. Soc. A.37320140164.  http://doi.org/10.1098/rsta.2014.0164

     “…the tuning of individual models to match specific metrics can cause a false sense of adequacy of the model for a particular purpose. If, say, a model is tuned to match the observed sea-ice area over the past 10 years, this does not imply that the model's physics allows the model to give credible projections of the future evolution of the sea-ice cover. ”
 
     "…the tacit assumption that we can infer the quality of simulating the future evolution of a climate observable from the quality of simulating its past evolution for which observational data might be available. However, the link between the model performance for a past evolution and the performance for the future evolution of the system is often not clear. "

     “… the multi-year sea ice that used to be the prevalent ice type in the Arctic until some years ago has distinctly different properties compared with the first-year ice that covers much of the Arctic Ocean today. If the processes that a particular model represents well are parametrized based on the properties of the multi-year sea ice, such a model is likely to suffer in performance when simulating the future evolution of the ice pack. ”

     “To establish a clear link between the past and the future evolution of a specific observable, one ideally uses observational data from periods where the climate state was similar to the one that one aims at simulating. This is reflected by the growing interest in paleo data in particular from those periods where the climate state of the Earth was distinctly different from what it is today. Observational data from such periods allow us to evaluate the model performance over a large range of climate states...”

     “Unfortunately, for many observables we currently have no reliable data that would allow us to test climate-model performance for different climate states. "

     “It is often assumed that a period of 30 years is sufficient to neglect internal variability of the Earth's climate system, but, as also shown in the following, this assumption usually does not hold during periods of a rapidly changing climate.”

     “A 30-year-long averaging period can be insufficient to substantially reduce the impact of internal variability, in particular during periods of a significant change in external climate forcing.”

-----------------
    Notz 2015 is a corrective reminder that just because I have a hammer, not everything is a nail.  (Regression is one form of statistical analysis I understand better than others, so I like to use it.)  My predilection for extending a linear regression trend forward is not necessarily legit.  The experts don't rely on such a simplistic method (then again, they sort of do sometimes, see Part 2 below.)
   
     Notz provides caveats about the difficulties of making projections about the future state of a highly variable, possibly chaotic system, that is undergoing rapid change, therefore preventing comparison to and trend analysis extracted from a rather short chronological record. Looking back, the Earth System models discussed by Notz have underestimated the rate of Arctic sea ice decline vs. observations.  Looking ahead, there was a wide spread in Earth System model estimates for when ASI extent would go below < 1M km2, as shown in chart below:



Figure 1. (a) Each dot specifies for a particular simulation the first year during which Arctic September sea-ice area drops below 1 million km2 for CMIP5 simulations under the scenario RCP 8.5. The respective model is identified along the y-axis. (b) Each dot specifies the CO2 concentration at which the Arctic summer sea-ice area drops below 1 million km 2 for the RCP 8.5 scenario. No dot indicates that the specific model only gets ice-free after the year 2100 and a CO2 concentration of more than 900 ppm.

     It will be really interesting to see what the new generation of CMIP6 models say about the future trends for annual ASI extent and volume.

********************
Part 2.   Notz and Julienne Stroeve coauthored a 2018 paper that associated global average surface temperature with when the Arctic sea ice Extent would begin to fall below 1M km2.
https://link.springer.com/article/10.1007/s40641-018-0113-2
 
      That temperature works out to be about 1.7C above the 1850-1900 average, which on our current trajectory we could reach between 2034-2046, with a narrower "best guess" range of 2036-2043. (Temperature estimates are based on a mixture of RCP4.5, RCP4.5 adjusted for observations, ditto RCP8.5 and 8.5 adjusted, and two methods to extend recent observed temperatures and rate increases into the future).  Note - these are the dates I came up with, they are not from Notz and Stroeve. 

      That study also correlated ASI extent going below 1M km2 with cumulative CO2 emissions.  Future emissions are of course unknown, but using an International Energy Agency projection for future emissions trend, the "CO2 - ASI extent" correlation gives an estimate of 2033-2036 for going below 1M km2.  Again - my dates, not from Notz and Strove.

158
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 15, 2020, 05:34:24 PM »
Wipneus rocks!

159
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 15, 2020, 05:08:01 PM »
Phoenix - I pulled the 2029 estimate for "BOE by September volume at ~0.8K km3" and 2024-2036 95% confidence interval from the Wipneus linear September volume chart at
https://sites.google.com/site/arctischepinguin/home/piomas

160
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 15, 2020, 09:33:57 AM »
RE:  CAB Sept. Volume data
  I think those values may be the minimum daily values, not the September average values. 
But that doesn't change the resulting inferences much.
2000:  8.370
2012:  3.399
2019:  3.794

161
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 15, 2020, 09:01:31 AM »
  I'll flaunt my ignorance one more time to say that I assume the current thickest September ASI, and last to melt residual ice, is along the northern edge of the CAA because the currents move the ice to pile up there.  Gerontocrat recently posted about the nooks and crannies of the CAA opening up and transitioning away from being a wall that allows ice to pile up, and into another gateway for ASI export southward into a lower latitude melting zone.  If so, yet another accelerating mechanism.  Melting begets melting.

162
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 15, 2020, 08:28:13 AM »
1) Do you have the CAB volume data by year from 2000 on to share?
       ***I pull Volume data from the twice monthly Wipneus PIOMAS updates.

I only have it by daily values.  Too many numbers to share and too late and not enough time to create a pivot table. 

CAB Sept. avg. Volume
2000:  8.370
2012:  3.399
2019:  3.794


2) You are using an upper case "M" for your volume measurements. This is generally representing millions. I think you meant to use a "k" for thousands of km3 in volume.
     ***ooops.    Thanks for catching that.  Now corrected.

3) The hypothesis of the remaining ice at minima is that the more resilient ice is based upon two criteria. 1) Bathymetry AND 2) Distance from a large heat advecting land mass. The second criteria is the more dominant variable and has a tad more nuance. Greenland should not be considered a large heat advecting land mass because it is covered in snow year round and doesn't experience heat waves like Alaska and Siberia which project heat well into the ocean. 

At the September minimum, there is no ice adjacent to Alaska, Siberia, Scandinavia or the Canadian continent which bleeds heat into the southern portion of the CAA. Greenland is the only large land mass which has ice adjacent to it and the theory attributes this to Greenland being a cold land mass. Pretty self explanatory.

Bathymetry is more relevant is trying to understand how far the Atlantic and Pacific intrude into the CAB. On the Atlantic side, there seems to be a pause at ~ 82N which corresponds to the area where the bathymetry shifts from the shallow Barents Shelf to the deep Nansen Basin. The most northern areas of the Beaufort and ESS have also been more resilient due to the combination of depth and distance from land.
   ***Lots of upthread discussion on bathymetry, e.g. https://forum.arctic-sea-ice.net/index.php/topic,2348.msg237718.html#msg237718.  I don't know enough to say anymore than that to my eye the pattern of current Sept. ice, and the distribution expected by experts for the last to melt ice to hug the CAA, does not appear to follow either bathymetry or distance from land

4) My limited understanding of the volume data is that the record low volume was set in 2012. If you are correct that the CAB volume declined by 55% from 2000 to 2019, then the decline from 2000 to 2012 would have been even greater than 55% with an increase since 2012. I don't have the numbers handy, so if you could provide that would be great.
***See #1.


163
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 15, 2020, 07:41:53 AM »
I agree with you binntho.  Humans are rather resilient.

    Different people in this discussion are defining the problem differently.  I agree that humans won't go extinct.  But wrecking the climate system we depend on to feed 7.5 billion people, forced migration from large areas of densely populated coastal areas, more forced migration by altered monsoon patterns, heat waves/flooding/drought etc. will lead to horrific consequences for many millions, and probably billions of human beings.  Humans will persist, but human civilization would/will suffer major involuntary evolution.

    And while I have the pulpit -- I agree that a 1 million km2 Sept. BOE definition is arbitrary, but it is not meaningless.  It serves as an important marker for when systemic change has passed an easily observable, intuitive (and thus politically significant), and functionally important milestone.  The threshold isn't zero because there will continue to a fraction of the original September Extent that hangs on much longer, but going below 1M km2 signifies a huge change from the preindustrial condition (the 1979-1984 average Sept. Extent was ca. 7.3M km2). 

     Comparing trend lines for Extent, Volume, and Thickness, and remembering that E = V/T, shows that when Extent reaches 1M km2, average Sept. Thickness will be at about 0.8 meter, and average Sept. Volume will be at about 0.8K km3.  The linear trend for volume decline indicates that there is a 50% chance of 0.8K km3 and Sept. BOE by 2029 (with a 95% confidence interval of 2024--2036), i.e. not long from now on our current trajectory.

     Extent is an incomplete measure of the status of the Arctic sea ice.  But an 87% reduction in September ice cover has major ecological and physical systemic consequences, such as the effect on subsequent ocean water insulation vs. heat exchange to the atmosphere leading into winter. 

      I suppose the albedo effect from Extent loss in September is probably minimal because the sun is so low in the Arctic sky by then, but once Sept. starts hitting "BOE", August will only be a few years behind.  And as August approaches 1M km2, that means that July is losing ice cover too.  The albedo impact from a reduction in ice cover Extent in August, and especially July, would have a strong effect on Arctic energy dynamics.

      More scary news: The current year to date global average surface temperature is running well ahead of where it "should" be, given that we are near the bottom of the solar cycle and in ENSO neutral territory.  Even accounting for incremental year-to-year warming from rising CO2e, 2020 should run a bit cooler than 2019 and well behind the current record holder for the warmest year in 2016.  But a projection for the final year-end 2020 average temperature is running just behind 2016 and ahead of 2019.  This suggests that the warming rate is accelerating.  None other than James Hansen noted the same in monthly NASA GISStemp message today. 

     As bad as the COVID pandemic is, all expectations are for it to subside within a few months (or a year or two at most).  If we disrupt the climate, the inertia of that system (ocean heat) and multi-decadal lag for surface weather impacts means we will be stuck with the damage for decades at the very least even with remedial GHG removals (for which we do not yet have scaleable methods), and more likely multiple centuries.  This is not a drill.  This is really happening.  I have to remind myself about that regularly because it is so hard to fathom. 

      It's a real morality tale. I agree with those who recognize the absolutely stunning pace of scientific knowledge acquisition and technological innovation occurring at the same time as we wreck the life support system of the only planet we have.  If we all pull in the same direction, and get rid of "leaders" who mislead, there is a chance for the disaster not to fully unfold.  But we are already too late to avoid the damage entirely as more than a little has already happened, and a lot more is coming in the next 20 years.

     

164
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 15, 2020, 06:45:07 AM »

While I'm far from certain, I'm proposing the possibility that ice N of 80N which is sitting above deep water and far  from land masses (other than snow covered Greenland which doesn't supply a lot of heat advection to the CAB) is a much more resilient animal which will last much longer than the rest of the "High Arctic". I'm basing this possibility upon observation to date. In the absence of data which measures the relationship of sea ice minima to bathymetry and proximity to land, I'm just throwing out an anecdotal argument.

     Sorry to repeat an upthread post - but there are data to address the "High Arctic will hold on longer" hypothesis:
    A linear trend line of whole-Arctic September Volume shows a decline from 11.1 to 4.2 K Km3 (edit)  a 62% decline from 2000 to 2019..

    For the CAB alone volume declined 55% , for the same time period (from 8.4 to 3.8 K km3).  So while the CAB lost volume at a slightly slower rate, it was not much slower.

     I think this argues against the idea that progression towards a largely ice-free September (followed by August, October, July) will be stalled because the final ice refuge is at too high a latitude.

      The Sept. ice is not centered around 90N anyway, but is centered south of 90N on the Greenland/Canadian side.  The location of the remaining Sept. ice does not match bathymetry very well.  So I don't see that as a saving grace either.  Protection by location matters even less when you factor in the increasing mobility of thinning ice, reduction of land-fast ice, increased open water/wind fetch, increased warm air incursion, and increased melt season storm potential as greenhouse gas loading and global heating exacerbated by Arctic amplification continue.

165
Arctic sea ice / Re: The 2020 melting season
« on: April 15, 2020, 06:20:27 AM »
I don't get it. How can this scale be in cm? Shouldn't that be decimeter? 72 cm is less than a meter. 70 dm is 7m.
Not much snow in Siberia, is there? But I'm pretty sure that's more than 2 cm...

Dr. Sean Birkel (who singlehandedly conceived, built, and runs Climate Reanalyzer) sent me this reply about the legend on the snow depth map:
"The plotted units were inches, while the title showed cm.  Found bug...now the plotted values are in cm set to a cm specific color scale."

   Thus, before the correction the snow depth indicated was only 40% of the actual.  Now corrected.

166
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 11, 2020, 08:59:10 PM »
    Thanks Gerontocrat.  That's devastating.  (That's like thanking a cancer doctor for news about a brain tumor.  But better to know the truth than not).

    One wonders what profound and cascading impacts an 85% loss in the 12-month running average Arctic sea ice volume would/will create, such as a decrease in April - August albedo, increase in October - March ocean heat transfer to the atmosphere, increase in Arctic water vapor, altered polar jet stream strength-path-stability, and altered ocean currents.  Individually each is ominous, and even worse when you consider the potential for interactions.

   It will be interesting to see what the CMIP6 models have to say.  The CMIP5 models did not represent ASI loss very well.  New factors have been added and refinements made to existing factors for the new generation of CMIP6 models.  The CMIP6 models are supposed to be operational by August 2020, though reportedly some portion won't make that deadline.  And it will probably take until the next IPCC reports in 2021 to see a comprehensive analysis of output from those supposedly enhanced models. 

     The next batch of IPCC reports are due in 2021 (April - physical science, September - mitigation, October - impacts, vulnerability, & adaptation).  The final synthesis report is due the first half of 2022.  Those reports could be the sink or swim message that finally generates concerted global action.  Maybe the current COVID pandemic provides a valuable lesson that the world can change quickly, that we are interdependent, and that global cooperation is essential.

     

167
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 09, 2020, 04:33:52 AM »
That seems like a ridiculously extreme standard to set? Do you really think there will be a point anytime in the next century when ice isn't breaking off of GIS or CAA? As long as that is going on, there will be SOME ice in the Arctic Ocean. Right? Am I missing something here?

     No, I don't think the Arctic Ocean and surrounding seas will have had a year that is entirely free of sea ice in September by 2030.  I agree that ice will be breaking of the GIS for centuries, thus preventing reaching absolute zero.

     It's not a prediction, it is just a hypothetical mathematical threshold for considering when the Arctic reaches some interpretation of being "effectively ice free". 

     Extrapolation of trends far into the future often results in unrealistic values.  But a straight line trend is less susceptible to this problem than a curved trend.  And in this case, 10 years from now is not that far beyond the 41-years of observations from which the trends were derived.

     Just as the Extent-based threshold for BOE leaves room for small pockets of residual resistant ice, and things like GIS calving, so should a Volume-based definition of BOE.  That's the reason for the follow-up post using a more lenient definition of BOE.

    The specific % and year numbers are not really the point.  They are just a vehicle to convey the fact that continuation of current trends leads to a radically altered Arctic in a very short number of years (actually, it has already been radically altered, but even more extreme change is coming).  The crisis is imminent.  We can stop using 2100 as the benchmark for climate change effects, because 2030 or 2040 will bring plenty of climate change impacts. 

    Anyone looking for a rationale for addressing climate disruption need look no further.  The Arctic alone provides irrefutable and compelling measured evidence that the current trajectory of greenhouse gas loading into the atmosphere will lead to catastrophic consequences much sooner than most people seem to realize.

    As the estimates show, even when there is high probability that a 1st September BOE has occurred, the following years are more likely than not to be above BOE status in September.  And even in the BOE years, there will be ice in August and October (for the early BOE years anyway).  The world won't end with first BOE.  But in terms of disrupting weather patterns, extreme weather, accelerated heating etc.,  Arctic Ocean BOE is a significant marker for the transition away from the climate stability that has allowed human civilization to thrive for the past 8,000 years. 

     Even with all our technological means to insulate ourselves from nature, agriculture and numerous other life support systems rely on a supportive climate foundation.  Food does not come from grocery stores.  Food calories ultimately depend on the right growing conditions defined by temperature, rainfall and other factors.

168
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 09, 2020, 04:25:51 AM »
  One more for the road.   Requiring zero volume for an estimate of BOE based on V = E*T estimate seems too demanding. 

   The Extent-based definition of BOE at 1 million km2 is 13.7% of the 1979-1983 5-year average September Extent (7.31 km2).

   Let's use the same ratio for a Volume-based BOE definition.  The average September Volume in 1979-1983 was 14.95 km3. 
0.137 * 14.95 = 2.05 km3.

   Using that as the threshold for a BOE gives the following probabilities.

Year      Single year      Cumulative
            chance for       chance for 1st year
           < 2.05 km3      of < 2.05 km3
2020        15.0%            15.0%
2021        17.0%            29.4%
2022        19.1%            42.9%
2023        21.4%            55.1%
2024        23.7%            65.7%
2025        26.1%            74.7%
2026        28.5%            81.9%
2027        31.0%            87.5%
2028        33.5%            91.7%
2029        36.0%            94.7%
2030        38.6%            96.7%


169
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 09, 2020, 03:57:05 AM »
Single year and Cumulative probabilities for a ZERO volume year (as estimated in previous post).  Zero volume is unrealistic and the strictest possible definition for a BOE, but we have to have some criterion to estimate a date for BOE.

   Single year      Cum chance of first,
   chance of 0 Vol.     0 Vol. year

2020       3.0%           3.0%
2021       3.6%           6.5%
2022       4.3%         10.5%
2023       5.1%         15.1%
2024       5.9%         20.1%
2025       6.9%         25.6%
2026       7.9%         31.5%
2027       9.0%         37.7%
2028     10.2%         44.1%
2029     11.5%         50.5%
2030     12.8%         56.9%
2031     14.2%         63.0%
2032     15.7%         68.8%
2033     17.2%         74.2%
2034     18.8%         79.0%
2035     20.4%         83.3%
2036     22.0%         87.0%
2037     23.6%         90.0%
2038     25.2%         92.6%
2039     26.8%         94.6%
2040     28.4%         96.1%

170
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 09, 2020, 03:22:21 AM »
   I confess to treating the Wipneus straight line PIOMAS September volume trend like gospel. 

    We all agree that when any of the three (Extent, Thickness, Volume) hits zero, that wipes out the other two.  I guess a case can be made that the assumption that Volume drives Extent is just an assumption and no more valid than putting Extent or Thickness in charge.

    If I use the same method to estimate future September Volume from extrapolated linear trends for September Extent and Thickness, here is what results

Year      Ext    Thick   Volume =E*T
2020      4.34   1.05      4.57
2021      4.25   1.03      4.37
2022      4.17   1.00      4.17
2023      4.09   0.97      3.98
2024      4.01   0.95      3.79
2025      3.92   0.92      3.61
2026      3.84   0.89      3.43
2027      3.76   0.87      3.26
2028      3.68   0.84      3.08
2029      3.59   0.81      2.92
2030      3.51   0.79      2.76
2031      3.43   0.76      2.60
2032      3.35   0.73      2.45
2033      3.26   0.70      2.30
2034      3.18   0.68      2.16
2035      3.10   0.65      2.02
2036      3.02   0.62      1.88
2037      2.93   0.60      1.75
2038      2.85   0.57      1.62
2039      2.77   0.54      1.50
2040      2.69   0.52      1.39
2041      2.61   0.49      1.27
2042      2.52   0.46      1.17
2043      2.44   0.44      1.06
2044      2.36   0.41      0.96
2045      2.28   0.38      0.87
2046      2.19   0.35      0.78
2047      2.11   0.33      0.69
2048      2.03   0.30      0.61
2049      1.95   0.27      0.53
2050      1.86   0.25      0.46
2051      1.78   0.22      0.39
2052      1.70   0.19      0.33
2053      1.62   0.17      0.27
2054      1.53   0.14      0.21
2055      1.45   0.11      0.16
2056      1.37   0.08      0.12
2057      1.29   0.06      0.07
2058      1.20   0.03      0.04
2059      1.12   0.00      0.00

   

171
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 09, 2020, 01:57:50 AM »
  The consensus definition of Arctic Ocean BOE is when Extent is below 1 million km2.

   The observed linear trend for decline in Volume is much steeper than the linear trend for decline of Extent.  Ultimately, zero Volume means zero Extent, so the two trends have to meet as Volume approaches zero.

   So instead of using the linear trend for observed Extent, I used the linear trend for Extent as estimated from Volume and Thickness, i.e. E = V/T.  The standard deviation of errors from using that method of estimating Extent from 1979 through 2019 was 0.543 km2.  (Linear trend Volume and linear trend Thickness were used to estimate Extent.  The estimate was compared to the observed Extent for each year to measure the annual estimate error.)
   
    The Volume and Thickness trends were extrapolated into the future and used to estimate future Extent.  The standard deviation for errors using that method and assumption of a normal distribution were used to estimate the probability for how likely Extent in that year would be below 1.0 million km2.  Individual year probabilities for <1 million km2 were used to calculate the cumulative chance for first BOE. 

     Extrapolating linear trends far into the future ignores potential negative suppressive and positive reinforcing feedbacks.  The resulting percentages are fairly consistent with estimates based on trends and correlations described by Notz and Stroeve 2018 and Stroeve and Notz 2018 (https://forum.arctic-sea-ice.net/index.php/topic,2348.msg239574.html#msg239574) but are earlier than inferred from statements in the 2019 IPCC special report on the cryosphere.

    The bottom line is that according to these trends, the first BOE is likely to have occurred by 2029 and very likely by 2031.  Also note that Arctic sea ice variability is so high that is been said (2016 study cited Daisy Dunne in Carbon Brief article, https://forum.arctic-sea-ice.net/index.php/topic,2348.msg239698.html#msg239698) that any such estimate needs to include a +/- 20 year window to account for that variability!  So perhaps a better estimate would be "The next extremely warm melt season combined with Arctic storm activity." 

     The significance of all these numbers is that a critically important component of the Earth's climate system that has been relatively stable for thousands of years is expected to transition to a radically different state very soon.  While scientists are still trying to understand the impact of such a change on climate and on weather, as Jennifer Francis put it “How can it not affect the weather? It’s such a huge loss in the Earth’s system.”

                                       Extent     Number of    Single year   Cum.
          Thickness   Vol.      = V/T     StdDev from  chance Ext.   chance
 Year       (m)     (M km3)  (M km2)    1.0 km2     <1M km2    1st BOE
                                    
2020        1.05      3.92    3.72           5.0              0.0%       0.0%
2021        1.03      3.60    3.50           4.6              0.0%       0.0%
2022        1.00      3.28    3.27           4.2              0.1%       0.1%
2023        0.97      2.95    3.03           3.7              0.2%       0.3%
2024        0.95      2.63    2.78           3.3              0.6%       0.9%
2025        0.92      2.31    2.51           2.8              1.6%       2.5%
2026        0.89      1.99    2.22           2.3              4.1%       6.5%
2027        0.87      1.66    1.92           1.7              9.6%     15.5%
2028        0.84      1.34    1.60           1.1            19.8%     32.3%
2029        0.81      1.02    1.25           0.5            36.0%     56.6%
2030        0.79      0.70    0.89          -0.2            56.4%     81.1%
2031        0.76      0.37    0.49          -0.9            76.4%     95.5%
2032        0.73      0.05    0.07          -1.7            90.6%     99.6%
 

172
Arctic sea ice / Re: Global sea ice area and extent data
« on: April 06, 2020, 03:33:11 AM »
Penguinia!

173
Arctic sea ice / Re: Global sea ice area and extent data
« on: April 06, 2020, 02:16:14 AM »
I liked it too.

174
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 06, 2020, 02:12:05 AM »
ooops, so indeed I was misreading it.   Big difference between an X and O! ::)

175
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 06, 2020, 12:39:39 AM »
Quote
2012 was a shooting star - phut, & it was gone. 2016 was the steady burn that really matters.
But there could be another shooting star in 202X. This will be at least as likely to be the first BOE as is a gradual drop down year by year.
There will be another (at least one) shooting star in 202X, including the first BOE year.
   I don't see a basis for expecting a BOE in 2020.  Granted the system is giving hints of qualitative, functional change (the Beaufort Sea could be the linchpin) but there is still too much ice to get to BOE this year. 

     Stephan - your own regressions say that we are still some years away from a likely BOE, and that end-of-March observations are not very predictive of September for Extent or Volume, so I don't understand your reasoning if I interpret your post as saying a BOE is likely in 2020.

     Are you expecting massive export in 2020 as ASI ice pack loses structural integrity and resistance to currents and wind, and just flushes out the Fram Strait?  That seems to be the only way to reach BOE in 2020.  Even a repeat of 2019's string of warm months was only able to melt the ice down to just above 4M km2.  What's going to cause an unprecedented 3M km2 drop in one year?

    Or did I misinterpret your post?

176
Arctic sea ice / Re: Global sea ice area and extent data
« on: April 06, 2020, 12:00:09 AM »
  1) Took me a few seconds to understand the date format Day.Month, thus 1.5 = May 1.

   2) Not related to above post, but how does Antarctic sea ice volume compare to Arctic?  I suspect the average thickness in Antarctic is less than Arctic because most of the Antarctic ice melts each summer, thus no MYI.  Thus, the difference between Antarctic and Arctic in volume would be less than difference in their Extents.

  3) It just occurred to me that the name Antarctic is northern hegemonistic bias!  Why is an entire continent and the biggest reservoir of fresh water and ice on the planet named only in relation to, and as the opposite of, another region?  It should have its own name.  Antarctic liberation!

   

177
Arctic sea ice / Re: Tides
« on: April 04, 2020, 07:20:36 PM »
     If the question is "Does Fram export vary with tidal forces", then getting the daily values used to create the Wipneus Fram export chart and checking for correlation with the lunar cycle would provide evidence to address the question.
https://forum.arctic-sea-ice.net/index.php/topic,119.msg258236.html#msg258236

178
Arctic sea ice / Re: Tides
« on: April 03, 2020, 04:13:48 PM »
  FWIW - It seems that the two sides in this debate are focused on different questions. 
     
     One side documents that tides affect the Arctic Ocean waters, ice, mixing, temperature gradients etc., and thus condition of the ASI. The other is focusing only on Fram Strait export, and saying the because tidal movement alternates, the movement of water south on an outgoing tide is matched by tidal movement north on the incoming tide, so in terms of Fram Export it has zero net effect.

     Maybe it's time for a real expert to address the original question directly:  Do changes in tidal forces across the lunar cycle influence the net amount of ASI export through the Fram Strait? 

     At least I think that is the question.  I don't know enough to have an opinion, just trying to clarify the discussion.  All I do know is that my friend retired from 30+ year career at National Weather Service said that tidal mathematics is really complicated!

179
Arctic sea ice / Re: The 2020 melting season
« on: April 03, 2020, 12:40:57 PM »
     ONI3.4 forecast (sea surface temperature in equatorial region of Pacific Ocean used to estimate ENSO El Nino / La Nina cycle) are updated monthly on 3rd Thursday at
 https://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/?enso_tab=enso-sst_table

180
Arctic sea ice / Re: The Rammb Slider Thread
« on: April 03, 2020, 12:28:28 PM »
     How weird is it for the ice at the North Pole to be cracking up this early?  That plus apparently strong Fram Export looks ominous.

181
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 03, 2020, 02:11:00 AM »
*******************
*******************
VOLUME
a. Exponential Volume trend
     Rationale – There have been rapid climatic shifts in the past. .
2020: 2.5M (0.3 – 4.9) km3 September average Volume.
First Year for <3M km3 = 2020 (2020 – 2024)
First Year for <2M km3 = 2021 (2020 – 2026)
First Year for <1M km3 = 2023 (2020 – 2027)
First Year for 0 km3 = 2025 (2021 – 2029)


---------------------------
b. Gompertz Volume curve (eyeball estimates from Wipneus chart at https://sites.google.com/site/arctischepinguin/home/piomas
     Rationale - Loose proxy for increased negative feedback as declining September minimum ASI results in more fall and winter open water and less Arctic Ocean water insulation and thus greater winter heat loss and more rapid winter refreeze,  i.e. a tip of the hat to the “long slow final decline” hypothesis.
2020:  2.8M (1.0 – 4.5) km3 September average Volume.
First Year for <3M km3 = 2021 (2020 – 2027)
First Year for <2M km3 = 2023 (2020 – ca. 2029)
First Year for <1M km3 = 2027 (2020 – ?)
First Year for 0 km3:  no data.


---------------------------
c. Linear Volume trend
      Rationale – The simplest model is the safest bet.  The extra term in the exponential regression was not statistically significant.
2020:  3.9M (1.2 – 6.6) km3 September average Volume.
First Year for <3M km3 = 2023 (2020 – 2032)
First Year for <2M km3 = 2026 (2020 – 2035)
First Year for <1M km3 = 2030 (2021 – 2038)
First Year for 0 km3 = 2033 (2024 – 2041)

---------------------------
Improved Volume prediction accuracy as melt season observations become available.
      R-square reduction in variability derived from R values posted by Stephan at https://imgur.com/a/O82kzZZ

      Linear model estimate for 2020 September average Volume before any 2020 observations:  3.9M (1.2 – 6.6) km3, (95% of outcomes expected to fall within 1.2 – 6.6M km3,
i.e  +/- 2.7M km3).
   
    With MARCH observation as predictor, confidence interval (CI) reduction for September average Volume estimate: 3.6%.
Width of 95% CI with March observation: +/- 2.6M km3
   
    With APRIL Volume observation, conf. interval reduction: 7.2%
Width of 95% CI with April observation: +/- 2.5M km3

    With MAY Volume observation, confidence interval reduction: 32%
Width of 95% CI with May observation: +/- 1.9M km3

    With JUNE Volume observation, confidence interval reduction: 63%
Width of 95% CI with June observation: +/- 1.0M km3

    With JULY Volume observation, confidence interval reduction: 83%
Width of 95% CI with July observation: +/- 0.5M km3

    With AUGUST Volume observation, conf. interval reduction: 94%
Width of 95% CI with August observation: +/- 0.2M km3

182
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: April 03, 2020, 02:07:55 AM »
Arctic Sea Ice September Minimum estimates by 1979-2019 trend extrapolations
     The consensus definition of the first “ice free Arctic summer” is when the September minimum EXTENT goes below 1 million km2. 
Volume = Extent x average Thickness
Extent = Volume / average Thickness
-------------
     Terminology key:
     First value is midpoint estimate.  (Low – High) = 95% confidence interval,
i.e. +/- 1.96 standard deviations. 
     Exponential trend = 2nd order polynomial regression model, i.e. simple curve model, for 1979-2019 observations.
     Linear trend = 1st order linear regression, i.e. straight line model, for 1979-2019 observations.
     Standard deviations used for confidence intervals based on annual errors of Linear model vs. 1979-2019 observed values.
     M km2 and M km3 are Millions of squared or cubic kilometers.

EXTENT
a)  Exponential Extent trend
    Rationale - Positive feedbacks from loss of MYI, thin ice physical and biological characteristics (e.g. algal darkening on the underside of thin floes), more open water causes decreased summer albedo, open water effects on wind fetch and ice mobility, increased Atlantification and Pacification of the Arctic, CAA becomes another export gateway, possible halocline breakdown (esp. in the Beaufort), more open water in winter causes more water vapor over the Arctic thus increasing the thermal blanket to moderate winter low temperatures, black carbon forest fires,  permafrost thaw, oops, we never thought about that, continued GHG loading, increasing global average temperature.   
    Opinion - Too aggressive for extrapolation because it ignores compensating negative feedback.

 
2020:  4.0 (3.0 – 5.0) km2 September average Extent.
First Year for <3M km2 = 2028 (2021 – 2034)
First Year for <2M km2 = 2034 (2028 – 2040)
First Year for <1M km2 =  2040 (2034 – 2045)
First Year for 0 km2 = 2045 (2040 – 2050)

---------------------------
b) Gompertz Extent curve - no data

---------------------------
c)  Linear Extent trend
     Rationale – The simplest model is the safest bet.  Occam’s razor.  The extra term in the exponential model was not statistically significant. Allows for both positive and negative feedbacks.

2020:  4.3M (3.3 – 5.3) km2 September average Extent

*** The extrapolated linear September Volume and Extent linear trends are incompatible.  If Volume reaches zero in 2033 (2024 – 2041), there would be no ice to create Extent.***   
First Year for <3M km2 = 2037 (2024 – 2049)
First Year for <2M km2 = 2049 (2037 – 2061)
First Year for <1M km2 = 2061 (2049 – 2073)
First Year for 0 km2 = 2073 (2061 – 2085)

---------------------------
Improved EXTENT prediction accuracy as melt season observations become available.
    R-square for reduction in variability of estimates derived from R values posted by Stephan at https://forum.arctic-sea-ice.net/index.php/topic,2888.msg248300.html#msg248300
 
    Confidence interval reduction for estimated September average Extent with MARCH, APRIL, or MAY observations as predictors: Not much.

---- See NSIDC “Maximum extent is not predictive of minimum extent” https://nsidc.org/arcticseaicenews/2020/03/
“Plotting the de-trended maximum versus minimum extent (Figure 2) shows a near-random distribution.” 
“The seasonal maximum extent and the September minimum extent are not correlated” … “because summer weather conditions strongly shape the September minimum.”

Figure 2. This plot compares de-trended maximum extent (x-axis) with minimum extent (y-axis). The yearly values shown are calculated by subtracting the linear trend value for that year from the total extent.  Credit: W. Meier, NSIDC
-----
     Linear model estimate for 2020 September average Extent before any 2020 observations:  4.3M +/- 1.0 km2, (95% of outcomes expected to be within 3.3 – 5.3M km2,
i.e  +/- 1.0M km2)

     With JUNE Extent observation, confidence interval reduction: 22%
Width of 95% CI with June observation:  +/- 0.8M km2
     
     With  JULY Extent observation, confidence interval reduction: 56%
Width of 95% CI with July observation:  +/- 0.5M km2
     
     With AUGUST Extent observation, conf. interval reduction: 87%
Width of 95% CI with August observation:  +/- 0.14M km2

183
Arctic sea ice / Re: The 2020 melting season
« on: April 01, 2020, 03:23:01 PM »
Deleted Confidence interval posts.  Will move to "When will Arctic Go Ice Free" later.

184
Arctic sea ice / Re: The 2020 melting season
« on: April 01, 2020, 08:21:50 AM »
moved to When Will Arctic Be Ice Free thread

185
Arctic sea ice / Re: The 2020 melting season
« on: March 31, 2020, 12:07:28 AM »
Nice work, thanks uniquorn!  I think that gets the Academy Award for technical achievement in Fram Strait documentation.  The different views complement each other and the time series overview provides superb historical context.

    After repeated watchings, my takeaway impression is that the ice in the north of Greenland - Fram Strait regions is very dynamic.  I should have known that from the analysis shown in:
"Spatiotemporal Variability of Sea Ice in the Arctic's Last Ice Area"
https://sci-hub.tw/https://doi.org/10.1029/2019GL083722# (link courtesy of blumenkraft) but the visual impression from 10 years of images is more convincing at a gut level.  While the interannual variability gets visually swamped by the within-year melt season - freezing season patterns, the overall impression is how it's always changing and that spring 2020 is not obviously different than in earlier years.

     That said, indicators of volume and thickness say that not only is the long term ASI decline continuing, but 2020 is heading into the melt season in wounded condition.   As others have noted, the supposedly strong refreeze in Jan - Feb 2020 looks like an easily reversed flash in the pan, i.e. weak thin ice that temporarily adds to the Extent value but is not indicative of improvement to the long term health of the ASI.

    I didn't see direct relevance of the Nullschool windspeed at 250 hPa image posted by Freegrass (important for steering weather patterns at jet stream height, but not directly influential like surface winds that interact with ice).  But that got me to check today's Nullschool and Climate Reanalyzer surface winds and temperature anomalies.  Those show what seems to be a significantly large and strong wind field from the Bering Strait bringing in unusually warm air almost reaching the North Pole.  And another large area of surface wind that is bringing warm air from the south directly toward north Greenland.  As or the "Polar Vortex", we need to define our terms and choose the right pressure level to distinguish between the stratospheric and tropospheric polar vortexes. 

     While not dramatically stronger than normal, the recently robust Fram Strait drift and export measures are another setup.  The occurrence of leads north of Greenland does not seem unprecedented in the noisy record over the previous 10 years in uniquorn's animations, but the overall ASI situation seems sensitive to rapid losses if strong melt season conditions arrive.  2020 could be a wild ride.

BTW - nice explanation of leads vs cracks vs polynas at https://en.wikipedia.org/wiki/Lead_(sea_ice)

186
Arctic sea ice / Re: The 2020 melting season
« on: March 30, 2020, 02:56:42 PM »
One thing that is different, or that I haven't seen before, is the large leads that have developed since feb15 making their way around north greenland so early in the season. With >80km/h winds forecast on apr1 we are likely to see them open up more.
Kaleschke SIC leads, oct1-mar29
Anybody else with historical perspective on how unusual it is for (what I think should thick) ice just north of Greenland to be fractured this early in the season?  Seems very strange and significant to me, but I don't have the years of observation to compare it to.

187
Arctic sea ice / Re: The 2020 melting season
« on: March 28, 2020, 12:33:30 AM »
GFS shows March ending with a blast of above normal temperature for the Chukchi, Beaufort, and much of the CAB
http://204.197.0.54/MEmodel/CR-GFS-Arctic2020-03-31.png

188
Arctic sea ice / Re: The 2020 melting season
« on: March 27, 2020, 04:02:26 PM »

189
Arctic sea ice / Re: The 2020 melting season
« on: March 26, 2020, 02:54:38 AM »
RE revisiting the upthread discussion on crummy looking ice in the Beaufort Sea:
That said, this drop highlights how the change in the quality of the ice is changing how the melt season progresses.
It is less about extent and area.
It is more about age, thickness and volume.
Most of the ice that's appeared this year in the Barents and Bering above and beyond what wasn't there the last few years is barely coherent, and doesn't have any ability to resist weather.
It will likely vanish like morning mist on a hot spring day.
... I also don't like all the yellow I'm seeing in this graphic.  That concentration is a lot lower than I'd like.

Re Bremen image and Beaufort.
It didn't look so bad on the 19th compared to 22nd.
I wonder is it sensor related or is that Beaufort thinning real ? 

 ArcticMelt2  ( https://forum.arctic-sea-ice.net/index.php/topic,2888.msg236503.html#msg236503 )
pointed out this study from August 2018 that seems relevant to the recent Beaufort observations:

Warming of the interior Arctic Ocean linked to sea ice losses at the basin margins
BY MARY-LOUISE TIMMERMANS, JOHN TOOLE, RICHARD KRISHFIELD
SCIENCE ADVANCES29 AUG 2018 : EAAT6773
https://advances.sciencemag.org/content/4/8/eaat6773
https://advances.sciencemag.org/content/advances/4/8/eaat6773.full.pdf
"Abstract
Arctic Ocean measurements reveal a near doubling of ocean heat content relative to the freezing temperature in the Beaufort Gyre halocline over the past three decades (1987–2017). This warming is linked to anomalous solar heating of surface waters in the northern Chukchi Sea, a main entryway for halocline waters to join the interior Beaufort Gyre. Summer solar heat absorption by the surface waters has increased fivefold over the same time period, chiefly because of reduced sea ice coverage. It is shown that the solar heating, considered together with subduction rates of surface water in this region, is sufficient to account for the observed halocline warming. Heat absorption at the basin margins and its subsequent accumulation in the ocean interior, therefore, have consequences for Beaufort Gyre sea ice beyond the summer season."

Some images copied from the Timmermans et al study:



A press story about the Timmermans et al 2018 study is at
https://phys.org/news/2018-08-archived-deep-arctic-interior.html

"The upper ocean in the Canadian Basin has seen a two-fold increase in heat content over the past 30 years, the researchers said. They traced the source to waters hundreds of miles to the south, where reduced sea ice has left the surface ocean more exposed to summer solar warming. In turn, Arctic winds are driving the warmer water north, but below the surface waters.

"This means the effects of sea-ice loss are not limited to the ice-free regions themselves, but also lead to increased heat accumulation in the interior of the Arctic Ocean that can have climate effects well beyond the summer season," Timmermans said. "Presently this heat is trapped below the surface layer. Should it be mixed up to the surface, there is enough heat to entirely melt the sea-ice pack that covers this region for most of the year."  "

Related press article at
https://www.livescience.com/arctic-ice-refuge-vanishing.html

Finally this one (abstract only unless you have paywall access)
Spatiotemporal Variability of Sea Ice in the Arctic's Last Ice Area
https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2019GL083722




190
Arctic sea ice / Re: The 2020 melting season
« on: March 18, 2020, 11:51:50 PM »
   Thanks, but instead of NH snow cover, I'm wondering about the snow cover directly on the ASI.  The MOSAIC scientist in the video blumenkraft posted says that snow quality (albedo, roughness, stratigraphy, crystal structure) has a huge effect on the atmosphere-ice interaction and melt season progression.  I suspect that these relationships are only beginning to be understood and that the scientists need more time to collect and crunch data before reaching any conclusions about the current situation.  Thus, there may not be an answer to my question at this time. 

    Snow cover characteristics on top of the ASI could be a missing factor in melt season variability that (in addition to weather, melt ponds, drift currents etc.) makes multi-month ASI prediction difficult.  Stephan shared regressions a month or so ago that showed Extent and Volume in prior months have poor correlation with September minimums.  Basically nil in May, weak in June.  It isn't until July that knowing those values gets you much predictive skill about September.

    Then again, Slater model and some other methods seem to do a halfway decent job of predicting Sept. minimums.  The more I think about this the less I pretend to know!

191
Arctic sea ice / Re: The 2020 melting season
« on: March 18, 2020, 07:48:13 PM »
    Given the importance of snow cover ...
 (see for ice dynamics https://forum.arctic-sea-ice.net/index.php/topic,2906.msg254713.html#msg254713 )
   

   ... is there a status report of how snow cover on top of the ASI at this time compared to same date in previous years, and what that suggests about the 2020 melt season?  I know Siberia has reduced snow cover and that has consequences for spring warm up.  But what about the snow cover directly on the ASI?  What is the current situation for that?


192
Arctic sea ice / Re: The 2020 melting season
« on: March 17, 2020, 05:52:10 PM »
     As I understand it -- SO2 primarily has an effect when large volcanic eruptions, esp. those near the equator, inject large amounts of SO2 into the stratosphere where they can persist for an extended period.  Lower height eruptions are less likely to have a significant effect on incoming solar radiation and global average surface temperature because the SO2 falls out rather quickly.

   The most recent years when volcanic SO2 aerosols had a major effect on temperature were 1982-1983 and 1992-1993.  There is about a 7 month lag between the measured global average aerosol level and an effect on global average surface temperature.  The temperature suppression in those years was on the order of 0.1 to 0.2 C below what the temperature would have likely been without the aerosol influence. 

    The “Year without a summer” in the Northeastern US in 1816 was caused in part by the Mt. Tambora eruption in 1815.  There was snow in Dennysville Maine on June 6, 1816.  Massachusetts had a severe frost in every month.  Less than a quarter of the corn crop was harvestable.  This was all caused by a decrease of average global temperatures of 0.4–0.7 °C (0.7–1.3 °F), and a decrease of average land temperature by about 1C.

    Monthly aerosol level is updated by 11th day of the following month at https://www.esrl.noaa.gov/gmd/webdata/grad/mloapt/mauna_loa_transmission.dat 
Values are transmission through atmosphere, thus lower values = more aerosol blockage.  Values above 0.9160 are unlikely to cause a noticeable temperature effect.

193
Arctic sea ice / Re: Glossary ... for newbies and others
« on: March 17, 2020, 03:21:54 PM »
The acronym definition for CAPIE includes an undefined acronym: IJIS

IJIS = IARC-JAXA Information System run by the International Arctic Research Center at the University of Alaska (IARC), and the Japan Aerospace Exploration Agency (JAXA).



194
Arctic sea ice / Re: The Fast Transition
« on: March 10, 2020, 12:58:30 AM »
RE Wipneus Feb 29 2020 thickness graph
https://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=119.0;attach=144514;image
and
RE 1.7-2m threshold thickness for seasonal ice
 https://forum.arctic-sea-ice.net/index.php/topic,1999.msg111458.html#msg111458

Jumping the gun, but with freezing season beginning to wane and so not too far from max thickness, areas that are yellow or green on the Wipneus graph are at high risk to be seasonal, thus to melt out by September (plus possible export of thick ice north of Greenland via the Fram Strait).

195
Arctic sea ice / Re: The Fast Transition
« on: March 10, 2020, 12:38:01 AM »
"Decadal Changes of the Reflected Solar Radiation and the Earth Energy Imbalance" by Dewitte , Clerbaux and Cornelis.
     For both polar regions, changes of the clear-sky RSR correlate well with changes of the Sea Ice Extent. In the Arctic, sea ice is clearly melting, and as a result the earth is becoming darker under clear-sky conditions. However, the correlation between the global all-sky RSR and the polar clear-sky RSR changes is low. Moreover, the RSR and the Outgoing Longwave Radiation (OLR) changes are negatively correlated, so they partly cancel each other. The increase of the OLR is higher than the decrease of the RSR. Also the incoming solar radiation is decreasing. As a result, over the 2000–2018 period the Earth Energy Imbalance (EEI) appears to have a downward trend of −0.16 ± 0.11 W/m2dec. The EEI trend agrees with a trend of the Ocean Heat Content Time Derivative of −0.26 ± 0.06 (1 σ) W/m2dec.
   Over the 2000–2018 period the Arctic clear-sky RSR shows a decreasing trend of −0.13 W/m2dec.

https://www.mdpi.com/2072-4292/11/6/663/htm#
And RE https://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=1999.0;attach=140635;image

Very interesting article.  But it seems to contradict other reports that show continued increase in total ocean heat content (OHC).  Also hard to understand how net  earth energy balance and OHC can be trending down at same time as continued increase in global CO2 and with relatively consistent increase in measured surface temperature over same period.  Or maybe I am misinterpreting the conclusions.  Explanation or discussion by those who actually understand this stuff welcomed.



196
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: March 04, 2020, 04:41:24 AM »
FYI:
Interactive: When will the Arctic see its first ice-free summer?
Words by Daisy Dunne. Design by Tom Prater.
https://interactive.carbonbrief.org/when-will-the-arctic-see-its-first-ice-free-summer/
   Article not dated, but must have been written after November 18, 2019, and it includes graphs showing 2019 minimum.

   "For example, in recent years, scientists have observed an increase in the speed at which sea ice grows in the winter. This is partly because “thinner ice can grow much faster than thicker ice”, says Tsamados. “This is a negative feedback – a kind of resilience in the system.”

    "However, the increase in sea-ice growth observed in winter is not enough to counter the rapid rise in melting seen in the summer months, he adds. “We’re putting out so much CO2 that the Arctic just cannot fight back. Right now, the positive feedbacks are winning against the negative feedbacks – and that means that sea ice is going down the drain.”  "

-------
If temperatures rise by 2C
    "...the Arctic has a one-in-five chance of seeing its first ice-free summer in 2035, according to the study. The chances of an ice-free summer in any given year rise to one-in-two by 2045."

-------
   "A landmark report on oceans and ice published this year by the Intergovernmental Panel on Climate Change (IPCC) found that up to half of the observed decline in summer sea ice could be down to natural variability in the Arctic climate."

    "A study published in 2016 calculated that natural variability in the Arctic system amounted to around two decades of uncertainty. This means that any ice-free summer forecast may need to have a 20-year window, just to account for the influence of natural events and processes."

197
Arctic sea ice / Re: What's new in the Arctic ?
« on: March 04, 2020, 04:23:11 AM »
  Does anyone know of any research or theory about how far this can go until the warmer water "flips" with the cold and rises to the surface?  It feels like the system has to reach a point where it becomes unstable and the warmer water comes to the top.

   Not an answer to your question, but in addition to the heat flow issue, declining ice cover and exposure of surface water to wind could play a significant role.  I can't remember source, but recent article discussed increased Ekman pumping from increased surface winds in the Arctic.

Elsewhere -
"Sea ice regulates exchanges of heat, moisture and salinity in the polar oceans."
https://nsidc.org/cryosphere/sotc/sea_ice.html
  - a good review by NSIDC, last updated: 11 October 2019.

------

  Another recent good overview:
In-depth: Understanding the impacts of changing Arctic storms
DAISY DUNNE  13.01.2020
https://www.carbonbrief.org/in-depth-understanding-the-impacts-of-changing-arctic-storms

    “There is some suggestion that Arctic cyclones may be more frequent now, but the problem is we don’t have a whole lot of measurements from before. Maybe the previous lower frequency we’ve observed is due to the fact that our models, or our reconstructions of the past, aren’t complete enough.”

---------

  But don't expect another 2012 Great Arctic Cyclone anytime soon.  Apparently it was truly an outlier event.  Compared to all storms on record at time of publication (1979–2012):

   " Even though, climatologically, summer is a ‘quiet’ time in the Arctic, when compared with all Arctic storms across the period it came in as the 13th most extreme storm, warranting the
attribution of ‘Great’.  "

    " Using our multiple-index approach (based on cyclone properties and longevity) we conclude that AS12 was the most extreme August Arctic  cyclone (out of a population of 1618). When all Arctic cyclones were considered (which included the more vigorous winter systems) AS12 ranked in position 13 out of a compilation of 19625 storms. This storm truly deserves the title of ‘The Great Arctic Cyclone of August 2012’. "

Source:  The great Arctic cyclone of August 2012.  Ian Simmonds and Irina Rudeva
GEOPHYSICAL RESEARCH LETTERS, VOL. 39, L23709, doi:10.1029/2012GL054259, 2012


198
Arctic sea ice / Re: Arctic Ocean salinity, temperature and waves
« on: February 27, 2020, 07:55:19 PM »
Edited quote
Arctic ice sets speed limit for major ocean current
Quote
The Beaufort Gyre is an enormous, 600-mile-wide pool of swirling cold, fresh water in the Arctic Ocean, just north of Alaska and Canada. In the winter, this current is covered by a thick cap of ice. Each summer, as the ice melts away, the exposed gyre gathers up sea ice and river runoff, and draws it down to create a huge reservoir of frigid fresh water, equal to the volume of all the Great Lakes combined.

 ..... Scientists at MIT have now identified a key mechanism, which they call the "ice-ocean governor," that controls how fast the Beaufort Gyre spins and how much fresh water it stores.

"If this ice-ocean governor goes away, then we will end up with basically a new Arctic ocean," Marshall says......
 
The research paper
If the Beaufort Gyre can reach the Atlantic Ocean, the reverse is not so far-fetched.  I guess this is what comes with an increasingly "Equable climate" where the poles are no longer isolated from the midlatitudes.  Which does not bode well for ASI longevity.

199
Arctic sea ice / Re: Arctic Ocean salinity, temperature and waves
« on: February 27, 2020, 07:38:45 PM »

Speaking of gyres ...
https://insideclimatenews.org/news/26022020/climate-oceans-weather-fishing-gyres-gulf-stream-sea%20level

   I suppose at ca. 1 km per year it won't happen anytime soon, but looking at the north end of that North Atlantic gyre loop in the map included with the article
https://insideclimatenews.org/sites/default/files/styles/colorbox_full/public/image_large/OceanGyres529px.png?itok=yoTQ6XPg
makes me wonder if someday it will loop over Greenland and go straight across the Arctic.  That would be "Atlantification" on steroids.



200
Arctic sea ice / Re: Glossary ... for newbies and others
« on: February 24, 2020, 10:09:58 PM »
ASCAT = Advanced Scatterometer instruments on multiple satellites that use radar to measure speed and direction of winds over the surface of the oceans.

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