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Messages - Glen Koehler

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1
Arctic sea ice / Re: Glossary ... for newbies and others
« on: Today at 08:20:50 PM »
AMSR = Advanced Microwave Scanning Radiometer    
     AMSR-E is the AMSR instrument on board AQUA satellite (NASA), and AMSR-2 the one on board GCOM-W1 satellite (JAXA)

JAXA = Japan Aerospace eXploration Agency

OSISAF = Ocean and Sea Ice Satellite Application Facility
    Satellite Application Facility = Utilising specialist expertise from the EUMETSAT Member States, Satellite Application Facilities (SAFs) are dedicated centres of excellence for processing satellite data. They form an integral part of the distributed EUMETSAT Application Ground Segment.

2
osisaf drift, beaufort, sep21-feb15

Thanks Uniquorn.  The changing directions and strengths of the Sept 21- Feb 15 drift observations looks more random than I expected.  I expected to see a consistent pattern of clockwise drift. 
   Is that a typical Sept - Feb drift pattern? 
   Does that view represent the famous Beaufort Gyre or is it just a subset of the larger system?
   Is there a seasonality for the Beaufort Gyre, i.e. is it more consistently clockwise during the melt season?

    PS In looking up "osisaf" (=Ocean and Sea Ice Satellite Application Facility), I found list of acronym definitions at http://www.osi-saf.org/?q=content/acronyms-and-links.  Most of the acronyms in that list are too narrow, technical. or not directly relevant ASI to add to the ASIF acronym list, but interesting to look through.

3
Arctic sea ice / Re: Gulf Stream stall
« on: February 09, 2020, 01:33:32 AM »
https://phys.org/news/2020-02-arctic-ice-ocean-currents.html
    Nice link NotaDenier.  In addition to the phys.org summary, while the source article is quite technical and over my level, it was worth looking at to get a sense of how dramatically the Beaufort Sea energy flows have changed.  Also, the related 2018 article linked at bottom of the phys.org article also provides good context to understand why this matters.

Less ice = more wind impact on Beaufort Gyre = faster spin = weaker halocline and thus more warm water & ice interaction. 

   Reading that stuff gave me extra appreciation for the significance of
 gerontocrat's post showing recent arrival of ice free days in the Beaufort Sea
https://forum.arctic-sea-ice.net/index.php/topic,2348.msg247559.html#msg247559

   
    While not described in the articles, all that has me wondering if a stronger gyre also brings more Central Arctic ice into the Beaufort Sea which is now warm enough to melt it.  Thus what used to be the Beaufort ice Nursery could be emerging as the Beaufort Bakery.  This is compounded by the incremental thinning and thus structural weakening and increased mobility of the ice pack overall. 

    I'm just arm waving of course, but this is the kind of scenario that allows for the end game of Arctic sea ice decline to proceed at an accelerated pace when certain structural/functional thresholds are breached.

4
Arctic sea ice / Re: "Stupid" Questions :o
« on: February 09, 2020, 12:56:31 AM »
     In something like RCP8.5, where the 8.5 is watts per square meter IIRC, how do you translate that to equilibrium temperature change?
     In a 2012 article by James Hansen et al. using an energy balance perspective to describe global warming, they state that each 1 watt/m2 of extra energy translates into about 0.75C warming once temperature has reached equilibrium.  But reaching equilibrium takes a long time (more than decades, call it 200 years if you want a number). 

    RCP8.5 refers to 8.5 watts/m2 by 2100.  So based on that ratio the RCP8.5 scenario should lead to ca. 6C warming.  But charts by IPCC, Global Carbon project, etc. show the RCP8.5 scenario global average surface temperature anomaly over preindustrial (when CO2 was ca. 278ppm vs ca. 1200ppm at 2100 in RCP8.5) as 3.2 to 5.4C, with a median estimate of 4.3C.  That is less than 6 because of the lag.  Thus, if CO2e stayed at 1200ppm for a long time, the temperature would gradually approach the +6C level over time.

   At least that is how I understand it from a "not a climate scientist" perspective.  The immediate temperature response (TCR - transient climate response) is substantially less than the long term equilibrium temperature response (ECS - equilibrium climate sensitivity).

   Some things to note - there has been some interesting commentary within the last few weeks about overuse/misuse of the RCP8.5 high end emissions scenario.  Hausfather and Peters recently published a commentary, which led to more commentaries by Michael Mann etc.  Among other things, RCP8.5 is quite unrealistic with an assumption of rapidly increasing coal consumption out to 2100. 

   There is consensus that RCP8.5 is an unlikely scenario, and Hausfather and Peters make the point that scientists should not point to that as the basis for future projections.  An article last summer also pointed out that RCP8.5 was never intended for how is too often used, i.e. as a prediction of what will happen. 

    But while there is consensus that RCP8.5 is not a forecast of what will be, there is recognition that it is also still within the realm of plausible outcomes and shouldn't be completely disregarded, especially as new observations and research find reinforcing (aka "positive") feedback mechanisms that are either previously unknown, more vigorous than previously estimated, or not represented in the previous generation of climate models.  There is also consensus that reducing the attention given to RCP8.5 in no way argues against the immediacy or severity of the climate crisis. See Michael Mann's short commentary to hear from somebody who actually knows this stuff
http://redgreenandblue.org/2020/02/05/michael-mann-just-bad-climate-change-kept-business-usual/ 
    (note - the chart Mann uses shows upper emissions curve from SSP85 not RCP8.5, with 2100 temperature anomaly at a rounded off 5C instead of the RCP8.5 median temp. of 4.3).

    If you want to really freak out, read about the first versions of new batch of CMIP6 climate models generating an ECS much higher than the previous generation.  Only a small portion of the CMIP6 models have published output yet, so this is still a developing story.  And experts seem to think that it is more likely a bias in the first implementations of the CMIP6 models than a new discovery of much higher sensitivity of the climate system to our CO2 highjinks.  But it also suggests that our understanding and best estimate of ECS (as measured by a doubling of CO2 after rising 1% per year) is not likely to go down with the new models. 

5
Arctic sea ice / Re: Near Real Time Sea Ice Volume
« on: February 05, 2020, 10:59:24 PM »
Interesting to have a near real time volume estimate.  Thanks for doing that.

What is the uncertainty range indicated on graph 95% CI (2.5% to 97.5% of estimate distribution)?

Is the current value calculated with same sources and methods as the 2011-2018 average?

How the Volume estimate using this method compare to PIOMAS volume for same dates?

6
Arctic sea ice / Re: The 2019/2020 freezing season
« on: February 05, 2020, 07:45:36 PM »
Nice!  Thanks!

7
Arctic sea ice / Re: The 2019/2020 freezing season
« on: February 05, 2020, 06:36:15 PM »
RE grixm
https://forum.arctic-sea-ice.net/index.php/topic,2888.msg247928.html#msg247928

     I thought we were done with this, but I have another favor to ask.  Can you extend the early vs Sept. Extent comparison charts to April-August? 

    You showed above that there is no correlation of March to September, but surely there must be correlation by August.  This is probably in a journal article somewhere, but your charts are lovely and can be up to date to include 2019.  Seeing the data point spread would be really interesting.   

     For sporting interest, I'll wager such charts would show R2 around:
April 10%
May 20%
June 30%
July 50%
August 80%

    And if anybody did the same for Volume, that would be icing on the cake.

PS in case you zipped past binntho's post in the data thread at
https://forum.arctic-sea-ice.net/index.php/topic,2975.msg247842.html#msg247842
   The articles he cites there provide really nice long-term context for ASI variability and current situation.  Good stuff.

8
Arctic sea ice / Re: The 2019/2020 freezing season
« on: February 04, 2020, 08:48:05 PM »
Thanks grixm!

9
Arctic sea ice / Re: The 2019/2020 freezing season
« on: February 04, 2020, 05:29:09 PM »
Therefore, I experimented with instead normalizing the years to their predicted average extent from a linear regression of all the years.
Your method is skewed by the fact that the long-term extent losses are happening more rapidly in September than in January/February/March.

September extent in the last few years is about 40% lower than in the 1980s, whereas March extent has decreased by only 10%.  So your "normalized" March extent has an upward trend over the last few decades, whereas the normalized September extent has a downward trend.  So it's not surprising that you get a negative correlation between them.  But that correlation is spurious.

A more meaningful method is to detrend the data (see e.g. here for some background on detrending).  It turns out that the correlation between the detrended March extent and the detrended September extent is very weak: the correlation coefficient is  -0.029.

    Many thanks to grixm and Steven et al. for wrestling with the numbers.  It looks like the jury is still out on this one.  While counter-intuitve [more Extent early leads to less 8 months later (Jan-Sept), 7 (Feb-Sept.), or 6 March-Sept.)], the insulating ice theory at least sounds plausible. 

    But assuming Steven's -0.029 correlation coefficient for March-September Extent is correct, that is low even for noise, and certainly not signal.  I find such a low correlation equally counter-intuitive.  My naive guess is that there would be some influence of March Extent on September Extent only 6 months later.

    Which leaves me even more jaded about Extent as being a flukey measure for status of the Arctic sea ice.  It is a real thing, and the most directly measurable, so I'm not discrediting it entirely.  But this episode seems to demonstrate that caution is needed in equating the annual maximum or minimum Extent as a precise measuring stick for ASI status and trend.  It is what it is, and the long-trend in Extent decline certainly shows us a real effect, but for year to year, or within-year, comparisons it seems too variable to draw short-term conclusions or predictions.

    If anybody is up for graphing a detrended March vs. September average Volume, that might be more conclusive.  But even that would still be subject to unknown melt season weather.  Given the considerable year to year variation we see in Volume also, as shown in the recently updated Wipneus PIOMAS volume graphs --
https://sites.google.com/site/arctischepinguin/home/piomas
it seems that what we need is a skilled forecast for melt season weather. 

    My amateur foray into estimating forecast skill at 6-9 month range for midlatitude U.S. (45 degrees N, 69W) temperature and precip found a little bit of skill beyond climatology out to 6 months for temperature, but nothing worth mentioning for precip beyond about a month.  ASI melt weather seems strongly influenced by clear vs. cloudy skies.  The inability to forecast precip at a more intensively monitored and presumably better understood temperate mid-latitude location beyond a month suggests that we will not have skillful multi-month Arctic melt season forecasts anytime soon.  So we'll just have to wait and see what happens in 2020.

    But there's still room for some alarmist notification and unmitigated voodoo.  The Wipneus exponential volume trend puts the 2020 Sept. minimum more than 1 million km3 BELOW 2012.  I put more faith in the straight line trend, but even that puts 2020 at matching the 2012 record low. 

     As for the voodoo,
1) the recent low snow cover post by Pavel https://forum.arctic-sea-ice.net/index.php/topic,2888.msg247615.html#msg247615,
2) the speculation by El Cid about a cold Alaska winter leading to a strong melt season. https://forum.arctic-sea-ice.net/index.php/topic,2888.msg247815.html#msg247815
3) the continuing trend to thinner ice and recent obliteration of old thick ice
4) and the animated ice pack image posted above by Alumimiun - which looks to me like the Atlantic front is already retreating (though that could just be daily variation) -
have got me suspecting that 2020 could have a very active melt season.  Maybe that will bring necessary attention to the larger problem.   
     
 


10
Arctic sea ice / Re: The 2019/2020 freezing season
« on: January 31, 2020, 09:30:11 PM »
binntho
  To resolve the earlier discussion, can you graph January Extent on X axis vs. September Extent on Y axis for 1979-2019?  Even better if you show not just the slope equation but the R2, F and df (all included in the output table if you are using Excel).  That would let us estimate statistical significance. 

    The March-Sept correlation is middling, but the original question was about predicting Sept. Extent from prior January, which is a lot more tenuous.  And of course, Extent is only part of the story.  (I think the main issue is ASIF folks with cabin-fever looking for something to argue about while waiting for the 2020 melt season).

     I may have over-reacted to the weak looking ice thickness map for Jan. 2020 vs. 2019 and 2018 as shown on Jim Hunt's Great White Con post. 
http://greatwhitecon.info/2020/01/wheres-the-thickest-arctic-sea-ice-gone/
The early January 2020 ice thickness map shown there may be simply be showing that the 2019-2020 freeze season got off to a late start.  A lot could change before March-April. 

     Any single year is short term noise around what really matters - the long term trend for less Arctic sea ice.  But 2020 is a particularly interesting year to watch. 

    By the long term volume trend, 2020 has about a 50:50 chance of going below the 2012 record low.  The long term trendline for Extent gives a 2020 estimate that is still roughly 20% above the 2012 record low.  The Great Arctic Cyclone caused a greater loss to Extent than it did to Volume. 

     As both values diminish, the Extent trend slope has to bend down faster to catch up to Volume - because at the end zero Volume dictates zero Extent.  The fact that thinner ice melts faster contributes to that.  An Extent maximum of 14.5 km2 in March 2020 will be more vulnerable to melt than the same Extent in earlier years when average thickness was thicker.  However, I don't think that effect has really taken hold yet, given that the March vs. September Extent correlation appears to still fit a straight line, with no suggestion of an increasing curve in the correlation that would/will become apparent when/if declining thickness causes faster Extent loss.

11
Arctic sea ice / Re: The 2019/2020 freezing season
« on: January 30, 2020, 11:22:25 PM »
Agreed, I was conflating "statistical insignificance" with meaningless.  Yes, there is value in knowing that something doesn't work. 

12
Arctic sea ice / Re: The 2019/2020 freezing season
« on: January 30, 2020, 10:35:00 PM »
XY Plot of NSIDC Average January extent versus the following September's min from year 2006 onwards.
TBH I think it is a bit of a meaningless plot

True that!  You'd be hard pressed to come up with a better example of random noise vs. a causal correlation.  Also, X drives Y so the graph should have January Extent on the X axis and following Sept. min. on the Y axis.

Nothing to see here folks, keep moving...

13
Arctic sea ice / Re: The 2019/2020 freezing season
« on: January 29, 2020, 12:12:04 AM »
    Is there an index that relates ice thickness to melt resistance?
    It would be interesting to see a calculation of the melt resistance for the total ASI melt resistance for standardized month/day dates compared across years.
    That might be a better indicator than even Volume for how much change has occurred to the ASI.  For example -- A million km3 of ice in 2020 might be more vulnerable to melt (require less melting energy) than a million km3 of ASI in 2010.

    In addition to thickness, other variables like continuity, average floe size and variability, and salinity could go into it.  That all seems intractably difficult, esp. since values of those characteristics for the Arctic ice pack are probably not available. But a measure of the average thickness for the ASI ice pack combined with some reasonably accurate method to account for the relative melt resistance for sea ice of different thicknesses could be enlightening.  (Though an Arctic wide melt resistance value would need to account for volume within each thickness category separately, so average ASI thickness would not suffice).

    But first things first.  Is there some formula for translating the thickness of a single chunk of ASI ice into a relative or absolute melt resistance value?   I postulated such a thing by reversing the Thorndike ice growth rate curve for different ice thicknesses a few months ago and posted it on ASIF, but was informed by ASIF contributors who actually know about these things that a simple reversal of the energy in/out equation was not valid.  Thorndike defined an ice growth vs. thickness curve, so it seems like Thorndike or somebody must have done the opposite, define a ice melt vs. thickness curve (for a fixed melting energy input).  That would give us another handle for understanding the significance of the loss of thickest oldest ice, and the overall decline in average ASI thickness.
 

14
Arctic sea ice / Re: The 2019/2020 freezing season
« on: January 28, 2020, 11:55:55 PM »
No.  Just less relevant.  Neither yields a perfect correlation, but extent does better.
Correlation of what with what?
Volume is the bottom line measure of how much ice there is. 
Thickness indicates a key component of the Volume calculation (Thickness x Extent or Thickness x Area).
  Also, it provides qualitative information about the condition of that ice.  Older thicker ice is more resistant to melt than younger, thinner ice.

Extent and Area are more directly related to the albedo impact of ASI decline.

So each measure has value for addressing different issues / answering different questions.

15
Arctic sea ice / Re: The 2019/2020 freezing season
« on: January 28, 2020, 05:37:41 PM »
I've done my due diligence this morning (UTC), and there's still a total absence of any ice >= 4m thick to be seen on the most recent CS2/SMOS reanalysis. Chapter and verse over at:
http://GreatWhiteCon.info/2020/01/wheres-the-thickest-arctic-sea-ice-gone/

Thanks Jim.  The  Jan 11, 2020 vs Jan 11, 2019 contrast in the Great White Con images is much less dramatic than the Jan 19, 2020 vs 2019 images posted upthread.  Ditto, the PIOMAS difference maps posted by Oren are not as dramatic either.  I suspect there is an issue with color scaling in the Jan 19, 2020 CryoSat image upthread.  So I consider that issue resolved or at least unimportant.

   What is important is the lack of >4m thick ice and overall thinner and less consistent thickness shown in your January 2020 Great White Con maps.  Not only is the thickest ice gone, but the ASI as whole looks weaker and more variable.  In particular, the Atlantic side from the North Pole down to Greenland and Fram Starit looks more vulnerable than same dates in 2019 and 2018.

   The 2020 melt season seems to have potential for dramatic acceleration relative to the long term trend.  In simpler words: it looks like it could be on the edge of falling apart by September 2020.

16
Arctic sea ice / Re: The 2019/2020 freezing season
« on: January 28, 2020, 01:54:24 AM »
Jim -
     Both Thickness and Extent seem to be much less in 2020 than 2019 in those images.  But the December PIOMAS Volume data show Dec 31 2019 only about 3% below Dec 31 2018.
https://forum.arctic-sea-ice.net/index.php/topic,119.msg242997.html#msg242997

 The dramatic difference in Thickness and Extent in those maps look like a lot more than a 3% Volume decline. 

    Or is the January PIOMAS going to deliver a bombshell?  But that also seems unlikely given robust Extent gains in recent  weeks.  And there has only been 19 days between Dec 31, 2019 and the Jan. 19, 2020 graph. 

   CryoSat vs. PIOMAS difference doesn't explain it either, since both images are CryoSat.  Something is not lining up.   The only explanation I can think of is a re-calibration of CryoSat.  But I don't have any info pointing to that. 

   Bottom line:  the 2019 to 2020 difference in those maps is too huge to believe.  If it is real then it looks the Arctic is going to get blitzed in the 2020 melt season.

    Or am I missing/misinterpreting something?

17
Dwindling Arctic Sea Ice May Affect Tropical Weather Patterns
A new study finds a possible link between Arctic warming and more frequent El Niños in the Central Pacific.
By Bob Berwyn, InsideClimate News   
Jan 27, 2020
https://insideclimatenews.org/news/26012020/arctic-sea-ice-melting-tropical-weather-el-nino-climate-change

"Kennel said it appears the sea ice decline passed a threshold with global consequences about 20 years ago.

"Sea ice reached a kind of tipping point around 1999," he said. "Before that, the seasonal melting from June to October was about the same size (each year). After that, it was much bigger."

"Francis, who was one of the first to propose that declining Arctic sea ice could intensify storm and drought extremes in the mid-latitudes, said that "interestingly, the Arctic connection was weak or non-existent during years before sea ice had declined substantially."

She added, "These authors present multiple lines of evidence that all fit the story that, when it comes to influences on mid-latitude weather, the tropics are no longer the only game in town."

Francis said another recent paper found different types of links between Arctic sea ice and the tropics. In the 2019 report in the journal Nature, the researchers wrote that extensive sea ice around Greenland and the Barents Sea favors El Niño conditions the following winter. "

&
""If this is true, it would mean that the impacts of Arctic sea-ice loss could literally affect the entire planet," she said. "Arctic sea ice melt is by no means only a polar bear problem."  "

18
Arctic sea ice / Re: The 2019/2020 freezing season
« on: January 27, 2020, 08:12:00 PM »
Sunday to Sunday ice drift map.
Thanks Blumenkraft.  Can you also post the drift anomaly?

19
Arctic sea ice / Re: "Stupid" Questions :o
« on: January 23, 2020, 11:14:09 PM »
  ???  Signs that ASI observation is getting a bit obsessive -- when you look forward to Wipneus updating the X axis on the PIOMAS monthly average ASI exponential volume trend graph like it is Christmas morning (so you can see where the curves go beyond 2020.) 

https://14adebb0-a-62cb3a1a-s-sites.googlegroups.com/site/arctischepinguin/home/piomas/grf/piomas-trnd2.png?attachauth=ANoY7cq_c4Na1cDAySBcSeePKB14HOJF_ARMYow00WMHIIZTjLWFdlxHPP3wW-FzPTCcs5uMnfVS2HURQ3QplDJcAVVMFY96prXMCYgaUTfsEmY2Z2xHmYHbLNiJVmLu3-tXXgX_-O1TDkUZPEqPjJFs8uNIsalCH_MRWTvVe9AKkohRYx49x3RhfyWB1OjfS6PmRbckQegXwFTw_umdKP9PrNHdAbLzSBLvFaXAfS4SrZIKizenTlMwP4DZOsN9Xv_SlsSYu24i&attredirects=0

I still wish he would do a straight line trend version.  As it is, the multi-month graph is one of the most informative visualizations for groking the ASI story.  Which needs to be told. 

Unfathomable that a crisis of this magnitude, consequence, and virtual permanence (as far as we know)... is unfolding before our eyes, ...and yet hardly anybody talks about it in daily conversation.  On the other hand, the idiocy of our current path is so obvious, what is there to say except to note that it is idiotic?   

Well, fighting for a price on carbon is one conversation that needs to move ahead.
2020 resolution -- continue proudly being a carbon fee and dividend climate nerd. 

PS That alone won't be enough. No silver bullets available, only silver buckshot.
      We need every tool in the kit and all hands on deck to turn this ship around.
        Ahoy mateys, anybody got a spare direct air CO2 capture machine I can borrow?

Thanks to Neven for ASIF and all those folks whose posts give us 2020 vision!

20
Angular momentum at zero essentially means that the planet's atmosphere is static relative to the surface with no prograde or retrograde net rotation.  It has no angular momentum to deposit or absorb.  You could say that any time vertical and zonal integral of relative AAM anomaly is positive, the atmosphere is rotating faster than the Earth,
-------

Either way, the completely Westerly tropical surface winds lately yielded an atmospheric acceleration faster than has ever before been observed.  This would be fascinating if it were happening on Mars.

Thanks Sark.  I still don't really understand the mechanisms or significance of the AAM stuff, but your post is the most helpful info I've seen about it.

21
Arctic sea ice / Re: What's new in the Arctic ?
« on: January 23, 2020, 03:02:22 AM »
Probably nothing, but struck me as interesting, given what happened in 2012!
Possibly related observation about 2012 -

     By filtering out long-term CO2 driven trend, ENSO (El Nino), Solar cycle, and Aerosol values, it is possible to remove a large portion of the year to year variation in annual average NASA GISS temperature for every one of the past 11 years except for 2012.  But the "model" fails miserably for predicting the difference between 2012 and 2011.  The only other year with a negative correlation between the model estimate and observed value also involves 2012 - the difference between 2013 and 2012. 

    So for reasons unknown to me (BTW - I'm not a climate scientist, just another ASIF onlooker hanging around the scene of the crime), 2012 was an oddball year with respect to a robust pattern that applies quite strongly to every other of the 11 years in 2009-2019.

    Of course, for the Arctic Ocean we have the great Arctic Cyclone of August 2012 to explain why Extent tanked that year.  Worth noting that
   a) the ASI low Volume record set in 2012 is much less extreme than the Extent record, and
   b) Extent and Volume recovered rather quickly. 

    Thus it seems that while 2012 remains an epic event in recent ASI history, it was largely a short-term disturbance that brought submerged heat to the surface and created a drastic but short-lived effect on Extent.  That loss of heat energy led to a pseudo-recovery over the following years.

    In comparison, while 2019 did not break the 2012 record, it shows a broader impact of continued warming in the condition of the remaining ice that is thinner, saltier, and less resistant to melt; has lost virtually all of the thickest multi-year "anchor" ice; and reflects a system that has been functionally altered (e.g. loss of Beaufort Gyre nursery). 

    While some idiot with bad hair might claim that "Hey, there's more September Arctic sea ice now than there was 7 years ago, what's the problem?", the situation is actually much more dire than a simple accounting of Extent or Area, or even the more informative Thickness and Volume, indicate.  The ASI is like a termite-riddled wooden beam.  The surface appearance does not fully indicate the structural weakness within. 

     I suspect that the next Arctic Cyclone with similar storm energy as the 2012 event will cause even more dramatic damage than 2012 because it will be interacting with a thinner and more fractured ice pack, will have longer wind fetch for wave generation from more open water, and have much higher levels of submerged heat energy to bring up.  In addition to all that, the probability of a storm as strong or stronger than 2012 increases with the continued warming of Arctic ocean water, more frequent and intense incursions of warm air masses, increasing Arctic humidity, weakening of the polar jet, Atlantification etc. 

    All amateur speculation of course, by someone who knows just enough to be emphatically wrong, but hey my GISS model works (except for 2012)!

    PS Lest you think I exaggerate the potential correlation between bad hair and stupidity, one such person recently tweeted that New York City should get ready with mops and buckets instead of considering an expensive public works infrastructure project to reduce risk from rising sea level.

22
Arctic sea ice / Re: Near Real Time Sea Ice Volume
« on: January 14, 2020, 02:36:59 AM »
    It could just be another example of year to year variation, but seen as a trend indicator, losing 13% of thickness over a one year span is ominous.  Really makes me wonder what the upcoming melt season will bring. 

    Apart from the direct effect on total volume, the change in ice quality does not bode well for ice survival.  Maybe the remaining 2020 winter will reverse the striking difference between 2019 and 2020 in fraction of ice over 3 meters thick.  If not, 2020 melt season will start with the ASI preconditioned to match or exceed previous record for amount of summer ice melt, and from a low volume starting point.  It is both interesting and devastating to witness this process unfold.

    The NASA and NOAA GISS temperature observations for December 2019 will come out next week and thus statements about the 2019 full-year global average surface temperature.  By the face value, 2019 will almost certainly rank #2, just a bit (ca. 0.02C) below 2016. 

    But 2016 was a monster El Nino year and at the peak of upward solar cycle influence on temperature.  Filtering out the effect of the ENSO ONI3-4 sea surface temperature, solar, and aerosol influences that cause year to year variation reveals the underlying trend.  Using a preliminary GISS-equivalent temperature for December and filtering out those short-term influences shows 2019 as the warmest year since modern records began.

23
This bit about the Australian fire season seems relevant to this thread

"Another contributing factor has been a “rare phenomenon called sudden stratospheric warming (SSW) that took place in Antarctica”, noted the Times. Back in September, “winds circling the South Pole about 30km high in the stratosphere went into reverse causing the temperature of the stratosphere to rocket by 40C”, the article explained.

This “added to the hot dry conditions by shifting the westerly winds, which usually lurk over the Southern Ocean, up onto the continent”, said ABC News.

SSW events, which also occur in the northern hemisphere, are “rare in the southern hemisphere with only one major event ever identified, in 2002”, noted another ABC News piece."

Source:   CarbonBrief.org, 7 January 2020
Media reaction: Australia’s bushfires and climate change
https://www.carbonbrief.org/media-reaction-australias-bushfires-and-climate-change

24
Arctic sea ice / Re: The 2019/2020 freezing season
« on: January 07, 2020, 09:22:20 PM »
gnnng sdlkto vlspto  ;)
Nice synoptic view.  Took me a while to figure out the legend - each frame is a day starting in September 2019 to Jan. 6, 2020.

25
Arctic sea ice / Re: The 2019/2020 freezing season
« on: January 02, 2020, 06:43:12 PM »
https://twitter.com/zlabe


Ignoring Hudson Bay, which is a different arena, compared to the other Arctic ocean regions, the CAA shows somewhat less extreme and less consistent decline than the others.  I suspect that is because wind and water currents pile up remaining ice in the CAA.  And with declining thickness and thus increased ice mobility, the piling ice effect continues as strong or stronger than pre-2000, supplying ice to the CAA from other regions.  That all fits with the idea that CAA will be the last refuge for declining Sept (then Aug/Oct/July) ice persistence.  Does this make sense, or am I just making this up?




26
Arctic sea ice / Re: "Stupid" Questions :o
« on: December 20, 2019, 03:13:44 AM »
But I prefer to see Stonehenge as an early silicon based computer running at 1 Hz / annum.
+1!

27
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: December 17, 2019, 04:05:02 AM »
[ Correction to earlier post:  A while back I threw in a comment that when ice thickness gets below 0.5-0.8 meter it becomes susceptible to flash melt, but that I could not remember the source.  Well, I still can't find it, and looking at ASI thickness data, the greatest one month decline in thickness during melt season (thickness values get skewed by refreezing ice in fall-winter) is less than 0.3m.  So I was wrong.  The annual pattern is about 0.8 to 1.0 meter thickness decline across each entire April to September melt season. ]

-------------------
 I came across some interesting tidbits about ASI thickness at https://nsidc.org/cryosphere/sotc/sea_ice.html

"Using data from submarine cruises, Rothrock and collaborators determined that the mean ice draft (the ice extending below the water surface) at the end of the melt season in the Arctic decreased by about 1.3 meters between the 1950s and the 1990s."

"Examining 42 years of submarine records (1958 to 2000), and a five years of ICESat records (2003 to 2008), the authors determined that mean Arctic sea ice thickness declined from 3.64 meters in 1980 to 1.89 meters in 2008—a decline of 1.75 meters."

(between 2003-2008 and 2010-2012)  "...sea ice volume declined by 4,291 cubic kilometers at the end of summer, and 1,479 cubic kilometers at the end of winter (Laxon et al. 2013)."

They include a chart from Kwok and Rothrock 2009 that shows nearly identical thickness declines of ~50% between 1958-76 and 2003-2007 in different Arctic subregions (Chukchi, Beaufort, Canada Basin, North Pole, Nansen Basin, Eastern Arctic.)   No apparent differentiation between North Pole and the others.

A linear trend line of whole-Arctic September Volume shows a decline from 11.1 to 4.2 M Km3 from 2000 to 2019, a 62% decline

For the CAB volume alone, the decline is from 8.4 to 3.8 M km3, a 55% decline.  So the CAB has lost volume at a slightly slower rate, but 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.  I think protection by location matters even less when you factor in the increasing mobility of thinning ice, reduction of land fast ice, and increased open water/wind fetch, and storm potential as Arctic water warms.

Based on all that it seems that the straight line trend for volume (e.g. Stephan, Wipneus) is the best predictor.  If so, then there will be a lot of headlines in 2032 to 2035 as September goes to Zero, followed shortly after by August and October.  I say will instead of "would" because with the lag of the effect on global average temperature from CO2 emissions being at least 10 years (for about half the temperature effect, to ca. 30 years for most of it), the fact that the projected zero monthly ASI volume dates are only 12-15 years away indicates that we already committed to those changes even if we finally got serious about reducing emissions starting in 2020 (which nobody thinks is going to happen in 2020).

The science on how ASI reduction affects weather is still unsettled, but regardless of the details, Jennifer Francis' quote makes a lot of sense ~ How could removing so much Arctic ice NOT affect the weather?

July hitting zero before August in Stephan's table must be a mathematical fluke caused by a slightly steeper decline rate being extrapolated into the future.  On the Wipneus graph, July volume lags about 12 years behind August, which does make sense. 
https://sites.google.com/site/arctischepinguin/home/piomas   


28
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: December 15, 2019, 01:15:47 AM »
"When will the Arctic see its first ice-free summer?"
  Nice review by Daisy Dunne at Carbon Brief.
https://interactive.carbonbrief.org/when-will-the-arctic-see-its-first-ice-free-summer/#

29
Arctic sea ice / Re: "Stupid" Questions :o
« on: December 07, 2019, 06:00:04 PM »
Edited quotes
I see that you have all been having a lot of fun debunking my claims. And perhaps they needed debunking, who knows.
--------
So global warming. Yes, it's a disaster. No, we are not going to stop it. So how much of a disaster is it going to be?
---------
The only true threat to global civlisation would be a large and consistent disruption in food production. And I'm not seeing anybody predicting such an outcome (although it does seem to me to be at least a possibility).
-----------
Another of the papers he links to makes some properly dystopian claims, e.g. that CO2 "... is rapidly heading towards levels last seen some 50 million years ago — in the Eocene — when temperatures were up to 14 °C higher than they were in pre-industrial times."
------------
Yes I know that end-of-world prophecies are exciting and lot's of people seem to wish for some sort of apocalypse. I don't
binntho - Disagreement is not opprobrium or personal attack.  You are well known in this forum for providing thoughtful opinion and insight.  If some nut job jumped onto the forum and wrote that disrupting the planetary climate would have minor effect on well being, people would just dismiss it and not bother to respond with forceful argument.  It is exactly because you do seem intelligent, informed, and curious that folks weigh in to redirect what I (and I presume others too) see as a colleague who is engaging in delusional thinking.  We argue with you because we care and trust that you have the ability to change your mind.  That requires the same of us.  I submit that the facts do not support your position. 

RE: "No, we are not going to stop it." 
     It is not a yes/no situation.  Significant damage has already been done.  Dorian/Great Barrier Reef/2003 Eur. heat wave, etc etc ad nauseum.  I personally don't see how there is ANY chance of not breeching 1.5 C, so I wish IPCC would stop paying it lip service.  But we still have the ability to halt the destruction, pain, and loss caused at 2C or 3C vs. 4C.  By numerous analyses by people who dedicate their professional lives to understand this stuff, getting to 4C could result in a runaway situation where human action is overwhelmed by natural reinforcing feedback mechanisms.

RE My #3 citation quoting Lenton et al. Nov. 2019 article in Nature --
     The list of authors for that piece includes many widely recognized top-tier experts (published in the 1st or 2nd most respected peer-reviewed journal).  "Trust the experts" has fallen out of favor now that with the internet anybody can "publish" any thought that bubbles up through their brain (self included). 

     But facts and expertise still matter.  I still trust the experts when I have a toothache or when the relevant experts tell me that the global ecosystem on which I and my children are utterly and entirely dependent is being irrevocably altered.  You misunderstand and misrepresent their statement about potential for a runaway temperature increase.  They did not say that human emissions alone would drive CO2 to 2500ppm.  But there are powerful feedbacks that can and have done exactly that.  That scenario is not merely hypothetical, it has happened before and can happen again.  It is an engineering analysis of physical properties, not a prophecy based on philosophy.  To ignore factual warnings by experts is self-destructive.

     Heeding warnings of impending destruction and attempting to avert it by spreading the alarm is not wishing for it.  The scale of response needed to reinvent and replace our energy system on a global scale is daunting and difficult.  To succeed will require unprecedented concerted action across political, ethnic, economic and other boundaries.  Humanity faces a sink or swim crisis. 

RE:  Not finding scientific evidence for climate change impact on agriculture
     All I can say is look again. It's there.  Lots of it.  Reduced crop yields as cropping areas exceed tolerances for plants already near their thermal maximum.  A CO2 fertilization effect that only allows crop plants more vegetative growth if water, temperature stability and other needs that are threatened by climate change are controlled.  And even if that vegetative growth does occur, it largely acts to dilute food nutrient density instead of increasing it.  As for, "we'll just move cropping areas north with the shifting isotherm", it isn't that simple.  The solar radiation supply required for photosynthesis is not moving north, nor are the soil resources farther north the same as current ag production zones.  Add in altered, and more likely more erratic, precipitation patterns and the prospects for simply shifting north become even more challenging.  As for that CO2 fertilization effect, here is some more bad news -- weeds are better adapted to benefit from it than crops.  Weeds already outpace insect and disease pests for crop production losses.

     There may be localized benefits for a few cool ag production areas where water supply is not reduced.  I happen to live and work in one such area.  But even here the cost-benefit ratio is not necessarily positive.  For the planet overall, the studies show net negative impacts that increase with additional warming.  The result  is stalled or reversed productivity when we need the opposite to feed a larger population.  = Supply-Demand Train wreck.

     Any "ism" taken to an extreme becomes destructive.  Capitalism run amok becomes Nazi fascism.  Socialism run amok becomes Animal Farm Big Brother 1984 totalitarian communism.   Religious isms run amok become the Crusades,the Jonestown massacre, or ISIS.  Maybe Humanism run amok becomes a sterile, isolated, solopsistic, empty narcissism, where the feelings and dignity of other creatures has zero value.  Utlimately that could include other people.  I wonder if the shrinking circle of that logic ends up as Meism.  That seems like the definition of hell.  I prefer a world of other beings that can delight, surprise, and teach me expressly because they are different from me, yet we share a common existence.

     Enough of my self-published internet philosophizing.  To bring it all all back to GDP, we could have a glorious world and a massive economic boon by taking the actions needed to prevent climate catastrophe.   I wish the big business interests would pull their heads out of their asses long enough to see that opportunity.   The money we spend on military budgets would probably be enough to pull it off.

30
Arctic sea ice / Re: "Stupid" Questions :o
« on: December 07, 2019, 12:29:07 AM »
     No, "life on Earth" is not at risk.
The cockroaches love this stuff.  They've seen it before.  Millions of years before the first human walked on two legs. Cockroaches just need some warmth, some organic matter to feed on, and a rock to hide under.  So they will be fine.

     It is this complicated set of brittle, tinker toy supply-chain connections that we call "society" that is vulnerable to catastrophic failure.
     It is the "organized (human) global community" that is at stake, i.e. "civilization".  Things like "cities" (esp. the many large coastal ones), "grocery stores", "phones", & "hospitals".

     My guess is that not all humans would die from hunger, increased health risks with broken sanitation and medical services, or war violence by other humans competing for reduced resources. I think there will be survivors.  Some. 
     How many, living how and where, I am less sure about.
     I wouldn't count on one-day Amazon delivery, an internet connection, or an electricity grid.
     "Do it yourself" would evolve from an interesting hobby to a survival skill.

     At least the obesity epidemic is likely to be reduced, if only because there are several billion fewer people to count.

     And if you think this view is pessimistic, ask yourself if you too have considered some dire projection for 2050, 2070, or 2100; did the math in your head; and concluded "Well, i'll be dead by then anyway".  Is "Better dead than alive" not the ultimate pessimism?  What does that view of the future say about our honor, our legacy, and our responsibility to people younger than ourselves?

     Remember/imagine a time when you looked FORWARD to the future with anticipation for all the cool stuff that was/is being invented by truly awesome human ingenuity.  I want to get back to that.  I think/hope (depends on the day) we can get back to that.  We better. 

    Sorry for preaching, but there is nothing more important than this topic.  Nothing.  Because it affects everything.

31
Arctic sea ice / Re: "Stupid" Questions :o
« on: December 07, 2019, 12:21:12 AM »
1. From The brutal logic of climate change
By David Roberts on Dec 6, 2011
https://grist.org/climate-change/2011-12-05-the-brutal-logic-of-climate-change/

Kevin Anderson, former Director, U.K. Tyndall Energy Program.
“...a 4 degrees C future is incompatible with an organized global community,
is likely to be beyond ‘adaptation’,
is devastating to the majority of ecosystems,
and has a high probability of not being stable.”


**************************
2. From:  Turn Down the Heat - Why a 4°C Warmer World Must be Avoided, A Report for the World Bank by the Potsdam Institute for Climate Impact Research and Climate Analytics.  2012
http://documents.worldbank.org/curated/en/865571468149107611/pdf/NonAsciiFileName0.pdf

"The 4°C scenarios are devastating: the inundation of coastal cities; increasing risks for food production potentially leading to higher malnutrition rates; many dry regions becoming dryer, wet regions wetter; unprecedented heat waves in many regions, especially in the tropics; substantially exacerbated water scarcity in many regions; increased frequency of high-intensity tropical cyclones; and irreversible loss of biodiversity, including coral reef systems. 
     And most importantly, a 4°C world is so different from the current one that it comes with high uncertainty and new risks that threaten our ability to anticipate and plan for future adaptation needs."

"It would be so dramatically different from today’s world that it is hard to describe accurately; much relies on complex projections and interpretations."

"We are well aware of the uncertainty that surrounds these scenarios and we know that different scholars and studies sometimes disagree on the degree of risk."

"Finding ways to avoid that scenario is vital for the health and welfare of communities around the world. While every region of the world will be affected, the poor and most vulnerable would be hit hardest.  A 4°C world can, and must, be avoided.

"Warming would not stop there. Because of the slow response of  the  climate  system,  the  greenhouse  gas  emissions  and  concentrations  that  would  lead  to  warming  of  4°C  by  2100  would  actually commit the world to much higher warming, exceeding 6°C or more, in the long term, ..."

********************
3.  From Climate tipping points — too risky to bet against
Timothy M. Lenton, Johan Rockström, Owen Gaffney, Stefan Rahmstorf, Katherine Richardson,
Will Steffen & Hans Joachim Schellnhuber, Nature.  27 November 2019
https://www.nature.com/articles/d41586-019-03595-0

"We argue that cascading effects might be common. Research last year analysed 30 types of regime shift spanning physical climate and ecological systems, from collapse of the West Antarctic ice sheet to a switch from rainforest to savanna. This indicated that exceeding tipping points in one system can increase the risk of crossing them in others. Such links were found for 45% of possible interactions.

In our view, examples are starting to be observed. For example, Arctic sea-ice loss is amplifying regional warming, and Arctic warming and Greenland melting are driving an influx of fresh water into the North Atlantic. This could have contributed to a 15% slowdown since the mid-twentieth century of the Atlantic Meridional Overturning Circulation (AMOC), a key part of global heat and salt transport by the ocean. Rapid melting of the Greenland ice sheet and further slowdown of the AMOC could destabilize the West African monsoon, triggering drought in Africa’s Sahel region. A slowdown in the AMOC could also dry the Amazon, disrupt the East Asian monsoon and cause heat to build up in the Southern Ocean, which could accelerate Antarctic ice loss."

 "...the Earth system has been unstable across multiple timescales before, under relatively weak forcing caused by changes in Earth’s orbit. Now we are strongly forcing the system, with atmospheric CO2 concentration and global temperature increasing at rates that are an order of magnitude higher than those during the most recent deglaciation."

Atmospheric CO2 "... is rapidly heading towards levels last seen some 50 million years ago — in the Eocene — when temperatures were up to 14 °C higher than they were in pre-industrial times."

"If damaging tipping cascades can occur and a global tipping point cannot be ruled out, then this is an existential threat to civilization. No amount of economic cost–benefit analysis is going to help us. We need to change our approach to the climate problem.
     Act now
In our view, the evidence from tipping points alone suggests that we are in a state of planetary emergency: both the risk and urgency of the situation are acute "

32
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: December 06, 2019, 01:10:47 AM »
Remember, all those MTs of CO2 are actually CO2e. We may emit that much sooner than you might think.
Agreed Tom. Though I am often not sure if people actually mean CO2e when they throw out cumulative emissions values.  But unless they specify CO2e one has to assume they mean what they say, i.e. CO2. 

Thus, as you point out, the real situation with CO2e increasing even faster makes the siutation... more worser?  Climate change trajectories are so bad they require new language. 

33
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: December 06, 2019, 01:03:08 AM »
As usual, I come to the conclusion that by far the best explanation of the behaviour of arctic ice, when it melts and how fast it melts, is found by looking at the changes in temperature ... etc."

Moving on to Notz and Stroeve 2018, it says
    "The sensitivity of Arctic sea ice as described by the linear relationship between global-mean temperature and Arctic sea-ice coverage has been found to remain constant in model simulations across a wide spectrum of temperature trajectories.  In particular, the linearity holds in all CMIP5 models until summer sea ice vanishes in individual simulations. Hence, the observed sensitivity can be extrapolated to directly estimate the response of the Arctic sea-ice cover to future warming."

After describing some complications, they go on to say:
     "Despite these uncertainties, the different estimates result in a relatively narrow range of additional warming above present that is required to obtain a near-ice free Arctic Ocean during summer, defined as the total sea-ice coverage dropping below 1 million km2."

Then they discuss specific temperatures, and variation around those, from which I derived a median estimate of 1.68 +/- 0.25C (95% CI) above the (inferred) 1850-1900 NASA GISS global average land and ocean surface temperature.  (inferred because GISSTemp doesn't start until 1880. Details to translate to 1850-1900 equivalent are trivial and don't affect the stated value).
And for those of you keeping score at home --- as of 2019 the running 5-year average GISSTemp is at +1.15 C.  In earlier post, I used observed recent GISSTemp trends compared to the 1.68 +/- 0.25C to make the year estimates for when Sept gets below 1M km2 Extent.

The 1.7C estimate fits with their statement:
     "As soon as the global-mean temperature has risen by slightly below 2 ◦C, the Arctic Ocean is expected to be on average nearly ice-free during September."

and slightly out of context, but still relevant:
     "A possible modification of these estimates might be caused by the future evolution of anthropogenic aerosols, as they are expected to become less abundant over the next few
decades. "   

     "... in climate-model simulations the expected aerosol reduction causes additional ice loss..."

    "This would imply that the estimates given here are too conservative."

And finally, they remind us that:
     "While the observed linear relationship between sea-ice coverage and global-mean temperature allows one to estimate the long-term average future evolution of the pan-Arctic ice cover, the evolution of the real ice cover will show substantial year-to-year variability because of internal variability."

-----------------
So it seems to me that binntho and crandles are both right!

34
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: December 06, 2019, 12:38:18 AM »
       Mining S&N 2018 again - these excerpts about the timing of Atlantification line up well with the discussion of possible mechanisms the 2001-2007 steep slope decline:

    "Another large pulse of warm water occurred in the 2000s, peaking in 2007..."
 
     "This ocean warming largely explains the observed Barents Sea winter ice variability and provides a useful predictor for the annual mean sea-ice cover in the Barents Sea.  The Barents Sea region has also been identified as key for explaining model differences between oceanic and atmospheric pathways of energy transfer to the central Arctic Ocean…” 

    "The Atlantification of the eastern Eurasian Basin may therefore provide an additional factor
behind sea ice reductions in that region, perhaps on the same order of magnitude as atmospheric thermodynamic forcing."
(citations removed)

-------------------
      And relevant to Crandles' invocation of the role of Beaufort Gyre decline in the 2001-2007 steep slope episode:

    "Over the last two decades, the amount of freshwater in the Arctic has increased. This is particularly evident in the Beaufort Gyre, which has accumulated an extra 5000 km3 of freshwater in the 2000s compared to the 1980s and 1990s..."

   "The large Eurasian and North American rivers input warm freshwater (on average 15 °C)..."

   "Peak discharge occurs in June and this water is immediately available to melt ice, helping to break up the fast ice. River discharge also adds a large amount of chromophoric dissolved organic matter, which absorbs sunlight at short wavelengths, further warming the surface layers of the ocean and increasing ice melt. On the other hand, increased ice melt and freshwater input increases summer stratification, allowing for more heat to be trapped in the upper ocean, which in turn delays ice formation in autumn."  (citations removed)

35
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: December 06, 2019, 12:31:56 AM »
Correction
   N&S 2018 correlation of ASI Extent with cumulative CO2 emissions puts the cumulative chance of 1st Aug. and Sept. as 'largely ice free' (which from my guesswork seems to line up with ca. < 2M km2 Extent, details later) at >50% chance by 2033, and regularly (individual year chance > 50%) by 2036.
     Finally, N&S 2018 give correlation of CO2 with July - October being "largely ice free" (which as above, I interpret as ca. < 2M km2 Extent).  For that I used observed emissions through 2019, and Intl Energy Agency emissions trend forecast of 1.1% continued emissions growth out to 2040, then reducing subsequent global emissions as per the observed US and EU combined downward trend since their recent peak.  With those CO2 assumptions, the cumulative 50% chance for a 1st July-Oct  that is "largely ice free" is by 2045, and regularly (individual year chance > 50%) by 2048. 
   -- Rereading Strove and Notz 2018 (which is a 19-page textbook on Arctic sea ice situation as of Sept. 2018, and serves as a background info for the more applied Notz and Stroeve 2018 companion article), I find this statement:
"Extrapolating the linear relationships into the future, we find that the Arctic Ocean completely loses its ice cover (emphasis mine) throughout August and September for an additional roughly 800 ± 300 Gt of anthropogenic CO2 emissions. For an additional 1400 ± 300 Gt of anthropogenic CO2 emissions, we estimate the Arctic to become sea-ice free from July throughout October ..."

    Those are the CO2-ASI correlations I used for that prior post, and it seems I was far too lukewarmist in my interpretation of what was meant by "largely ice free" in the companion Notz and Stroeve article.  Thus, instead of those projected dates being when Aug-Sept, or July-Oct could get below 2M km2 Extent, they may actually be estimates for when those months can have virtually Zero Extent.   Ouch.  I keep thinking climate projections can't get worse, then they do.

     But just to keep things confusing, I settled on the meaning of Aug-Sept being "largely ice free" as < 2M km2 Extent because the extrapolated dates for N&S Aug-Sept "largely ice free" almost match the N&S extrapolated dates for Sept. <1M km2, and the fact that Aug Extent runs about 0.8M km2 higher than Sept Extent.  So my original interpretation still makes more sense to me, but hard to argue against statement by same two authors writing about the same topic at the same time.  So take your pick, and 'Caveat emptor'.  Either way, it doesn't give the Arctic sea ice much time.

   What remains the same is that the timing depends upon the future emissions trend.  The CO2 regime I used assumes that global emissions do not peak until 2040 (as per 2019 IEA estimate).  Unfortunately, that seems to be a plausible scenario.  As suggested by S&N and N&S papers, that emission scenario obliterates ASI in Aug-Sept by the mid 2030s, and for July-Oct by the late 2040s.  That is not a good prospect for human civilization.  But it does not have to be that way.
 

36
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: December 05, 2019, 03:07:48 AM »
    With Arctic albedo already increasing radiative forcing by about 25% of the GHG influence (forget the source, could look it up if somebody really needs it), consider how much MORE albedo impact would arise from July being "largely ice free".  Remember, if July (a high solar gain month in it's own right) has hugely reduced Extent by 2048, then June must also have much lower Extent than at present. Wide expanses of open Arctic Ocean in June and July = Albedo nightmare.

    That makes 2050 look like end of the line for a planet any of us would recognize.  If Jennifer Francis et al. are even half-right about weather impacts of Arctic warming and ASI decline at 2010-2019 levels, the effects by 2040-50 would be off the charts.

    I believe that with collective human ingenuity just about anything is possible.  But the performance to date for human wisdom with regard to climate management does not make for an optimistic outlook.  By the ASI situation alone (ignoring the many other vectors), it looks like human civilization could be in dire straits by, or well before, 2050 unless things start changing radically and soon.  So let's stop using 2100 as the benchmark and focus on how humans can get past 2050.

37
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: December 05, 2019, 02:18:38 AM »
1.
Does the following image help show a high MYI level then a low level?

http://nsidc.org/arcticseaicenews/files/1999/11/Figure5-1-350x443.png

Crandles' theory makes sense to me.  But I would change "The 2-3 year ice is pretty steady til 2002, then downwards every year til 2008.... etc." to "The 2+ year old ice...". 
     It is the combination of decline in the 2-3, , 3-4 and 4+ age categories (esp. the 4+ year ice) that causes the steep slope ca. 2001-2007. 

     The transition of the Beaufort gyre from a nursery to a melting zone seems to fit as a qualitative transitional event that gave rise to the observed trends. 

2.
Looks like the CAA's ability to block ice export from the Arctic Ocean is reducing. Maybe one of those small things with large consequences?
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GL085116?af=R
The Dynamic Response of Sea Ice to Warming in the Canadian Arctic Archipelago

This seems like another qualitative change that could accelerate the end game for late summer ASI decline.  Adding another doorway for ice export can't be good for retaining ice.


3.
    The remaining area is also not really sticking to Greenland for safety as we had hoped for a long time so what is left might get really floaty at some point. Or just disintegrate and die in place.
 
A-Team used to say "we could have a total late summer blow out any year now". (I'm paraphrasing).  I agree.  One summer, any summer, the remaining ice will be thin and fragile enough to become a completely shattered, mobile mess by season's end.

See ice thickness on gerontocrat's last graph over in the PIOMAS thread at https://forum.arctic-sea-ice.net/index.php/topic,119.msg239492.html#msg239492

Not sure where I saw it, but somebody (Notz and Strove 2018?)  suggested that once thickness gets below 0.5 to 0.8m, flash melt under the right conditions becomes possible.  Looking at the thickness trend, the combination of trend + high melt conditions could bring Sept. Extent below 1M km2 as early as mid 2020s. 

4.  Independent of above, Notz and Strove 2018 article gives info to correlate Sept. Extent with Global avg. temperature.  That points to cumulative probability of the 1st Sept with < 1M km2 exceeding 50% by 2035, and regularly (each individual year chance >50%) by 2037. 
(My dates, not theirs, details later.)

   N&S 2018 correlation of ASI Extent with cumulative CO2 emissions puts the cumulative chance of 1st Aug. and Sept. as 'largely ice free' (which from my guesswork seems to line up with ca. < 2M km2 Extent, details later) at >50% chance by 2033, and regularly (individual year chance > 50%) by 2036.

   Finally, N&S 2018 give correlation of CO2 with July - October being "largely ice free" (which as above, I interpret as ca. < 2M km2 Extent).  For that I used observed emissions through 2019, and Intl Energy Agency emissions trend forecast of 1.1% continued emissions growth out to 2040, then reducing subsequent global emissions as per the observed US and EU combined downward trend since their recent peak.  With those CO2 assumptions, the cumulative 50% chance for a 1st July-Oct  that is "largely ice free" is by 2045, and regularly (individual year chance > 50%) by 2048. 

 


38
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: November 19, 2019, 06:09:27 PM »
A reminder of minimums and bathy since 2012. I would say there is some correlation on the atlantic side.
Wow, uniquorn - you've done some great images in the past, but this one sets a new standard.  Really great work.  Thanks.

39
Arctic sea ice / Re: Global sea ice area and extent data
« on: November 15, 2019, 11:15:37 PM »
I compared the actual JAXA extent data with the averages from 1980s to 2010s.
Arctic sea ice extent of 2019 is 4 days behind schedule if compared with the 2010s average. In the Antarctic 2019 is ahead by 7 days, which sums up to 11 days of difference.
These differences are bigger in comparison with earlier decades:
2019 vs 2000s: 15 days Arctic, 8 days Antarctic = 23 days
2019 vs 1990s: 25 days Arctic, 8 days Antarctic = 33 days
2019 vs 1980s: 29 days Arctic, 9 days Antarctic = 38 days
This is a difference of more than a month!

    That is an interesting way to capture the trend Stephan.  Perhaps we can compare the invidual decadal rates by subtracting each one from the previous decade.  (I think but not sure this is kosher.)
     Thus 1990s vs. 1980s:    5 more days
             2000s vs. 1990s:  10 more days
            2010s vs. 2000s:   23 more days
            2020s vs. 2010s:   46 more?? more days (since there a doubling for each previous step)
     Just a wild guess.  There may be constraints on continued growth at a doubling every decade.

The Arctic-only version:
            1990s vs. 1980s:    4 more days
             2000s vs. 1990s:  10 more days
            2010s vs. 2000s:   15 more days
            2020s vs. 2010s:   20 more??  (since each prior step added about 5 days)

The Antarctic-only version:
            1990s vs. 1980s:    1 more day
             2000s vs. 1990s:   0 more days
            2010s vs. 2000s:    8 more days
            2020s vs. 2010s:    8 more??  (since previous step added 8 days)

     At first glance, you might think that the big difference in the Arctic vs. Antarctic trends shows a problem with using this method.  But I think it reflects an actual characteristic of the data.  In the 1980s and 1990s, the Antarctic sea ice was not showing a trend from global warming. 

     I'm surprised that the Antarctic 2010s vs 2000s even showed an increase because I thought it was only in the last few years that Antarctic sea ice Extent was declining.  (or am I completely misunderstanding the dates Stephan is citing for Antarctic sea ice?)

     That possible rapid acceleration for the Arctic looks worrisome.  Good thing we have smart and wise political leadership at the helm to steer us through what could be a time of difficult choices and profound but necessary changes to reduce the harm.
      What... we don't have that?   Uh oh. 


40
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: November 15, 2019, 10:03:16 PM »
After looking at graphs of individual seas and making comments on them, this is the quote that seems valid, and  even more so, for many of the individual seas.

Changing state of Arctic sea ice across all seasons
Julienne Stroeve and  Dirk Notz

Quote
5. Accelerated sea ice loss during all months of the year is additionally driven by a lengthening of the melt season. As assessed for the Arctic as a whole through April 2018, melt onset is occurring 3 days earlier per decade, and freeze-up is happening 7 days later per decade (figure 3). Over the 40 year long satellite record, this amounts to a 12 day earlier melt onset and a 28 day later freeze-up.
[/size]

The summer melt turns from a V shape  into a U shape

     Interesting graphical insight gerontocrat.  Seeing those V curves turn into flat bottomed U shapes is a useful visualization of the concept of individual Arctic seas reaching cumulative losses to the point of having temporary ice extinctions.

      Another insight arises from reading your quoting item 5 about the Arctic as a whole gaining 10 days of melt season per decade (starts 3 days earlier, ends 7 days later per decade).  That trend gives a shorthand way of projecting dates for when additional BOE landmarks will occur.  If that rate continued, then once we have September regularly going below the 1M km2 BOE threshold, then every 3 decades after that, at the 1979-2018 melt season expansion rate, the duration of the BOE period would expand by another 30-days.

      I suppose the added low ice/BOE period would be an additional 9 days before and 21 days after the date of annual minimum.  Seems to me that the low ice period would continue to expand forward and backward from the current mid-Septemberish date for annual minimum at the same ratio as before.  Or will that the ratio change as the ice-free period runs into the darkening days of October vs. the sunny dog days of August?  Why is the observed ratio not not the same on either side of the annual minimum, i.e. why 3 days earlier start but 7 days later finish instead of 5 & 5?

     Correlation of global average surface temperature and cumulative CO2 emissions with Arctic sea ice decline stated in the Notz and Stroeve 2018 article at  .....
https://forum.arctic-sea-ice.net/index.php/topic,2348.msg236344.html#msg236344
   ( Oy, citing my own ASIF posts - all I need now is the ability to Like them and my little bubble of narcissism would be complete.  Maybe we should give Trump a special ASIF member privilege to do that in hopes that it would provide a relief valve for his apparently bottomless need for affirmation, and cut back on his Twitterbation.  By now he must be developing the apocryphal hairy thumbs. 
Double oy - I usually discover later than what I criticize in others is often a reflection of some aspect of myself!  So I am ending this digression right now.)

..... suggest a much faster expansion of melt season for the Arctic as a whole than a new month every 30 years.   I suspect that is because the 3 days earlier - 7 days later per decade trend, being based on the 1979-2018 record, is slower than the rate of melt season advancement more recently.  I'll take a second look at Notz and Stroeve to see what date estimates can be extracted for when BOE for Aug, Oct, and July might be expected based on current trends. 

41
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: November 15, 2019, 01:12:12 PM »
      Yeah that one kind of stuck out to me too.   But in my haste I didn't think about it long enough to realize that by removing it from its surrounding context it wasn't adding value. I think the larger point was that the transition of the Arctic seas, and the Arctic as a whole, from one mode and system state to a new condition happens gradually for a long time, then all of sudden it's done.  Similar to thin edge ice hanging on for a long time until it seemingly goes poof. 

       But you are right, the statement standing alone just looks dumb due to my editing, not the author's original intent.  I have taken it out since by itself it doesn't add value.   

         My editing glitches aside, the Stroeve and Notz, and the Notz and Stroeve 2018 papers together serve as a good comprehensive and fairly up to date (changes every day!) primer to the ASI story.  It addressed a lot of the questions I had in an understandable plain language way, and the authors are recognized experts in that arena.  Both articles are free online with open access (no paywall). 

42
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: November 14, 2019, 11:58:16 PM »
One more time, same source article:
Changing state of Arctic sea ice across all seasons
Julienne Stroeve and  Dirk Notz
2018 Environ. Res. Lett.13 103001
https://iopscience.iop.org/article/10.1088/1748-9326/aade56

New topics.  As before, I think this use is allowed under source article CC license. 
"Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence.  Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI."

Here we go:
-------------------

"A study by Burgard and Notz (2017) has found that CMIP5 models disagree on whether the anomalous heating of the Arctic Ocean, and thus the loss of Arctic sea ice, primarily occurs through changes in vertical heat exchanges with the atmosphere (as is the case in 11 CMIP5 models), primarily through changes in meridional ocean heat flux (as is the case in 11 other CMIP5 models) or through a combination of both (as is the case in 4 CMIP5 models). This suggests that our understanding of how precisely the heat for the observed sea ice melt is provided to the sea ice is still surprisingly limited."

---------
~ (words are quotes but citations removed for clarity) **Focusing first on the atmosphere, changes in the sea-ice cover can occur through dynamical changes that drive ice export, thermodynamical influences , or a combination of both.**
---------

"Williams et al (2016) found winter preconditioning continues to play a large role in September sea ice  variability. In particular, winter ice export out of Fram Strait is strongly correlated to the anomaly of the following September SIE, allowing for the possibility of forecasting sea ice conditions in September several months in advance."

-------
" Ding et al (2017) provides the most recent characterization of the role of atmospheric variability on the observed summer sea ice, showing that trends in atmospheric circulation patterns in summer (i.e. a more anticyclonic circulation pattern) have increased the downwelling longwave radiation towards the surface as a result of a warmer and moister atmosphere. They further suggest that these circulation changes dominate summer ice variability rather than feedbacks from a changing sea ice cover."

--------
"The Atlantification of the eastern Eurasian Basin may therefore provide an additional factor
behind sea ice reductions in that region, perhaps on the same order of magnitude as atmospheric thermodynamic forcing."

(skipping Pacification, they discuss it, but no succinct summary quotes.)

-------
    "The large Eurasian and North American rivers input warm freshwater (on average 15 °C) with a distinct seasonal  cycle along the shallow shelf seas (e.g. Carmack et al 2016). Peak discharge occurs in June and this  water is immediately available to melt ice, helping to break up the fast ice. River discharge also adds a large amount of chromophoric dissolved organic matter, which absorbs sunlight at short wavelengths (Griffin et al 2018), further warming the surface layers of the ocean and increasing ice melt.  On the other hand, increased ice melt and freshwater input increases summer stratification, allowing for more heat to be trapped in the upper ocean, which in turn delays ice formation in autumn."

--------------
"While it is understood that changes happening within the Arctic do not stay there, it is less certain whether current Arctic warming is already driving an increase in storm frequency and extreme weather events across the mid-latitudes, including extreme heat and rainfall events, and more severe winters."

-------
"Conclusions
Through novel analysis and a review of recent studies, we have examined the ongoing ice loss of Arctic sea ice across all seasons. We have established the following key results:

1. With respect to the 1981–2010 reference period, relative ice loss has been more significant during autumn, winter and spring the last two years than during summer (figure 1).

2. The ice cover has not only retreated in its areal extent, it has also become much younger (figure 4) and thinner (figure 5) in recent years. In April 2018, only about 2% of the winter sea-ice cover consisted of sea ice older than 5 years, compared to almost 30% of the April sea-ice cover in 1984.

3. The thinning of the ice cover and the overall warming of the Arctic have increased the likelihood
of rapid ice-loss events during summer in recent years (figure 6). On the other hand, the larger expanses of open water have similarly increased the likelihood of rapid ice-growth events during autumn.

4. The increasing relative loss of winter sea ice is in part related to the fact that more and more regions of the Arctic Ocean completely lose their sea-ice cover during summer (figure 2). This limits the potential for a further acceleration of summer sea ice loss, and causes accelerating sea ice loss during winter.

5. Accelerated sea ice loss during all months of the year is additionally driven by a lengthening of the melt season. As assessed for the Arctic as a whole through April 2018, melt onset is occurring 3 days earlier per decade, and freeze-up is happening 7 days later per decade (figure 3). Over the 40 year long satellite record, this amounts to a 12 day earlier melt onset and a 28 day later freeze-up.

6. The recent winter sea ice loss is driven by increased inflow of warm air from the south and an overall warming of the Arctic, which both have substantially reduced the number of freezing
degree days in recent years (figures 8 and 9).

7. The primary cause of the ongoing changes in all months are anthropogenic CO2 emissions, with a clear linear relationship between sea ice loss and cumulative anthropogenic CO2 emissions in all
months (figure 7). The sensitivity ranges from an ice loss per ton of anthropogenic CO2 emissions
of slightly above 1m2 during winter, to more than 3m2 throughout summer."

-------   
 "Extrapolating the linear relationships into the future, we find that the Arctic Ocean completely loses its ice cover throughout August and September for an additional roughly 800 ± 300 Gt of anthropogenic CO2 emissions. For an additional 1400 ± 300 Gt of anthropogenic CO2 emissions, we estimate the Arctic to become sea-ice free from July throughout October (see Notz and Stroeve 2018 for details on these estimates, in particular regarding the uncertainty arising from internal variability).

Given today’s emission rate of about 40 Gt CO2 per year, the time window is closing very rapidly to preserve Arctic sea-ice cover all year round."

43
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: November 14, 2019, 11:32:42 PM »
      Neven has said he does not like long wordy posts, which this certainly is.  If it violates some ASIF code I am unaware of and it gets snipped, no offense taken.  I wanted to make these excerpts for my own use anyway.

     This post consists of some of the best sentences from the paper cited below.  The whole paper is well worth reading and is written in understandable language.  They do dig into the details of various sensors in the methods section, but you can gloss over that stuff. 

     By the way, if you are not used to reading science journal articles, here is a little secret.  Almost nobody completely understands every sentence.  Sometimes not even the authors.  You learn how to read to get what you can get and when it gets obscure you just move on.  Always good to start with the abstract, then it is fair game to skip to the conclusions, and look at some graphs along the way to decide if you to read the whole thing.  Sorry if this comes across as patronizing.  I just figure a lot of people are not used to professional "science culture", I know I certainly had no clue about it through 7 years of on-again off-again undergrad.  Once you realize it is just people, it becomes less intimidating and more fun.

     As for protocol and rightful use of such extensive quoting, the source article has a license statement that looks favorable. "Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence.  Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI."

     These topics arise repeatedly in the forum and Stroeve and Notz do a nice job of laying it on the table.  My guess is that as the paper is over a year old and as they are passengers on this planet too, Stroeve and Notz would approve of using the forum to spread their findings.

Source for all of the excepts below:
Changing state of Arctic sea ice across all seasons
Julienne Stroeve and  Dirk Notz
2018 Environ. Res. Lett.13 103001
https://iopscience.iop.org/article/10.1088/1748-9326/aade56

        Placement of "-------" indicates larger than usual amount of text was skipped prior to following quote.  All right, here we go.
--------------------

    “There are two ways in which the climate system can reduce the amount of sea ice within the Arctic Ocean:  first by local melting within the Arctic Ocean, and second by export of sea ice through outward sea ice drift. As outlined in the following sections, a number of studies have found the local melting of sea ice to be by far the main contributor to the observed loss, and we hence need to identify the main driver for increased sea ice melting if we are to identify the main driver for the substantial sea ice loss in recent decades.”
--------------

"4.2. Stability of the ice cover
    In addition to changes in the external forcing and internal variability, a self-amplification of the ongoing ice-loss could in principle have contributed to the rapid ice loss in recent years. Such self-amplification is usually discussed in the context of so-called tipping points or nonlinear threshold, which are often defined as processes in the climate system that show substantial hysteresis in response to changed forcing.

     The best known example for such possible hysteresis behavior is related to the ice-albedo feedback  mechanism: a reduced ice cover in a given summer will cause increased absorption of solar radiation by the ocean, contributing to further reductions in the ice cover.  Such positive feedback loop can cause the irreversible loss of Arctic sea ice in idealized studies based for example on energy-balance models (see review by North 1984), and have hence been suggested to possibly  be relevant also for the real world.

     However, an analysis of the existing observational record and a substantial number of respective modeling studies with complex ESMs all agree that such a ‘tipping point’ does not exist for the loss of Arctic summer sea ice. For example, Notz and Marotzke (2012) found a negative auto-correlation of the year-to-year changes in observed September SIE. Hence, whenever SIE was substantially reduced in a given summer, the next summer usually showed some recovery of the ice cover. This was further supported by Serreze and Stroeve (2015). Such behavior suggests that the sea-ice  cover is at least currently in a stable region of the phase space, as otherwise one would then expect that any year with a really low ice coverage should be followed by a year with an even lower ice coverage, driven by the ice-albedo feedback mechanism. As shown by Tietsche et al (2011), the contrasting behavior of the real ice cover can be explained by compensating negative feedbacks that stabilize the ice cover despite the amplifying ice-albedo feedback. The most important of these stabilizing feedbacks relates to the fact that during winter the ocean very effectively releases heat from those areas that became ice free during summer, thus over-compensating for any extreme ice loss in a preceding summer. Ice that is formed later in the season also carries a thinner snow cover and can hence grow more effectively during winter (e.g., Notz 2009).  Stroeve et al (2018) suggest, however, that this stabilizing feedback mechanism is becoming weaker and weaker as Arctic winters become warmer and warmer.  Increased winter cloud cover after summer sea ice loss as found by Liu et al 2012 also weakens the stabilizing
feedback, as it reduces the loss of heat from the ocean surface."


44
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: November 14, 2019, 03:22:00 AM »
This situation is getting worse fast

From today
The Arctic's Most Stable Sea Ice Is Vanishing Alarmingly Fast
By Mindy Weisberger
https://www.livescience.com/arctic-ice-refuge-vanishing.html
https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2019GL083722

From August 2018.
'Archived' heat has reached deep into the Arctic interior, researchers say
By Yale University.
https://phys.org/news/2018-08-archived-deep-arctic-interior.html
https://advances.sciencemag.org/content/advances/4/8/eaat6773.full.pdf
Thanks to ArcticMelt2 for bringing attention to this one with post at
https://forum.arctic-sea-ice.net/index.php/topic,2888.msg236503.html#msg236503

"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." "

The region discussed in the second article abuts the area described in the first article, i.e. the wedge of thickest overwintering that runs from the north coast of Greenland along the northern edge of the CAA. Not a good place to store a reservoir of warm water.


45
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: November 12, 2019, 04:50:20 PM »
Edited quote
Since the third term is a calculated average (and not a finite measure as the other two) then flipping them around makes no sense.

At least we have identified where we disagree,
I submit that mathematically all are true.
E*T=V
E = V/T
T = V/E

It does not matter to their mathematical relationship which one you solve for, the relation stays the same.  In your examples you solve for T based on set values for E and V, and you get a T that is greater than E.  But that is not an inherent requirement.  It is simply an artifact of the values you set for E and V.  You could set E and V to different values and find that the resulting T is less than E.

For example:  As you found
 If E = 0.99 and V = 0.98
then T = V/E = 0.9898
T decline (=1 - 0.9898) is greater than E (1-0.99).

 But
 If E = 0.9898 and V = 0.98
then T = V/E = 0.99
T decline (=1 - 0.99) is greater less than E (1-0.9898)

It does not matter which is directly measured and which is inferred.  Mathematically they are all equally real.  (And BTW, Thickness IS measured.  Volume is calculated from Extent and Thickness).
But if you want to define E and V and then calculate T, that is fine.  Doing so does not require T to be smaller or larger than E.  All that matters is the relative sizes of the E and V values you choose.  Specifically, if E - V is larger or smaller than 1 - E 

For example, if E = 0.9 and V = 0.85,
T = V/E
T = 0.94
T is larger than E
 E - V = 0.05
1 - E = 0.1
E-V is less than 1-E, so T is greater than E

 if E = 0.95 and V = 0.85,
T = V/E
T = 0.89
T is less than E
E - V = 0.10
1 - E = 0.05
E-V is larger than 1-E, so T is less than E


RE:  Oren.  Close but no cigar.  You are using E + T = V. 
It is  E * T =V.
Multiplication vs. Addition.

Addendum to the end game scenario.  Extent losses are largely due to the loss of thin ice at the edge of the pack.
As the pack shrinks, that edge area becomes an increasing proportion of the total pack area.  Circumference to area ratio gets larger.
 
(This is analogous to the surface to volume ratio that lets insects do things we can't, and also why insects have to be small to do what they do, but I digress)

So, as the percentage of the total ice pack subject to edge area losses gets larger, the percentage rate of Extent losses will increase. 

***Not sure about this next statement.  Math fatigue setting in.***
The straight line trend for Extent losses will begin to curve downward unless it is counteracted by a decline in rate of thickness loss around that edge, which does not seem likely.

*** Then again, the absolute amount edge = Extent loss would not increase, and in fact with smaller absolute edge area, absolute Extent losses would decrease.  But the amount of extent loss would be higher ratio relative to the amount of previous year Extent.  So it may just come down to whether you report Extent losses as absolute number of km2 or % of previous year.  Math fatigue now math exhaustion.  This is becoming a "how many angels fit on the head of a pin discussion".  Who cares.  It does not matter. 

    What matters is that the ASI is nosediving.  Because of albedo and other effects, how the Extent trend will evolve is of interest.  Thanks to Notz and Stroeve and their colleagues, we have insight on how the ASI situation will dramatically evolve over the next 10-30 years.  It is a scary, ominous story.  Maybe if the immediacy of ASI collapse is better understood it will help us make difficult decisions to reduce the damage we are doing to ourselves.




46
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: November 12, 2019, 06:54:21 AM »
Edited quote
As an example, if extent is falling by 1% per year, and volume by 2%, then thickness falls by very close to, but ever so slightly above, 1%. If extent is at 1% and volume at 3%, thickness clocks in at slightly above 2%.

Try one more cup of coffee and you may reach a level of caffeine induced enlightenment where this becomes obvious. ;D

Using your example, but merely flipping Thickness and Exent:
If Thickness is falling by 1% per year, and volume by 2%, then Extent falls by very close to, but ever so slightly above, 1%.
If Thickness loss is at 1% and volume at 3%, then Extent clocks in at slightly above 2%.

In your example, Thickness loss is always a bit greater than Extent loss.  In my flipped version, Extent loss is always a bit greater than Thickness loss.  You say TomAto, I say ToMAHto! :o

The point being that either the Thickness term or the Extent term can be the larger of the two.  It does not matter.  Either way, when they are both are negative, the resulting product of their multiplication (i.e. Volume) is smaller than either of them individually.  So when Extent trend is negative, AND the Thickness trend is also negative, then the Volume loss has to be more negative than either the Extent or Thickness trend individually.  But as for Extent and Thickness, either one of them could more more negative than the other.

47
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: November 12, 2019, 06:11:30 AM »
Well if binntho agrees with me, he must be right! 

    But here is another perspective about a possible Extent pause.  I am (almost) sure that if Tamino bit into the Extent numbers he would, as he did with global average surface temperature faux pause, show that there is no statistical justification for the relatively small number of yearly data points in the presumed Extent hiatus period to be called a significant violation of the long term linear trend that is derived from a much larger set of of data points with considerable year to year variability.  (BTW Tamino's wife announced on his blog that he had surgery recently.  Sending him wishes for healing and good health.) 

    But I submit to the jury that even if Extent did have a statistically valid hiatus, it would not matter.  There could be a scenario where Volume losses continue their inexorable decline, yet a prolonged series of years with conditions favorable for greater ice dispersion resulted in Extent value flat-lining for enough years in sequence to pass a statistical test for truly being a hiatus.   

     But so what?  In terms of progressive ice decline, that would not change the underlying fact that Volume losses were still proceeding toward zero.  A hiatus in Exent would only temporarily increase the discordance between the Extent and Volume trends.  The increased difference would have to be compensated for at the end.  The only consequence of an Extent hiatus would be that the Extent trend would have to fall that much farther faster when the zero Volume-Thickness-Extent day of no ice reckoning finally arrived. 

    The 10-30 year lag for the majority of global warming impact from elevated greenhouse gas levels to be expressed means that the warming and ice melt trends for the next 10-30 years have already largely been set by our previous emissions.  The fact that the trend-projected date for the first zero ASI Volume event is now within the next 20 years means that it is probably unavoidable at this point even if we sharply reduced further GHG additions.  Then again, Notz and Stroeve point to an 800 Gt CO2 of additional emissions needed after 2018 for the total GHG load to be enough to result in Volume reaching zero.  So in theory at least, keeping total emissions below that amount could presumably prevent the Volume losses from reaching the zero point. 

     (On the other other hand, --- running out of hands ---, I suspect that even if emissions ceased immediately, with enough time and the slow depletion of existing CO2 from the atmosphere, even the GHG emissions already made thus far, bolstered by some permafrost thaw and other feedbacks, would eventually result in ASI Volume-Thickness-Extent reaching zero.)

     That is a moot point for the real world situation.  It does not seem at all likely that humans will cut emissions sharply enough and soon enough to prevent exceeding the 800 additional Gt CO2 after late 2018 threshold.  And therefore, assuming the Notz and Stroeve relationship between total CO2 emissions and ASI Volume is correct, the Extent trend will meet up with the Volume trend at the zero point.  Which year that happens depends on how fast we move towards that 800 Gt CO2 post 2018 threshold.  This being the end of 2019, we have probably reduced the remaining budget to 760 already. 

     Extent can go where it will prior to the zero day of reckoning, but when the Volume trend reaches the point where there is no ice to spread around, Extent will also be at zero.

   Edited quote
And we already know that volume is falling faster than extent, which means that thickness is falling faster than extent.
    I don't agree with the second part, "... which means that thickness is falling faster than extent. " 
    Yes, we know that Volume is falling faster than Extent.  Because Volume is the product of Extent x Thickness, Volume has to fall faster than Extent unless there is either Thickness gain or zero loss.  But Thickness does not have to fall faster than Extent for Volume loss to be less than Extent loss.  It does not matter which of two (Extent or Thickness loss) is greater, or if they are exactly equal, all that matters is the product of Extent x Thickness, because that is what defines Volume.

   

48
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: November 11, 2019, 11:53:08 PM »
Edited quote
... this short video of ice melting explains why I think it will look basically okay in terms of area and extent right up until it isnt.



Nice.  Exactly!  Watch the footprint of that ice cube as it melts.  The area covered declines at a much slower rate than volume as the thickness declines.  Until the thickness gets so small that continued losses come at the expense of the area covered (Extent).  Then it rapidly declines at the very end as Extent loss (footprint) finally catches up the Volume loss (shrinking ice cube).

49
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: November 11, 2019, 11:17:09 PM »
Conversely, volume cannot be zero, if extent and thickness are not.  Volume, being three-dimensional, will always change faster than thickness (one-dimensional) or extent/area (two-dimensional).  At some point, they must converge.  What is your reasoning to believe that volume is the key metric over the others?

I agree that "At some point, they must converge."  That was the reason for my quest -- (cue Man of La Mancha music): How/when will the Extent trend and Volume trends meet?

I suppose you can frame the same question as "When will the Volume trend flatten out so that it can meet the Extent trend?"  I don't see reason for that to happen.  The linear volume trend looks pretty inexorable.  And while, as gerontoacrat noted, Volume measurement has its problems, Extent is not so pristine either.  A pixel with 16% ice counts as 1, with 14% counts as 0; melt ponds misidentified as open water etc. 

     And even if measured perfectly, Extent in the real world is subject to being altered by wind patterns, compaction vs. dispersal.  That is also why I think 2012, while certainly an important event as we watch the ASI go down the tubes, is overrated.  It was hyuge (new American English spelling, as in 'our politics and planet are hyugely screwed up') Extent event, but a less cataclysmic Volume event, and thus less of an informative marker for progressive ASI decline.  Thus Extent is the more mercurial hare, subject to temporary conditions, while good ole Volume is the sober implacable tortoise plodding its way towards cryospheric Armageddon. 

Maybe it is arbitrary that I start with the presumption that you can't have Extent of ice without any Volume of ice to create it.  But that makes more sense to me than the other way around.  Stuff has to exist before you deal with how it is spread around.

I am more likely to buy into gerontocrat's argument that the Volume measures are more subject to error, so this discordance between the Extent and Volume trends (that I repeat, we all agree have to meet up in the end) could be due to spurious Volume measurements.
.... But not really.  Because it makes perfect sense that what we see (Extent loss) is multiplied by what we can't see (simultaneous Thickness loss) to create Volume losses that are bigger than Extent losses.  In fact, the only way Extent losses could keep up with Volume losses is if there was NO Thickness loss. So of course Extent losses lag behind Volume losses.  How could it be otherwise? 

    And it makes sense to me that Thickness is being affected by the same forces that are depleting Extent and Volume.  And it makes no sense to think that Thickness is not being depleted.  And regardless of what you or I think, hard working scientists and other folks take measurements that show that Thickness is indeed going down.

I defer to the great Juan C. Garcia.  His message tag line points to Volume losses being a more important indicator than Extent because Extent, as you noted, is missing a dimension, the key dimension of concurrent thickness losses. 
"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."

50
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: November 11, 2019, 10:47:18 PM »
I always end up with the observation that nature (mostly) abhors a straight line.

For a long time the linear relationship may look the best, but it most often breaks down eventually. So will it be KK's long-tailed gompertz slow  / minimal decline or will it fall apart with a crash

So I just can't go along with Stroeve et al when linear is pushed out to the end. It just ain't like that.

ps: And 2007 and 2012 pushed the max dip in an annual variation well over 1 million km2 when melting conditions are almost perfect.
pps: Volume divided by extent is not a good measure of thickness at minimum, especially using NSIDC data. This is because the ice is very spread out with lots of open water at minimum, concentration getting as low as 55%. Volume divided by Area is a much better measure at minimum.

I think the poof scenario meets the definition of "fall apart with a crash".
It does not rely on linear trend right to end, in fact it demonstrates why that won't be the case. 

We all agree they have to meet up at the end (i.e. Zero Volume & Extent).  And this is how it happens.  Extent decline can keep up its straight line trend that is slower than volume decline, but only for a while. When thickness gets so thin that it is susceptible to flash melt, that is when the Extent trend curves sharply downward and catches up within a single year.  Thus an Extent crash.

RE ps   I used 10-day Extent losses, but I think you are right (whether you meant to imply that or not) that it would be better to use year to year Extent changes as the indicator to estimate when Extent is low enough to suffer a within-one-year loss large enough to get below the 1M km2 threshold.  Being much larger than the 10-day losses, using the year to year losses strengthens the argument for the potential for a single year to go below the BOE threshold.

RE pps I used PIOMAS September average thickness data.  That's all I have to work with.  That is the minimum monthly average, not the minimum day.  I agree that using annual minimum thickness values from November would be unhelpful because those values are very distorted by expanding area of thin refreezing ice.  But comparing the Sept. average Thickness across years seems like a reasonable way to measure a trend for ice thickness.

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