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

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

Total Members Voted: 64

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

Author Topic: When will the Arctic Go Ice Free?  (Read 130963 times)

grixm

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Re: When will the Arctic Go Ice Free?
« Reply #1200 on: September 15, 2019, 03:48:34 PM »

Meanwhile I don't see any serious attempts from the scientists in these organizations to get fancy with 3 or 4 or god forbid 5 parameter regression curves. Why do you think that is?

Really?

https://www.searcharcticscience.org/files/search/sea-ice-outlook/2011/07/pdf/pan-arctic/hamilton_panarctic_july.pdf

https://www.esrl.noaa.gov/psd/events/2014/arctic-predictions-science/presentations/wed/arctic-wkshp-051414-stroeve.pdf

Yes, there's a reason why I qualified my statement with the word "serious". Of course there will be the occasional reference to every kind of model just for experimentation's sake, it's only serious if they catch on and become the generally accepted way to model trends or is used in official outward-facing presentation of the data. And if those are the only such references you can find I'm especially unconvinced, as they aren't even particularly relevant to what makes the gompertz functions in this thread controversial, namely that they predict a slowing of the melt, while the ones in your links are only made to fit the accelerating melt up until around 2010 and remain fairly linear after that (and are only 3-parameter rather than 4 or 5).

EDIT: Also:

I want to emphasise all models are wrong. We don't know shape of trend; it could be anything between 4 parameter gompertz at one extreme, Tamino's 3 linear pieces, anything in between, or perhaps having a steeper trend now than Tamino shows.

A couple of ways of deciding which to prefer between these include:
What has least parameters while still giving a good fit.
What looks like most of the models as a physical explanation for what is likely to happen.

Of course this is true, I'm not saying that I am absolutely certain that a gompertz trend is definitely going to be inaccurate in the future, we don't know for sure. I am just saying that with those very two criteria you post on the bottom of the quote, a linear fit seems very much like the most reasonable assumption for a future trend, and based on what the expert institutions use in their presentations they seem to largely agree.
« Last Edit: September 15, 2019, 05:32:25 PM by grixm »

crandles

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Re: When will the Arctic Go Ice Free?
« Reply #1201 on: September 15, 2019, 05:55:40 PM »

I want to emphasise all models are wrong. We don't know shape of trend; it could be anything between 4 parameter gompertz at one extreme, Tamino's 3 linear pieces, anything in between, or perhaps having a steeper trend now than Tamino shows.

A couple of ways of deciding which to prefer between these include:
What has least parameters while still giving a good fit.
What looks like most of the models as a physical explanation for what is likely to happen.

Of course this is true, I'm not saying that I am absolutely certain that a gompertz trend is definitely going to be inaccurate in the future, we don't know for sure. I am just saying that with those very two criteria you post on the bottom of the quote, a linear fit seems very much like the most reasonable assumption for a future trend, and based on what the expert institutions use in their presentations they seem to largely agree.

I estimate that the steep slope in tamino's piecewise linear fit is around 7.5 times steeper than the recent slope. To suddenly change the slope that much seems unlikely to me.

As Tamino has found the slow down in rate is statistically significant, then I think we should be preferring a model that does this one way or another. Not impossible this is wrong and a straight line through all data would be better but I think when it is statistically significant the odds favour a model that shows a slow down in the rate. (Hopefully odds are better by more than 19:1 because of using what the models show to choose an appropriate function.)

Between models that do show a slow down in the rate: We cant tell the difference, and anyone is entitled to their own priors. To me a smooth curve seems more likely than a sudden change in rate circa 7.5 less steep but going absolutely horizontal is also unlikely. A curve somewhere between Tamino straight lines and the 4 parameter gompertz seems to me to be more plausible than either. Other are welcome to have different priors that may prefer straight lines.


RoxTheGeologist

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Re: When will the Arctic Go Ice Free?
« Reply #1202 on: September 15, 2019, 07:22:53 PM »

Whenever a curve or line is fitted to a graph it is to illustrate a correlation; such a correlation is the decline in sea ice volume over the last few decades. I'm no expert in sea ice modelling but, there is a fundamental need to understand how one would apply a model to be able to predict future conditions.

To understand a correlation a model is built. The model can perhaps take the starting data and then show how sea ice has changed on a year to year basis (hind casting). It can then be used to predict the future, and it's skill tested by it's ability to do so. Models are only as good as the test conditions applied. Hindcasting can be tricky as there is the temptation to model fit the data.

Obviously models based on a line fit are incorrect, they can be trivial disproved by projecting backwards in time and showing that there wasn't that much ice 10000 years ago. I hear the 'but there wasn't GHG emissions" so immediately the model has to include global warming from GHG gases. Assumptions are disproved, the model improves. If a model can effectively hind cast current sea ice from pre industrial times, then we perhaps have a chance of predicting more accurately what the future holds.

At least correlate global temperatures with sea ice volume, that seems like a better starting point than time.




HapHazard

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Re: When will the Arctic Go Ice Free?
« Reply #1203 on: September 15, 2019, 08:43:37 PM »
I'm reminded of folks who draw lines and such on charts in stock market & cryptocurrency sites.

Wake me up when one of you strike it rich.  ;D

SteveMDFP

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Re: When will the Arctic Go Ice Free?
« Reply #1204 on: September 15, 2019, 08:49:09 PM »

Whenever a curve or line is fitted to a graph it is to illustrate a correlation; such a correlation is the decline in sea ice volume over the last few decades. I'm no expert in sea ice modelling but, there is a fundamental need to understand how one would apply a model to be able to predict future conditions.

To understand a correlation a model is built. The model can perhaps take the starting data and then show how sea ice has changed on a year to year basis (hind casting). It can then be used to predict the future, and it's skill tested by it's ability to do so. Models are only as good as the test conditions applied. Hindcasting can be tricky as there is the temptation to model fit the data.

Obviously models based on a line fit are incorrect, they can be trivial disproved by projecting backwards in time and showing that there wasn't that much ice 10000 years ago. I hear the 'but there wasn't GHG emissions" so immediately the model has to include global warming from GHG gases. Assumptions are disproved, the model improves. If a model can effectively hind cast current sea ice from pre industrial times, then we perhaps have a chance of predicting more accurately what the future holds.

At least correlate global temperatures with sea ice volume, that seems like a better starting point than time.

Thank you.  This is a very nice summary of the issues at hand in the matter of projecting ongoing arctic sea ice loss.

crandles

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Re: When will the Arctic Go Ice Free?
« Reply #1205 on: September 16, 2019, 01:10:45 PM »

Whenever a curve or line is fitted to a graph it is to illustrate a correlation; such a correlation is the decline in sea ice volume over the last few decades. I'm no expert in sea ice modelling but, there is a fundamental need to understand how one would apply a model to be able to predict future conditions.

To understand a correlation a model is built. The model can perhaps take the starting data and then show how sea ice has changed on a year to year basis (hind casting). It can then be used to predict the future, and it's skill tested by it's ability to do so. Models are only as good as the test conditions applied. Hindcasting can be tricky as there is the temptation to model fit the data.

Obviously models based on a line fit are incorrect, they can be trivial disproved by projecting backwards in time and showing that there wasn't that much ice 10000 years ago. I hear the 'but there wasn't GHG emissions" so immediately the model has to include global warming from GHG gases. Assumptions are disproved, the model improves. If a model can effectively hind cast current sea ice from pre industrial times, then we perhaps have a chance of predicting more accurately what the future holds.

At least correlate global temperatures with sea ice volume, that seems like a better starting point than time.

Arctic temperatures are in part caused by sea ice retreat, so I see you avoided that.

Global temperatures: the general trend is upwards at a fairly steady rate and so this is no different than using time. So it is about the variations about the trend. The largest variation about the trend is caused by ENSO and it is not at all clear whether there is any effect up in the arctic. If there is an effect it is small and likely to be delayed.

So interesting idea, but unfortunately it doesn't work.

The same can be said about using GHG levels.

If there was a sudden change in the rate of global temperature rise (or GHG levels) then it probably would be useful.

Other improvements can be added to models to make them better (more physically based) than a trend line fit. However, We already have global climate models and they don't agree on the level of sea ice we should have. In a sense they are not good enough for this purpose. However, I still maintain vast majority show similar pattern and this is helpful for deciding what sort of shape extrapolation should be done.

Anyway despite having sophisticated models, they disagree with each other, so it seems to me we are back to either
1) Trend line fits but hopefully with some hints of what sort of extrapolation to do, or
2) Using models with some bias corrections (which may amount to something fairly similar to trend lines).

El Cid

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Re: When will the Arctic Go Ice Free?
« Reply #1206 on: September 16, 2019, 02:16:33 PM »
I posted this on the main thread but might be more relevant here. I took every year's average temp from Jan to Aug (NOAA ESRL North of 70 degrees and SIE) and that year's September extent (2019 is the red dot with 4 M sq km extent presumed)
The good news is that I can tell you when we get a BOE: when average temps hit -6 C vs the current cca -9 C. Tha bad news: nobody knows when that happens :)

Average temps for the
80s: -11,9 C
90s: -11,2 C
00s:  -10,2 C
10s: - 9,1 C
We should get there by the 2040s based on the above. There will also be some outliers, so I think the first BOE is in the 30s

El Cid

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Re: When will the Arctic Go Ice Free?
« Reply #1207 on: September 16, 2019, 02:19:40 PM »
...or the correlation might break down completely :)
Same data on a chronological chart:

RoxTheGeologist

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Re: When will the Arctic Go Ice Free?
« Reply #1208 on: September 16, 2019, 07:24:12 PM »
...or the correlation might break down completely :)
Same data on a chronological chart:

It'd be worth looking at the coherence of the data, and figure out at what frequencies the correlation is strong.

dnem

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Re: When will the Arctic Go Ice Free?
« Reply #1209 on: September 16, 2019, 08:07:05 PM »
Very interesting charts. You can certainly squint at them and convince yourself that the correlation is becoming poorer in recent years.

Richard Rathbone

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Re: When will the Arctic Go Ice Free?
« Reply #1210 on: September 20, 2019, 07:22:46 AM »
If you are going to do a simple plot, the thing to plot ice against is CO2 emissions.

Extent loss is pretty linear if plotted against CO2 emissions. Each tonne of CO2 you emit costs the arctic 3 m2 of summer sea ice.

Notz & Stroeve, Science, 2016

https://science.sciencemag.org/content/354/6313/747

The trend hits BOE levels in the 2040s if emissions are constant at 2016 levels. Again, assuming constant emissions there's at least a decade before then in which a BOE is within range of a high melt year.

Read the paper for a simple analysis of why some reasons it might be expected to be non-linear tend to cancel out in the historical record and why they would be expected to continue to cancel out up to BOE territory.

There are several more recent and much more detailed papers by the same authors that don't change this conclusion, but do give a much more comprehensive treatment of the uncertainty levels.

2.18 10^6 km2 less ice than 2012 for BOE in an extreme melt year. 730 Gt is the post 2012 CO2 budget to hit that level. Without significant changes to BAU that is spent by about 2030. No BOE in the 2020s, but with BAU it becomes increasingly likely in the 2030s, and virtually certain to have happened by 2050. (This is based on JAXA daily minimum, ice-free September average will take a bit more CO2)

One of the interesting applications of this Notz & Stroeve result, is that if you want to see a BOE as soon as possible, it tells you what to do. Each tonne of carbon dioxide you can put into the atmosphere brings it 3m2 closer. You can rely on BAU and luck and hope for 2030, or take an extra first class trans-Atlantic flight and burn it 16 m2 closer. I'm clearly slacking, the myclimate footprint calculator estimates me at a mere 12 m2 per year. If I'd flown to hear Greta speak in the US I could have more than doubled that!

El Cid

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Re: When will the Arctic Go Ice Free?
« Reply #1211 on: September 20, 2019, 08:13:18 AM »
If you are going to do a simple plot, the thing to plot ice against is CO2 emissions.
...


The trend hits BOE levels in the 2040s if emissions are constant at 2016 levels. Again, assuming constant emissions there's at least a decade before then in which a BOE is within range of a high melt year.
No BOE in the 2020s, but with BAU it becomes increasingly likely in the 2030s, and virtually certain to have happened by 2050.

Richard, that is EXACTLY the same conclusion I came to based on the above temperature-ice extent correlation chart.

No surprise, since plotting Co2 vs extent is the same as temp vs extent - provided that temperatures and Co2 are closely correlated. They are

crandles

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Re: When will the Arctic Go Ice Free?
« Reply #1212 on: September 20, 2019, 12:55:41 PM »


Quite linear til we get down to about 1m km^2 area

Plots are against cumulative CO2 emissions.

Archimid

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Re: When will the Arctic Go Ice Free?
« Reply #1213 on: September 22, 2019, 03:17:42 PM »
It seems PIOMAS reached a minimum. Here is the updates maximum vs  loses graph. The ice free prediction moves closer to 2031. Average loss updated for 2019.
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Michael Hauber

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Re: When will the Arctic Go Ice Free?
« Reply #1214 on: October 04, 2019, 02:46:54 AM »
I still say never is a reasonable possibility.  Or at least not this century, and on a regular basis.

Model predictions for Arctic ice under RCP 4.5 suggest ice extent above 1m for the rest of the century, although lower years could well go a fair way below 1m, this is not likely on a consistent basis.  I have updated a comparison of model to actual conditions.  This is based on a published chart which I have saved as a picture backdrop for an excel chart, where I have plotted NSIDS September monthly ice extent.  These observations don't match up perfectly with what was quoted as observations in the published chart, but are pretty close.

Climate change:  Prepare for the worst, hope for the best, expect the middle.

dnem

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Re: When will the Arctic Go Ice Free?
« Reply #1215 on: October 04, 2019, 01:04:49 PM »
One could look at that image and say "Wow, data for last 10-15 years BELOW the prediction every single year."  One year also blasts way below the uncertainty estimates for the model.
« Last Edit: October 04, 2019, 01:38:02 PM by dnem »

Shared Humanity

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Re: When will the Arctic Go Ice Free?
« Reply #1216 on: October 04, 2019, 03:47:09 PM »
One could look at that image and say "Wow, data for last 10-15 years BELOW the prediction every single year."  One year also blasts way below the uncertainty estimates for the model.

Never mind that RCP 4.5 is now fantasyland.

oren

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Re: When will the Arctic Go Ice Free?
« Reply #1217 on: October 04, 2019, 04:04:47 PM »
One could look at that image and say "Wow, data for last 10-15 years BELOW the prediction every single year."  One year also blasts way below the uncertainty estimates for the model.

Never mind that RCP 4.5 is now fantasyland.
My thought exactly!

Michael Hauber

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Re: When will the Arctic Go Ice Free?
« Reply #1218 on: October 06, 2019, 05:51:10 AM »
RCP assumes emissions keep growing until about 2035, and allow emissions at 50% of 2005 values to continue until the end of the century.  Continued growth in emissions could continue somewhat past 2035 if we cut emissions back further in the second half the century.  RCP4.5 still allows for a substantial (but definitely smaller than today) fossil fuels industry even in 2100.  Why would anyone think this is fantasy land?
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oren

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Re: When will the Arctic Go Ice Free?
« Reply #1219 on: October 06, 2019, 07:18:25 AM »
MH, do you have a chart handy that shows RCP4.5 emissions per year? And even better, expected CO2 and other GHGs concentration per year?
BTW IIRC I once saw these same charts for RCP8.5, and got the impression they (intentionally?) had very high CO2 concentration growth in the initial years, thus giving the impression we are better than expected.

Stephan

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Re: When will the Arctic Go Ice Free?
« Reply #1220 on: October 06, 2019, 10:23:23 PM »
It is time for the monthly update of my extrapolation when the extent [Extent], volume [Volumen], thickness [Dicke] and area [Fläche] will reach zero. The extrapolation occured linearly and by a logarithmic function; the latter one almost constantly resulting in earlier times (valid for volume, area and thickness, not for extent in the winter months). September value now includes 2019.
Extent and volume for September 2019 lie slightly, thickness largely below the long-term linear trend lines, whereas area was above that trend line. These anomalies decreased the "BOE numbers" by 4 years (extent) and 1 year (volume, thickness) compared to last year and increased by 3 years for area.
The order (earlier → later BOE) generally is volume < thickness < area < extent.

Please note that this is not a forecast but a trend!
See attached table.
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Glen Koehler

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Re: When will the Arctic Go Ice Free?
« Reply #1221 on: October 09, 2019, 03:57:32 PM »
     Thanks Stephan.  A zero Arctic sea ice volume date for September, and shortly thereafter for August and October has been on my radar for a long time from the Wipneus and your earlier graphs. 
 
      But zero ASI volume-in-July estimates of 2034 (linear) or 2038 (log) are shocking to even my jaded eyes.  Yikes.  The albedo impact of losing ice coverage in July is much greater than August and very much greater than September.  Actually, the whole situation is shocking, but we just get used to the evolving catastrophic trends as a new abnormal.  If that zero Arctic sea ice estimate in July date is anywhere near accurate then we are in big trouble sooner than previously realized.  Remember, you can't have Extent or Area without Volume, so 0 Vol in 2034/2038 also = 0 Ext. 

     FWIW, the September 2019 IPCC cryosphere report shows Extent becoming asymptotic at about 10% of the 2000 level around 2070. 
https://report.ipcc.ch/srocc/pdf/SROCC_FinalDraft_FullReport.pdf
     
     Given the length and detail of the IPCC cryosphere report, there is a surprisingly brief discussion of Arctic sea ice trends.  ASIF is a better source than IPCC! (seriously). After a quick search, I found nothing in the IPCC report about ASI volume projections.  Figure 3.3 on page 3-13 is the closest information.  It charts ASI Extent under the RCP scenarios.  In those projections, even the RCP8.5 scenario retains 10% September Extent for 2070-2100. 

      The scientists who donate their hard work to IPCC reports are the experts and I feel like an ungrateful flea telling the dog what to do in critiquing their work.  But my small fevered brain is unable to reconcile the trends charted by Wipneus and Stephan, or that I can see for myself in the data from PIOMAS, with the IPCC statements shown below from page 3-25.  To be blunt, I suspect that the IPCC is under-estimating the severity of the ASI trends.  If that were in fact the case, it would almost certainly be due to the political (in addition to scientific) consensus required before IPCC reports are released.  But let me not digress into conspiracy theory.  Here is the gist of what the IPCC Cryosphere report has to say about the expected future ASI:

      "There is a large spread in the timing of when the Arctic may become ice free in the summer, and for how long during the season (Massonnet et al., 2012; Stroeve et al., 2012a; Overland and Wang, 2013) as a result of natural climate variability (Notz, 2015; Swart et al., 2015b; Screen and Deser, 2019), scenario uncertainty (Stroeve et al., 2012a; Liu et al., 2013), and model uncertainties related to sea ice dynamics (Rampal et al., 2011; Tandon et al., 2018) and thermodynamics (Massonnet et al., 2018). Internal climate variability results in an uncertainty of approximately 20 years in the timing of seasonally ice-free conditions (Notz, 2015; Jahn, 2018), but the clear link between summer sea ice extent and cumulative CO2 emissions provide a basis for when consistent ice-free conditions may be expected. For stabilized global warming of 1.5°C, sea ice in September is likely to be present at end of century with an approximately 1% chance of individual ice-free years (emphasis mine) (Notz and Stroeve, 2016; Sanderson et al., 2017; Jahn, 2018; Sigmond et al., 2018); after 10 years of stabilized warming at a 2°C increase, more frequent occurrence of an ice-free summer Arctic is expected (around 10-35%) (Mahlstein and Knutti, 2012; Jahn et al., 2016; Notz and Stroeve, 2016)."

    They do say elsewhere in the report that CMIP5 models have relatively poor ability to recreate Arctic sea ice behavior.  The new generation of CMIP6 models are coming out and have improved capabilities.  It will be interesting to see what they have to say about ASI projections.  So far the only statements I have seen on output from the few CMIP6 model results being reported is that they (i.e. the multiple new component models of the new CMIP6 set) are consistently showing greater sensitivity of global surface temperature to rising CO2 levels than the CMIP5 estimates. 

       None of this bodes well for the ASI, or for human civilization unless we finally take heed and respond to the crisis with the intensity and commitment it requires.  Make your support for any politician explicitly contingent on their climate policy.  Talk about it even if you annoy people by doing so.  Vote climate as if your life depended on it.  Because it does.
« Last Edit: October 10, 2019, 12:59:21 AM by Glen Koehler »

Tom_Mazanec

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Re: When will the Arctic Go Ice Free?
« Reply #1222 on: October 09, 2019, 06:08:21 PM »
I get your point, Glen, but I vote as if my soul depends on it.
That's why this pro-life voter voted for Kasich in the Primary but Trump in the election (and hated it)>
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jdallen

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Re: When will the Arctic Go Ice Free?
« Reply #1223 on: October 10, 2019, 07:21:53 AM »
I get your point, Glen, but I vote as if my soul depends on it.
That's why this pro-life voter voted for Kasich in the Primary but Trump in the election (and hated it)>
Tom, for someone so intelligent, I have a very hard time squaring that with such complete foolishness.

He is actively working for the destruction of our environment.  How could you?
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Tom_Mazanec

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Re: When will the Arctic Go Ice Free?
« Reply #1224 on: October 10, 2019, 01:32:13 PM »
jdallen:
The choice was between Hillary and the Donald.
Hillary was actively promoting the murder of something like a million preborn babies a year in the United States. A baby is far more important than any furbish lousewort (or even a mongoose).
How could I not vote for him?
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Shared Humanity

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Re: When will the Arctic Go Ice Free?
« Reply #1225 on: October 10, 2019, 07:38:06 PM »
jdallen:
The choice was between Hillary and the Donald.
Hillary was actively promoting the murder of something like a million preborn babies a year in the United States. A baby is far more important than any furbish lousewort (or even a mongoose).
How could I not vote for him?

And Trump is aggressively pursuing a policy that will lead to the deaths of billions this century and destroy God's creation (Mother Earth) if you are a believer. I believe he tasked us with caring for his creation in Genesis.

Now back to the question posed by this thread...

jdallen

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Re: When will the Arctic Go Ice Free?
« Reply #1226 on: October 11, 2019, 06:35:55 AM »
jdallen:
The choice was between Hillary and the Donald.
<snippage>


And Trump is aggressively pursuing a policy that will lead to the deaths of billions this century
<snippage>

<sadly disappointed head shake>
This is by definition a question of faith(s), and impossible to argue over rationally.

Now back to the question posed by this thread...

Indeed!

<snippage>
     FWIW, the September 2019 IPCC cryosphere report shows Extent becoming asymptotic at about 10% of the 2000 level around 2070. 
<more snippage>

I've been slowly arriving at a similar conclusion, as a result of a confluence of factors we've covered all over the forums.  Key among them are total system enthalpy, ocean enthalpy, the dynamics of seasonal changes in the radiative energy budget... but other things like just the nature of ocean surface dynamics and the physical chemistry of water come in to play as well.

I think before that last 10% or so disappears for good, there will need to be a lot more support for atmospheric heating at high latitudes.  Along the way, this will create conditions for stupendous storms at much higher latitude than we've ever imagined. 

The drop off insolation at the end of the melt season will be like a vaccuum collapsing with everything rushing in to fill it.  I think we'll see more continuous flow out of the tropics all the way to the Arctic, with no Ferrel or Arctic cells to speak of long before the ice fully disappears consistently in the summer.
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Juan C. García

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Re: When will the Arctic Go Ice Free?
« Reply #1227 on: October 11, 2019, 07:15:32 AM »
     FWIW, the September 2019 IPCC cryosphere report shows Extent becoming asymptotic at about 10% of the 2000 level around 2070. 
https://report.ipcc.ch/srocc/pdf/SROCC_FinalDraft_FullReport.pdf
     
     Given the length and detail of the IPCC cryosphere report, there is a surprisingly brief discussion of Arctic sea ice trends.  ASIF is a better source than IPCC! (seriously). After a quick search, I found nothing in the IPCC report about ASI volume projections.  Figure 3.3 on page 3-13 is the closest information.  It charts ASI Extent under the RCP scenarios.  In those projections, even the RCP8.5 scenario retains 10% September Extent for 2070-2100. 

      The scientists who donate their hard work to IPCC reports are the experts and I feel like an ungrateful flea telling the dog what to do in critiquing their work.  But my small fevered brain is unable to reconcile the trends charted by Wipneus and Stephan, or that I can see for myself in the data from PIOMAS, with the IPCC statements shown below from page 3-25.  To be blunt, I suspect that the IPCC is under-estimating the severity of the ASI trends.

Same conclusions (on bold, made by me), long time ago. The IPCC is in fact, avoiding the discussion of when the Arctic will be ice free. It is easier to simulate that they are doing their work, at the same time that they respect politicians.

On the other hand, some of them are politicians!
 ---> IPCC: Intergovernmental Panel of Climate Change.

Edit:
Quote
Greta Thunberg speech at UN Climate Change COP24 Conference:

We have not come here to beg world leaders to care. You have ignored us in the past and you will ignore us again.
We have run out of excuses and we are running out of time.
We have come here to let you know that change is coming, whether you like it or not. The real power belongs to the people.
"...we are running out of time" but the IPCC is still talking about 2100.
"...The real power belongs to the people." ---> ASIF?  ;)
« Last Edit: October 11, 2019, 07:40:41 AM by Juan C. García »
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

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.

Tom_Mazanec

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Re: When will the Arctic Go Ice Free?
« Reply #1228 on: October 11, 2019, 01:16:33 PM »
The next question is, when will the Arctic be ice covered again? 102,019 AD?
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Re: When will the Arctic Go Ice Free?
« Reply #1229 on: October 11, 2019, 04:32:13 PM »

<snippage>
     FWIW, the September 2019 IPCC cryosphere report shows Extent becoming asymptotic at about 10% of the 2000 level around 2070. 
<more snippage>

I've been slowly arriving at a similar conclusion, as a result of a confluence of factors we've covered all over the forums.  Key among them are total system enthalpy, ocean enthalpy, the dynamics of seasonal changes in the radiative energy budget... but other things like just the nature of ocean surface dynamics and the physical chemistry of water come in to play as well.

I think before that last 10% or so disappears for good, there will need to be a lot more support for atmospheric heating at high latitudes.  Along the way, this will create conditions for stupendous storms at much higher latitude than we've ever imagined. 

The drop off insolation at the end of the melt season will be like a vaccuum collapsing with everything rushing in to fill it.  I think we'll see more continuous flow out of the tropics all the way to the Arctic, with no Ferrel or Arctic cells to speak of long before the ice fully disappears consistently in the summer.

That conclusion appears more likely than many here would like to admit, although there have been a few here that have supported it.  An ice-free Arctic in the next decade or so seems unlikely.

gerontocrat

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Re: When will the Arctic Go Ice Free?
« Reply #1230 on: October 11, 2019, 08:56:56 PM »
NSIDC appear to be a bit supportive of a "hiatus" in Arctic Sea Ice Loss.

Here is their spiel about it from Oct 3  https://nsidc.org/arcticseaicenews/ (Graph also attached)

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

Who am I, a mere observer to disagree - but I do...

Evidence 1
Let us assume that 2007 & 2012 are outliers - i.e. caused by a combination of climatic occurrences that converged to produce the maximum possible ice loss at that time. If so, it is legitimate to exclude those years from the data.

The result  (see graph attached, that has both sets of data, i.e. with & without 2012 and 2007),
- a far more orderly progression in a downwards direction.
- no real sign of a hiatus
- a slightly better linear trend R2 value.,
- average annual loss reduced by 5k (82 to 77k)

Note well:- all I did was tell the spreadsheet to make the graphs & add the trend lines. No manipulation by yours truly

Evidence 2
All the data now indicates that the October Average is likely to be a record low, even if area and extent gain revert back to average levels.

Evidence 3
There is likely to be a new record low 365 day average in early to middle 2020

So my statement that belongs to me is that 2007 and 2012 distort the trends to the extent that they create the illusion of a hiatus where none exists..


« Last Edit: October 11, 2019, 09:11:30 PM by gerontocrat »
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Ken Feldman

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Re: When will the Arctic Go Ice Free?
« Reply #1231 on: October 11, 2019, 09:26:05 PM »
     FWIW, the September 2019 IPCC cryosphere report shows Extent becoming asymptotic at about 10% of the 2000 level around 2070. 
https://report.ipcc.ch/srocc/pdf/SROCC_FinalDraft_FullReport.pdf
     
     Given the length and detail of the IPCC cryosphere report, there is a surprisingly brief discussion of Arctic sea ice trends.  ASIF is a better source than IPCC! (seriously). After a quick search, I found nothing in the IPCC report about ASI volume projections.  Figure 3.3 on page 3-13 is the closest information.  It charts ASI Extent under the RCP scenarios.  In those projections, even the RCP8.5 scenario retains 10% September Extent for 2070-2100. 

      The scientists who donate their hard work to IPCC reports are the experts and I feel like an ungrateful flea telling the dog what to do in critiquing their work.  But my small fevered brain is unable to reconcile the trends charted by Wipneus and Stephan, or that I can see for myself in the data from PIOMAS, with the IPCC statements shown below from page 3-25.  To be blunt, I suspect that the IPCC is under-estimating the severity of the ASI trends.

Same conclusions (on bold, made by me), long time ago. The IPCC is in fact, avoiding the discussion of when the Arctic will be ice free. It is easier to simulate that they are doing their work, at the same time that they respect politicians.

On the other hand, some of them are politicians!
 ---> IPCC: Intergovernmental Panel of Climate Change.

Edit:
Quote
Greta Thunberg speech at UN Climate Change COP24 Conference:

We have not come here to beg world leaders to care. You have ignored us in the past and you will ignore us again.
We have run out of excuses and we are running out of time.
We have come here to let you know that change is coming, whether you like it or not. The real power belongs to the people.
"...we are running out of time" but the IPCC is still talking about 2100.
"...The real power belongs to the people." ---> ASIF?  ;)

Each of the IPCC reports issued this decade has made projections of when the Arctic will be ice free.

AR5 (2013) Chapter 11, page 995
http://www.climatechange2013.org/images/report/WG1AR5_Chapter11_FINAL.pdf

Quote
Though most of the CMIP5 models project a nearly ice-free Arctic (sea ice extent less than 1 × 106 km2 for at least 5 consecutive years) at the end of summer by 2100 in the RCP8.5 scenario (see Section 12.4.6.1), some show large changes in the near term as well. Some previous models project an ice-free summer period in the Arctic Ocean by 2040 (Holland et al., 2006), and even as early as the late 2030s using a criterion of 80% sea ice area loss (e.g., Zhang, 2010). By scaling six CMIP3 models to recent observed September sea ice changes, a nearly ice-free Arctic in September is projected to occur by 2037, reaching the first quartile of the distribution for timing of September sea ice loss by 2028 (Wang and Overland, 2009). However, a number of models that have fairly thick Arctic sea ice produce a slower near-term decrease in sea ice extent compared to observations (Stroeve et al., 2007). Based on a linear extrapolation into the future of the recent sea ice volume trend from a hindcast simulation conducted with a regional model of the Arctic sea ice–ocean system (Maslowski et al., 2012) projected that
it would take only until about 2016 to reach a nearly ice-free Arctic Ocean in summer. However, such an approach not only neglects the effect of year-to-year or longer-term variability (Overland and Wang, 2013) but also ignores the negative feedbacks that can occur when the sea ice cover becomes thin (Notz, 2009). Mahlstein and Knutti (2012) estimated the annual mean global surface warming threshold for nearly ice-free Arctic conditions in September to be ~2°C above the present derived from both CMIP3 models and observations.
An analysis of CMIP3 model simulations indicates that for near-term predictions the dominant factor for decreasing sea ice is increased ice melt, and reductions in ice growth play a secondary role (Holland et al., 2010). Arctic sea ice has larger volume loss when there is thicker ice initially across the CMIP3 models, with a projected accumulated mass loss of about 0.5 m by 2020, and roughly 1.0 m by 2050, with considerable model spread (Holland et al., 2010). The CMIP3 models tended to under-estimate the observed rapid decline of summer Arctic sea ice during the satellite era, but these recent trends are more accurately simulated in the CMIP5 models (see Section 12.4.6.1). For CMIP3 models, results indicate that the changes in Arctic sea ice mass budget over the 21st century are related to the late 20th century mean sea ice thickness distribution (Holland et al., 2010), average sea ice thickness (Bitz, 2008; Hodson et al., 2012), fraction of thin ice cover (Boe et al., 2009) and oceanic heat transport to the Arctic (Mahlstein et al., 2011). Acceleration of sea ice drift observed over the last three decades, underestimated in CMIP3 projections (Rampal et al., 2011), and the presence of fossil-fuel and biofuel soot in the Arctic environment (Jacobson, 2010), could also contribute to ice-free late summer conditions over the Arctic in the near term. Details on the transition to an ice-free summer over the Arctic are presented in Chapter 12 (Sections 12.4.6.1 and 12.5.5.7).

Special Report Global Warming of 1.5C (2018) Chapter 3, Page 205

https://www.ipcc.ch/site/assets/uploads/sites/2/2019/06/SR15_Chapter3_Low_Res.pdf

Quote
3.3.8 Sea Ice
Summer sea ice in the Arctic has been retreating rapidly in recent decades. During the period 1997 to 2014, for example, the monthly mean sea ice extent during September (summer) decreased on average by 130,000 km² per year (Serreze and Stroeve, 2015). This is about four times as fast as the September sea ice loss during the period 1979 to 1996. Sea ice thickness has also decreased substantially, with an estimated decrease in ice thickness of more than 50% in the central Arctic (Lindsay and Schweiger, 2015). Sea ice coverage and thickness also decrease in CMIP5 simulations of the recent past, and are projected to decrease in the future (Collins et al., 2013). However, the modelled sea ice loss in most CMIP5 models is much smaller than observed losses. Compared to observations, the simulations are less sensitive to both global mean temperature rise (Rosenblum and
Eisenman, 2017) and anthropogenic CO2 emissions (Notz and Stroeve, 2016). This mismatch between the observed and modelled sensitivity of Arctic sea ice implies that the multi-model-mean responses of future sea ice evolution probably underestimates the sea ice loss for a given amount of global warming. To address this issue, studies estimating the future evolution of Arctic sea ice tend to bias correct the model simulations based on the observed evolution of Arctic sea ice in response to global warming. Based on such bias correction, pre-AR5 and post-AR5 studies generally agree that for 1.5°C of global warming relative to pre-industrial levels, the Arctic Ocean will maintain a sea ice cover throughout summer in most years (Collins et al., 2013; Notz and Stroeve, 2016; Screen and Williamson, 2017; Jahn, 2018; Niederdrenk and Notz, 2018; Sigmond et al., 2018). For 2°C of global warming, chances of a sea ice-free Arctic during summer are substantially higher (Screen and Williamson, 2017; Jahn, 2018; Niederdrenk and Notz, 2018; Screen et al., 2018; Sigmond et al., 2018). Model simulations suggest that there will be at least one sea ice-free Arctic5 summer after approximately 10 years of stabilized warming at 2°C, as compared to one sea ice-free summer after 100 years of stabilized warming at 1.5°C above pre-industrial temperatures (Jahn, 2018; Screen et al., 2018; Sigmond et al., 2018). For a specific given year under stabilized warming of 2°C, studies based on large ensembles of simulations with a single model estimate the likelihood of ice-free conditions as 35% without a bias correction of the underlying model (Sanderson et al., 2017; Jahn, 2018); as between 10% and >99% depending on the observational record used to correct the sensitivity of sea ice decline to global warming in the underlying model (Niederdrenk and Notz, 2018); and as 19% based on a procedure to correct for biases in the climatological sea ice coverage in the underlying model (Sigmond et al., 2018). The uncertainty of the first year of the occurrence of an icefree Arctic Ocean arising from internal variability is estimated to be about 20 years (Notz, 2015; Jahn et al., 2016).
The more recent estimates of the warming necessary to produce an icefree Arctic Ocean during summer are lower than the ones given in AR5 (about 2.6°C–3.1°C of global warming relative to pre-industrial levels or 1.6°C–2.1°C relative to present-day conditions), which were similar to the estimate of 3°C of global warming relative to pre-industrial levels (or 2°C relative to present-day conditions) by Mahlstein and Knutti (2012) based on bias-corrected CMIP3 models. Rosenblum and Eisenman (2016) explained why the sensitivity estimated by Mahlstein and Knutti (2012) might be too low, estimating instead that September sea ice in the Arctic would disappear at 2°C of global warming relative to pre-industrial levels (or about 1°C relative to present-day conditions), in line with the other recent estimates. Notz and Stroeve (2016) used the observed correlation between September sea ice extent and cumulative CO2 emissions to estimate that the Arctic Ocean would become nearly free of sea ice during September with a further 1000 Gt of emissions, which also implies a sea ice loss at about 2°C of global warming. Some of the uncertainty in these numbers stems from the possible impact of aerosols (Gagne et al., 2017) and of volcanic forcing (Rosenblum and Eisenman, 2016). During winter, little Arctic sea ice is projected to be lost for either 1.5°C or 2°C of global warming (Niederdrenk and Notz, 2018).
5

Special Report on Oceans and Crysphere (2019) Chapter 3, Page 3-25

https://report.ipcc.ch/srocc/pdf/SROCC_FinalDraft_Chapter3.pdf

Quote
3.2.2 Projected Changes in Sea Ice and Ocean
 
3.2.2.1 Sea Ice
 
The multi-model ensemble of historical simulations from CMIP5 models identify declines in total Arctic sea ice extent and thickness (Sections 3.2.1.1.1; 3.2.1.1.2; Figure 3.3) which agree with observations (Massonnet et al., 2012; Stroeve et al., 2012a; Stroeve et al., 2014a; Stroeve and Notz, 2015). There is a range in the ability of individual models to simulate observed sea ice thickness spatial patterns and sea ice drift rates (Jahn et al., 2012; Stroeve et al., 2014a; Tandon et al., 2018). Reductions in Arctic sea ice extent scale linearly with both global temperatures and cumulative CO2 emissions in simulations and observations (Notz and Stroeve, 2016), although aerosols influenced historical sea ice trends (Gagné et al., 2017). The uncertainty in sea ice sensitivity (ice extent loss per unit of warming) is quite large (Niederdrenk and Notz, 2018) and the model sensitivity is too low in most CMIP5 models (Rosenblum and Eisenman, 2017). Emerging evidence suggests, however, that internal variability, including links between the Arctic and lower latitude, strongly influences the ability of models to simulate observed reductions in Arctic sea ice extent (Swart et al., 2015b; Ding et al., 2018).
 
CMIP5 models project continued declines in Arctic sea ice through the end of the century (Figure 3.3) (Notz and Stroeve, 2016) (high confidence). There is a large spread in the timing of when the Arctic may become ice free in the summer, and for how long during the season (Massonnet et al., 2012; Stroeve et al., 2012a; Overland and Wang, 2013) as a result of natural climate variability (Notz, 2015; Swart et al., 2015b; Screen and Deser, 2019), scenario uncertainty (Stroeve et al., 2012a; Liu et al., 2013), and model uncertainties related to sea ice dynamics (Rampal et al., 2011; Tandon et al., 2018) and thermodynamics (Massonnet et al., 2018). Internal climate variability results in an uncertainty of approximately 20 years in the timing of seasonally ice-free conditions (Notz, 2015; Jahn, 2018), but the clear link between summer sea ice extent and cumulative CO2 emissions provide a basis for when consistent ice-free conditions may be expected. For stabilized global warming of 1.5°C, sea ice in September is likely to be present at end of century with an approximately 1% chance of individual ice-free years (Notz and Stroeve, 2016; Sanderson et al., 2017; Jahn, 2018; Sigmond et al., 2018); after 10 years of stabilized warming at a 2°C increase, more frequent occurrence of an ice-free summer Arctic is expected (around 10-35%) (Mahlstein and Knutti, 2012; Jahn et al., 2016; Notz and Stroeve, 2016). Model simulations show that a temporary temperature overshoot of a warming target has no lasting impact on ice cover (Armour et al., 2011; Ridley et al., 2012; Li et al., 2013).



Wherestheice

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Re: When will the Arctic Go Ice Free?
« Reply #1232 on: October 11, 2019, 09:48:56 PM »
     FWIW, the September 2019 IPCC cryosphere report shows Extent becoming asymptotic at about 10% of the 2000 level around 2070. 
https://report.ipcc.ch/srocc/pdf/SROCC_FinalDraft_FullReport.pdf
     
     Given the length and detail of the IPCC cryosphere report, there is a surprisingly brief discussion of Arctic sea ice trends.  ASIF is a better source than IPCC! (seriously). After a quick search, I found nothing in the IPCC report about ASI volume projections.  Figure 3.3 on page 3-13 is the closest information.  It charts ASI Extent under the RCP scenarios.  In those projections, even the RCP8.5 scenario retains 10% September Extent for 2070-2100. 

      The scientists who donate their hard work to IPCC reports are the experts and I feel like an ungrateful flea telling the dog what to do in critiquing their work.  But my small fevered brain is unable to reconcile the trends charted by Wipneus and Stephan, or that I can see for myself in the data from PIOMAS, with the IPCC statements shown below from page 3-25.  To be blunt, I suspect that the IPCC is under-estimating the severity of the ASI trends.

Same conclusions (on bold, made by me), long time ago. The IPCC is in fact, avoiding the discussion of when the Arctic will be ice free. It is easier to simulate that they are doing their work, at the same time that they respect politicians.

On the other hand, some of them are politicians!
 ---> IPCC: Intergovernmental Panel of Climate Change.

Edit:
Quote
Greta Thunberg speech at UN Climate Change COP24 Conference:

We have not come here to beg world leaders to care. You have ignored us in the past and you will ignore us again.
We have run out of excuses and we are running out of time.
We have come here to let you know that change is coming, whether you like it or not. The real power belongs to the people.
"...we are running out of time" but the IPCC is still talking about 2100.
"...The real power belongs to the people." ---> ASIF?  ;)

Each of the IPCC reports issued this decade has made projections of when the Arctic will be ice free.

AR5 (2013) Chapter 11, page 995
http://www.climatechange2013.org/images/report/WG1AR5_Chapter11_FINAL.pdf

Quote
Though most of the CMIP5 models project a nearly ice-free Arctic (sea ice extent less than 1 × 106 km2 for at least 5 consecutive years) at the end of summer by 2100 in the RCP8.5 scenario (see Section 12.4.6.1), some show large changes in the near term as well. Some previous models project an ice-free summer period in the Arctic Ocean by 2040 (Holland et al., 2006), and even as early as the late 2030s using a criterion of 80% sea ice area loss (e.g., Zhang, 2010). By scaling six CMIP3 models to recent observed September sea ice changes, a nearly ice-free Arctic in September is projected to occur by 2037, reaching the first quartile of the distribution for timing of September sea ice loss by 2028 (Wang and Overland, 2009). However, a number of models that have fairly thick Arctic sea ice produce a slower near-term decrease in sea ice extent compared to observations (Stroeve et al., 2007). Based on a linear extrapolation into the future of the recent sea ice volume trend from a hindcast simulation conducted with a regional model of the Arctic sea ice–ocean system (Maslowski et al., 2012) projected that
it would take only until about 2016 to reach a nearly ice-free Arctic Ocean in summer. However, such an approach not only neglects the effect of year-to-year or longer-term variability (Overland and Wang, 2013) but also ignores the negative feedbacks that can occur when the sea ice cover becomes thin (Notz, 2009). Mahlstein and Knutti (2012) estimated the annual mean global surface warming threshold for nearly ice-free Arctic conditions in September to be ~2°C above the present derived from both CMIP3 models and observations.
An analysis of CMIP3 model simulations indicates that for near-term predictions the dominant factor for decreasing sea ice is increased ice melt, and reductions in ice growth play a secondary role (Holland et al., 2010). Arctic sea ice has larger volume loss when there is thicker ice initially across the CMIP3 models, with a projected accumulated mass loss of about 0.5 m by 2020, and roughly 1.0 m by 2050, with considerable model spread (Holland et al., 2010). The CMIP3 models tended to under-estimate the observed rapid decline of summer Arctic sea ice during the satellite era, but these recent trends are more accurately simulated in the CMIP5 models (see Section 12.4.6.1). For CMIP3 models, results indicate that the changes in Arctic sea ice mass budget over the 21st century are related to the late 20th century mean sea ice thickness distribution (Holland et al., 2010), average sea ice thickness (Bitz, 2008; Hodson et al., 2012), fraction of thin ice cover (Boe et al., 2009) and oceanic heat transport to the Arctic (Mahlstein et al., 2011). Acceleration of sea ice drift observed over the last three decades, underestimated in CMIP3 projections (Rampal et al., 2011), and the presence of fossil-fuel and biofuel soot in the Arctic environment (Jacobson, 2010), could also contribute to ice-free late summer conditions over the Arctic in the near term. Details on the transition to an ice-free summer over the Arctic are presented in Chapter 12 (Sections 12.4.6.1 and 12.5.5.7).

Special Report Global Warming of 1.5C (2018) Chapter 3, Page 205

https://www.ipcc.ch/site/assets/uploads/sites/2/2019/06/SR15_Chapter3_Low_Res.pdf

Quote
3.3.8 Sea Ice
Summer sea ice in the Arctic has been retreating rapidly in recent decades. During the period 1997 to 2014, for example, the monthly mean sea ice extent during September (summer) decreased on average by 130,000 km² per year (Serreze and Stroeve, 2015). This is about four times as fast as the September sea ice loss during the period 1979 to 1996. Sea ice thickness has also decreased substantially, with an estimated decrease in ice thickness of more than 50% in the central Arctic (Lindsay and Schweiger, 2015). Sea ice coverage and thickness also decrease in CMIP5 simulations of the recent past, and are projected to decrease in the future (Collins et al., 2013). However, the modelled sea ice loss in most CMIP5 models is much smaller than observed losses. Compared to observations, the simulations are less sensitive to both global mean temperature rise (Rosenblum and
Eisenman, 2017) and anthropogenic CO2 emissions (Notz and Stroeve, 2016). This mismatch between the observed and modelled sensitivity of Arctic sea ice implies that the multi-model-mean responses of future sea ice evolution probably underestimates the sea ice loss for a given amount of global warming. To address this issue, studies estimating the future evolution of Arctic sea ice tend to bias correct the model simulations based on the observed evolution of Arctic sea ice in response to global warming. Based on such bias correction, pre-AR5 and post-AR5 studies generally agree that for 1.5°C of global warming relative to pre-industrial levels, the Arctic Ocean will maintain a sea ice cover throughout summer in most years (Collins et al., 2013; Notz and Stroeve, 2016; Screen and Williamson, 2017; Jahn, 2018; Niederdrenk and Notz, 2018; Sigmond et al., 2018). For 2°C of global warming, chances of a sea ice-free Arctic during summer are substantially higher (Screen and Williamson, 2017; Jahn, 2018; Niederdrenk and Notz, 2018; Screen et al., 2018; Sigmond et al., 2018). Model simulations suggest that there will be at least one sea ice-free Arctic5 summer after approximately 10 years of stabilized warming at 2°C, as compared to one sea ice-free summer after 100 years of stabilized warming at 1.5°C above pre-industrial temperatures (Jahn, 2018; Screen et al., 2018; Sigmond et al., 2018). For a specific given year under stabilized warming of 2°C, studies based on large ensembles of simulations with a single model estimate the likelihood of ice-free conditions as 35% without a bias correction of the underlying model (Sanderson et al., 2017; Jahn, 2018); as between 10% and >99% depending on the observational record used to correct the sensitivity of sea ice decline to global warming in the underlying model (Niederdrenk and Notz, 2018); and as 19% based on a procedure to correct for biases in the climatological sea ice coverage in the underlying model (Sigmond et al., 2018). The uncertainty of the first year of the occurrence of an icefree Arctic Ocean arising from internal variability is estimated to be about 20 years (Notz, 2015; Jahn et al., 2016).
The more recent estimates of the warming necessary to produce an icefree Arctic Ocean during summer are lower than the ones given in AR5 (about 2.6°C–3.1°C of global warming relative to pre-industrial levels or 1.6°C–2.1°C relative to present-day conditions), which were similar to the estimate of 3°C of global warming relative to pre-industrial levels (or 2°C relative to present-day conditions) by Mahlstein and Knutti (2012) based on bias-corrected CMIP3 models. Rosenblum and Eisenman (2016) explained why the sensitivity estimated by Mahlstein and Knutti (2012) might be too low, estimating instead that September sea ice in the Arctic would disappear at 2°C of global warming relative to pre-industrial levels (or about 1°C relative to present-day conditions), in line with the other recent estimates. Notz and Stroeve (2016) used the observed correlation between September sea ice extent and cumulative CO2 emissions to estimate that the Arctic Ocean would become nearly free of sea ice during September with a further 1000 Gt of emissions, which also implies a sea ice loss at about 2°C of global warming. Some of the uncertainty in these numbers stems from the possible impact of aerosols (Gagne et al., 2017) and of volcanic forcing (Rosenblum and Eisenman, 2016). During winter, little Arctic sea ice is projected to be lost for either 1.5°C or 2°C of global warming (Niederdrenk and Notz, 2018).
5

Special Report on Oceans and Crysphere (2019) Chapter 3, Page 3-25

https://report.ipcc.ch/srocc/pdf/SROCC_FinalDraft_Chapter3.pdf

Quote
3.2.2 Projected Changes in Sea Ice and Ocean
 
3.2.2.1 Sea Ice
 
The multi-model ensemble of historical simulations from CMIP5 models identify declines in total Arctic sea ice extent and thickness (Sections 3.2.1.1.1; 3.2.1.1.2; Figure 3.3) which agree with observations (Massonnet et al., 2012; Stroeve et al., 2012a; Stroeve et al., 2014a; Stroeve and Notz, 2015). There is a range in the ability of individual models to simulate observed sea ice thickness spatial patterns and sea ice drift rates (Jahn et al., 2012; Stroeve et al., 2014a; Tandon et al., 2018). Reductions in Arctic sea ice extent scale linearly with both global temperatures and cumulative CO2 emissions in simulations and observations (Notz and Stroeve, 2016), although aerosols influenced historical sea ice trends (Gagné et al., 2017). The uncertainty in sea ice sensitivity (ice extent loss per unit of warming) is quite large (Niederdrenk and Notz, 2018) and the model sensitivity is too low in most CMIP5 models (Rosenblum and Eisenman, 2017). Emerging evidence suggests, however, that internal variability, including links between the Arctic and lower latitude, strongly influences the ability of models to simulate observed reductions in Arctic sea ice extent (Swart et al., 2015b; Ding et al., 2018).
 
CMIP5 models project continued declines in Arctic sea ice through the end of the century (Figure 3.3) (Notz and Stroeve, 2016) (high confidence). There is a large spread in the timing of when the Arctic may become ice free in the summer, and for how long during the season (Massonnet et al., 2012; Stroeve et al., 2012a; Overland and Wang, 2013) as a result of natural climate variability (Notz, 2015; Swart et al., 2015b; Screen and Deser, 2019), scenario uncertainty (Stroeve et al., 2012a; Liu et al., 2013), and model uncertainties related to sea ice dynamics (Rampal et al., 2011; Tandon et al., 2018) and thermodynamics (Massonnet et al., 2018). Internal climate variability results in an uncertainty of approximately 20 years in the timing of seasonally ice-free conditions (Notz, 2015; Jahn, 2018), but the clear link between summer sea ice extent and cumulative CO2 emissions provide a basis for when consistent ice-free conditions may be expected. For stabilized global warming of 1.5°C, sea ice in September is likely to be present at end of century with an approximately 1% chance of individual ice-free years (Notz and Stroeve, 2016; Sanderson et al., 2017; Jahn, 2018; Sigmond et al., 2018); after 10 years of stabilized warming at a 2°C increase, more frequent occurrence of an ice-free summer Arctic is expected (around 10-35%) (Mahlstein and Knutti, 2012; Jahn et al., 2016; Notz and Stroeve, 2016). Model simulations show that a temporary temperature overshoot of a warming target has no lasting impact on ice cover (Armour et al., 2011; Ridley et al., 2012; Li et al., 2013).

They have avoided the "Discussion", not the projections.
"When the ice goes..... F***

be cause

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Re: When will the Arctic Go Ice Free?
« Reply #1233 on: October 11, 2019, 11:00:36 PM »
cheers Gerontocrat .. though your post could be lost here .. it deserves attention. Reminiscent of the great global warming hiatus 1998 - 2012 . I agree with your disagreement .   b.c.
2007 + 5 = 2012 + 4 = 2016 + 3 = 2019 ...

philopek

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Re: When will the Arctic Go Ice Free?
« Reply #1234 on: October 11, 2019, 11:52:36 PM »
NSIDC appear to be a bit supportive of a "hiatus" in Arctic Sea Ice Loss.

Here is their spiel about it from Oct 3  https://nsidc.org/arcticseaicenews/ (Graph also attached)

Who am I, a mere observer to disagree - but I do...


You are in good company i'm sure, at least and no matter that it does not matter,
I'm seconding every jota of your post, hence:

+1

Klondike Kat

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Re: When will the Arctic Go Ice Free?
« Reply #1235 on: October 12, 2019, 12:05:19 AM »
NSIDC appear to be a bit supportive of a "hiatus" in Arctic Sea Ice Loss.

Here is their spiel about it from Oct 3  https://nsidc.org/arcticseaicenews/ (Graph also attached)

Who am I, a mere observer to disagree - but I do...


You are in good company i'm sure, at least and no matter that it does not matter,
I'm seconding every jota of your post, hence:

+1

Not everyone.  I am in agreement with the NSIDC scientists. 

gandul

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Re: When will the Arctic Go Ice Free?
« Reply #1236 on: October 12, 2019, 12:37:46 AM »
NSIDC appear to be a bit supportive of a "hiatus" in Arctic Sea Ice Loss.

Here is their spiel about it from Oct 3  https://nsidc.org/arcticseaicenews/ (Graph also attached)

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

Who am I, a mere observer to disagree - but I do...

Evidence 1
Let us assume that 2007 & 2012 are outliers - i.e. caused by a combination of climatic occurrences that converged to produce the maximum possible ice loss at that time. If so, it is legitimate to exclude those years from the data.

The result  (see graph attached, that has both sets of data, i.e. with & without 2012 and 2007),
- a far more orderly progression in a downwards direction.
- no real sign of a hiatus
- a slightly better linear trend R2 value.,
- average annual loss reduced by 5k (82 to 77k)

Note well:- all I did was tell the spreadsheet to make the graphs & add the trend lines. No manipulation by yours truly

Evidence 2
All the data now indicates that the October Average is likely to be a record low, even if area and extent gain revert back to average levels.

Evidence 3
There is likely to be a new record low 365 day average in early to middle 2020

So my statement that belongs to me is that 2007 and 2012 distort the trends to the extent that they create the illusion of a hiatus where none exists..

Evidence 2 and 3 point, I completely agree,  to a lack of real hiatus, and to disruptions of the Arctic far beyond the summer. There was no hiatus in AGW, and there won’t be in its polar effects.

However, evidence 1 smells to cherry-picking (apologies). I prefer to think on physical factors that are slowing down the decrease of minimum September, such as more difficulty of ocean and atmospheric heat to really affect the CAB for different reasons (bathymetry; snow cover; melting momentum starting well entered the season; thicker ice laying there).

But warming may keep ramping up the suffocating heat and humidity over Fall and Winter, the probable culprit being the more and more heat stored during Summer in the peripheral seas and then released in Oct to Jan, as well as the direct inputs of heat and humidity from the Tropics if the atmospheric circulation is disrupted due polar heat excess.

No me lo trago

gerontocrat

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Re: When will the Arctic Go Ice Free?
« Reply #1237 on: October 12, 2019, 12:48:45 AM »
NSIDC appear to be a bit supportive of a "hiatus" in Arctic Sea Ice Loss.

Who am I, a mere observer to disagree - but I do...

Evidence 1
Let us assume that 2007 & 2012 are outliers - i.e. caused by a combination of climatic occurrences that converged to produce the maximum possible ice loss at that time. If so, it is legitimate to exclude those years from the data.

The result  (see graph attached, that has both sets of data, i.e. with & without 2012 and 2007),
- a far more orderly progression in a downwards direction.
- no real sign of a hiatus
- a slightly better linear trend R2 value.,
- average annual loss reduced by 5k (82 to 77k)

Note well:- all I did was tell the spreadsheet to make the graphs & add the trend lines. No manipulation by yours truly
However, evidence 1 smells to cherry-picking (apologies). I prefer to think on physical factors that are slowing down the decrease of minimum September, such as more difficulty of ocean and atmospheric heat to really affect the CAB for different reasons (bathymetry; snow cover; melting momentum starting well entered the season; thicker ice laying there).

I thought hard before excluding 2007 & 2012 from the data. Nevertheless, I think it is more valid to look at trends in ordinary years - i.e. excluding exaggerated effects. That is my defence - but all we have to do is wait & see (just a few years).
__________________________________________________
EDIT: In early November I will give my open water graphs an airing. They will include the Aug-Sept-Oct averages to give a better view
« Last Edit: October 12, 2019, 12:54:08 AM by gerontocrat »
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oren

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Re: When will the Arctic Go Ice Free?
« Reply #1238 on: October 12, 2019, 12:49:41 AM »
As much as I admire the NSIDC for the important work they do, I think they are erring in their analysis by focusing on:
* Extent, rather than also area, and volume based on modelled and measured thickness.
* Total extent, rather than also regional behavior.
* September, rather than all months. Separately, grouped seasonally, and annually.

Were they to widen their focus, they would find the "hiatus" since 2007 is not cobfirmed by many of the sub-trends.

Juan C. García

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Re: When will the Arctic Go Ice Free?
« Reply #1239 on: October 12, 2019, 12:55:06 AM »
NSIDC appear to be a bit supportive of a "hiatus" in Arctic Sea Ice Loss.

Here is their spiel about it from Oct 3  https://nsidc.org/arcticseaicenews/ (Graph also attached)

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

Who am I, a mere observer to disagree - but I do...

NSIDC should include the author of the monthly analysis. Some times I agree with them. Other times I feel that a denier wrote a statement. Surely there are different people doing this task.
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

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.

gandul

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Re: When will the Arctic Go Ice Free?
« Reply #1240 on: October 12, 2019, 01:04:04 AM »
NSIDC appear to be a bit supportive of a "hiatus" in Arctic Sea Ice Loss.

Who am I, a mere observer to disagree - but I do...

Evidence 1
Let us assume that 2007 & 2012 are outliers - i.e. caused by a combination of climatic occurrences that converged to produce the maximum possible ice loss at that time. If so, it is legitimate to exclude those years from the data.

The result  (see graph attached, that has both sets of data, i.e. with & without 2012 and 2007),
- a far more orderly progression in a downwards direction.
- no real sign of a hiatus
- a slightly better linear trend R2 value.,
- average annual loss reduced by 5k (82 to 77k)

Note well:- all I did was tell the spreadsheet to make the graphs & add the trend lines. No manipulation by yours truly
However, evidence 1 smells to cherry-picking (apologies). I prefer to think on physical factors that are slowing down the decrease of minimum September, such as more difficulty of ocean and atmospheric heat to really affect the CAB for different reasons (bathymetry; snow cover; melting momentum starting well entered the season; thicker ice laying there).

I thought hard before excluding 2007 & 2012 from the data. Nevertheless, I think it is more valid to look at trends in ordinary years - i.e. excluding exaggerated effects. That is my defence - but all we have to do is wait & see (just a few years).
__________________________________________________
EDIT: In early November I will give my open water graphs an airing. They will include the Aug-Sept-Oct averages to give a better view
I’m not saying that you did cherrypick, and I understand your reasons, I just don’t like it for the reasons exposed.
What does not make sense is the NSIDC text saying that they have shown “very little decline” since 2007, when all kinds of statistics show the decline continues at slower but significant pace. I can’t imagine a year rebounding to over 5 millions after 2014, and it was often in the 2000’s.
No me lo trago

Juan C. García

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Re: When will the Arctic Go Ice Free?
« Reply #1241 on: October 12, 2019, 01:06:46 AM »
… but all we have to do is wait & see (just a few years).
I definitely don't like the "wait & see". I am concerned about passing no-return points. If we look at volume, we lost almost 1/3 on 2000-2009 and almost 2/3 on 2010-2019, against the 1979-2000 average.

That is too much!

The 2007, 2012 and 2019 are outliers when you see NSIDC extent figures, but not with PIOMAS volumes. I also don't like monthly averages on extent. 2016 was a terrible year, but because it had an early refreeze, doesn't look that bad. 2017 was also a terrible year looking at volume the whole year. It was just ok around September.

IMO, 2020-2029 will be pretty bad, even if we only have 2 or 3 years like 2012. We don't need a BOE, if Greenland ice and permafrost accelerate their melt.

P.D. Of course, following the events on the ASIF, I am on the "wait & see". But I am becoming more an activist also.
« Last Edit: October 12, 2019, 01:13:14 AM by Juan C. García »
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

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.

gerontocrat

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Re: When will the Arctic Go Ice Free?
« Reply #1242 on: October 12, 2019, 01:17:15 AM »
P.D. Of course, following the events on the ASIF, I am on the "wait & see". But I am becoming more an activist also.
Go for it, Juan!
"Para a Causa do Povo a Luta Continua!"
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Juan C. García

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Re: When will the Arctic Go Ice Free?
« Reply #1243 on: October 12, 2019, 01:44:41 AM »
P.D. Of course, following the events on the ASIF, I am on the "wait & see". But I am becoming more an activist also.
Go for it, Juan!
Instead of tolerate what we cannot change,
we must change what we cannot tolerate
 ;)
(message from one of my daughters).

(back to topic  ;D )
« Last Edit: October 12, 2019, 04:54:33 AM by Juan C. García »
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

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.

Klondike Kat

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Re: When will the Arctic Go Ice Free?
« Reply #1244 on: October 12, 2019, 02:16:43 AM »
NSIDC appear to be a bit supportive of a "hiatus" in Arctic Sea Ice Loss.

Who am I, a mere observer to disagree - but I do...

Evidence 1
Let us assume that 2007 & 2012 are outliers - i.e. caused by a combination of climatic occurrences that converged to produce the maximum possible ice loss at that time. If so, it is legitimate to exclude those years from the data.

The result  (see graph attached, that has both sets of data, i.e. with & without 2012 and 2007),
- a far more orderly progression in a downwards direction.
- no real sign of a hiatus
- a slightly better linear trend R2 value.,
- average annual loss reduced by 5k (82 to 77k)

Note well:- all I did was tell the spreadsheet to make the graphs & add the trend lines. No manipulation by yours truly
However, evidence 1 smells to cherry-picking (apologies). I prefer to think on physical factors that are slowing down the decrease of minimum September, such as more difficulty of ocean and atmospheric heat to really affect the CAB for different reasons (bathymetry; snow cover; melting momentum starting well entered the season; thicker ice laying there).

I thought hard before excluding 2007 & 2012 from the data. Nevertheless, I think it is more valid to look at trends in ordinary years - i.e. excluding exaggerated effects. That is my defence - but all we have to do is wait & see (just a few years).
__________________________________________________
EDIT: In early November I will give my open water graphs an airing. They will include the Aug-Sept-Oct averages to give a better view

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

Klondike Kat

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Re: When will the Arctic Go Ice Free?
« Reply #1245 on: October 12, 2019, 03:40:32 AM »
As much as I admire the NSIDC for the important work they do, I think they are erring in their analysis by focusing on:
* Extent, rather than also area, and volume based on modelled and measured thickness.
* Total extent, rather than also regional behavior.
* September, rather than all months. Separately, grouped seasonally, and annually.

Were they to widen their focus, they would find the "hiatus" since 2007 is not cobfirmed by many of the sub-trends.

NSIDC does look at many other factors.  The September sea ice has gotten the most attention because it has showed the largest decline.  The decline in sea ice minimum was greatest during the decade of the 2000s.  The decline in maximum sea ice has been greatest in the most recent decade.  As far as this thread is concerned, the minimum extent is most relevant.  NSIDC showed that the largest 13-year decline was 200,000 km2/yr.  During the most recent 13-year period, it has been only 1,200 km2/yr.  That is quite the swing, and unlikely due to random variation.

Juan C. García

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Re: When will the Arctic Go Ice Free?
« Reply #1246 on: October 12, 2019, 03:58:49 AM »
Each of the IPCC reports issued this decade has made projections of when the Arctic will be ice free.

AR5 (2013) Chapter 11, page 995
http://www.climatechange2013.org/images/report/WG1AR5_Chapter11_FINAL.pdf

Quote
Though most of the CMIP5 models project a nearly ice-free Arctic (sea ice extent less than 1 × 106 km2 for at least 5 consecutive years) at the end of summer by 2100...

They have avoided the "Discussion", not the projections.

I completely agree with Wherestheice.

After the 2007 and especially the 2012, other institutions changed the forecast of an ice-free Arctic to "before 2050". The IPCC, on their report ended 29 of January of 2016 (even that they started on 2013), instead of discusing when it could happened, they just change the definition of ice-free Arctic! Edit: Maybe I remembered it wrong. I will check this statement and come back.

Adding "...for at least 5 consecutive years" was a very low action coming from the IPCC.
« Last Edit: October 12, 2019, 06:09:08 AM by Juan C. García »
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

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.

philopek

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Re: When will the Arctic Go Ice Free?
« Reply #1247 on: October 12, 2019, 04:04:03 AM »
<Snip> During the most recent 13-year period, it has been only 1,200 km2/yr.  That is quite the swing, and unlikely due to random variation.

It was totally clear what the Gero's message was and there is not much room to see this
differently, but this is not the reason why I reply.

The reason is that you and many others forget that the more the ice retires towards the pole(s) the lesser are a few factors in favour of melt and in the process numbers can indeed show a slow down as far as the REST is concerned:

a) Insolation strength (energy applied)

b) Insolation time related to strength

c) Water temperatures

d) Air temperatures

e) Average ice age

etc. etc.

All this has the effect that it gets harder to melt the reminder and the total ice loss in a given year with a low maximum can be less than in earlier years where we came from much higher down to similar minimums.

I cannot understand how anyone can even seriously discuss whether we're losing ice or not and whether it's slowly or fast.

IT DOES NOT MATTER because even those of you who opt for the slowest supportable way of seeing things will easily see that it's still extremely fast and in fact it does really not matter whether any one of the hurting effects will hit us a bit earlier or later. Most of you will live to see it and our kids and grand kids definitely will, while I and a hand full of others have a tiny chance to dodge that
bullet ;) ;)


Glen Koehler

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Re: When will the Arctic Go Ice Free?
« Reply #1248 on: October 12, 2019, 06:33:47 AM »
All good points philopek, but here is an alternate view:

1) If the 80N+ circle is so much less susceptible to melt then why does that straight line downward trend in ASI volume give such a good fit, with 2019 exactly on target?
https://forum.arctic-sea-ice.net/index.php/topic,119.msg232085.html#msg232085 
        If the remaining most northerly areas are going to decline at a slower rate then that effect bettter kick in soon, because the straight line September minimum volume trend hits zero in 2032, and the August and October volumes only trail September by a few years.  If the 80N+ CAB ice is to be a long term survivor, I would expect that straight line trend to be bending upward by now.  But so far at least, the data do not indicate a rate change in volume decline.
   Similarly, there is no apparent rate change to justify other than a continued straight line trend in the September monthly average volume as charted by Jim Hunt  https://forum.arctic-sea-ice.net/index.php/topic,119.msg232040.html#msg232040

2)  Yes, water temperatures are lower in the icey CAB vs. peripheral seas, but those peripheral sea water temperature anomalies are large and encroaching at an unprecedented rate (as far as I know), e.g. https://forum.arctic-sea-ice.net/index.php/topic,2888.msg232462.html#msg232462
    And with declines in ice coverage of the peripheral seas, the effect of albedo decline to warm surface water during the brief summer edges ever closer to the North Pole.

3)  Observations of jet stream weakening and unusual if not freakish warm fronts crossing the North Pole do not bode well for the future of Arctic thermal isolation.  I confess to not understanding the details of Sark's analysis, e.g.  https://forum.arctic-sea-ice.net/index.php/topic,2692.msg232323.html#msg232323 but his scenario seems include loss of Arctic thermal isolation, and thus even greater polar amplification of warming.  Altered, equable weather patterns could also lead to increased ocean heat transport into the Arctic, which seems to already be happening.  What I understand better is the analysis of Jennifer Francis et al. that Arctic air spillage over my head in eastern North America appears to be increasing.  Which bolsters Sark's view in that if cold air is spilling out of the Arctic, then warmer air from the south must be migrating in to take its place.
     And the Arctic is of course part of the bigger picture.  CO2 & CH4 and other GHG emissions, levels in the atmosphere, and surface warming all continue to increase at essentially the RCP8.5 trajectory.  If the global system temperature was static, then the factors working against melt at 80+N might show up in the ice volume data.  But the global heat reservoir continues to increase, and at an increasing rate.  And the vast majority of that heat ends up in the ocean surface layer, where it can be carried to the high Arctic. 

4) As for average ice age, the Wipneus images at  https://forum.arctic-sea-ice.net/index.php/topic,119.msg232086.html#msg232086
https://forum.arctic-sea-ice.net/index.php/topic,119.msg232040.html#msg232040 show that the CAB ice fortress isn't what it used to be, i.e. it is no longer composed of thick, melt-resistant multi-year ice.  I suspect that the reduction of ice quality and "communal integrity" does not get enough attention.  That may be the factor that tips the balance to overcome lesser insolation at the North Pole. 

     So contrary to a long asymptotic stabilization, I can see just the opposite happening -- an accelerated chaotic ASI system breakdown.  With thinner fractured fresher ice replacing the previous thicker saltier MYI, loss of the Beaufort gyre nursery to replace MYI, currents and wind patterns to which the CAB was previously resistant may be able to cause accelerated CAB pack rotation.  That increased mobility could greatly accelerate export to lower latitude melt zones or out of the Arctic entirely through the Fram Strait.  And now the Nares may be a smaller secondary doorway that also allows greater ice pack mobility. Continued Arctic albedo decline moving northward.  Warm humid air fronts reaching the NP.  Continued Atlantification and Pacification of the Arctic Ocean with escalated SST moving closer to the NP.   

    If this view of the situation is correct, then we could be close to a systemic breakdown of the ASI, or at least a continuation of current trend despite higher latitude for the remaining ice.  We may get insight soon enough - if the the straight-line trend continues, that suggests that the 2012 minimum Sept. volume record has a > 50% chance of being superseded in the next two years.

     There are people much smarter than me who study this for entire careers and their understanding as shown in the IPCC reports etc. does not call for such radical change in the next 13 years. With my superficial understanding, I don't hold too much faith in my own opinion.  I may be spinning a few facts into conceptual storytelling. I really would love to be wrong.

    But I keep coming back to that linear ASI volume graph.  Until I see that trend change, my gut says trust the observations.

     

 
« Last Edit: October 13, 2019, 12:23:13 AM by Glen Koehler »

Juan C. García

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Re: When will the Arctic Go Ice Free?
« Reply #1249 on: October 12, 2019, 07:22:56 PM »
Each of the IPCC reports issued this decade has made projections of when the Arctic will be ice free.

AR5 (2013) Chapter 11, page 995
http://www.climatechange2013.org/images/report/WG1AR5_Chapter11_FINAL.pdf

Quote
Though most of the CMIP5 models project a nearly ice-free Arctic (sea ice extent less than 1 × 106 km2 for at least 5 consecutive years) at the end of summer by 2100...

They have avoided the "Discussion", not the projections.

I completely agree with Wherestheice.
Is the IPCC under-estimating the severity of the ASI trends and AGW in general? I surely can start a topic about this subject, but at this time, let’s just complete the comment that I made yesterday.

The first graph became famous from the first version, back to February or March 2007 (before the melting season that we suffered that year, so the under-estimating of the IPCC models is more obvious after the melting season!!!). This is a 2012 version.

The second graph comes from the US National Climate Assessment 2014. I like the conclusion: “Extrapolation of the present observed trend suggests an essentially ice-free Arctic in summer before mid-century”. I also agree that the standard definition of ice-free Arctic is “less than one million square kilometers”, even that I would prefer other definitions based on area or volume, not extent and not monthly average (NSIDC standard).

But the IPCC didn’t include this graph on the WG1AR5 report, as far as I know. Instead, they included other graphs less clear (Graph 3 and Image 4). And from my point of view, the chances that we have pass the point of no-return on having an ice-free Arctic are big, regardless of the IPCC greenhouse gases emission scenarios. Finally, they add the "...for at least 5 consecutive years" to the definition, that I certainly don’t agree. I also believe that this definition change should not have a scientific consensus. I believe some people in the IPCC report included this definition, trying to avoid the real scientific discussion.
« Last Edit: October 12, 2019, 09:03:01 PM by Juan C. García »
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

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.