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Author Topic: Arctic sea ice changes: Natural variation vs human influence  (Read 23363 times)

AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #100 on: March 23, 2017, 10:29:05 AM »
Back on-topic to the discussion of the Ding et al paper, I would like to point to an excellent rebuke of the Ding paper on a scientific basis, written by Rob Dekker in a long comment on the Stoat blog, which you all can find here:
http://scienceblogs.com/stoat/2017/03/15/influence-of-high-latitude-atmospheric-circulation-changes-on-summertime-arctic-sea-ice/#comment-58495
Here is Rob's conclusion, with which I agree 100%:
That would have been a fine conclusion, but is completely different from their conclusion that “summertime atmospheric circulation” may have contributed as much as 60% to the September sea-ice extent decline since 1979.
It’s not “summertime atmospheric circulation” that caused it; it is “summertime climate change (with ALL the variables, including temperature) being the cause. And with AGW being real, we know that temperature for one is NOT a natural variability variable.

So Ding et al 2017 made the ASSUMPTION that the temperature TREND in the Arctic is part of natural variability and they base their conclusions on that.

Needless to say that that assumption (in a warming world) is quite preposterous, and I wonder what the authors were thinking when they drew their conclusions.

(emphasis mine)

(btw, I just noticed that Rob Dekker is also a registered ASIF member, I hope he can (re-)post his rebuke in this thread)

And Rob, since you asked this question "I wonder what the authors were thinking when they drew their conclusions(?)", my answer is that they already had the preposterous claim that the disappearance of sea ice is up to 50% due to natural variability in mind, and just found the models and performed the simulations (which they call "experiments") that would somehow support their a priori conclusion.

Also, if I may add, it is a well-known fact here at ASIF, that the weather (natural variability) during the months of June-July-August is a determining factor in how low September ice extent will go. But that in no way is the correct attribution for the year-round exponential decrease TREND in Arctic sea ice volume, which we can observe since the beginning of satellite records, as evidenced by this excellent chart:
« Last Edit: March 25, 2017, 07:25:44 AM by AndrewB »

ktonine

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #101 on: March 23, 2017, 05:30:09 PM »
And Rob, since you asked this question "I wonder what the authors were thinking when they drew their conclusions(?)", my answer is that they already had the preposterous claim that the disappearance of sea ice is mostly due to natural variability in mind, and just found the models and performed the simulations (which they call "experiments") that would somehow justify their a priori conclusion.

AndrewB - did you bother to read Eric Steig's comment at Stoat's?  What is with this constant character assassination of climate scientists in these threads lately?  I feel like I'm at WUWT.

So, we have a peer-reviewed paper by a plethora of well-respected and leading climate scientists that challenge your beliefs.  OTOH we have a few paragraphs by a non-scientist on a blog.  Occam's razor would lead you to believe the non-scientist's blog post is correct.  Good grief, Charlie Brown.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #102 on: March 23, 2017, 06:05:33 PM »
And Rob, since you asked this question "I wonder what the authors were thinking when they drew their conclusions(?)", my answer is that they already had the preposterous claim that the disappearance of sea ice is mostly due to natural variability in mind, and just found the models and performed the simulations (which they call "experiments") that would somehow justify their a priori conclusion.

AndrewB - did you bother to read Eric Steig's comment at Stoat's?  What is with this constant character assassination of climate scientists in these threads lately?  I feel like I'm at WUWT.

So, we have a peer-reviewed paper by a plethora of well-respected and leading climate scientists that challenge your beliefs.  OTOH we have a few paragraphs by a non-scientist on a blog.  Occam's razor would lead you to believe the non-scientist's blog post is correct.  Good grief, Charlie Brown.
Careful how you apply that razor - it may be cutting things you want to keep. You've used an ad hominem argument against an ad hominem statement.

Criticism from non-professionals is still relevant when well founded.  The correct take on this should be, how well supported is the critique, and does it raise reasonable questions?

Pertinent to the first statement - a conclusion against paradigm does not necessarily establish any fact regarding the person (s) making it.  Who wrote a paper is fairly irrelevant.  What is relevant is its content.

That is what should be under discussion, not personalities.
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Archimid

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #103 on: March 23, 2017, 06:55:30 PM »
Yep. I agree with jdallen. Who wrote it or on what medium does not matter. The only thing that matter is the content. Most of the content of the paper in question is scientifically valid but there are large claims whose validity was not demonstrated but assumed.

Extraordinary claims require extraordinary evidence. Claiming that atmospheric variation is natural is an extraordinary claim. Common sense dictates that there are both natural and anthropogenic elements to atmospheric variation. Good science would quantify how much of the atmospheric variation is anthropogenic and how much is natural.Then they can make correct attributions.
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Archimid

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #104 on: March 23, 2017, 07:34:30 PM »

Looks to mirror the overall pattern for extent loss.  A faster period after 2000, and then a slower period in the last 5 or so years. 

I think there is more to it that meets the ice. The first image is that of maximum volume and minimum volume. I would call to your attention that for 2017 the record max volume is very likely to be quite a bit lower than the record minimum. If that comes true that reinforces the downward trend.


I would agree with you that after 2007 something changed.

I took Max Volume - Min Volume as the volume lost in a year and Min Volume - Max Volume of the following year as the volume gained in a year. Those are the 2nd and 3rd charts.

I  think the most interesting of those graphs is the volume gain, which shows a side effect of the phenomenon you and Tamino are pointing at. After 2007 the arctic started creating much more ice every year than before.

Here are the stats for the whole data set, for 1980-2006 and for 2007-2016

AvgVolGain       16.59010811
MedianVolGain      16.455
MaxVolGain      19.659
MinVolGain      14.709
Variance      1.373940821
      
AvgVolGain 1980-2006      16.13581481
MedianVolGain  1980-2006      16.3
MaxVolGain  1980-2006      17.62
MinVolGain  1980-2006      14.709
Variance 1980-2006      0.519474464
      
AvgVolGain  2007-2016      17.8167
MedianVolGain 2007-2016      17.864
MaxVolGain 2007-2016      19.659
MinVolGain 2007-2016      14.872
Variance 2007-2016      1.704214678


Both the average and median after 2007 are higher than the max before 2007 with twice as much variance. Something certainly changed. The Arctic is making much more ice than before because there is a lot less old ice. That making of ice is what Tamino, the slow transition and others are pointing at as the savior of the ice.

But here is the thing. The more ice the arctic makes each year the higher temperatures become. The more ice the arctic makes the more fdd's go into making ice instead of showing up as a colder atmosphere. The inevitable result of higher temperatures is that less ice is made. Heat keeps being added to the system due to CO2, lower albedo for longer and changes in the atmospheric current that bring even more water into the system. This is likely to get worse before it gets better.


Which brings me back to Ding et al. Did they rule out whether causation goes the other way? Changes in the ice causes changes in the atmospheric circulations?




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Steven

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #105 on: March 23, 2017, 07:47:41 PM »
my answer is that they already had the preposterous claim that the disappearance of sea ice is mostly due to natural variability in mind, and just found the models and performed the simulations (which they call "experiments") that would somehow justify their a priori conclusion.


You are misrepresenting the Ding et al. paper.  They never claimed that the disappearance of sea ice is mostly due to natural variability.  Quote from the abstract:

Internal variability dominates the Arctic summer circulation trend and may be
responsible for about 30–50% of the overall decline in September sea ice since 1979.


http://www.atmos.washington.edu/~david/Ding_etal_inpress_2017.pdf

Steven

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #106 on: March 23, 2017, 07:54:35 PM »
Claiming that atmospheric variation is natural is an extraordinary claim. Common sense dictates that there are both natural and anthropogenic elements to atmospheric variation. Good science would quantify how much of the atmospheric variation is anthropogenic and how much is natural.Then they can make correct attributions.

Again, this is addressed in the paper.  Ding et al. estimate that:

(1) about 60% of the September Arctic sea-ice extent decline since 1979 is caused by trends in summertime atmospheric circulation. 
(2) about 70% of those atmospheric circulation trends is caused by internal variability (and hence the remaining 30% is anthropogenic). 

Combining those two estimates, they get:

we estimate that about
~42% (70% × 60%) of the sea-ice decline observed since 1979 in
September is due to internal variability.
« Last Edit: March 23, 2017, 08:01:50 PM by Steven »

Neven

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #107 on: March 23, 2017, 07:57:29 PM »
So when can we expect this natural variability to flip back again and see a reduction in the rate of Arctic sea ice loss?
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jai mitchell

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #108 on: March 23, 2017, 08:17:39 PM »
So when can we expect this natural variability to flip back again and see a reduction in the rate of Arctic sea ice loss?


guess we will just have to . . .wait. . .and. . .see. . . . .. . . . . . . . . .. . .. . .  .. .. . .
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AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #109 on: March 23, 2017, 08:27:15 PM »
...
You are misrepresenting the Ding et al. paper.  They never claimed that the disappearance of sea ice is mostly due to natural variability.
...

From the abstract, in both the submitted and published versions:

Our experiments indicate that the circulation trend may have contributed as much as 60% to the decline of the September sea ice extent minimum since 1979.

From the conclusion in the final submitted version:

The forcing of the summer sea ice by the trends in large-scale circulation, which are likely due mostly to natural variability, represents an important driver of the observed Arctic climate change.
(emphasis on the word 'mostly' mine)

That last phrase was completely removed in the published version of the paper.


magnamentis

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #110 on: March 23, 2017, 08:36:52 PM »
at times it's trouble some to discuss things that seem obvious just because there are people how try to stand out by opposing anything that is based on common sense and try to land a lucky punch that way with a chance to boost their carrier. it wouldn't matter so much if it would not cost us time and energy that would be essential to be used to find solutions, workarounds and damage minimization instead of fighting the trolls.

that said, why did i say that:

a) the speed of warming without obvious natural cause leaves little to no room to believe it's natural  (at least not mainly)

b) the correlation between the development of our climate to the warmer side with the level of civilization, industrialization and wealth ( use of energy consuming technology and comfort tools) leaves no to little room
to assume that the warming at the current speed and exactly during the given period is naturally caused, again at least not mainly,

i' know it's bold and somehow not correct to say so but i think there always is a point where certain discussions and/or doubts should simply be banned due to be provenly wrong.

this what we are facing here is obviously mainly man-made and any energy that goes into convincing the always yesterday people should be gathered for productive thoughs and action instead.

[rant end LOL]
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Archimid

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #111 on: March 23, 2017, 11:12:11 PM »

Again, this is addressed in the paper.  Ding et al. estimate that:

(1) about 60% of the September Arctic sea-ice extent decline since 1979 is caused by trends in summertime atmospheric circulation. 
(2) about 70% of those atmospheric circulation trends is caused by internal variability (and hence the remaining 30% is anthropogenic). 

Combining those two estimates, they get:

we estimate that about
~42% (70% × 60%) of the sea-ice decline observed since 1979 in
September is due to internal variability.



I don't contend anything in the paper except the attribution to "natural variability" vs anthropogenic. I think my problem is on Page 10 line 222 of this version:http://www.atmos.washington.edu/~david/Ding_etal_inpress_2017.pdf

Second, to estimate the anthropogenic contribution to the observed warming and sea ice reduction in the Arctic, two additional experiments are conducted. Exp-7 and 8 are equivalent to the Exp-2 but we remove the effects of global warming on the high latitude winds, which are used to constrain the model in Exp-2 .


I would love to see how they define the "effects of global warming". Is it just CO2 and Methane or  are albedo changes, glacier changes, sea temperature changes or any secondary effect of CO2 induced warming included? What about non GHG human forcings like deforestation, industrial gases, heat island effects, air travel, do they account for those?

 I tried to dig deeper but this is what I find on  EXP-7

Same as Exp-2, except that ECHAM5 is nudged to a modified observed wind patterns in which the long term trends of simulated winds (zonal and meridional winds) in the ensemble mean (26 members) of CMIP5 during 1979 to 2014 are removed from observation.

 
So they removed the trends and what remains is the natural variability?

Let's dig deeper, what is experiment 2?

>Same as Exp1, except that a simple slab ocean/sea ice model is used in the Arctic, north
445 of 60ºN.

A simple slab?  I understand the computational limitations, and I further understand that insight can be gained even with gross simplifications.  But if you are going to attribute changes of sea ice I hope that slab is not as simple as it sounds simple.

So on to Exp1

Because we are interested in the impact of the long-term trend of the observed circulation in our model simulations, and to facilitate our computation efforts, we interpolate observed monthly ERA-I data to daily fields for nudging. We use a very weak damping term to nudge the 3-D (from surface to the top of atmosphere) divergence and vorticity fields of the model to the observed monthly (smoothly interpolated to daily) fields in the last 36 years; this weak damping allows the model to generate its own day-to-day variability but constrains the model to be very close to the observed circulation on monthly and longer time scales. In the lower boundary, we impose climatological SST/sea ice everywhere. Anthropogenic forcings are held constant in this experiment.



I wonder what forcings they include as anthropogenic forcings. I also wonder what they mean by holding them constant.
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Michael Hauber

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #112 on: March 24, 2017, 12:39:32 AM »
So when can we expect this natural variability to flip back again and see a reduction in the rate of Arctic sea ice loss?

Five years ago.

Or maybe not.  We'll see.....
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #113 on: March 24, 2017, 03:29:52 AM »
So when can we expect this natural variability to flip back again and see a reduction in the rate of Arctic sea ice loss?

Well, with 'business as usual' (or just a minor methane burp) we could see global mean wet bulb temperatures cross human body core temperatures for a few days a year.  That will tidy up most warm blooded animals, including the chief operators of anthropogenic CO2 emitting systems.

Then, with no further non-natural emissions, we (sorry, 'Gaia', we will be gone) then Gaia is left to break down methane and draw down CO2 by natural processes, until CO2 'flips back again' to pre-Anthropocene levels. 

So - when?  In a few million years.  And of our 'civilisation'?  A thin stain in a strata of rocks and a peculiar level of background radiation as 50,000 tonnes of reactor fuel plumed into the atmosphere from 500 out of control nuke power plants whose deceased operators had stopped twiddling the knobs.

(Sorry, OT, but you did ask!)

epiphyte

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #114 on: March 24, 2017, 04:23:55 AM »
So when can we expect this natural variability to flip back again and see a reduction in the rate of Arctic sea ice loss?

Well, with 'business as usual' (or just a minor methane burp) we could see global mean wet bulb temperatures cross human body core temperatures for a few days a year.  That will tidy up most warm blooded animals, including the chief operators of anthropogenic CO2 emitting systems.

Then, with no further non-natural emissions, we (sorry, 'Gaia', we will be gone) then Gaia is left to break down methane and draw down CO2 by natural processes, until CO2 'flips back again' to pre-Anthropocene levels. 

So - when?  In a few million years.  And of our 'civilisation'?  A thin stain in a strata of rocks and a peculiar level of background radiation as 50,000 tonnes of reactor fuel plumed into the atmosphere from 500 out of control nuke power plants whose deceased operators had stopped twiddling the knobs.

(Sorry, OT, but you did ask!)

Can't remember who wrote it, but when I was a kid I read a science fiction story about a time traveler who came to a sticky end when he went back to find out what happened to the dinosaurs. only to discover that the velociraptors all had guns, and were gearing up for a nuclear war.

I wonder if they would have been skeptical about the possibility of Sauriogenic global cooling (!)

Rob Dekker

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #115 on: March 24, 2017, 05:36:19 AM »
Andrew, thank you for guiding me to this thread in ASIF about Ding et al 2017.

I looked in detail at the science of the paper, and discovered that it does not sustain the conclusions. Not at all. There simply is no evidence in the (methods and experiments of the) paper that ANY "internal variability" played ANY role in "the overall decline in September sea ice since 1979" as the paper asserts in the abstract.

I have attempted to explain the problems in the paper on several posts on William Connolley's "stoat" site, with the most detailed technical analysis here :
http://scienceblogs.com/stoat/2017/03/15/influence-of-high-latitude-atmospheric-circulation-changes-on-summertime-arctic-sea-ice/#comment-58495

Now that comment was pretty technical, so I've posted a new comment that tries to explain the problem in simpler terms :

From the abstract we read “trends in summertime atmospheric circulation may have contributed as much as 60% to the September sea-ice extent decline since 1979”.

However, that is NOT what the paper’s methods show.

For starters, in the methods (model experiments) “atmospheric circulation” variable is represented by “geopotential height” over the Arctic summer, specifically Z200 (geopotential height at 200 mb). So the correct conclusion would be “trends in summertime geopotential height may have contributed as much as 60% to the September sea-ice extent decline since 1979”.

With that conclusion, you can feel the correlation-versus-causation issue coming up : Arctic temperature increase (due to AGW) may be the cause of or geopotential height increase.
And consequently you can no longer claim that the (up) trend in both variables is a source of “internal variability”.

And thus the final conclusion (that “Internal variability dominates the Arctic summer circulation trend and may be responsible for about 30–50% of the overall decline in September sea ice since 1979”) no longer holds.


I'd invite anyone here to challenge my findings, but please use the paper's technical information as arguments. If I'm correct, then the paper is scientifically deceiving, and the way in which this deception is done is not unlike what I've seen in papers from Richard Lindzen and Willie Soon.
But since this paper has names like Alex Schweiger and Eric Steig (both of whom I greatly respect) on it, I wonder how much these guys were involved. I hope not much.

In summary : Ding et al 2017 does NOT provide ANY evidence of ANY influence of "internal variability" on Arctic sea ice decline since 1979.

So we are still stuck with the ONE long term cause for Arctic sea ice decline : AGW.
« Last Edit: March 24, 2017, 06:28:13 AM by Rob Dekker »

AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #116 on: March 24, 2017, 06:47:15 AM »
Thank you Rob for your brilliant dissection of the Ding et al paper. We are still waiting for any of the authors to manifest themselves and respond to your sharp criticism or any of the other questions raised by their scientifically questionable and evidence-defying "natural climate variability" attribution for Arctic sea ice decline, here on ASIF or on the Stoat blog comments section.

Meanwhile, 2017 just saw the lowest maximum Arctic sea ice extent on record, 2016 was the third hottest year on record in a row and 1.1C above pre-industrial, and atmospheric CO2 concentration has passed the 405ppm threshold, 125ppm above pre-industrial and probably the highest it has been in over 1 million years. And 25% of the world's corals died last year.
« Last Edit: March 24, 2017, 07:00:28 AM by AndrewB »

ktonine

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #117 on: March 24, 2017, 07:00:51 AM »
So they removed the trends and what remains is the natural variability?

Let's dig deeper, what is experiment 2?

>Same as Exp1, except that a simple slab ocean/sea ice model is used in the Arctic, north
445 of 60ºN.

A simple slab?  I understand the computational limitations, and I further understand that insight can be gained even with gross simplifications.  But if you are going to attribute changes of sea ice I hope that slab is not as simple as it sounds simple.

The above criticism is nonsense. 

The general circulation model used to perform the experiments (Exps-1 to 4,7 and 8 ) in this study is the ECHAM5 atmospheric general circulation model,with a horizontal resolution of T42 (∼2.8◦latitude ×2.8◦longitude) and 19 vertical levels. In Exps-2, 3, 7 and 8, we coupled the ECHAM5 to a slab ocean in the high latitudes to assess the role of prescribed circulation in driving the SST and sea ice in the Arctic.

They are using an *atmospheric circulation model* to assess atmospheric circulation and only tying it to an ocean module when they want to see the near surface effects on SSTs (top 50 meters). If you believe this is insufficient, then perhaps you should cite from the peer-reviewed literature *why* it is insufficient.

AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #118 on: March 24, 2017, 07:23:32 AM »
...
They are using an *atmospheric circulation model* to assess atmospheric circulation and only tying it to an ocean module when they want to see the near surface effects on SSTs (top 50 meters).
...
Of course they are using an (obsoleted version of an) atmospheric circulation model (ECHAM5). Because they want to show that the decline in Arctic sea ice in September is mostly due to atmospheric circulation variability in the Arctic in June-July-August, which they then attribute to "natural climate variability".

In other words, Ding et al are using the specific model that best supports the conclusion they want to reach.

Why don't they use the specific Arctic sea ice model from the Max Planck Institute for Meteorology? Why don't they quantify the skill of the models they use, and compare them to other models for Arctic sea ice? https://en.wikipedia.org/wiki/Forecast_skill

« Last Edit: March 24, 2017, 02:38:19 PM by AndrewB »

Archimid

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #119 on: March 24, 2017, 12:38:48 PM »


The above criticism is nonsense. 



It may be. This paper is way above me as I do not know the intricacies of the models used, but is so contrarian to everything else I know that I must do what I can to either confirm it or deny it for my own peace of mind. So far the small part I understand from the paper tell me that the "natural variation" claim is BS. Other more knowledgeable members have provided good arguments to confirm that.

They are using an *atmospheric circulation model* to assess atmospheric circulation and only tying it to an ocean module when they want to see the near surface effects on SSTs (top 50 meters). If you believe this is insufficient, then perhaps you should cite from the peer-reviewed literature *why* it is insufficient.

I'm sure a simplification of the ocean/atmosphere interaction is sufficient for many applications. But in a paper examining cause and effect of arctic sea ice and a paper that attempts to quantify the attribution of the changes in sea ice using such a simplification is very suspicious.

I am an energy reservoir seemingly intent on lowering entropy for self preservation.

ktonine

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #120 on: March 24, 2017, 02:38:11 PM »

Of course they are using an (obsoleted version of an) atmospheric circulation model (ECHAM5). Because they want to show that the decline in Arctic sea ice in September is mostly due to atmospheric circulation variability in the Arctic in June-July-August, which they then attribute to "natural climate variability".

In other words, Ding et al are using the specific model that best supports the conclusion they want to reach.


Basically slander.  This belongs on the pages of WUWT. 

Zero evidence for,"... they *want* to show...."
Zero evidence for, "using the specific model that best supports the conclusion they want to reach..."

It's really become sad that this forum has degenerated into nothing but an analogue to WUWT comments - just with a different perspective.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #121 on: March 24, 2017, 02:53:51 PM »
The whole forum? Or just one (or a couple) out of 1200+ members?
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AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #122 on: March 24, 2017, 02:54:11 PM »
...
Zero evidence for,"... they *want* to show...."
Zero evidence for, "using the specific model that best supports the conclusion they want to reach..."
...

From the Ding et al paper:

In this paper we examine the contribution of the atmospheric circulation to Arctic sea ice variability by utilizing an atmospheric general circulation model (ECHAM5) in which the circulation field is nudged to observations.

And further down:

How sea ice variability and trends can impact the Arctic atmospheric circulation is an area of vigorous research. Studies suggest numerous mechanisms in which sea ice loss modulates the large-scale circulation in the lower troposphere in winter. This paper, instead, focuses on how the high-latitude circulation impacts sea ice.
(emphasis mine)


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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #123 on: March 24, 2017, 03:00:47 PM »
Please remember:--

Occam's razor
KISS (Keep It Simple, Stupid!)

Ding et al 2017 have blinded me with science (I am not competent to judge their methods) and just leave me trying to decide whether there is truth in their summary.
By Occam's razor, earlier forcasts that predicted climate change as a result of increased CO2 (especially in polar regions) appear to coming true, so extra complicated models with all manner of caveats just serve to confuse (or encourage cherry-picking?) and are not necessary.
As people see it, it will come down to "60% natural variability (+40% human influence?)" versus "human influence" - there is a common factor if it is mentioned!
KISS!

ktonine

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #124 on: March 24, 2017, 03:04:32 PM »
The whole forum? Or just one (or a couple) out of 1200+ members?

Unfortunately, I'd say a growing number.  And what we also witness is the herd mentality where those who make such asinine statements are not called out by others.  I.e., I don't like the paper results either so I won't bother to chastise him for being an idiot about it - or some such logic.

The first rule of Dunning-Kruger is if you think an expert is wrong, you probably don't understand something.  Do we want to count the dozens - possibly hundreds - of climate papers the authors of Ding et al have been part of?

Have we forgotten Tietsche et al already?  Just because you don't like a result doesn't mean it's incorrect.   The paper may be fatally flawed, but if it is it will be much more subtle than anything dreamed up here.  The idea that simple errors were missed by the authors or the peer-reviewers is rather hard to swallow given the conclusion. 

Jim Williams

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #125 on: March 24, 2017, 03:22:04 PM »
Please remember:--

Occam's razor
KISS (Keep It Simple, Stupid!)

Ding et al 2017 have blinded me with science (I am not competent to judge their methods) and just leave me trying to decide whether there is truth in their summary.
By Occam's razor, earlier forcasts that predicted climate change as a result of increased CO2 (especially in polar regions) appear to coming true, so extra complicated models with all manner of caveats just serve to confuse (or encourage cherry-picking?) and are not necessary.
As people see it, it will come down to "60% natural variability (+40% human influence?)" versus "human influence" - there is a common factor if it is mentioned!
KISS!
Actually, I think that is more in keeping with the definition of a prophet (one who only makes predictions which turn out to come to pass), but I have to agree that we ought to pay more attention to those who warned us that CO2 would cause the the air to warm than to those who stir the pot and say it wasn't so much the CO2.

Occam's razor, though stated in several forms, is more along the lines of: don't suggest more entities (causes) than you need to to explain the data.

ktonine

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #126 on: March 24, 2017, 03:25:52 PM »
...
Zero evidence for,"... they *want* to show...."
Zero evidence for, "using the specific model that best supports the conclusion they want to reach..."
...

From the Ding et al paper:

In this paper we examine the contribution of the atmospheric circulation to Arctic sea ice variability by utilizing an atmospheric general circulation model (ECHAM5) in which the circulation field is nudged to observations.

And further down:

How sea ice variability and trends can impact the Arctic atmospheric circulation is an area of vigorous research. Studies suggest numerous mechanisms in which sea ice loss modulates the large-scale circulation in the lower troposphere in winter. This paper, instead, focuses on how the high-latitude circulation impacts sea ice.
(emphasis mine)

And here is the word *WANT* AndrewB ???  You said they wanted to reach a certain conclusion.  That's scientific fraud.  You said they chose the model that would give them the result they *WANTED*. 

Go tell these scientists they rigged the results to get the conclusion they wanted.

Qinghua Ding
Axel Schweiger.
Stephen Po-Chedley.
Eric Steig.
Michelle L'Heureux.
David Battisti.
Nathaniel C. Johnson.
Eduardo Blanchard Wrigglesworth.
Qin Zhang.
Kirstin Harnos.
Ryan Eastman.

Do you even recognize these names?  Do you know just who it is you're accusing?  You're a nut.  The analog to the typical commenter at WUWT.

AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #127 on: March 24, 2017, 03:41:49 PM »
...
Go tell these scientists they rigged the results to get the conclusion they wanted.
...

I never wrote "they rigged the results to get the conclusion they wanted." I wrote, and confirm that I meant exactly that, Ding et al chose the models to support the conclusion that they wanted to arrive at.

You are suggesting that they didn't, in other words you are suggesting that they randomly chose some climate models, ran their simulations, and then were collectively surprised to find out that "atmospheric circulation" in the months of June-July-August shows a high correlation with Arctic sea ice extent in September, in their simulation runs.

Archimid

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #128 on: March 24, 2017, 03:43:38 PM »

Of course they are using an (obsoleted version of an) atmospheric circulation model (ECHAM5). Because they want to show that the decline in Arctic sea ice in September is mostly due to atmospheric circulation variability in the Arctic in June-July-August, which they then attribute to "natural climate variability".

In other words, Ding et al are using the specific model that best supports the conclusion they want to reach.


Basically slander.  This belongs on the pages of WUWT. 

Zero evidence for,"... they *want* to show...."
Zero evidence for, "using the specific model that best supports the conclusion they want to reach..."

It's really become sad that this forum has degenerated into nothing but an analogue to WUWT comments - just with a different perspective.


Funny how I see something entirely different. I see several people taking a stab at the science and trying to get to the bottom of this extraordinary claim.

For example Rob Dekker's claim:

For starters, in the methods (model experiments) “atmospheric circulation” variable is represented by “geopotential height” over the Arctic summer, specifically Z200 (geopotential height at 200 mb). So the correct conclusion would be “trends in summertime geopotential height may have contributed as much as 60% to the September sea-ice extent decline since 1979”.

I can certainly agree that conclusion. I think is a good scientific conclusion with dire implications. However that's where science ends.  The authors take the attribution a step further without providing any evidence . They conflate  the trends of geopotential heights and winds to "natural variability".

May I recommend that instead of engaging in ad hominems and appeals to authority yourself you explain how values for pressure and wind used in this experiment are free of anthropogenic influence? Maybe answering Neven's question, "when is this cycle turning around?" would yield better results.


Forget about the authors. Let's talk about the content.

I am an energy reservoir seemingly intent on lowering entropy for self preservation.

ktonine

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #129 on: March 24, 2017, 03:55:14 PM »
I never wrote "they rigged the results to get the conclusion they wanted." I wrote, and confirm that I meant exactly that, Ding et al chose the models to support the conclusion that they wanted to arrive at.

How is that substantively different than rigging the results?  And you reinforce my point about a conclusion they *wanted* -- but you have zero evidence for either claim, both of which are essentially academic malfeasance or scientific fraud.

Don't worry, Archimid will pat you on the back.

You *don't* know who these authors are, do you?  LOL.

Axel Schweiger - PIOMAS

Neven

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #130 on: March 24, 2017, 04:00:44 PM »
Okay, enough now. ktonine has a point that we should try not to imply malfeasance or ignorance on the part of scientists. At the same time this paper was spinned by the people who wrote the press release or whatever, and this was then spinned further by those who have nothing to offer but spin. So, it's understandable that people are upset by this.

Either way, back to content. Or just let this fizzle out, as it doesn't mean all that much in the big picture. But let's not fight over this.
Il faut cultiver notre jardin

Archimid

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #131 on: March 24, 2017, 04:09:05 PM »

Don't worry, Archimid will pat you on the back.


**Archimid pats AndrewB's back**

Let's do it buddy, truth is on our side.

You *don't* know who these authors are, do you?  LOL.

No, and I don't care. I only care about the truth in their science. Do you realize that your argument is appeal to authority? That might work with Trump or the WUWT community, but it doesn't work for me. I only care about the message, not the messenger or the medium for the message.

Let's get back to science shall we? Help me get rid of my ignorance. How and why trends in geopotential heights equal "natural variability"?
I am an energy reservoir seemingly intent on lowering entropy for self preservation.

Archimid

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #132 on: March 24, 2017, 04:26:13 PM »
Okay, enough now. ktonine has a point that we should try not to imply malfeasance or ignorance on the part of scientists.

I agree with malfeasance. However, isn't the purpose of science to eradicate ignorance? It is ok to not know. Science is the mechanism to cure not knowing.

At the same time this paper was spinned by the people who wrote the press release or whatever, and this was then spinned further by those who have nothing to offer but spin. So, it's understandable that people are upset by this.

I couldn't agree more. I think this was blown out a proportions by a malicious use of "natural variation" implying that the reduction of the sea ice is mostly not anthropogenic. Do a search in the document for "natural variation". Is not even there. The 60% attribution to natural variation  was the spin the media gave it.


But the document does use language loosely and can very easily be interpreted as what the media portrays.


This will be my last post on this topic, unless meaningful discussion resumes.
I am an energy reservoir seemingly intent on lowering entropy for self preservation.

ktonine

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #133 on: March 24, 2017, 04:31:51 PM »
I only care about the truth in their science. Do you realize that your argument is appeal to authority? That might work with Trump or the WUWT community, but it doesn't work for me. I only care about the message, not the messenger or the medium for the message.

Let's get back to science shall we? Help me get rid of my ignorance. How and why trends in geopotential heights equal "natural variability"?

Dunning - Kruger.  If you believe that an expert opinion in a field is the same as a random blog comment, then you are insane.

From Ding et al,

Regressing the domain-averaged sea-ice anomaly time series against the JJA geopotential height at 200 hPa (Z200) in ERA-I, we find that decreasing sea ice is accompanied by increasing Z200, withmaximum amplitude over Greenland (Supplementary Fig. 1).

These same interrelationships between the trends in the indices of JJA Z200, temperature, water vapour, DLR and September sea-ice concentration are also apparent using detrended indices: an Arctic summer with higher than normal Z200 over Greenland,greater DLR at the surface, and increased low-level water vapour and temperature over the Arctic is followed by negative sea-ice anomalies in September (Fig. 1c); for example, detrended indices of temperature and specific humidity are correlated atr = 0.89; detrended indices of sea-ice concentration and DLR are correlated at r = −0.75. Importantly, the detrended data shows that the summertime anomalies in the indices of near-surface temperature, DLR, and water vapour are simultaneously associated with a common pattern of atmospheric circulation variability (seeFig. 1d–g), and that this circulation pattern is very similar to the circulation pattern that is associated with the sea-ice interannual variability in September (see Fig. 1d–g). These correlation maps also compare well with the p an-Arctic Z200 and surface wind trends inJJA (Fig. 1b), which feature a strong high over northeastern Canada,Greenland, and t he Arctic Ocean.

I suggest you read the paper.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #134 on: March 24, 2017, 04:38:33 PM »
Dunning - Kruger.  If you believe that an expert opinion in a field is the same as a random blog comment, then you are insane.

...

I suggest you read the paper.

A reminder from way back about half-an-hour ago:

Okay, enough now. ktonine has a point that we should try not to imply malfeasance or ignorance on the part of scientists. At the same time this paper was spinned by the people who wrote the press release or whatever, and this was then spinned further by those who have nothing to offer but spin. So, it's understandable that people are upset by this.

Either way, back to content. Or just let this fizzle out, as it doesn't mean all that much in the big picture. But let's not fight over this.

Thanks!

AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #135 on: March 24, 2017, 04:41:34 PM »
...
Either way, back to content. Or just let this fizzle out, as it doesn't mean all that much in the big picture. But let's not fight over this.

Neven, I am not quite sure what to make of what you just wrote here, so please help me out here.
  • Are we ignoramuses just supposed to shut up unless we agree with every word in the Ding et al paper?
  • Should we kowtow every time the name of one of the eleven co-authors is mentioned?
  • Or should we just go about our own lives, because the Ding et al paper is just an insignificant bit of bad science, not worth spending our precious internet time on?
;)
(I hope a little bit of humor is allowed in this thread, to lighten up the atmospheric circulation mood)

« Last Edit: March 24, 2017, 05:00:14 PM by AndrewB »

AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #136 on: March 24, 2017, 04:47:23 PM »

**Archimid pats AndrewB's back**


**AndrewB thanks Archimid and pats Archimid's back back**

 :)

...
Do a search in the document for "natural variation". Is not even there. The 60% attribution to natural variation  was the spin the media gave it.
...

Ding et al don't use the expression "natural variation". They use, abundantly and at different times, either "natural variability", "natural climate variability" or "internal variability" to signify non-anthropogenic forcing.

The 30~50% attribution is found in the abstract:
"Internal variability dominates the Arctic summer circulation trend and may be responsible for about 30-50% of the overall decline in September sea ice since 1979."
« Last Edit: March 24, 2017, 07:55:05 PM by AndrewB »

Archimid

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #137 on: March 24, 2017, 05:09:00 PM »
Sorry Neven, I feel like I must answer this, including the ad hominem.


Dunning - Kruger.  If you believe that an expert opinion in a field is the same as a random blog comment, then you are insane.

If you believe that experts are always correct you are also insane. As I said, I judge what I read by the content not by the messenger or medium. I value expert opinion very highly, but not blindly. I also value peer reviewed publications over all other forms of publications.

From Ding et al,

Importantly, the detrended data shows that the summertime anomalies in the indices of near-surface temperature, DLR, and water vapour are simultaneously associated with a common pattern of atmospheric circulation variability (seeFig. 1d–g), and that this circulation pattern is very similar to the circulation pattern that is associated with the sea-ice interannual variability in September (see Fig. 1d–g).


I do not contend that is false. It makes sense to me and I think it is very bad news. What I contend is that the  atmospheric circulation variability is not necesarilly "natural variability".  It is natural variability only in that it varied randomly since 1979.

Neven, this time I'm done for real.
I am an energy reservoir seemingly intent on lowering entropy for self preservation.

Yuha

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #138 on: March 24, 2017, 05:10:51 PM »
I've looked Ding et al. in some detail and in the end came to the conclusion that there is nothing really new or surprising in their experimental results. They simply verify what was already known or suspected.

The issue with their conclusions about natural variation is not with the experiments but with the more fundamental premise that the CMIP5/LENS model ensemble mean represents the actual AGW effect cleaned of natural variation and that any deviation from the model mean is natural variation. If that is the premise, there is nothing surprising in the conclusions.

I know that many consider that premise obviously wrong but it is not quite that simple. Individual model runs do exhibit large deviations from the mean sometimes lasting several years, so it isn't out of the question that what we are seeing in the real world is something similar. On the other hand, declaring an observed deviation from the model mean automatically as natural variation rather than a potential model error seems to me equally unfounded. But then I'm not an expert so what do I know.

So the question really is, are models right or wrong (or perhaps something in between), and I don't think this paper provides much help in answering that.

ktonine

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #139 on: March 24, 2017, 05:18:32 PM »
I've looked Ding et al. in some detail and in the end came to the conclusion that there is nothing really new or surprising in their experimental results. They simply verify what was already known or suspected.

I quite agree.  A couple years ago here on the forum Chris Reynolds and I came to much the same conclusion regarding summer vs winter.  Might be in the Slow Transitions topic.  Essentially we were able to convince ourselves that the data supported that both winter and summer were contributing to the decline, but that extra warm summers had a very large effect.

2007 is often referred to as the perfect melt season - well, that's natural variability. 
PIOMAS reached it's all-time low in 2012 and hasn't returned to that level since.  That's natural variability.

The trend is all going in one direction and that's due to AGW, but simply writing off natural variability is ignoring science, the data, and the facts.

AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #140 on: March 24, 2017, 05:28:44 PM »
...
So the question really is, are models right or wrong (or perhaps something in between), and I don't think this paper provides much help in answering that.

"Essentially, all models are wrong, but some are useful" - George Box

The Ding paper unfortunately does not explain in details how the decision to use the models they used came about, nor does it quantify the skill of the models they used, or compare their skill to other models, including sea ice specific models that they fail to mention and did not use.

Models are widely used and a most important tool for research in climate science. Just because the Ding et al paper raises so many questions about the models they used and the conclusion they apparently derived from them, does not in any way invalidate the use of models in climate research.

Two videos with Gavin Schmidt about the use of models in climate science:
https://www.youtube.com/watch?v=JrJJxn-gCdo (TED talk)
https://www.youtube.com/watch?v=WfwgaMHmLkU (1 hour lecture, with very bad sound unfortunately)
« Last Edit: March 24, 2017, 05:39:50 PM by AndrewB »

ktonine

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #141 on: March 24, 2017, 06:07:19 PM »

If the arctic climate were in perfect balance then all of the melt in any given year would be replaced by an equal amount of freeze.  We would have a seasonal cycle that wouldn't necessarily be a sine wave, but it would be repeated year after year with equal amplitude minimums and maximums.

The fact that there is overall loss does NOT mean the process is driven by more melt - only that melt exceeds freeze. As I tried to explain, there are 3 possibilities mathematically (assuming the process is thermodynamic and the loss is not due to chaotic variability and the time window open to us just happens to be when the random chaotic features lead to a loss).

If we accept that the loss is a trend, and we know there are only 3 possible explanations, examination of the data tells us which of these possibilities is actually in effect - both melt and freeze are increasing, but melt is on average larger than freeze. But even knowing this does not tell us whether the losses are due to winter or summer processes.

We know that global warming does not just manifest itself in a particular month or season, but that does not mean that it's uniform.  Chris is actually asking (I think), Is the Arctic thermal balance more anomalous in winter or summer?  Arctic sea ice extent, area and volume anomalies are just indicators of this energy imbalance. 

The intuitive answer is that the losses are driven by summer melt processes.  The data seems to bear intuition out: The correlations between the preceding winter and summer melt are very low.  The correlations between melt and the following freeze are significant (though barely at 95% and with a small sample size).

BUT .... arctic winter warming is 4 times larger than summer warming! Hmmm .... back to the drawing board.

A consistent story has to mesh with all the facts.  The fact that winter warming is greater than summer warming in the Arctic is not, on its face, consistent with an explanation that says summer processes are responsible for the ice losses.

In looking for a freeze-melt correlation - and finding none - I believed the preceding winter's volume gain told us little about the summer melt losses.  This may be misleading.  Just because it's true doesn't actually prove anything.  What if volume gain isn't a particularly significant attribute of winter?

In fact, after a couple days reflection I believe that is actually the case - that volume gain per PIOMAS tells us very little about winter.  Arctic temperatures historically on average fall to -45 C°.  That's far lower than necessary to create ice.  There is also a thermodynamic limit to how thick sea ice can grow over the winter. So a 5 C° warming during winter may not lead to any less ice, but it will lead to more summer losses - since less energy is needed to raise the ice temperature to the melting point.

Take a look at the Interpolated surface OLR for February 2013 and compare it to previous Februarys.  One has to go back to at least 2004 to find anything similar.  Probably 2002 or earlier.  It's also pretty easy to show that the February OLR plots are very closely related to the summer losses.  Rank them in order just by visual appearance and you'll come out very close to the same order as the actual losses.

In summary, the fact that PIOMAS volume gains for the preceding winter do not correlate to summer losses is probably misleading.  We used this lack of correlation to prove to ourselves that winter didn't determine summer losses - but the lack of correlation only tells us that volume gain is not correlated to summer losses, not winter in general. 

The winter OLR plots, particularly January and February, tell a different story.  The OLR plots should be a rough proxy for ice temperature.  And there's a huge energy difference between melting ice that might be at -40 C° as opposed to ice that might be 'only' -30 C°.

Of course I reserve the right to change my mind - again :)

Yuha

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #142 on: March 24, 2017, 06:48:02 PM »
Models are widely used and a most important tool for research in climate science. Just because the Ding et al paper raises so many questions about the models they used and the conclusion they apparently derived from them, does not in any way invalidate the use of models in climate research.

I fully agree. Models are really our only chance of separating trend from natural variation in recent events. We do not have multiple earths or an ability to rerun history or to see in the future. And models are remarkably skillful and getting better all the time. I'm eagerly waiting results from the next generation of models.

However, arctic is probably the most difficult place on earth to model because of ice and snow, the large temperature differences and the complex geography.

jplotinus

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #143 on: March 24, 2017, 07:18:05 PM »
<snip, it really has been enough now; N.>
« Last Edit: March 24, 2017, 07:35:51 PM by Neven »

AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #144 on: March 24, 2017, 07:53:24 PM »
...
However, arctic is probably the most difficult place on earth to model because of ice and snow, the large temperature differences and the complex geography.

I agree. The Arctic is particularly difficult to model, as you say because of ice, snow, the ocean, the temperature range, the geography, the huge scale and numerous feedbacks and how all these interact. It's a complex system with a lot of chaos.
You might be interested in checking this paper:
The CMIP6 Sea-Ice Model Intercomparison Project (SIMIP): understanding sea ice through climate-model simulations
by Dirk Notz, Alexandra Jahn, Marika Holland, Elizabeth Hunke, François Massonnet, Julienne Stroeve, Bruno Tremblay and Martin Vancoppenolle

Somehow, the Ding et al paper "forgot" to even mention it...
http://www.geosci-model-dev.net/9/3427/2016/gmd-9-3427-2016.pdf

Steven

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #145 on: March 24, 2017, 08:28:20 PM »
Somehow, the Ding et al paper "forgot" to even mention it...
http://www.geosci-model-dev.net/9/3427/2016/gmd-9-3427-2016.pdf


Your criticism is absurd.  That Notz et al. paper was still undergoing peer review when Ding et al. was submitted.

Notz et al. paper in its final revised form was published on 23 September 2016. 

Ding et al. paper was submitted on 26 July 2016.

AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #146 on: March 24, 2017, 08:40:44 PM »
Somehow, the Ding et al paper "forgot" to even mention it...
http://www.geosci-model-dev.net/9/3427/2016/gmd-9-3427-2016.pdf


Your criticism is absurd.
...
Ding et al. paper was submitted on 26 July 2016.


Steven, the Notz paper was submitted on 29 March 2016, four months before the Ding et al paper was submitted. With 11 co-authors, you would expect at least one among Ding et al. would have been aware of the Notz et al paper about the Sea-Ice Model Intercomparison Project (SIMIP), or at least about the SIMIP project itself, which exists since late 2015/early 2016 as far as I can tell. The climate model community is not that large.
Also, check where Notz works and where Ding et al got the ECHAM5 model from.
« Last Edit: March 24, 2017, 09:40:34 PM by AndrewB »

Neven

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #147 on: March 24, 2017, 08:46:51 PM »
How do you mention a paper that hasn't even been published yet?

AndrewB, you've made your point. Now don't reiterate it constantly by nitpicking details. Thanks.

And don't tell people to go and do this or that.
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AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #148 on: March 24, 2017, 08:53:21 PM »
How do you mention a paper that hasn't even been published yet?

APA REFERENCE STYLE: Unpublished Sources
http://linguistics.byu.edu/faculty/henrichsen/APA/APA14.html
: Neven
AndrewB, you've made your point. Now don't reiterate it constantly by nitpicking details. Thanks.

You are welcome, Neven. Keep up the good work.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #149 on: March 25, 2017, 08:04:08 AM »
Back to content.
I realized that my previous post I was not clear enough about the science to be convincing.
So let me try again, this time pointing out exactly what is wrong with the conclusions of Ding et al 2017.

First of all, what does Ding et al claim.
I think it was Steven who correctly pointed out that there are TWO parts to Ding et al's claims of influence of "internal variability" on Arctic sea ice :

(1) about 60% of the September Arctic sea-ice extent decline since 1979 is caused by trends in summertime atmospheric circulation. 
(2) about 70% of those atmospheric circulation trends is caused by internal variability (and hence the remaining 30% is anthropogenic). 

Now the problem I have with the paper are very clearly in point (1) :
It started with Ding et al claim in the abstract of that point :

Here, we present evidence that trends in summertime atmospheric circulation may have contributed as much as 60% to the September sea-ice extent decline since 1979.

In my previous post, I noted that Ding et al uses "GL-Z200" (geopotential height at 200 mb, over Greenland) as their metric for "atmospheric circulation" over the Arctic.
That immediately means that the conclusion should have read something like this :

Here, we present evidence that trends in summertime geopotential height may have contributed as much as 60% to the September sea-ice extent decline since 1979.

Now, this should raise some eyebrows here and there, since geopotential height is clearly directly correlated with temperature. If the temperature goes up, so does geopotential height.
In fact, the ideal gas law (PV=nRT) DICTATES that geopotential height goes up with temperature.
Which is sustained in the ERA data set, where Ding et al itself reports that there is a R=0.94 correlation between geopotential height and temperature.

So AGW, which is certainly a part (if not all) of the trend in temperature over the Arctic is certainly also a part (if not all) of the trend in geopotential height.
And thus Ding et al 2017 can no longer claim that the Z200 trend (which they call "atmospheric circulation trend") is a source of "internal variability".

But that's not all.
The even bigger problem with the paper is in which they determined the influence of "atmospheric circulation" (oops, I mean geopotential height) on Arctic sea ice decline.

If you want to investigate that influence with a sea ice/climate model, you would run the model with the ERA climate parameters, and compare it with a run that has geopotential height adjusted (subtract the geopotential height anomalies from the ERA data).

But that is not what Ding et al did.
They adjusted ALL variables (geopotential height, temperature, moisture content, downwelling LW radiation etc), essentially making the 'climate' constant.
Specifically, this is described here in the paper :

Exp-6: Same as Exp-5 except that the atmospheric forcing is modified to excise the forcing associated with the trends in the Greenland circulation pattern. To remove the circulations trend from the observat ions, we first construct the thirty-six-year seasonal (JJA) averaged time series of the Z200 index over Greenland, Z200 GL (GL-Z200 in Fig. 1c). We then linearly regress a key variable B
against this time series to obtain spatial pattern β(x,y) of the variable associated with the Greenland circulation index. Specifically, for the variable B we have

B(x, y, t) = β(x, y) × Z200 GL (t) (1)

where B represents a forcing field (for example, 10 m zonal wind, DLR, temperature, and so on), x and y indicate the location, t indicates time (JJA), Z200 GL is the Greenland Z200 index (GL-Z200 in Fig. 1c), and β is the regression coefficient. In the second step, the seasonal mean anomalous value of each forcing field is subtracted from the observed daily (or 6-hourly) forcing data during the summer—rendering a modified forcing that does not include variability or trends in variables that are asso ciated with Z200 GL. In the nine non-summer months, the forcing is exactly the same as that used in the Exp-5 control experiment. Given a strong correlation between circulation and surface winds, temperature, specific humidity, sea-level pressure, and downwelling long wave radiation in the Arctic, variability and trends in these six variables that are associated with Z200 GL are processed and removed from the forcing. The initial states of ocean, sea ice and atmosphere in Exp-5 and Exp-6 are exactly the same.

I highlighted in bold the section that describes that indeed they adjusted ALL variables to the extent that they linearly associate with Z200 GL. And because the correlation between all these variables and Z200 is very high (see figure 1c in the paper), they effectively eliminated ALL trends in ALL variables from their Exp-6 run, which means they effectively made the climate constant in that run.
Since the climate did not change in that run, they obtained a much lower ice melt rate.
Essentially the conclusion should thus have been :

Here, we present evidence that trends in summertime climate change may have contributed as much as 60% to the September sea-ice extent decline since 1979.

Which means that (this experiment 5 versus 6 suggests that) :
60% of Arctic sea ice reduction is caused by summer-time climate change, while 40% is caused by climate change over the remaining 9 months.

Which is an interesting conclusion, but as you can see it has NOTHING to do with ANY sort of "natural variability", so Ding et al cannot use it in their variability conclusion either.

You can still choose not to believe that this paper is seriously flawed, but you can no longer claim that you did not know.