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Archimid

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #200 on: March 30, 2017, 04:16:54 AM »
The PDO has only oscillated once.  A trend analysis on PDO data since 1979 reveals a substantial downward trend. 

I stand corrected. I was thinking of the century dataset when I was speaking of the dataset after 1979.

Quote
Although I don't think it can be as simple as cool PDO implies fast melt, otherwise the relationship would have been discovered long ago.

I think a warm PDO implies fast melt because warmer air temperatures  will eventually teleconnect with the Arctic.  The signal of the PDO could not be detected in the 20th century because there was a thick ice cap and the planet was cold enough. At some point near the turn of the century the ice got too small and/or the planet too warm. In a warmer earth with much less ice, the signal of the PDO has a greater impact on air temperatures and in turn, on the ice.

 
Quote
Maybe the start of a second oscilation if it turns out that the warm PDO for the last few years is a real warm phase and not a false alarm

The downward trend of the PDO is clear and I think that, as you say, the current positive phase is not the real positive phase. I think the PDO is to a great extent solar cycle driven.  The Sun is schedule for weaker cycles until it reaches a minimum in 2030.  Unless something big changes (like aerosols) the PDO should enter a cooler phase next year or the one after.

The problem is that the last time we got a cool phase (the "hiatus") there was more ice and the air temperatures were colder, yet the melt continued. I have no reason to think that during the (hopefully) coming cooler phase the melt will stop and the ice recover to levels of the 20th century. If it was melting .1 C colder and many thousands of km3 of ice ago, it will keep melting even if we enter another "hiatus". 

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

AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #201 on: March 30, 2017, 08:45:44 AM »
...
The concept of "tipping point" does not apply to the Barnes ice cap.
...
I say it does!  The ice cap wasn't melting faster than it was expanding for a very long time, and now it is.  (And what caused approximately 100% of this change, I'm sure, is AGW.)
...

We essentially agree then.  ;)

I would point you to a tipping point page on Wikipedia but imho the Wikipedia page on climate tipping points is not that good. Keeping it simple: there are no "tipping points" for a simple chunk of ice, however large it may be such as the Barnes ice cap: it's not a complex system, there are no positive feedbacks, and it melts linearly to the amount of energy/heat you apply to it.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #202 on: March 30, 2017, 09:25:21 AM »
'...melts linearly...'  Mmm.  Isn't it likely that the ratio of surface area exposed to warm air versus volume of remaining ice will increase as the melting progresses, giving a rather more exponential melt rate versus linear for given temperature conditions? 

Sure, not a 'tipping point', but classic Seneca Cliff decline would seem likely, as the next best (or worst) thing.

DrTskoul

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #203 on: March 30, 2017, 10:47:32 AM »
'...melts linearly...'  Mmm.  Isn't it likely that the ratio of surface area exposed to warm air versus volume of remaining ice will increase as the melting progresses, giving a rather more exponential melt rate versus linear for given temperature conditions? 

Sure, not a 'tipping point', but classic Seneca Cliff decline would seem likely, as the next best (or worst) thing.


Without feedbacks the melting rate depends on the heat imbalance. If there is a constant imbalance x Watts then the mass rate of melting will be constant and the mass decrease linear. If there is a constant temperature difference then the melting rate will be proportional to the external surface area and it will slow down with time.

AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #204 on: March 30, 2017, 10:53:21 AM »
'...melts linearly...'  Mmm.  Isn't it likely that the ratio of surface area exposed to warm air versus volume of remaining ice will increase as the melting progresses, giving a rather more exponential melt rate versus linear for given temperature conditions? 

Sure, not a 'tipping point', but classic Seneca Cliff decline would seem likely, as the next best (or worst) thing.

That's the heat(energy) transfer rate that varies according to various parameters, such as humidity, wind, etc. The linear relationship between melt and energy still holds, because it's just a basic physics law (if it takes X Joules to melt 1kg of ice, it takes 2X Joules to melt 2kg of ice, etc).
The end of my phrase, which you have somehow cut away, indicates this clearly:
"... it [a chunk of ice] melts linearly to the amount of energy/heat you apply to it."

But that's nitpicking on details. My point is that there are no "tipping points" to be considered in the case of the Barnes ice cap, so it's not like equal shares of "natural climate variability" + AGW have suddenly triggered a positive feedback which is leading to the demise of the Barnes ice cap.

Again, just to keep it simple: the Barnes ice cap is disappearing because AGW has caused 100% of the unprecedented recent warming observed in the northeastern Canada and Greenland region. That's what the physical evidence over more than 2,000 years shows.
If Ding et al claim otherwise because they derive some unwarranted conclusions from their model simulations, they are wrong.
And since they used the same methodology and derived similar conclusions in their 2017 paper that attributes 30~50% of the recent Arctic sea ice decline (in September) to "natural climate variability" (in the months of June July August), they are wrong about that too.
« Last Edit: March 30, 2017, 11:07:21 AM by AndrewB »

DrTskoul

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #205 on: March 30, 2017, 11:35:44 AM »
Andrew.  You have a gut feeling they are wrong. You cannot prove they are wrong.

Not every paper out there will be right but they all contribute, if nothing else, showing where the pitfalls are. You made your point. Don't need to drag them in every answer to an unrelated question.

AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #206 on: March 30, 2017, 01:02:06 PM »
...
You cannot prove they are wrong.
...

You are assuming I cannot scientifically prove they are wrong.

But if that's indeed the case, then we are back to an invisible flying spaghetti monster situation. Or see here: https://en.wikipedia.org/wiki/Russell%27s_teapot
Or here: https://en.wikipedia.org/wiki/The_Demon-Haunted_World#Dragon_in_the_garage

The burden of proof is on Ding et al, not on me or others who think like me that the demise of Arctic sea ice is 100% due to AGW.

Check points 4 to 8 of jai mitchell's first post in this thread (post #15). Michael E. Mann has expressed serious doubts about the validity of the attribution conclusion in the Ding et al 2017 paper.

BTW, that none of the 11 co-authors accepted to answer questions on a public forum about their paper says a lot to me. While I agree that the comments section of a blog such as Stoat is not an ideal forum, here on ASIF or on RC I would imagine it would generate an interesting and informative thread.
« Last Edit: March 30, 2017, 01:14:26 PM by AndrewB »

DrTskoul

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #207 on: March 30, 2017, 01:37:25 PM »
Fair, I fell in the same trap... I am assuming....  but with the same logic is the burden of the proof on climate scientists to prove they are right when the denialati spew their nonsense?
We cannot have it both ways...

all they did was do some calculations based on some hypothesis and convinced themselves they are right. They might or might not... somebody else will come and prove them wrong... that is how science works...  if there is a flaw in the setup of simulations will be proven by somebody repeating those calculations in a different way not by public debate. Especially since they did not make a prediction that can be observed or not. They compared A vs B where they thought that B has not anthropogenic influence. That cannot be experimentally observed ... we do not have an alternative Earth. Past climates also had their own trajectories and state variable values that are different than today.


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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #208 on: March 30, 2017, 03:07:00 PM »
Fair, I fell in the same trap... I am assuming....  but with the same logic is the burden of the proof on climate scientists to prove they are right when the denialati spew their nonsense?
We cannot have it both ways...
In the specific case of the Ding et al 2017 paper, the burden of proof lies on the 11 co-authors because they come up with a new (and some would say ad-hoc) hypothesis to explain why existing sea ice models that rely on anthropogenic forcing do not match the observed Arctic sea ice decline. Instead of simply stating that existing sea ice models do not capture all the mechanisms by which anthropogenic forcing affects Arctic sea ice, and trying to improve those models (cf my various references to the Sea Ice Model Intercomparison Project - SIMIP), they hypothesize that it is "natural climate variability" that has affected atmospheric circulation that in turn is causing "30~50%" of the observed rapid decline in Arctic sea ice.
Replacing "natural climate variability" by "Invisible Flying Spaghetti Monster" or "the dragon in my garage" changes practically nothing in their argumentation, because we don't have the data for the Arctic before 1979, so it's impossible to scientifically prove them wrong with hard physical evidence or historical records.

This is what Neven wrote in reply#1 in this thread:
Quote
"... no one has said that all of Arctic sea ice loss is 100% caused by AGW*. It might be, but we can't know for sure. It might even be more than 100% if natural variation would otherwise have caused the ice to grow. We don't know."

So it's really the case that nobody can prove Ding et al 2017 are wrong, but we can argue that it is most likely that they are wrong: that's the argument that one-sided "natural variability" for 40 years straight is highly unlikely. Or that we are still waiting and will probably still be waiting by the end of the century for "natural variability" to flip around and bring back the September Arctic sea ice (which will be gone for good in less than 10 years from now).

As to your question "... is the burden of the proof on climate scientists to prove they are right when the denialati spew their nonsense?", the simple answer is no. Because there is a ton of reliable, irrefutable and crystal clear evidence about AGW.

Tor Bejnar

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #209 on: March 30, 2017, 06:34:18 PM »
...
Keeping it simple: there are no "tipping points" for a simple chunk of ice, however large it may be such as the Barnes ice cap: it's not a complex system, there are no positive feedbacks, and it melts linearly to the amount of energy/heat you apply to it.
It isn't a "simple chunk of ice". (My bias is geology.)  It has glaciers coming off of it (source of ice loss) and it snows (source of ice gain), among other influences. 

According to the Canadian Glacier Inventory Project:
Quote
...
Many studies have shown that recession has been taking place for centuries, especially in the south and west, but the recession has not been uniform along the margin
...
All research suggests that should continued warming take place, shrinking of the Barnes Ice Cap will accelerate
...
The Ice Cap’s configuration was reached approximately 5000 years B.P., and further evidences indicate some parts of the ice cap had readvanced just 100 years ago
 ...
Field studies in the early 1950s found that all of the Ice Cap’s winter accumulation is usually melted in the summer, and the Ice Cap is maintained close to equilibrium through the formation of superimposed ice (Bell and Jacob, 1997). [superimposed ice = frozen melted snow]
...

30-some years ago I was led to believe that AGW might cause so much more high-latitude winter precipitation that Arctic glaciers would expand.  It turns out that it does snow more, but that this extra snow is almost always more than offset by increasing melt.

In Washington, glaciers formed on Mount St. Helens after she blew her top.  Under the right conditions, glaciers can still thrive.  (But it'll continue to get rarer and rarer.)
Arctic ice is healthy for children and other living things.

Rob Dekker

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #210 on: March 31, 2017, 05:12:12 AM »
There have been some developments in my discussion with the authors of Ding et al 2017 regarding the issues with the method used in their paper.

Here is my most recent post on William Connolley's "stoat" site :

http://scienceblogs.com/stoat/2017/03/15/influence-of-high-latitude-atmospheric-circulation-changes-on-summertime-arctic-sea-ice/#comment-58653

---

After Qinghua posted his findings that the adjusted forcing for experiment 6 still had a trend (in post 61; thank you Qinghua) I decided respectfully take the conversation private (polite email with the authors).

Yet now Eric Steig decided to take his opinion about me and the process of expressing scientific criticism on his paper in this fine blog public in a rather unprofessional rant of 9 twitter posts :
https://twitter.com/ericsteig

Now, since Eric decided to take the discussion public again, why not take the scientific discussion public again also :

The main problem with Ding et al 2017 is that the regression method they used for experiment 6 :

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

eliminates ANY trend in ANY of the variables, regardless of if these trends are "anthropogenic" or "natural variability" in nature.
And thus they can no longer claim to attribute any part to "natural variability" alone.

Their method essentially makes the climate constant during JJA in experiment 6. When confronted about that (by me in post 58).
Qinghua presented a graph (in post 61) which still has a (35%) residual trend.

The problem is that this graph represents the annual average climate used in experiment 6, and decidedly NOT the summertime (JJA) average, which shows no trend.
The residual 35% trend is the contribution from the other 9 months, where they let the climate follow the original ERA data (which still shows an uptrend since 1979).

We KNOW that Qinghua's graph does not show JJA climate in experiment 6, since when I asked Eric to look at that data he replied (on twitter) that he had to "re-do a bunch of calculations" to obtain that data :
https://twitter.com/ericsteig/status/847494244524736517

The flaw in Ding et al 2017 is there for everyone to see, if you just follow the science.
I'm disappointed that instead of embracing the criticism and engaging in a technical discussion, Eric Steig instead resorted to an argument of authority on twitter.
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DrTskoul

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #211 on: March 31, 2017, 05:39:43 AM »
There have been some developments in my discussion with the authors of Ding et al 2017 regarding the issues with the method used in their paper.

Here is my most recent post on William Connolley's "stoat" site :

http://scienceblogs.com/stoat/2017/03/15/influence-of-high-latitude-atmospheric-circulation-changes-on-summertime-arctic-sea-ice/#comment-58653

---

After Qinghua posted his findings that the adjusted forcing for experiment 6 still had a trend (in post 61; thank you Qinghua) I decided respectfully take the conversation private (polite email with the authors).

Yet now Eric Steig decided to take his opinion about me and the process of expressing scientific criticism on his paper in this fine blog public in a rather unprofessional rant of 9 twitter posts :
https://twitter.com/ericsteig

Now, since Eric decided to take the discussion public again, why not take the scientific discussion public again also :

The main problem with Ding et al 2017 is that the regression method they used for experiment 6 :

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

eliminates ANY trend in ANY of the variables, regardless of if these trends are "anthropogenic" or "natural variability" in nature.
And thus they can no longer claim to attribute any part to "natural variability" alone.

Their method essentially makes the climate constant during JJA in experiment 6. When confronted about that (by me in post 58).
Qinghua presented a graph (in post 61) which still has a (35%) residual trend.

The problem is that this graph represents the annual average climate used in experiment 6, and decidedly NOT the summertime (JJA) average, which shows no trend.
The residual 35% trend is the contribution from the other 9 months, where they let the climate follow the original ERA data (which still shows an uptrend since 1979).

We KNOW that Qinghua's graph does not show JJA climate in experiment 6, since when I asked Eric to look at that data he replied (on twitter) that he had to "re-do a bunch of calculations" to obtain that data :
https://twitter.com/ericsteig/status/847494244524736517

The flaw in Ding et al 2017 is there for everyone to see, if you just follow the science.
I'm disappointed that instead of embracing the criticism and engaging in a technical discussion, Eric Steig instead resorted to an argument of authority on twitter.

Whoever relies on Twitter to whine like that is an arrogant prick...

AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #212 on: March 31, 2017, 12:50:10 PM »
...

Their method essentially makes the climate constant during JJA in experiment 6. When confronted about that (by me in post 58).
Qinghua presented a graph (in post 61) which still has a (35%) residual trend.

The problem is that this graph represents the annual average climate used in experiment 6, and decidedly NOT the summertime (JJA) average, which shows no trend.
The residual 35% trend is the contribution from the other 9 months, where they let the climate follow the original ERA data (which still shows an uptrend since 1979).

...
(emphasis mine)
Rob, we don't have access to the graph that you mention.

From Qinghua post #61 on Stoat:
Quote from: Qinghua Ding
...
Actually, we did all these calculations before we implemented Exp. 6. The test shows we still have 35% of trend retained after that Z200-GL influence is removed. I have sent a figure to Rob.
...
(emphasis mine)
Please, could you share that graph which apparently Qinghua Ding sent to you by email with the rest of us here?

As for Eric Steig's Twitter rant, well, I disapprove. It seems both Steig and Qinghua Ding are running away from a technical discussion. If 2017 Ding et al are so sure they made no mistake, why not seize this opportunity to completely clarify this matter, cross all the t's and dot all the i's?

Jim Hunt

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #213 on: March 31, 2017, 01:00:44 PM »
Yet now Eric Steig decided to take his opinion about me and the process of expressing scientific criticism on his paper in this fine blog public in a rather unprofessional rant of 9 twitter posts

I tweeted Eric again:

https://twitter.com/jim_hunt/status/847764942665248768

I wonder if I'll get a reply this time?
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Neven

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #214 on: March 31, 2017, 01:17:51 PM »
Yes, that Twitter rant is painful, especially when someone says that online discussions aren't productive. On the other hand, Steig had a very nasty experience many years ago when Iago McIntyre came after him (for some paper on Antarctic warming). But Rob Dekker isn't a climate risk denier and he's not responsible for other people implying malice.

Anyway, that Stoat thread is a mess now.
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Jim Hunt

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #215 on: March 31, 2017, 03:16:20 PM »
Steig had a very nasty experience many years ago when Iago McIntyre came after him

Speaking of which, and only marginally off topic!

https://twitter.com/jim_hunt/status/847696552046993409

See also:

http://GreatWhiteCon.info/2017/03/the-house-science-climate-model-show-trial/#Mar-31
Reality is merely an illusion, albeit a very persistent one - Albert Einstein

Steven

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #216 on: March 31, 2017, 03:26:06 PM »
The main problem with Ding et al 2017 is that the regression method they used for experiment 6 :

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

eliminates ANY trend in ANY of the variables, regardless of if these trends are "anthropogenic" or "natural variability" in nature.
And thus they can no longer claim to attribute any part to "natural variability" alone.

Their method essentially makes the climate constant during JJA in experiment 6. When confronted about that (by me in post 58).
Qinghua presented a graph (in post 61) which still has a (35%) residual trend.

The problem is that this graph represents the annual average climate used in experiment 6, and decidedly NOT the summertime (JJA) average, which shows no trend.
The residual 35% trend is the contribution from the other 9 months, where they let the climate follow the original ERA data (which still shows an uptrend since 1979).

You're confused.  I'm pretty sure that Qinghua Ding's comments on the Stoat blog are correct.

I opened Figure 1c of the Ding et al. 2017 paper with some graphics software (GIMP), and estimated the coordinates of all the data points in the black and purple curves in that Figure:  http://i.imgur.com/QeDGIMR.png. 

Next, I inserted those numbers in a spreadsheet, and I performed the linear regression that Ding et al. used in their paper.

According to my calculation, about 33% of the trend of downwelling longwave radiation (LW) during summer (JJA) remains after the regression.  That is very close to the 35% number that Ding mentioned.  My calculation gives an original trend of about 2.08 W/m2/decade,  and after the regression it's about 0.68 W/m2/decade:  http://i.imgur.com/FhyMYog.png.
 
« Last Edit: March 31, 2017, 04:17:54 PM by Steven »

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #217 on: March 31, 2017, 04:57:06 PM »
Quote
I think I made it very clear in my plot and email to rob that the curve is for jja only .
It is Not annual mean. it doesn’t include any non summer month. It is June-July-august.
The regression we used can only partially remove the signals in jja since correlations between the z200 index with those jja variables are around 0.7 to 0.8. Please see our fig 1 .
There is still 30to 40% stuff left in exp6 that includes both residual trends and year to year changes.

Rob D. -- at what point do you give this up?  You have been told in no uncertain terms that the regression is for JJA and that 35% of the trend remains.  All you have done so far is continually assert that the authors are incorrect.  That the regression is for annual, that all trend is removed.

This means A.) the authors don't understand regression.  They don't understand the variables they're working with.  They can't understand it *even* when pointed out to them.

Or B.)   *you* are mistaken.

This has gone beyond silly.



AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #218 on: March 31, 2017, 05:09:47 PM »
The main problem with Ding et al 2017 is that the regression method they used for experiment 6 :

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

eliminates ANY trend in ANY of the variables, regardless of if these trends are "anthropogenic" or "natural variability" in nature.
And thus they can no longer claim to attribute any part to "natural variability" alone.

Their method essentially makes the climate constant during JJA in experiment 6. When confronted about that (by me in post 58).
Qinghua presented a graph (in post 61) which still has a (35%) residual trend.

The problem is that this graph represents the annual average climate used in experiment 6, and decidedly NOT the summertime (JJA) average, which shows no trend.
The residual 35% trend is the contribution from the other 9 months, where they let the climate follow the original ERA data (which still shows an uptrend since 1979).

You're confused.  I'm pretty sure that Qinghua Ding's comments on the Stoat blog are correct.

I opened Figure 1c of the Ding et al. 2017 paper with some graphics software (GIMP), and estimated the coordinates of all the data points in the black and purple curves in that Figure:  http://i.imgur.com/QeDGIMR.png. 

Next, I inserted those numbers in a spreadsheet, and I performed the linear regression that Ding et al. used in their paper.

According to my calculation, about 33% of the trend of downwelling longwave radiation (LW) during summer (JJA) remains after the regression.  That is very close to the 35% number that Ding mentioned.  My calculation gives an original trend of about 2.08 W/m2/decade,  and after the regression it's about 0.68 W/m2/decade:  http://i.imgur.com/FhyMYog.png.
 

Steven,
Thank you for your effort in making these two charts, one "reverse-engineered" and the second computed by you. If any of the 11 co-authors had the data I am sure it would have taken just a few minutes of their time to post them as well as the spreadsheet data, and settle the matter - if only it were that simple.
There were a couple of follow-up posts by Rob and Qinghua Ding on Stoat that make the matter more confusing, but they are very interesting.
Quote from: Rob Dekker
Qinghua.
Thank you for your reply.
If you used simple linear regression, then your method will eliminate any trend in the JJA record.
The graph you showed still shows a 35% residual trend, which suggest it is NOT the JJA climate for experiment 6.
After all, where would that residual 35% trend come from ?

Unfortunately Qinghua Ding pulls a "but the dragon in my garage is invisible" as a response, while implicitly admitting to the mistake Rob has pointed since the beginning.

Quote from: Qinghua Ding
the residual trend could be due to Co2 or cloudiness changes that are not related to the Z200 index.
the Z200 index has a strong interdecadal jump around 2003-2005. In our 2014 paper, we have argued that this interdecadal jump is not totally due to the Co2 rise.
So our regression can only remove this interdecadal like jump in the forcing fields. Some slowing increasing trends, as those due to Co2 forcing, cannot be removed by this regression.

At this stage, this could go on forever, because the dragon (in this case the cause of the 35% residual trend) can be made weightless, odorless, etc, etc, etc.

(see https://en.wikipedia.org/wiki/The_Demon-Haunted_World#Dragon_in_the_garage and https://en.wikipedia.org/wiki/Ad_hoc_hypothesis)

To me, this last exchange between Rob and Qinghua Ding is absolutely illuminating.

Neven

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #219 on: March 31, 2017, 05:35:10 PM »
Maybe Rob Dekker and Steven can work this out further now, because if Ding and Steig are right, this is a waste of their time.
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jai mitchell

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #220 on: March 31, 2017, 06:50:08 PM »
This just published yesterday.

http://onlinelibrary.wiley.com/doi/10.1002/2017GL073138/abstract

North Pacific 20th century decadal-scale variability is unique for the past 342 years
Williams et al. (2017)

Abstract

Reconstructed sea surface temperatures (SSTs) derived from Mg/Ca measurements in nine encrusting coralline algal skeletons from the Aleutian archipelago in the northernmost Pacific Ocean reveal an overall increase in SST from 1665 to 2007. In the Aleutian SST reconstruction, decadal-scale variability is a transient feature present during the 1700s and early 1800s and then fully emerging post-1950. SSTs vary coherently with available instrument records of cyclone variance and vacillate in and out of coherence with multi-centennial Pacific Northwest drought reconstructions as a response to SST-driven alterations of storm tracks reaching North America. These results indicate that an influence of decadal-scale variability on the North Pacific storm tracks only became apparent during the mid-20th century. Furthermore, what has been assumed as natural variability in the North Pacific, based on 20th century instrumental data, is not consistent with the long-term natural variability evident in reconstructed SSTs pre-dating the anthropogenic influence.
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Darvince

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #221 on: March 31, 2017, 07:14:46 PM »
That seems nearly too well timed to have been random chance. ;D

Although, I did read several PDO papers several months ago and they all seemed to point towards the cycle speeding up around 1850, coincidentally (or not?) when human CO2 emissions began to have an effect on the biosphere. The flips between negative and positive won't have any sum detrimental effect on the sea ice, as the loss during negative phases may be more rapid (and PDO, was mostly negative from 1998 to 2013, and flipped since then, with losses slowing during the positive phase. During the negative phase trapped heat is stored in the oceans, accelerating SLR, while during the positive phase the trapped heat is released into the atmosphere. The flip was to such a strong positive mode that I doubt that it will return to being strongly negative next year.

http://research.jisao.washington.edu/pdo/

Archimid

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #222 on: March 31, 2017, 07:28:04 PM »
Thanks jai mitchell.

Without considering the technical details and just by reading the abstract of the Williams et al paper,  the conclusions of Ding et al are compatible with Williams et al but only if Ding et al attributes the changes in tropospheric currents to variations of pacific sst's, not natural variation. In a different world that would be a trivial technicality, but if the proper political context is acknowledged, it is a very important distinction.

That said thanks to Rob Dekker, steven, Ding and Steig and everyone trying to get the best possible truth out of this. I have learned a lot.
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Archimid

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #223 on: March 31, 2017, 07:39:07 PM »
That seems nearly too well timed to have been random chance. ;D


  ;D I thought the same thing, but is so convenient that I had to take it. I would love to see the whole paper.
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Steven

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #224 on: March 31, 2017, 09:21:13 PM »
Maybe Rob Dekker and Steven can work this out further now, because if Ding and Steig are right, this is a waste of their time.

Neven, I think it's clear that Ding and Steig are right about this.

In case Rob Dekker wants to check my calculations in Reply #216 upthread:  below are the numbers that I used in the calculation.  As mentioned, the two middle columns were estimated from Figure 1c in Ding et al. 2017.  All those numbers are for summer (JJA).  The units for the LW numbers are W/m2, whereas the GL_Z200 numbers are expressed in meters.

Code: [Select]
year      LW     GL_Z200   LW_after_regression
1979    -1.11    -23.24     0.60
1980    -3.43      8.30    -4.00
1981    -1.77     -3.32    -1.51
1982    -4.43    -15.49    -3.28
1983    -2.99    -58.09     1.23
1984    -1.55     -1.66    -1.40
1985    -0.77    -14.38     0.29
1986    -2.21    -33.75     0.25
1987    -1.44     25.45    -3.25
1988    -0.55      1.11    -0.61
1989    -1.44    -31.54     0.86
1990     0.06     -3.32     0.32
1991    -0.06    -29.88     2.13
1992    -5.86    -86.31     0.39
1993    -1.27      5.53    -1.65
1994    -3.04    -67.50     1.85
1995     0.83      3.87     0.58
1996    -6.14    -68.05    -1.21
1997    -3.32    -13.83    -2.30
1998     1.49     38.73    -1.27
1999     0.83    -14.38     1.89
2000    -2.77    -14.94    -1.66
2001    -1.88     -9.96    -1.14
2002     1.55      8.30     0.98
2003     1.27     44.26    -1.89
2004     2.27     12.17     1.42
2005     6.20     24.90     4.43
2006     3.43     12.72     2.54
2007     6.86     54.77     2.94
2008     1.72     32.64    -0.61
2009     1.77     27.66    -0.20
2010     4.59     55.33     0.63
2011     4.98     55.33     1.01
2012     6.64     75.24     1.24
2013    -0.66    -26.00     1.24
2014     2.05     39.83    -0.80

Jim Williams

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #225 on: March 31, 2017, 09:43:10 PM »
This just published yesterday.

http://onlinelibrary.wiley.com/doi/10.1002/2017GL073138/abstract

North Pacific 20th century decadal-scale variability is unique for the past 342 years
Williams et al. (2017)

Abstract

Reconstructed sea surface temperatures (SSTs) derived from Mg/Ca measurements in nine encrusting coralline algal skeletons from the Aleutian archipelago in the northernmost Pacific Ocean reveal an overall increase in SST from 1665 to 2007. In the Aleutian SST reconstruction, decadal-scale variability is a transient feature present during the 1700s and early 1800s and then fully emerging post-1950. SSTs vary coherently with available instrument records of cyclone variance and vacillate in and out of coherence with multi-centennial Pacific Northwest drought reconstructions as a response to SST-driven alterations of storm tracks reaching North America. These results indicate that an influence of decadal-scale variability on the North Pacific storm tracks only became apparent during the mid-20th century. Furthermore, what has been assumed as natural variability in the North Pacific, based on 20th century instrumental data, is not consistent with the long-term natural variability evident in reconstructed SSTs pre-dating the anthropogenic influence.

This makes more sense to me than the whole of what I have read before in this thread.  I will read about it -- and continue to ignore the GCM intercomparisons.

Rob Dekker

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #226 on: April 01, 2017, 02:48:32 AM »
Steven, thank you so much for the idea to use fig1c for the data !
I duplicated your results (I get 30-35% residual trend for both LW and temperature).

I went a step too far, and made a mistake.
I made my apology to Qinghua and Eric on the 'stoat' site :

http://scienceblogs.com/stoat/2017/03/15/influence-of-high-latitude-atmospheric-circulation-changes-on-summertime-arctic-sea-ice/#comment-58681
---
Thanks to 'Steven' at the ASIF, I realized that I don't need to do a full ERA data download and a gridded regression analysis to test how much of the trend in summertime temperature and LW is taken out by Z200 changes if we apply the Ding et al 2017 regression method.

We can get a pretty good estimate by using the data from fig1c and run the numbers.
I did that today, and indeed it shows (just like Qinghua already told me) a 35% residual trend for LW. Temperature shows a similar (35%) residual trend.

So, even though I find it difficult to accept that 65% of the trend in summertime Arctic temperatures would be caused by 'atmospheric circulation' (natural variability), leaving only 35% for AGW, I do understand the mistake I make and I (humbly) apologize to Qinghua and Eric for my arrogant stand on the issue.
---

I'm going to be very quiet for a while now.
This is our planet. This is our time.
Let's not waste either.

Archimid

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #227 on: April 01, 2017, 03:35:10 AM »
Rob Dekker  I lack the necessary technical knowledge to challenge the technical merits of the paper, so I accept the paper as technically correct. Your challenge of the paper gives me even more confidence that the technical aspects of the paper are correct. Thank you.

 I still challenge the assertion that the seemingly random variability of an atmospheric current is equivalent to natural variability.
 
 In fact, I think that this result is really bad news. The way I see it what Ding et al proved was that the atmosphere has gained enough "momentum" due to AGW, that it now overshadows CO2 induced warming as the primary driver of arctic sea ice loss.
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #228 on: April 01, 2017, 06:26:07 AM »
Rob Dekker  I lack the necessary technical knowledge to challenge the technical merits of the paper, so I accept the paper as technically correct. Your challenge of the paper gives me even more confidence that the technical aspects of the paper are correct. Thank you.

 I still challenge the assertion that the seemingly random variability of an atmospheric current is equivalent to natural variability.
 
 In fact, I think that this result is really bad news. The way I see it what Ding et al proved was that the atmosphere has gained enough "momentum" due to AGW, that it now overshadows CO2 induced warming as the primary driver of arctic sea ice loss.

Kind of like hitting the curb too hard when parking? Once you knock it out of balance the steering shakes, and if you ignore it for long enough then eventually the lugs shear and the wheel falls off.

epiphyte

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #229 on: April 01, 2017, 07:21:24 AM »
Randy,

The majority of the scientists and engineers do not have the skills to be concise,  on target and quick on come backs. It is unfortunate...

Yesterday I asked one of my kids (a west-coast engineering major home for spring break) to proofread a draft of the white paper I'm writing to illustrate the value offered by a technology startup of which I'm a co-founder. He said something to the effect of :

"Dad, this is good... but most people can hold fewer than five things in working memory. If you make an argument which requires more than three, you're pitching on the wrong end of the bell curve."

 - out of the mouths of babes...


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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #230 on: April 01, 2017, 09:33:51 AM »
...
The way I see it what Ding et al proved was that the atmosphere has gained enough "momentum" due to AGW, that it now overshadows CO2 induced warming as the primary driver of arctic sea ice loss.
Hi Archimid,
Sorry, but I don't think they proved that at all, and not even their conclusion states that.

I just re-read this entire thread here on ASIF, then the comments section on Stoat. I still feel the Ding et al 2017 article (and by extension the Ding et al 2014 article) deserves a public debate about the assumptions, methodology, and conclusion, but with the willing participation of Ding, Steig and other co-authors.

Dragging unwilling scientists into a discussion on a comments section of a blog is a useless exercise, and the worst way to get any real debate going.

Meanwhile...
« Last Edit: April 01, 2017, 09:50:50 AM by AndrewB »

Neven

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #231 on: April 01, 2017, 10:06:39 AM »
Quote
I just re-read this entire thread here on ASIF, then the comments section on Stoat. I still feel the Ding et al 2017 article (and by extension the Ding et al 2014 article) deserves a public debate about the assumptions, methodology, and conclusion, but with the willing participation of Ding, Steig and other co-authors.

How about sitting it out and letting the peer-review process do its thing? If Ding et al. is flawed, it will show up in the data. It will still have been useful as a pointer in the right direction.

Rob Dekker, I commend you for trying to get to the bottom of things and admitting you've made a mistake. All I could do, was scan the paper for typos (found two).

If it weren't for people implying malice, I think the scientists wouldn't have been bothered by this at all.
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #232 on: April 01, 2017, 11:36:19 AM »
Yesterday I asked one of my kids (a west-coast engineering major home for spring break) to proofread a draft of the white paper I'm writing to illustrate the value offered by a technology startup of which I'm a co-founder. He said something to the effect of :

"Dad, this is good... but most people can hold fewer than five things in working memory. If you make an argument which requires more than three, you're pitching on the wrong end of the bell curve."

 - out of the mouths of babes...

That is a fabulous explanation, and I am henceforward going to use it to train all my PhD students and postdocs in grant writing. Please thank your son for me!

Archimid

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #233 on: April 01, 2017, 12:51:57 PM »
Hi Archimid,
Sorry, but I don't think they proved that at all, and not even their conclusion states that.

Hi AndrewB,
They don't reach that conclusion because they conflate natural variability with anthropogenicaly altered random variability.  In a way the math is right, but the interpretation of it is wrong.

Quote
Dragging unwilling scientists into a discussion on a comments section of a blog is a useless exercise, and the worst way to get any real debate going.

It is not a useless exercise. It is just that the results of this exercise gets lost in the noise. But if only a few people gained a better understanding of models, the scientific process, the climate or variability the discussion was not useless.
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #234 on: April 01, 2017, 01:04:12 PM »
...
they conflate natural variability with anthropogenicaly altered random variability.
...

No, I don't think they conflate anything such, whatever you may mean by "anthropogenicaly altered random variability".  ??? (I'll politely decline your explanation of what you mean by that)

Quote from: Archimid
Quote from: AndrewB
Dragging unwilling scientists into a discussion on a comments section of a blog is a useless exercise, and the worst way to get any real debate going.

It is not a useless exercise.

I guess we'll have to agree to disagree on that too.  ;D

GeoffBeacon

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #235 on: April 01, 2017, 02:19:28 PM »
AndrewB

I'd quite like to know what Archimid meant by "anthropogenicaly altered random variability".
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #236 on: April 01, 2017, 02:30:39 PM »

No, I don't think they conflate anything such, whatever you may mean by "anthropogenicaly altered random variability".  ??? (I'll politely decline your explanation of what you mean by that)

I like epiphyte's analogy:

"Kind of like hitting the curb too hard when parking? Once you knock it out of balance the steering shakes, and if you ignore it for long enough then eventually the lugs shear and the wheel falls off."

The physical attributes of the wheel and the car dictate the way the wheel should spin. Small forcings from wear and tear caused by regular use and misuse slightly alter the way the wheel should spin. Over time these "forcings" increase in magnitude. At some point a tipping point is reached and the wheel falls off.


In this analogy a brand new car with intact suspension system dictate the natural variability of the wheels. Use and misuse of the car is antropogenic forcings. In this analogy Ding et al measures the variability of the wheel of an old car and claims the variations in wobbles and angles of the wheel is the intended natural variability of the car. But it is not. The variation he is measuring has already changed due to use and misuse.







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 #237 on: April 01, 2017, 02:38:17 PM »
AndrewB

I'd quite like to know what Archimid meant by "anthropogenicaly altered random variability".

A fair six sided dice has a natural variability. If you change the weight of one of the sides of the dice it will still have random variability but it will be a different variability. The variability of the weighted dice is "anthropogenicaly altered random variability"
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gerontocrat

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #238 on: April 01, 2017, 02:54:15 PM »
Given the sheer amount of additional heat absorbed and accumulated in the oceans over the last n years (where n is a largish number) due to AGW, is anything that happens in the oceans and the atmosphere purely a result of natural variation ? I think I am just supporting the anthropogenetically altered random variability suggestion, which certainly struck a chord with me.

And I don't just mean effects on arctic sea ice or ENSO etc. I mean just about anything that is happening in / to the biosphere.

 
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #239 on: April 01, 2017, 06:28:58 PM »
AndrewB

I'd quite like to know what Archimid meant by "anthropogenicaly altered random variability".

A fair six sided dice has a natural variability. If you change the weight of one of the sides of the dice it will still have random variability but it will be a different variability. The variability of the weighted dice is "anthropogenicaly altered random variability"

Archimid,
Actually if the dice is weighted the bias will quickly show, and you can mathematically separate it from the inherent randomness of the dice. In climate science where you have essentially "noisy" data, you can extract a "signal" of anthropogenic warming by various techniques (and in some cases by simply plotting a trend line), same as you can extract seasonality effects, leaving just the "natural climate variability". The expression "anthropogenicaly altered random variability" is not used. I now see that what you mean by that expression is the sum of natural variability + anthropogenic forcing signal.

Let me give you an example using Arctic sea ice extent in September.

In the chart below, you can choose a trendline, and you can see that the actual measured sea ice extent is randomly above and below the trendline.

What the Ding et al paper 2017 claims is that you can actually extract the trendline and then split the trend into two parts: 50-70% being anthropogenic forcing and 30-50% being "natural climate variability", or what they attribute to random long-term changes in atmospheric circulation. They make that claim based on how the models they used behave when the trend in GL-Z200 is removed from the data fed to the models, which they then notice have noticeably less ice loss, etc, etc, etc.

They also separate the anthropogenic signal from the noisy data in GL-Z200. Accordingly, they determine that changes in atmospheric circulation are mostly due to "natural climate variability" and in a smaller part due to anthropogenic forcing.

So your objection is indeed covered in the 2017 paper by Ding et al.

If there is anything you don't think I have made myself clear about in the above, don't hesitate to ask.

 

AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #240 on: April 01, 2017, 06:34:21 PM »
Given the sheer amount of additional heat absorbed and accumulated in the oceans over the last n years (where n is a largish number) due to AGW, is anything that happens in the oceans and the atmosphere purely a result of natural variation ?
...

No, nothing that happens these days in the oceans or the atmosphere is purely the result of natural climate variability, and nothing is purely the result of anthropogenic forcing. You use mathematical techniques to extract the anthropogenic forcing signal from the data. Extracting a "natural climate variability" signal from the data in much harder, because how do you extract an inherently random signal from noisy data? Mathematically, it's impossible.

This is why the Ding et al paper goes in a sort of convoluted reasoning about this: they run their model first with the the complete data, and then they remove what they claim is the "natural climate variability" signal (the trend in GL-Z200) from the data and assume what happens in the following model run is the anthropogenic forcing. See the objection to this by Michael E. Mann which I have already mentioned in one of my comments above.
« Last Edit: April 01, 2017, 06:47:04 PM by AndrewB »

epiphyte

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #241 on: April 01, 2017, 08:30:03 PM »
Yesterday I asked one of my kids (a west-coast engineering major home for spring break) to proofread a draft of the white paper I'm writing to illustrate the value offered by a technology startup of which I'm a co-founder. He said something to the effect of :

"Dad, this is good... but most people can hold fewer than five things in working memory. If you make an argument which requires more than three, you're pitching on the wrong end of the bell curve."

 - out of the mouths of babes...

That is a fabulous explanation, and I am henceforward going to use it to train all my PhD students and postdocs in grant writing. Please thank your son for me!

I'll do that :)   

... I'm chagrined to admit that it's close to the top of my own "Things I wish I'd Known 20 Years Ago" list!

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #242 on: April 01, 2017, 08:58:06 PM »
Yesterday I asked one of my kids (a west-coast engineering major home for spring break) to proofread a draft of the white paper I'm writing to illustrate the value offered by a technology startup of which I'm a co-founder. He said something to the effect of :

"Dad, this is good... but most people can hold fewer than five things in working memory. If you make an argument which requires more than three, you're pitching on the wrong end of the bell curve."

 - out of the mouths of babes...

That is a fabulous explanation, and I am henceforward going to use it to train all my PhD students and postdocs in grant writing. Please thank your son for me!

I'll do that :)   

... I'm chagrined to admit that it's close to the top of my own "Things I wish I'd Known 20 Years Ago" list!

Absolutely!  That was a jem..

Lennart van der Linde

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #243 on: April 01, 2017, 10:30:24 PM »
Just for the record Ding's reply to Rob Dekker's apology:
http://scienceblogs.com/stoat/2017/03/15/influence-of-high-latitude-atmospheric-circulation-changes-on-summertime-arctic-sea-ice/#comment-58682

“Hi Rob,
I really appreciate that you said that. I also learned something from you. The paper is very condensed because we submitted it as a letter. So we couldn’t cover everything in the main text. But I think we should include more description of Exp6 in the method part given its important role in illustrating our main conclusion.

In addition, we argued in the paper that 30% of the Z200 change over Greenland could still be due to anthropogenic forcing. So combining 60% and 70% (100% minus 30%) together (60% *70%) eventually gives us that about 40% of the sea ice trend since 1979 could be owing to a natural source. As I said, this is a very condensed letter-style article, which leaves almost no room for us to discuss this natural variability in detail. I think we will do better in the future if we would publish anything on a similar topic.
.
Again I really appreciate your interests and comments on our paper.

Have a nice weekend!

Best

Qinghua

Steven, I really appreciate your help in sorting this out. Many thanks!!”

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #244 on: April 01, 2017, 10:31:11 PM »

Yesterday I asked one of my kids (a west-coast engineering major home for spring break) to proofread a draft of the white paper I'm writing to illustrate the value offered by a technology startup of which I'm a co-founder. He said something to the effect of :

"Dad, this is good... but most people can hold fewer than five things in working memory. If you make an argument which requires more than three, you're pitching on the wrong end of the bell curve."

 - out of the mouths of babes...


Perhaps I'm confused.
If the objective of your paper is to win the hearts and minds of the (below)average consumer your son is correct. But if the aim is to influence professionals charged with corporate buying who are educated in the field, and who have been selected for their intellect as well as their education and experience, won't you lose a few by dumbing down your presentation?
Depending on the product of course, I'd assume that a rifle shot, or multiple shots, would be more effective than a presentation designed to be inclusive for those on the left side of the curve.


Not meaning to rain on your parade
Terry

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #245 on: April 01, 2017, 10:45:49 PM »
Thanks for all your interests in our paper.  I told Rob when I got his first email that I would like to discuss with anyone on stoat about our study. Since most scientific discussions about our paper have been happening on ASIF, I decide to start a discussion here. But what I will say only represents my own personal view and not that from the other 10 coauthors. I want to make this point very clear in the beginning. 

I think our paper is not a study to play with those trends/interdecadal changes or regression procedures. We actually provide a different perspective to understand the warming process in the arctic in the past three-four decades.

In the paper, we didn't only focus on temporal variability. We focused on spatial changes of the large scale circulations in the Arctic.
 
Under CO2 forcing, the ensemble mean of all IPCC models ( these are almost the best models we can use, trust and learn from) gives us a very uniform rise of Z200 everywhere in the Arctic and a much less rise in the lower levels of the troposphere (Fig. 4 of our paper).  This is because uniform CO2 warming( the greenhouse effect) will increase the depth of each atmospheric layer a little bit and thus the heights in the upper levels have the largest increase because of a cumulative effect of all small increases of layers below. So we can only see less increases of the heights in the lower levels but higher increases of heights at the higher levels.   

In contrast , the observation show a very different structure with the most significant rise of geopotential height over Greenland at all levels from the surface to the upper troposphere.  we call this type of change as a barotropic structure change.
 
I think my understanding of this difference is that the observed circulation pattern is a classical heat wave pattern that favors maximum warming in the lower boundary to melt sea ice and the build-up of the heat wave pattern over the Arctic in the past decades is due to some low-frequency variability of atmospheric Rossby wave originated from the tropics.

In other words, the wind changes due to some remote forcing  in the past 30to 40 years pushed more air masses into the Arctic and then air there became more condensed and warmed. I think this is an important dynamical factor that caused so fast sea ice melting in the past decades.   

It is still under debate whether this remote tropical forcing is internal or forced by the CO2 rise. What I learned from those IPCC models is that the observed tropical forcing pattern since 1979, especially in the recent decade is not the pattern favored by CO2 forcing. Please see our 2014 paper on this tropical linkage.

please see here about heat wave
http://scijinks.gov/heat/

or here on wiki page: the formation part

 https://en.wikipedia.org/wiki/Heat_wave

however, the temperature warming pattern/structure favored by anthropogenic forcing in JJA in the Arctic is uniform everywhere with weaker intensity in the boundary layer. That is why, ( my personal view), most iPCC models cannot reproduce so fast sea melting as that observed if the models are only forced by Co2 forcing. 

An analogy of this comparison is that anthropogenic forcing on the Arctic can be looked as turning on a furnace to warm a room. Internal forcing looks like putting a heated blanket on someone who feels cold. So this blanket ( as extra warming in the boundary layer in the real world) warms the guy faster.

In this paper, we just tried to use a model approach to remove this blanket and see how the room temperature increase melts sea ice. We also realized that some heating from the heated blanket to ice may also be due to the room temperature increase. In our attempt to do a final attribution analysis, we further removed that part and eventually got to that 40% contribution.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #246 on: April 01, 2017, 11:14:43 PM »
Welcome to the ASIF, Qinghua, and thanks for dropping by to further explain the paper.
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #247 on: April 01, 2017, 11:50:00 PM »
Quote
In contrast , the observation show a very different structure with the most significant rise of geopotential height over Greenland at all levels from the surface to the upper troposphere.  we call this type of change as a barotropic structure change.
 
I think my understanding of this difference is that the observed circulation pattern is a classical heat wave pattern that favors maximum warming in the lower boundary to melt sea ice and the build-up of the heat wave pattern over the Arctic in the past decades is due to some low-frequency variability of atmospheric Rossby wave originated from the tropics.

In other words, the wind changes due to some remote forcing  in the past 30to 40 years pushed more air masses into the Arctic and then air there became more condensed and warmed. I think this is an important dynamical factor that caused so fast sea ice melting in the past decades.
This was noted by some commenters on the Arctic Sea Ice Blog back in 2011 and 2012 (the Forum didn't exist yet), notably by bloggers like Wayne Davisdon and Chris Reynolds. I wrote a blog post about it called Signs of Arctic climate change. I believe Wayne posited that it had to do with the Cold Pole shifting to Greenland because the sea ice-covered Arctic Ocean no longer got cold enough to keep the Cold Pole there.

In a discussion on this Cold Pole here on the Forum in 2013, Chris Reynolds wrote:

Quote
I have some sympathy with Wayne's cold pole idea. However the geopotential height well still centres clearly on the Arctic ocean, and I still see this as an important problem with Wayne's view. I need to explain.

(...)

Now the centre of action of the new summer circulation is over Greenland. From the GPH plot it can be seen that there is a ridge of GPH over Greenland. There always has been a ridge, but it is now about 50m higher than typical heights pre 2007. But it is clear that from the point of view of GPH the centre of action remains over the ice pack, not over Greenland. The Jetstream flows around the GPH well.

This GPH ridge is the cause of the new summer pattern, what causes the ridge is not known with certainty, it may be due to Eurasian snow retreat, but there may be a role for Arctic sea ice loss and formation of low pressure over the Siberian coast. I suspect that once the ridge is formed it creates connections with a region around it (3000km distant) via atmospheric waves which drive the formation of a belt of low pressure tendency in response to the Greenland GPH ridge.
And over on the Blog, a year earlier, he wrote:

Quote
This high pressure anomaly over Greenland is actually the result of a GPH ridge extending northwards from the mid latitudes, Due to the dominant wavenumber of the rossby waves, wavelength and speed, they set up a semi permanent standing wave that creates this ridge over Greenland.

This is exactly what Dr Francis was talking about in her paper on patterns in the jet stream getting stuck! The relevant pattern of the jetstream is even printed in one of the figures.

And I didn't think to connect the two patterns.

Stupid!
But to get back to Qinghua's quote. It's an interesting idea that "the wind changes due to some remote forcing  in the past 30to 40 years pushed more air masses into the Arctic and then air there became more condensed and warmed. I think this is an important dynamical factor that caused so fast sea ice melting in the past decades".

That brings me to the question I have had since first reading about the paper: Let's say most of the natural variability has to do with wind changes pushing more air masses into the Arctic. Do we have any way of knowing when this natural variability might switch again and thus slow down the current rapid rate of Arctic sea ice loss? Or is that now a new research route?
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #248 on: April 02, 2017, 12:18:08 AM »
Dear Quinghua

Nice to see you pop out of the blue just like that.

Since Neven and I seem to be the only ones awake at this time of night, I will also have a go at your thoughts.

Concerning “anthropogenic forcing in JJA” , I have previously argued on the Forum ( see http://neven1.typepad.com/blog/2014/05/piomas-may-2014.html?cid=6a0133f03a1e37970b01a73dc49f69970d#comment-6a0133f03a1e37970b01a73dc49f69970d )  that a large increase in Tropical cyclone activity in 2004-6 could have contributed to the advection of hot, dry air aloft, which could have reached Greenland and caused the observed jump in Z200 around that time.

Concerning your idea of “putting a heated blanket on someone who feels cold. So this blanket ( as extra warming in the boundary layer in the real world) warms the guy faster.” It is actually not what happens in real life. If the temperature of a body has become too low for the heart to beat properly and pump blood around in the body, it will not warm the guy faster, if you put a heated blanket (e.g. as snow cover in the real world) on the poor guy. It will actually isolate his cold body from the heat in the room! If the Arctic sea ice is genuinely cold, as it was before 2005 roughly speaking, it was almost impossible to get rid of the multi-year sea ice, no matter how hard you tried to heat it.

The heat waves identified by you in the reanalysis may only be visible over Greenland due to the fact that very few upper air balloons are launched regularly outside Greenland these days. Previously, a number of observational platforms were in use (e.g. ice islands, submarines, ice-breakers and research stations etc.) in the Arctic. The decline in Arctic upper-air observations is a serious threat – even though we tend to think that Reanalysis nowadays come close to the real thing.

Cheers P



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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #249 on: April 02, 2017, 12:25:38 AM »
Hi Neven,
To be honest, I don't know the answer.
In my view, The easiest way to check our finding is to examine a long free run of a fully coupled model ( that includes air-ocean-sea ice)  without CO2 forcing. There are plenty of these runs available in our community. I am sure the heat wave circulation pattern would be the key player in these runs to melt sea ice in JJA.
 
We have got some very positive results on this direction and I am working on a paper with Axel and Eric so I don't want to say too much about it. I hope you can understand it.
Through understanding this internal sea ice melting mode, which is similar to what we have observed in the real world, in a long free run, we would know better about its periodicity, evolutions and oceanic or atmospheric preconditions of turning points, etc.