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Author Topic: Arctic sea ice changes: Natural variation vs human influence  (Read 150747 times)

Qinghua ding

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #250 on: April 02, 2017, 12:40:24 AM »
Hi P-maker ,
Thanks for your comment. I will read the thread you referred to.
I agree reanalysis is not perfect to reflect what is really happening over the Arctic ocean. But I also checked satellite temperature data ( I think it is RSS or UAH or something else) . It is very consistent with reanalysis over the ocean showing a temperature warming trend in the troposphere. I will show you a plot if you are interested to take a look. Actually, I think all these satellite informations have been assimilated into reanalyses.
Best
Qinghua 

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #251 on: April 02, 2017, 04:04:09 AM »
Dr. Qinghua,

First I would like to thank you warmly for accepting to participate in a discussion of your Arctic sea ice 2017 paper here on ASIF, which I believe is a much better venue than the comments section on the Stoat blog.

Personally I have two burning questions for you. The first is a scientific question, the second is in the moral/philosophical domain. Here they are:

1. In the abstract of your 2017 paper, one can read: "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." My question (in two parts) is: how confident are you and your co-authors about these numbers, and what scientific experiment could be made, or physical evidence would be required, if any, to invalidate this claim?

2. 2017 just saw the lowest maximum Arctic sea ice extent on record (NSIDC), 2016 was the third hottest year on record in a row and 1.1C above pre-industrial (WMO), 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 according to ice core data (Keeling curve). And 25% of the world's corals died in 2016, as a result of ocean warming.
As a climate scientist and seeing we as human beings are on a path to a global climate disaster, do you feel any sense of responsibility or moral conflict when authoring a paper that clearly weakens the scientific, economic and political case for the urgent adoption of radical emissions reductions policies, to avoid the worst effects of global warming / climate change / ocean acidification?

Thank you again for willingly joining this discussion here on ASIF.

GeoffBeacon

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #252 on: April 02, 2017, 05:49:49 AM »
Welcome Dr. Qinghua,

Quote
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.


I remember asking one climate scientist what he thought about Jennifer Francis' claims that a warmer Arctic slows down the jet stream and creates meridional jet stream flow, changing the pattern of Rossby waves. I asked if changes in weather patterns were due to such an effect?

At that time, he said it wasn't certain whether the changes were best explained this way. The alternative explanation was the the Pacific Decadal Oscillation.

Dr Francis' describes a change driven by anthropogenic greenhouse gas emissions but the PDO is internal variability.

Do you have a view on Dr Francis' work?

Is a Francis/PDO dichotomy still reasonable?
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Neven

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #253 on: April 02, 2017, 11:39:18 AM »
Quote
As a climate scientist and seeing we as human beings are on a path to a global climate disaster, do you feel any sense of responsibility or moral conflict when authoring a paper that clearly weakens the scientific, economic and political case for the urgent adoption of radical emissions reductions policies, to avoid the worst effects of global warming / climate change / ocean acidification?

This again feeds into the myth that mainstream scientific opinion has been that 100% of Arctic sea ice loss was due to anthropogenic causes, and that now suddenly this paper puts a spanner in the work. This is what climate risk deniers use for their spin.

But it isn't true. The question has always been how much of a role natural variability plays in the rapid decline we have seen over the past 30 years. There are numerous papers on the influence of the PDO, the AMO, etc. This is just one more such paper.

The paper doesn't 'clearly weaken the scientific, economic and political case for the urgent adoption of radical emissions reductions policies' in itself. It's the spin that does that.

I don't know what can be done wrt science communication to prevent this kind of spin. Does that mean that Ding and his co-authors shouldn't pursue what they deem interesting, constructive science? I'd say no.

But this is an entirely different discussion and I'd rather we'd take it elsewhere, and use this thread to focus on the science in the paper.
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Random_Weather

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #254 on: April 02, 2017, 11:57:47 AM »
@ Qinghua

"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).  "

y, i have look your used models as shown in the Supplementary. It turns out, that the mean of model you used have to much ice, to strong aplitude and a to low sea ice trend. On the other Hand, z200 is strong correlate with SIC (Sea-Ice-Concentration) in Models, since the Models you used have a less trend then observed, its no wonder, that increase of z200 is less. Also the pattern, you cant rule out, that this pattern would not exist if Models would loose ice the same as in Observation.

Anyway, as also shown on stoat, if you pick the best model to the parameters Annual Extent, Trend and Amplitude ( MPI-ESM-MR*) its nearly perfect reproduce the observed SIC-Minimum (September)

http://www.directupload.net/file/d/4674/5kode2k9_png.htm

See also here:
http://scienceblogs.com/stoat/2017/03/15/influence-of-high-latitude-atmospheric-circulation-changes-on-summertime-arctic-sea-ice/#comment-58603
http://scienceblogs.com/stoat/2017/03/15/influence-of-high-latitude-atmospheric-circulation-changes-on-summertime-arctic-sea-ice/#comment-58580

*via climate-explorer RCP2.6


In other Words, if you say, the models show the forced response mainly due GHGs, this would imply, that the discrepance trend and pattern in z200 can also be just a result of unrealistic arctic sea ice states in Models.

Lennart van der Linde

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #255 on: April 02, 2017, 11:59:53 AM »
Dear dr Ding,

Thank you for replying here at the ASIF.
What I'm wondering about after reading your paper is how it relates to the work of Maslowski et al 2014:
http://www.iopan.gda.pl/profima/Strona%20RO/chapter_5.pdf

They say:
“Based on our model results and limited observations, we found that heat content of the Western Arctic ocean in the top 120 m has been increasing since the late 1990s and appears to be contributing to the rapid sea ice decline there. Our model analysis implies that the advection of warm water from Bering Strait regulates the retreat of sea ice and contributes to the relatively high surface air-sea fluxes over the Chukchi shelf. Earlier ice melt in the Chukchi Sea allows increased absorption of solar radiation and warming of water over the shelf, before it is exported into the Beaufort Sea where it can further contribute to sea ice melt. Based on evidence from observations and from our model, we argue that not all the heat content in the western Arctic Ocean gets removed back to the atmosphere every year before freezing in fall and early winter. We hypothesize that instead the remaining heat above the halocline and below the mixed layer acts to reduce sea ice growth in winter and preconditions an earlier ice melt each year, which further increases heat content in the region, thus resulting in a positive feedback accelerating summer reduction of the sea ice cover. The presence and spreading of a subsurface heat source in the western Arctic Ocean and the large-scale sea ice drift of the Beaufort Gyre help explain why the sea ice has continued to decline most dramatically in that part of the Arctic Ocean, even when large-scale atmospheric conditions were not always most favorable to such a decline (i.e. when the Arctic Oscillation Index was neutral or extremely negative).”

Earlier Maslowski et al 2012 had said:
http://www.oc.nps.edu/NAME/Maslowski%20et%20al.%202012%20EPS%20Future%20of%20Arctic%20Sea%20Ice.pdf

“a system-level understanding of critical Arctic processes and feedbacks is still lacking. To better understand the past and present states and estimate future trajectories of Arctic sea ice and climate, we argue that it is critical to advance hierarchical regional climate modeling and coordinate it with the design of an integrated Arctic observing system to constrain models…

There are many Arctic climatic processes that are omitted from, or poorly represented in, most current-generation GCMs. These processes include the following: oceanic eddies, tides, fronts, buoyancy-driven coastal and boundary currents, cold halocline, dense water plumes and convection, double diffusion, surface/bottom mixed layer, sea ice–thickness distribution, concentration, deformation, drift and export, fast ice, snow cover, melt ponds and surface albedo, atmospheric loading, clouds and fronts, ice sheets/caps and mountain glaciers, permafrost, river runoff, and air–sea ice–land interactions and coupling…

the development and use of high-resolution regional Arctic climate and system models and process-level subsystem models are important stepping stones in the coming decade for dedicated studies of regional processes and feedbacks, tests of new parameterizations and ensemble simulations, and the prediction of sea ice and other components of the Arctic System in a warming climate.”

And more recently Notz et al 2016 say:
http://www.geosci-model-dev.net/9/3427/2016/gmd-9-3427-2016.pdf

“it is sobering to see to which degree simulations of its past and future evolution differ across large-scale coupled models (e.g. Massonnet et al., 2012; Stroeve et al., 2012), how much retrieved sea-ice properties from one satellite product differ from another satellite product (e.g. Meier and Notz, 2010; Ivanova et al., 2015), and in how many aspects the simulations and observations differ from each other (e.g. Massonnet et al., 2012; Stroeve et al., 2012; Turner et al., 2013; Stroeve et al., 2014; Gagné et al., 2015; Shu et al., 2015).We do not yet know how much these differences are irreducible, for example because they are due to internal variability of the climate system, and how much they reflect biases in the model’s representation of the functioning of the climate system in high latitudes. This lack of understanding hinders further improvements of our models, an identification of observational needs, and a robust assessment of the most likely future evolution of sea ice in response to the ongoing climatic changes on Earth.”

I guess this comes down to the question AndrewB asks above about how confident we can be about the model results of your recent paper. Are these models good enough yet to warrant our confidence in them, or should we be quite sceptical still until they have been substantially improved, as Maslowski et al and Notz et al seem to imply?
« Last Edit: April 02, 2017, 12:29:17 PM by Lennart van der Linde »

epiphyte

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #256 on: April 02, 2017, 05:31:28 PM »
@Qinghua ding - Wonderful to see you here!

And of course I have a question for you... Given that the current state of the arctic is a result of anthropogenic forcing and natural variation in exactly the proportions your paper suggests, what does that portend for the future? Do the fluctuations caused by natural variation accelerate the transition to a new regime, or rather do they retard or even prevent it?

(Needless to say, I have my own opinion on this, but it's hardly an informed one, so I'll keep it to myself for now!)

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #257 on: April 02, 2017, 06:08:45 PM »
First, thanks to Dr. Ding for writing this paper and taking the time to post here.

Thanks AndrewB for your detailed response. You are very much right when you say:

"I now see that what you mean by that expression is the sum of natural variability + anthropogenic forcing signal".


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".

I understand that is what they did. I think they removed any known variation relevant to their experiment and the remaining noise they call "natural variation" for the 1979-2014 time period. I think they would have been right in call it random variation or climate variability, noise or any other word that didn't imply lack of human interference.

But when they call the noise "natural variation" they imply that the noise is free of human interference. Given the shortness of the experiment and given knowledge of how sensitive sst's are to human forcings and given current events(which are outside their experiment), I find it very highly unlikely that the noise has no anthropogenic signature. Specially if they refer to AGW as just CO2 warming. If they disregard other anthropogenic forcings like aerosols and deforestation, or if they disregard feedback effects of CO2 forcing like albedo changes and changes in the hydrologic cycle, all of which have temporal and spatial effects on natural variability, then the use of "natural variability" becomes even worse.

My argument is that their semantics are wrong, not their methods. I admit, the semantic may seem trivial because calling the noise "natural variation" may be correctly interpreted by many scientist as just noise. So calling the noise "natural variation" may be very convenient. But in a politically charged, life and death argument like the climate change argument, utmost precision is required.

 When they say that atmospheric currents may be up to 60% responsible for Arctic sea ice reduction I agree with them because it makes sense. But if they say natural variation  may be up to 60% responsible for Arctic sea ice reduction that flies in the face with everything else I know. Climatologically speaking, pure natural variation dictates that the earth should be well underway to the next ice age. According to the most pure signal of natural variation, Arctic sea ice should be growing. Instead we are seeing a flash melt (in climatological terms).


I fear that I may be speaking over you and others and that is certainly not my intention. I hope I made my point more clear.

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Jim Williams

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #258 on: April 02, 2017, 06:22:02 PM »
I still do not see how you can purport to distinguish signal from noise using models with no proven skill.

Jim Pettit

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #259 on: April 02, 2017, 07:01:04 PM »
I still do not see how you can purport to distinguish signal from noise using models with no proven skill.

There are a lot of people here; to which "you" are you referring?

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #260 on: April 02, 2017, 07:09:42 PM »
I still do not see how you can purport to distinguish signal from noise using models with no proven skill.

There are a lot of people here; to which "you" are you referring?

Well...since it is the skill of the GCM I question that would have to be anyone who attempts to use the GCM to make a point.

We now have weather models that work just fine for about ten days before failing badly.  I've seen no evidence at all that the GCM can even do 10 days -- and I've seen quite a bit of evidence they cannot do one year.

<JP: This thread is about a particular published paper that discusses spatial changes in large scale Arctic circulations, and their effect on things such as ice coverage, etc. It's not the place to rehash and reteach the difference between weather and climate, and why comparisons between short-term weather forecasts and long-term climate predictions aren't particularly valid. (See more here if you're interested)>

<Jim W., I'll let this one go through, but it's really WUWT-level. I would kindly ask others to not react to this; N.>
« Last Edit: April 02, 2017, 09:04:10 PM by Neven »

jai mitchell

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #261 on: April 02, 2017, 08:24:44 PM »
Dr. Ding,

the 2003-2005 increase in Chinese high-temperature aerosols has been identified as a driver in the negative PDO during that decade.  These were confirmed by CMIP5.

However, the CMIP5 does not include the suppression of lapse rate feedbacks from upper troposphere aerosols.  Secondary cloud effects of SO2 aerosols are also not well modeled.

Many studies have shown that these aerosols also work much more intensely in providing cooling in the arctic, with some estimates that over 50% of GHG forcing could be offset by these aerosols.  Leading to a nearly instant jump of temperatures by 1.8C (edit note: regionally in the arctic not globally averaged)

In view of the rapid changes in atmospheric circulation/translation from the tropics both from the East Pacific Warm Pool and the Gulf of Mexico this last winter, and the observation that China has significantly reduced their aerosol emissions from high-temperature industrial processes, it is very clear that the current models do not accurately capture these impacts.

with the paleoclimate analysis of the early Pliocene period where we had similar CO2 levels showing a north Canadian equable climate regime.  It is clear that these SO2 emissions have prevented a shift into a climate regime much more in line with the early Pliocene period that the one we have been studying for the last 50 years.  A bifurcated state of the global climate, one that is not captured by the CMIP5 ensembles.

I assert that, in the total absence of aerosol emissions and at 560 CO2e GHG abundance, we will see an arctic ice free condition during the Summer Solstice.  I also assert that we will continue to see rapid changes in atmospheric circulation, far above the modeled predictions, and that we will see an effective ice free state in the arctic in the next 6 years (Sept. minimum).

This means that we have already surpassed the threshold for 2.3 C, that rapid feedbacks will destabilize the boreal forest, the amazonian tropical forest and the boreal permafrost, at rates far greater than the decomposition that we are already noting are far and above the predictions of CMIP5.  These feedbacks and others (ocean acidification impacts on Dimethyl Sulfide production), Arctic ocean albedo shifts from algae blooms, reduction in far-infrared emissivity from open ocean in the Arctic) will produce additional warming, in the absence of anthropogenic activity that will lock-in >3.2C of warming at current GHG abundance levels (and in the absence of aerosols).

And yet our best scientists still talk as though we may avoid +1.5C of warming, that we still have a carbon budget left and that the Summer arctic sea ice will likely be maintained through 2060.  Axel has stated this to me very recently and unequivocally.

So how are we supposed to take a body of scientists who speak in terms that fit a prescribed narrative, are technically constrained by 'common knowledge' assumptions and even terminologies like 'natural variability' that are assigned to things like atmospheric circulation patterns that have a definitive anthropogenic fingerprint?

Especially in the view that anthropogenic aerosols have significantly reduced the rate of sea ice loss over the last 4 decades, and in their absence the expected loss would far exceed the 30%-60% 'natural variability' that your paper attributes to Z200 GPH tropical translations.
« Last Edit: April 02, 2017, 10:04:10 PM by jai mitchell »
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #262 on: April 02, 2017, 09:06:29 PM »
Lots of questions. I'm sure everyone understands if Qinghua is too busy to answer.  :)
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Qinghua ding

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #263 on: April 02, 2017, 10:50:37 PM »
Many thanks for all your interesting/burning/critical/constructive comments and questions on our paper and my thoughts.

The first thing I want to say is that no one should expect that our short paper could fully address the most challenging question we are facing now in the polar community.

I am 100% sure that the mechanism of that "polar heat wave idea" is correct, since this is the only way ( in my personal view) to explain everything ( "everything" here means changes in sea ice, winds, temperature, vertical velocity and radiation fields) that we have observed in the Arctic  since 1979.  If we only considered CO2 forcing, it always puzzled me that some observed features in the Arctic cannot be well supported by either model results or dynamics of the Co2 greenhouse effect. But I have to say that we didn't consider aerosol in our work.

That 40% contribution from natural forcing is what we concluded based on the facts of our modeling experiments and a IPCC/NCAR model evaluation task.

In the paper, we used three steps of experiment/evaluation to reach to this number.

A. the first set of experiments

model: ECHAM5 with a simple ocean/sea ice:

purpose:
to determine the direction of causality of observed connections between the circulation and all other variables.

conclusion:
1. the experiments qualitatively prove that the observed circulation change is important to regulate all other variables 
2. and these atmospheric changes in JJA cannot be explained by sea ice melting if we only put Arctic sea ice decline in the model

B. IPCC/NCAR models evaluation 
purpose: to consider whether forced responses of models to CO2 forcing can explain some observed features and understand how much the observed circulation change is still forced by CO2 forcing

Conclusion: we found that CO2 forcing cannot reproduce some features in the observation and only a part of the circulation change in the arctic is due to CO2 . 

C. the third set of experiments:

model: a more sophisticated sea ice and ocean model ( a part of CESM) without atmosphere.
purpose: quantify how much of sea ice melting is due to the circulation change
conclusion: circulation related forcing at the interface between sea ice and atmosphere can substantially melt sea ice

This is our strategy to tackle the problem. I think this is not the perfect one but the best one we could come up with by using available in-house tools. As I know, our study is the first one to use a numerical model to tease the influence of the circulation on sea ice apart from other influences.  So I think it is an important step forward to open up a new direction to understand arctic sea ice.

In the paper ( the first paragraph in the conclusion part) , we acknowledged this limitation.
"
 Our conclusions are based on experiments involving several models
rather than one integrated model. POP2CICE4 simulations are
used to allow for a realistic simulation of sea-ice variability, while
ECHAM5 simulations allow for realistic simulations of the linkage
between circulation and thermodynamic drivers of sea-ice loss,
while permitting nudging to observed wind fields. The close
agreement of patterns of thermodynamic forcing on sea ice between
the ECHAM5 and POP2CICE4 provides confidence in combining
these two tools."

another part in the paper to discuss a possible way to improve our understanding

"Therefore, a substantial
contribution of tropical Pacific variability on sea ice loss via this
teleconnection is to be expected. A further examination of this
question will require a modelling framework that reproduces the
tropics high latitude linkage faithfully and efficiently."

In my current work, I am working on a new project to repeat the experiments using a fully coupled model. That means combining  sets A and C together into one integrated experiment to understand how the recent wind changes influence sea ice. I am sure with this better approach, we will move closer  to the real contribution of natural forcing on sea ice melting but I still wouldn't say that I am 100% sure that the new number is correct because we never know whether another model would give the same number.


 
« Last Edit: April 02, 2017, 10:58:20 PM by Qinghua ding »

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #264 on: April 03, 2017, 12:16:31 AM »
What I don't understand in all this discussion is why that presumed natural variability that shows as a GPH ridge over Greenland and all associated perturbed circulation so detrimental for the ice cannot have been caused, indirectly, by the so many changes AGW has directly caused, in the SSTs, the humidity, the glaciers, the sea ice and so on. Just what comes first to the head of a layman...

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #265 on: April 03, 2017, 03:26:34 AM »
I still do not see how you can purport to distinguish signal from noise using models with no proven skill.

Within the limits of the models, signal from noise can be mathematically distinguished. But when the real world is taken into account, the models become wrong.

Let's think of a very basic model that is right so often that most people accept it as truth. Distance = Time x Speed. That model, D=ST is wrong if enough accuracy is required. To meet that accuracy other models are incorporated like friction, acceleration, wind speed, wind direction, air composition. Once these models are added accuracy increases but only to a point. If extreme accuracy is needed then more models must be added and sometimes completely replaced to meet the need.


Climate models are no different. They have been built with sweat and toil over time to account for more and more accuracy, more and more phenomena. Will they ever be complete? I mean will they ever predict the climatic condictions with 99.99% accuracy for every location of the world for decades even centuries ahead? I think they will, just like astronomists have the movements of the universe figured out to an extreme degree and particle physicists have the small scales figured out.

Are the models there yet, no. Regrettably not. Have they shown enough skill to take action? God yes. Specially with the preponderance of evidence from virtually all sciences.



Qinghua ding:

Quote

 But I have to say that we didn't consider aerosol in our work.

...snip...

"Therefore, a substantial contribution of tropical Pacific variability on sea ice loss via this teleconnection is to be expected. A further examination of this question will require a modelling framework that reproduces the tropics high latitude linkage faithfully and efficiently."


I look forward to your next work.
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GeoffBeacon

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #266 on: April 03, 2017, 04:32:48 AM »
Overland et.al. Nonlinear response of mid-latitude weather to the changing Arctic

Abstract:
Quote
Are continuing changes in the Arctic influencing wind patterns and the occurrence of extreme weather events in northern mid-latitudes? The chaotic nature of atmospheric circulation precludes easy answers. The topic is a major science challenge, as continued Arctic temperature increases are an inevitable aspect of anthropogenic climate change. We propose a perspective that rejects simple cause-and-effect pathways and notes diagnostic challenges in interpreting atmospheric dynamics. We present a way forward based on understanding multiple processes that lead to uncertainties in Arctic and mid-latitude weather and climate linkages. We emphasize community coordination for both scientific progress and communication to a broader public.

Relevant here?
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #267 on: April 03, 2017, 09:24:11 AM »
Many thanks for all your interesting/burning/critical/constructive comments and questions on our paper and my thoughts.

Many thanks for taking the time and trouble to provide so much input here. I have taken the liberty of reproducing your comment (together with one of Rob's) over at:

http://GreatWhiteCon.info/2017/03/is-arctic-ice-loss-driven-by-natural-swings/#comment-221177

I hope that's OK with you both? Please let me know ASAP if not!
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #268 on: April 03, 2017, 11:27:21 AM »
From 2008:

Point of No Return
Quote
A new study completed by a team of US, Norwegian and German researchers may now provide some clues. Published in the scientific journal Geophysical Research Letters in November, the study posits that a dramatic change in atmospheric circulation patterns has taken place since the beginning of the decade, with centers of high pressure in winter shifting toward the north-east. The new pattern of sudden climate change is characterized by "poleward atmospheric and oceanic heat transport," the authors write in the study, a transport which drives temperature increases in the Arctic. The discovery was made using specialized filters that allow one to follow changes to high pressure centers over time.

Behind the complex language and impenetrable calculations upon which the study is based, however, is a frightening possibility: climate change in the Arctic could already have reached the point of no return. Climate researchers have long been warning of such "tipping points," and that crossing them could mean irreversible developments for eco-systems and humanity. In the case of the Arctic, that could mean a complete disappearance of ice in the region during the summer months. Such an eventuality would then further magnify global warming, due to the fact that bright white ice reflects sunlight back into the atmosphere whereas dark colored land and ocean absorbs heat.

"In the case of Arctic Sea ice, we have already reached the point of no return," says the prominent American climate researcher James Hansen, director of the Goddard Institute for Space Studies at NASA.

Winter in the Arctic has long been determined by what researchers refer to as a "tri-polar" pattern. The interaction among the Icelandic Low, the Azores High and the subtropical high in the Pacific led to primarily east-west winds, a pattern which effectively blocked warmer air from moving northward into the Arctic region.

But since the beginning of the decade, the patterns have changed. Now, a "dipolar" (bipolar) pattern has developed in which a high pressure system over Canada and a low pressure system over Siberia have the say. The result has been that Artic winds now blow north-south, meaning that warmer air from the south has no problem making its way into the Arctic region. "It's like a short-circuit," says Rüdiger Gerdes, a scientist at the Alfred Webener Institute for Polar and Marine Research and one of the five authors of the study.

Gerdes and his co-authors fear that the changes in the Arctic could mean that a "new era of global-warming-forced climate change" has begun. The volume of greenhouse gas emissions like CO2 and methane into the Earth's atmosphere could have resulted in a permanent change in the global climate system.
link


And while looking for that paper I found this:

http://onlinelibrary.wiley.com/doi/10.1029/2006GL027146/abstract


The way I read it is, greenhouse gas induced warming in the 1990s reduced sea ice thickness, which initiated changes in Arctic atmospheric circulation, bringing warm air into the Arctic, amplifying melting.

So much for 'natural' variability. 

« Last Edit: April 03, 2017, 12:16:16 PM by Cid_Yama »
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crandles

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #269 on: April 03, 2017, 01:18:08 PM »
Given the way certain people have been quoted over on Stoat, I find it distrurbing and embarrassing that those people find it ok to proceed to ask questions (and presumably think they deserve some sort of answer) without at least first giving some sort of apology. This forum has gone a long way downhill. I would like to offer my apologies to Qinghua Ding and other scientists for what they have to put up with.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #270 on: April 03, 2017, 02:22:04 PM »
Heartily seconded, crandles.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #271 on: April 03, 2017, 02:28:19 PM »
I agree with the apology, but I think it's also good that scientists try to understand where it comes from and don't take it personally.
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #272 on: April 03, 2017, 02:50:32 PM »
I dont think so, because for making constructive critics there should not be a apology, only if someone is making claims about the person which is always not constructive. Its also okay for the Autors, which are able to see, how their Paper make an impact to the public and get some thougths about what could cause missunderstandings from the Paper.

So, because you indirect speaking here of me, i never aks about a answer to my question, its enough if he reads what i had asked. To make my standing clear, i dont claim there is a error in the Paper, i only want to tell, that there driven conclusion (about nat. Variability) is not highly confident, because their choosen Models(in the Paper) show to much (in Hindcast) Extent, to strong Extent-Aplitude and a to low Extent-Trend, if you choose the best model to this parameter, the decrease in ice(after 2005) is nearly like observed, so if the Autors of the Paper claim, that the mean of the models would represent the forced response (mainly GHG) and the rest is more like nat. Variability, the claim would be weak, because its depends on the model which are used, since Models have a to weak decrease in sea-ice, its not clear that the models z200 (also the Pattern) would not produce nearly the same pattern of z200 if they are allowed to decrease ice the same much as in observation.

In other words:
The Model which is nearly the observed Parameters (Annual-Extent, Extent-Aplitute and Trend) in Hindcast 1979-2005, also have no problem to decrease strong as in observation since 2005...

So my Question for you is: Why should i apologie for this?

Given the way certain people have been quoted over on Stoat, I find it distrurbing and embarrassing that those people find it ok to proceed to ask questions (and presumably think they deserve some sort of answer) without at least first giving some sort of apology. This forum has gone a long way downhill. I would like to offer my apologies to Qinghua Ding and other scientists for what they have to put up with.
« Last Edit: April 03, 2017, 02:56:39 PM by Random_Weather »

DrTskoul

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #273 on: April 03, 2017, 03:07:07 PM »
I agree with the apology, but I think it's also good that scientists try to understand where it comes from and don't take it personally.

Exactly...

It also comes with the territory of public engagement.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #274 on: April 03, 2017, 05:54:22 PM »

So my Question for you is: Why should i apologie for this?

Constructive criticism is great, no problem with that.

Ideally, it is possible to phrase constructive criticism or a question with appropriate respect where it is due. Phrasing as a question rather than stating as a clear certainty may help. For example: Perhaps I am missing something, but doesn't X imply Y?

The parts quoted on Stoat (see comment 107), are not constructive criticism, more like deliberate denigration. I don't have any problem with you or anyone else asking a question or providing constructive criticism. Deliberate disrespectful denigration is another matter.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #275 on: April 03, 2017, 06:09:53 PM »
Given the way certain people have been quoted over on Stoat, I find it distrurbing and embarrassing that those people find it ok to proceed to ask questions (and presumably think they deserve some sort of answer) without at least first giving some sort of apology. This forum has gone a long way downhill. I would like to offer my apologies to Qinghua Ding and other scientists for what they have to put up with.
Since I am one of those "certain people" that were quoted on the Stoat blog by a commenter who goes by the name of Kevin O'Neill there and I suspect is ktonine here on ASIF, I will just state for the record that I don't feel my phrase that ktonine/Kevin O'Neill cross posted requires an apology, and I certainly do not intend to apologize for it.
Here is the phrase that was quoted:
Quote
"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."
If you read the Ding et al 2014 paper, then read the Ding et al 2017 paper, it is quite obvious that both papers use a similar methodology, rely on similar or identical assumptions (for example, that geopotential height is representative of atmospheric circulation changes), and reach a similar if not identical conclusion: the attribution of up to 50% of the observed warming or up to 50% of observed Arctic sea ice decline, to "natural climate variability".

ktonine then misconstrued my phrase into an accusation of "rigging the results" or malfeasance or whatever went through his mind at the time. Perhaps then it is ktonine who should apologize for this, and not me? :P
« Last Edit: April 03, 2017, 08:38:56 PM by AndrewB »

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #276 on: April 03, 2017, 06:30:50 PM »
Andrew, now that you insist, to insinuate of having preposterous claims and using tools that justify priori conclusions sound like some of the worst insults you can throw to a scientist or to anyone doing or pretending to do an investigative work with rigor.
I mean, isn't it obvious?
But yeah, don't apologize, you're behind, hidden in your desk, safe, Eric S. has shown really ugly arrogance too.
Dr. Ding and Rob Dekker keeping the level so high in contrast. Chapeau

Random_Weather

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #277 on: April 03, 2017, 06:37:21 PM »

Constructive criticism is great, no problem with that.

Hope so :-)


Ideally, it is possible to phrase constructive criticism or a question with appropriate respect where it is due. Phrasing as a question rather than stating as a clear certainty may help. For example: Perhaps I am missing something, but doesn't X imply Y?

I agree, but on online discussion we often forgott this, because we are in a distance of a face to face discussion. I therefore i think ist pretty normal..

The parts quoted on Stoat (see comment 107), are not constructive criticism, more like deliberate denigration. I don't have any problem with you or anyone else asking a question or providing constructive criticism. Deliberate disrespectful denigration is another matter.

We both on the same side, such comments as you referred, are always to ignor, its just a loos of lifetime..


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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #278 on: April 03, 2017, 06:45:37 PM »
As far as apologies go, there are only two options for characterization of this paper.  the first is CYA as described below:

Quote
an attempt to shift blame of the failure of the models that radically underestimated current (and rapidly growing) climate impacts with much earlier than projected tipping point feedback engagements, an attempt to "Cover Your Ass" (CYA).

or the second, caveat to the first, as quoted below

http://forum.arctic-sea-ice.net/index.php/topic,1920.msg106582.html#msg106582

Quote
I guess you are right Neven, it is impossible to say if this is a CYA paper from entrenched arctic scientists who have dedicated their lives to learning and teaching about these things or if their unsubstantiated interpretations of global atmospheric circulations being 'natural' even though recent studies indicate a significant anthropogenic component (due to many feedbacks, ENSO impacts and aerosol impacts) are rather based on institutional thinking, bias toward confidence in their previous work (models), failure on the SLD (Side of Least Drama) and trying to find a reason an explanation why their models are so pathetically, horribly, dis-servingly off base.

In any event, I assert that, once the arctic melts out (and I have said very clearly that I expect this to happen in the next 2 to 6 years) I can guarantee you that we will hear this paper referenced by those who want to do little or nothing in the way of climate mitigation (as we already are).

I would also like to restate that:

http://forum.arctic-sea-ice.net/index.php/topic,1920.msg106582.html#msg106582
Quote
I can guarantee you that this physical reality and the consequences of China shutting down its 30 most sulfur producing coal mines and installing scrubbers is NOT considered in their model as anthropogenic but is rather attributed to 'natural variability'.

quote below: not only are powerful dynamics NOT included in the models, the spacial resolution of the models and impacts on atmospheric circulation are not competent enough to accurately project the impacts that ARE included due to regional scale impacts on atmospheric circulation

Quote
Results from general circulation models show almost no
changes in the relative humidity in a changing climate (Held
and Soden, 2000; Soden et al., 2005). However, very few
general circulation models have so far begun to include the
effects of aerosols on deep convective clouds (Boucher et
al., 2013; Khain et al., 2015). Namely, as noted by Khain
et al. (2015), the only feasible option in current general circulation
models is to use bulk microphysics parameterisation
schemes. However, bulk microphysics schemes have trouble
producing the effects of aerosols on cloud cover and cloud
top height. As a result, the effect of aerosols on UTH is
not correctly included in the current projections of climate
change produced by general circulation models. Estimates
of climate sensitivity that combine temperature observations
with estimates of greenhouse gas and aerosol-induced radiative
forcing should also be reconsidered.

Note: as Dr. Ding stated these effects were not looked at by the paper since the rapid reduction of high-temp SO2 emissions were not included (not in the study period).

However, the flip-side of not including the rapid RAMP UP of these emissions (2003-2006) were also not included, AND their impacts are poorly represented in the GCM models shown.  Only very recently these components were identified as primary anthropogenic contributors to the 'natural variability' that is identified in the study.

---------------
frankly, I find the idea of apologies reprehensible. 

This is why:

If I am right, if we do achieve a summer ice free condition in the next 2-6 years, if, in the absence of aerosol emissions we have already locked in +2.3C with much more rapid warming in the arctic, leading to wide-scale boreal forest conflagration and massive permafrost destabilization far ahead of the models, then we have already locked in a 2100 globally averaged temperature of a~3.5C (and a 2200 temp of greater than +8C).

It is time to leave our egos behind and get to work, if we want to prevent >+4.0C and the total global destabilization of our interdependent modern economic system.

It is time to quit talking and acting like we are not.
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GeoffBeacon

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #279 on: April 03, 2017, 07:04:20 PM »
Just found this from Francis and Vavrus in 2015

Quote
New metrics and evidence are presented that support a linkage between rapid Arctic warming, relative to Northern hemisphere mid-latitudes, and more frequent high-amplitude (wavy) jet-stream configurations that favor persistent weather patterns. We find robust relationships among seasonal and regional patterns of weaker poleward thickness gradients, weaker zonal upper-level winds, and a more meridional flow direction. These results suggest that as the Arctic continues to warm faster than elsewhere in response to rising greenhouse-gas concentrations, the frequency of extreme weather events caused by persistent jet-stream patterns will increase.

Link

Does an increase in "extreme weather events caused by persistent jet-stream patterns" account for any of the "natural variability" of Ding et.al. ?
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AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #280 on: April 03, 2017, 07:07:44 PM »
... using tools that justify priori conclusions... sound like some of the worst insults you can throw to a scientist...

First, that's not what I wrote, and second, the standard procedure is for scientists to use whatever instruments can result in the best quality data available, so that they can be confident of whatever conclusion that can be drawn from the data.

And it's pretty obvious that Ding et al, for example, used an atmospheric circulation model (ECHAM) to examine atmospheric circulation changes in the period they considered (1979-2014): they say so themselves in the paper!

Check my posts again, I was criticizing the choice of models and the fact that the skill of the models used by Ding et al is not quantified. That is a valid criticism of their methodology and not intended as an insult whatsoever.

It is also the reason I asked Dr. Qinghua my question no. 1: how confident are the co-authors about the "natural climate variability" attribution numbers (30%-50%)?

By the way, also about the methodology: if the model you are using presents, let's say, a 25% uncertainty, and you run the model twice with different data and them subtract one result from the other (Exp6 - Exp5) in the Ding et al 2017 paper, you end up with a number with 50% uncertainty. Do you see the methodological problem or not?

I'll pass on the "hidden behind your desk" and other nonsense in your post, just as I ignored most of ktonine's/Kevin O'Neill posts that just misrepresent what I wrote.
« Last Edit: April 03, 2017, 07:55:04 PM by AndrewB »

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #281 on: April 03, 2017, 08:00:18 PM »
I agree that some here owe the authors of the subject paper an apology. Mr Dekker has already done so, and that reflects well on him. Not so for others.

I see that many have strong feelings about the paper. I suggest they write up their objections and submit them for publication.

I suspect, however, that no apologies will be forthcoming, and, nor will a publication. But if they do, I shall be pleasantly surprised.

sidd

jai mitchell

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #282 on: April 03, 2017, 08:05:20 PM »
early mortality projections, mainly in sub-sahara Africa  and SE Asia under a >2.0C warming scenario are in excess of 1 billion human beings.

think about that for a minute.
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #283 on: April 03, 2017, 08:10:06 PM »
Okay, enough about the apologies. Let's keep it to the science from now on, and if we have all said everything there is to say, we can always come back to this thread if some new papers or theories wrt natural variation vs human influence pop up.
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #284 on: April 03, 2017, 08:17:55 PM »
Here is a link to the paper referred to in my previous post.

 Recent radical shifts of atmospheric circulations and rapid changes in Arctic climate system


And a more recent paper on the Arctic Dipole:

The recent shift in early summer Arctic atmospheric circulation


And the sensitivity to the location of regional ice loss:

The Impact of Regional Arctic Sea Ice Loss on Atmospheric Circulation and the NAO
« Last Edit: April 03, 2017, 08:46:01 PM by Cid_Yama »
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #285 on: April 03, 2017, 08:57:26 PM »
AndrewB

Quote
And it's pretty obvious that Ding et al, for example, used an atmospheric circulation model (ECHAM) to examine atmospheric circulation changes in the period they considered (1979-2014): they say so themselves in the paper!

Really? As refered in the Supplementary: http://www.nature.com/nclimate/journal/vaop/ncurrent/extref/nclimate3241-s1.pdf

Quote
Supplementary Table 1:26 climate models in the CMIP5 historical experiment.Listof 26 CMIP5 CGCMs used in Fig. 4 to examine the forced response of the climate system to anthropogenic and natural external forcing, along with the number of atmospheric horizontal grids.

GeoffBeacon

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #286 on: April 03, 2017, 09:09:58 PM »
jai
Quote
early mortality projections, mainly in sub-sahara Africa  and SE Asia under a >2.0C warming scenario are in excess of 1 billion human beings.
I'd be interested in a source for that.
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AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #287 on: April 03, 2017, 09:19:13 PM »
AndrewB

Quote
And it's pretty obvious that Ding et al, for example, used an atmospheric circulation model (ECHAM) to examine atmospheric circulation changes in the period they considered (1979-2014): they say so themselves in the paper!

Really?
...

Really really!

From the Ding et al 2017 paper (as published):

lines 46-47:
"In this paper, we examine the contribution of the atmospheric circulation to Arctic sea ice variability by utilizing an atmospheric general circulation model (ECHAM5)..."

lines 120-125:
"To better understand the direction of causality, we conduct two model experiments to examine the influence of the observed high-latitude circulation trends on sea ice and other key variables. The first experiment (Exp-1) is a 36-year historical run with the ECHAM5 atmospheric model, in which the global atmospheric circulation (vorticity and divergence from the surface to the top of the atmosphere) is weakly nudged to the corresponding daily reanalysis data (see Methods)."
« Last Edit: April 03, 2017, 09:25:37 PM by AndrewB »

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #288 on: April 03, 2017, 09:23:24 PM »
Soory, my fault, ECHAM was used for atmosphere circulation, i do have read they used it for the forced response. Thanks for reply!

AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #289 on: April 03, 2017, 09:34:30 PM »
Soory, my fault, ECHAM was used for atmosphere circulation, i do have read they used it for the forced response. Thanks for reply!
No problem.

jai mitchell

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #290 on: April 03, 2017, 09:41:44 PM »
jai
Quote
early mortality projections, mainly in sub-sahara Africa  and SE Asia under a >2.0C warming scenario are in excess of 1 billion human beings.
I'd be interested in a source for that.

http://apps.who.int/iris/bitstream/10665/134014/1/9789241507691_eng.pdf

Quote
Climate change is projected to have substantial adverse impacts on future mortality, even
under optimistic scenarios of future socioeconomic development. Under a base case
socioeconomic scenario, we estimate approximately 250 000 additional deaths due to climate
change per year between 2030 and 2050.

here is the temperature range they were looking at



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Random_Weather

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #291 on: April 03, 2017, 09:59:39 PM »
And that make it quit interresting, they used (as refered in the Supplementary) 26 Models for the forced response, which i has shown, only MPI-ESM-MR is good in Hindcast the sea ice also in forecast. Then they used ECHAM5 which is the amtosphere modul of MPI-ESM-MR to examine atmospheric circulation.

Well, if you look Exp(1) of the Paper, it show, that the Pattern from ECHAM5 is looking nearly like the observation. This would imply that most of change is not independent of ice decrease(this is likly because the mean of Models fail to reproduce the Pattern and also fail to decrease as much as in Observation)

Therfore,  to examine independent atmospheric circulation impacts on trends, it should not be used the mean of this 26 Models just only the divergence to ECHAM5

AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #292 on: April 03, 2017, 10:23:44 PM »
...
Then they used ECHAM5 which is the amtosphere modul of MPI-ESM-MR to examine atmospheric circulation.
...
was, actually. ECHAM6 is the new atmospheric circulation module of the Max Planck Institute for Meteorology's MPI-ESM model.
See attached figure.

But I agree with your remark.

AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #293 on: April 03, 2017, 10:31:32 PM »
Okay, enough about the apologies. Let's keep it to the science from now on, and if we have all said everything there is to say, we can always come back to this thread if some new papers or theories wrt natural variation vs human influence pop up.

Not sure this qualifies as a new paper (it's from 2016), but it certainly suggests human influence on Arctic sea ice:

Notz, D. & Stroeve, J. (2016). Observed Arctic sea-ice loss directly follows anthropogenic CO2 emission. Science, 354, 747-750 , doi:10.1126/science.aag2345

Abstract

Arctic sea ice is retreating rapidly, raising prospects of a future ice-free Arctic Ocean during summer. Because climate-model simulations of the sea-ice loss differ substantially, we used a robust linear relationship between monthly-mean September sea-ice area and cumulative carbon dioxide (CO2) emissions to infer the future evolution of Arctic summer sea ice directly from the observational record. The observed linear relationship implies a sustained loss of 3 ± 0.3 square meters of September sea-ice area per metric ton of CO2 emission. On the basis of this sensitivity, Arctic sea ice will be lost throughout September for an additional 1000 gigatons of CO2 emissions. Most models show a lower sensitivity, which is possibly linked to an underestimation of the modeled increase in incoming longwave radiation and of the modeled transient climate response.

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« Last Edit: April 03, 2017, 11:14:47 PM by Cid_Yama »
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AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #295 on: April 04, 2017, 12:03:37 AM »
...
Here is a link to the actual paper:
http://sci-hub.bz/10.1126/science.aag2345

Thanks for the link to the PDF.

Three suggested charts to go when reading the Notz & Stroeve quite short paper (3 pages + 1 page of mostly references).

Did I mention the paper suggests 100% attribution of Arctic sea ice decline to anthropogenic forcing? Actually it pretty much contradicts the Ding et al 2017 paper, here:

"Our  results  also  suggest  that  regional  differences  in  atmospheric  heat-flux  convergence  or  wind  forcing  do  not  significantly  affect  the  Arctic-wide  mean  energy  balance  on  the  time  scales that  we  consider  here.  On  the  other  hand this  also  explains  why  the  linear  relationship  does  not  hold  in  the  Antarctic,  where  dynamical  forcing  from  wind  and oceanic heat transport are key drivers of the large-scale sea-ice evolution."

Cid_Yama

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #296 on: April 04, 2017, 12:26:07 AM »

Published online:27 March 2017

Influence of Anthropogenic Climate Change on Planetary Wave Resonance and Extreme Weather Events
Quote
Persistent episodes of extreme weather in the Northern Hemisphere summer have been shown to be associated with the presence of high-amplitude quasi-stationary atmospheric Rossby waves within a particular wavelength range (zonal wavenumber 6–8). The underlying mechanistic relationship involves the phenomenon of quasi-resonant amplification (QRA) of synoptic-scale waves with that wavenumber range becoming trapped within an effective mid-latitude atmospheric waveguide. Recent work suggests an increase in recent decades in the occurrence of QRA-favorable conditions and associated extreme weather, possibly linked to amplified Arctic warming and thus a climate change influence. Here, we isolate a specific fingerprint in the zonal mean surface temperature profile that is associated with QRA-favorable conditions. State-of-the-art (“CMIP5”) historical climate model simulations subject to anthropogenic forcing display an increase in the projection of this fingerprint that is mirrored in multiple observational surface temperature datasets. Both the models and observations suggest this signal has only recently emerged from the background noise of natural variability.
Full Text
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DrTskoul

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #297 on: April 04, 2017, 12:41:50 AM »

Published online:27 March 2017

Influence of Anthropogenic Climate Change on Planetary Wave Resonance and Extreme Weather Events
Quote
Persistent episodes of extreme weather in the Northern Hemisphere summer have been shown to be associated with the presence of high-amplitude quasi-stationary atmospheric Rossby waves within a particular wavelength range (zonal wavenumber 6–8). The underlying mechanistic relationship involves the phenomenon of quasi-resonant amplification (QRA) of synoptic-scale waves with that wavenumber range becoming trapped within an effective mid-latitude atmospheric waveguide. Recent work suggests an increase in recent decades in the occurrence of QRA-favorable conditions and associated extreme weather, possibly linked to amplified Arctic warming and thus a climate change influence. Here, we isolate a specific fingerprint in the zonal mean surface temperature profile that is associated with QRA-favorable conditions. State-of-the-art (“CMIP5”) historical climate model simulations subject to anthropogenic forcing display an increase in the projection of this fingerprint that is mirrored in multiple observational surface temperature datasets. Both the models and observations suggest this signal has only recently emerged from the background noise of natural variability.
Full Text

Convenient pdf

Lennart van der Linde

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #298 on: April 04, 2017, 10:21:23 AM »
Thanks, StevenB for pointing to Notz & Stroeve 2016.

They say:
“during the transition to a seasonally ice-free Arctic Ocean, the 30-year running mean of monthly mean September Arctic sea-ice area is almost linearly related to cumulative anthropogenic CO2 emissions… In the model simulations, the linear relationship holds until the 30-year running mean, which we analyze to reduce internal variability, samples more and more years of a seasonally ice-free Arctic Ocean, at which point the rela-tionship levels off toward zero…

the observed linear relationship allows us to estimate a sensitivity of 3.0 ± 0.1 m2 of September Arctic sea-ice loss per ton of anthropogenic CO2 emissions during the observational period 1953–2015… the linear relationship allows for a robust evaluation of climate-model simulations. While a number of previous studies have found that the observed sea-ice retreat has been faster than projected by most climate-model simulations, it has remained unclear whether these differences are primarily a manifestation of internal variability. The sensitivity that we estimate here is, in contrast, based on the average evolution over many decades, thus eliminating internal variability to a substantial degree. A mismatch between the observed and the simulated sensitivity hence robustly indicates a shortcoming either in the model or in the external forcing fields used for a simulation…

On a more regional scale, our conceptual explanation allows us to ascribe a minor role for the overall evolution of sea ice to processes that are unrelated to the large-scale change in atmospheric forcing. This includes a minor role of oceanic heat transport on the time scales that we consider here, since we can derive a linear relationship without considering these transports. While it might alternatively be possible that the oceanic heat transports have changed monotonously in recent decades, we have no indication that this is the case from either observations or model simulations.

The current minor role of oceanic heat transports implies that on time scales of several centuries, the linearity will most likely no longer hold, since sensitivity will increase once changes in oceanic heat content start measurably affecting Arctic sea-ice coverage. Our results also suggest that regional differences in atmospheric heat-flux convergence or wind forcing do not significantly affect the Arctic-wide mean energy balance on the time scales that we consider here.”

This indeed seems to be a quite different conclusion from Ding et al. So, of course, I would be very interested to hear what Dr. Ding thinks of Notz & Stroeve 2016.

AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #299 on: April 04, 2017, 11:47:13 AM »
If you are interested in the Notz & Stroeve paper but can't be bothered with reading it, there is a short YouTube video (< 5 minutes) with Dr. Notz presenting essentially the same ideas during the COP21, with various charts, etc.
Here: