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Sterks

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #300 on: April 04, 2017, 02:16:31 PM »

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.

Ok, it was not fair from me to write that (behind my own desk), I am sorry.


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:

The example of scientific paper that contradicts Ding et al that you bring about is not that good. I think they directly assume no internal variability. How's that for a model? They could have used something fancier. In fact, they could have used some model.
But no, it is sort of a direct ad-hoc linear correlation C02 -> ice loss only meant to work for the NH with kind of a moral intention (you burn this? then you are responsible of the loss of that amount of ice). And as a side, projecting their correlation into the future we can keep our party and our burning rates until 2040 or 2050, that the Arctic will keep some ice in September, then we stop, and fix it. It is just linear, isn't it?

Bad example really.
« Last Edit: April 04, 2017, 02:22:50 PM by Sterks »

Cid_Yama

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #301 on: April 04, 2017, 03:18:44 PM »
Appears to be not based on a model but on past observations.

Quote
...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 sensitivity that we estimate here is, in contrast, based on the average evolution over many decades...

So what they are stating is limited to past observations during the period examined.  And they say as much, merely stating that current models do not reflect past observations, but that their observations of a linear relationship will not hold under future conditions.

Fair enough.  But then they go on to project into the future based on past observations, where they already stated in essence, "past observations are not an indication of future performance".

 

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Lennart van der Linde

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #302 on: April 04, 2017, 04:42:30 PM »
I think they directly assume no internal variability. How's that for a model? They could have used something fancier. In fact, they could have used some model.

Notz & Stroeve start with analysing the models and find a linear relationship between cumulative CO2-emissions and Arctic sea ice extent over 30-yrs periods (running mean). Then they analyse the observations over the past six decades and also find a linear relationship, but on average almost twice as strong as in the models (which probably underestimate the negative aerosol forcing).

They say:
“Evaluating the simulated sensitivity, we find that most CMIP5 models systematically underestimate the observed sensitivity of Arctic sea ice relative to anthropogenic CO2 emissions of 3.0 ± 0.3 m2. Across the full transition range to near ice-free conditions, the multimodel mean sensitivity is only 1.75 ± 0.67 m2 loss of Arctic sea ice per metric ton of anthropogenic CO2 emissions. Because of the linear response, a similar sensitivity is obtained for subperiods of the transition period that have the same length as our observational record, with overall maximum sensitivities over such 61-year-long time periods from individual simulations of 1.95 ± 0.70 m2/ton. Note that these estimates of the models’ sensitivity might be biased somewhat high, as previous studies found that the aerosol forcing of CMIP5 simulations might have been too weak in recent decades. This would give rise to artificially amplified warming and thus amplified sea-ice loss in these simulations, rendering the true sensitivity of the models to be even lower than the values we estimate here.”

They also say:
"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"

So the question is how much natural variability remains after averaging over six decades? Maybe some, but probably less than by averaging over 3-4 decades as Ding et al do. So maybe the model Ding et al use is not yet fit enough for the job (assuming the observations are basically correct)?
« Last Edit: April 04, 2017, 04:51:54 PM by Lennart van der Linde »

AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #303 on: April 05, 2017, 04:41:29 AM »
...
So maybe the model Ding et al use is not yet fit enough for the job (assuming the observations are basically correct)?
A climate model is a mathematical tool, you can't blame the tool for any deficiencies in a climate science paper.
Again, if the Ding et al paper had quantified the skill of the POP2+CICE4 sea ice model they used for Exp5 and Exp6, from which they derive their preposterous natural variability attribution claim, I personally would be much less critical about it.

Lennart van der Linde

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #304 on: April 05, 2017, 07:48:36 AM »
Again, if the Ding et al paper had quantified the skill of the POP2+CICE4 sea ice model they used for Exp5 and Exp6, from which they derive their preposterous natural variability attribution claim, I personally would be much less critical about it.

I suppose that's a better way of putting it, yes...

jai mitchell

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #305 on: April 05, 2017, 09:24:44 PM »
Pre-publish presentation by Dr. Kim Cobb and her expanded series of ENSO variability trends over the last 7,000 years.  Her preliminary results show a much greater rate of ENSO intensity during the industrial period as compared to all pre-industrial samples.

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Lennart van der Linde

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #306 on: April 07, 2017, 10:03:51 PM »
Another part of the puzzle maybe, Polyakov et al 2017, Greater role for Atlantic inflows on sea-ice loss in the Eurasian Basin of the Arctic Ocean:
http://science.sciencemag.org/content/early/2017/04/05/science.aai8204

With coverage by Chris Mooney in Washington Post:
https://www.washingtonpost.com/news/energy-environment/wp/2017/04/06/scientists-say-the-unique-arctic-ocean-is-being-transformed-before-our-eyes/?tid=ss_tw&utm_term=.b76837f8095d

Abstract
Arctic sea-ice loss is a leading indicator of climate change and can be attributed, in large part, to atmospheric forcing. Here, we show that recent ice reductions, weakening of the halocline, and shoaling of intermediate-depth Atlantic Water layer in the eastern Eurasian Basin have increased winter ventilation in the ocean interior, making this region structurally similar to that of the western Eurasian Basin. The associated enhanced release of oceanic heat has reduced winter sea-ice formation at a rate now comparable to losses from atmospheric thermodynamic forcing, thus explaining the recent reduction in sea-ice cover in the eastern Eurasian Basin. This encroaching “atlantification” of the Eurasian Basin represents an essential step toward a new Arctic climate state, with a substantially greater role for Atlantic inflows.

Rob Dekker

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #307 on: April 11, 2017, 07:01:57 AM »
I know that I've burned up much of my credibility during the recent exchange with Qinghua Ding and Eric Steig.

So I don't expect anyone to take the following notes seriously.

First of all, the subject is important.

If Arctic sea ice declines to record levels, this paper suggests that 30-50% is due to natural variability, and thus that it could revert if the "weather" changes.

However, I can't deny that I believe Ding et al 2017 still may have some serious flaws which were summarized best by Michael Mann :

https://twitter.com/MichaelEMann/status/841362467603255298
"study doesn't support that conclusion. Atmospheric circulation changes may have anthropogenic component."

Let's take this one step at a time.
Ding et al 2017 has a claim that :

Quote
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.

This claim consists of two parts :

1) Cause :
Quote
Here, we present evidence that trends in summertime atmospheric circulation may have contributed as much as 60% to the September sea-ice extent decline since 1979.
Now, this claim is based on the Exp.5. and Exp.6. differences.
Here, Ding et al 2017 runs a model between two 'climate' regimes : One with the ERA climate data, and one with ERA data adjusted to exclude the Z200 geopotential height trend since 1979, and also adjusted 'temperature' and 'LW downwelling radiation' and 'humidity' variables, which are adjusted to the extent that Z200 changed. Their regression method causes these variables to knock out 65% of the long term trend. This all suggests that Z200 long term changes are the "cause" of the trend in temperature, humidity and LW downwelling radiation. But it may very well be that the "cause" is the long term trend in 'temperature' which may very well be (entirely or partially) anthropogenic (see Mann's note).

Which brings us to 'attribution' :

2) Attribution :
Ding et al 2017 suggests that 70% of the 60% ice loss from (1) is caused by natural forcing, leading to their final conclusion of some 40% natural cause for ice loss in the Arctic.
This (70%) is based on their experiment 7 and 8.
There, they took out the long term trend in 'high latitude wind', assuming that (30%) was anthropogenic.
However, the 'high latitude winds' may very well be caused by increase in Z200GL geopotential height increase. After all, increase in geopotential height over the Arctic leads to reduced cyclonic winds. If you assume that Z200GL increase is largely (or half, according to Ding et al 2014) caused by natural variability, then these long term changes in 'high latitude winds' that cause 30% ice loss may be caused by 'natural variability' and the remaining 70% may be caused by anthropogenic forcings.

Which turns the tables around since now 'natural variability' only causes 30% of the 60% (from point (1)) and thus only 18 % could be caused by 'natural variability', and only 9 % if half of Z200GL is caused by natural forcing.

Needless to say that there is much to argue about this paper's findings.
« Last Edit: April 11, 2017, 07:49:56 AM by Rob Dekker »
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ktonine

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #308 on: April 11, 2017, 08:59:54 AM »
Needless to say that there is much to argue about this paper's findings.

Rob, I think you're still missing the larger point; the models simply don't show transpiring what you claim.  If there's an AGW forcing for the magnitude of sea ice loss, then what is the physical flaw in the models? 

Obviously they've gone over the models dozens of times trying to figure out why they don't match observations.  At some point (Ding et al) someone was bound to come up with the rational idea that maybe it's not being entirely forced, but simply natural variation.

We always hesitate to put anything down to cycles because they're generally the first refuge of deniers like the denizens at WUWT.  But occasionally there *are* cycles that need to be taken into account.  If I recall iceberg recordss in the north Atlantic do tend to  show a 60 year cycle and this could be part of that natural variation.

Saying "it could still be AGW" without actually having any proof is really nothing more than saying I don't like the result.  It really brings to mind many peoples reaction to the Tietsche paper.  Just because Ding et al is out there doesn't for a moment mean it's accepted gospel, but better silence on the subject until something definitive is in hand to rebut it.

Archimid

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #309 on: April 11, 2017, 01:25:07 PM »
I think that the forcing they choose to call natural variation is just the "momentum" accumulated in the atmosphere after 200 years of AGW. This paper is really bad news because if we could magically reduce CO2 in the atmosphere to pre industrial times in a day,  the atmosphere will probably still melt the ice for some years.

Honestly, how can they call "natural variation" from a data set that is only 37 years old? DO they expect me to believe that the natural variation over the last 37 years was the same as 200 years ago or 10,000 years ago.

No, sorry. Their use of the term natural variation is wrong for an attribution study. 
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Gray-Wolf

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #310 on: April 11, 2017, 01:35:38 PM »

Honestly, how can they call "natural variation" from a data set that is only 37 years old? DO they expect me to believe that the natural variation over the last 37 years was the same as 200 years ago or 10,000 years ago.

No, sorry. Their use of the term natural variation is wrong for an attribution study.

I have to agree and the changes over the last 5 years, across the Arctic, has taken us well beyond the 'old' workings of the basin. Most every paper we read has a fat tail of data in the 'old' basin and so tends to not provide a satisfactory view of the basin that is. I have not read any 'transition' papers but surely this is where we are with a new seasonal basin in the offing and the old , myi crammed full basin, is now lost!

Though changes to the weather (WACCy impacts) are easy for us to accept we are still in 'hot debate' ,as to whether these changes are driven by low ice across the basin, in meteorology generally and so to talk of such in weather forums is still difficult if you are not ready to face abuse.....

This is not the basin that was there when I entered this life back in 63'!!!
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #311 on: April 11, 2017, 01:49:00 PM »
In their study they make the following simplification:

CO2 forcing = AGW
Everything Else = Natural variation.

In reality  AGW is much more than just CO2 forcing. For example, AGW may be the culprit behind the cold blob to the south of Greenland. I don't need to be an expert to understand that cold blob must be having effect on the atmosphere above. In the study, the changes to the sst's to the south of Greenland and their effect on the atmosphere are counted as Natural Variation, but it was CO2 induced warming that melted the ice, that changed the sst, that changed the atmosphere.

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ktonine

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #312 on: April 11, 2017, 03:32:06 PM »
In their study they make the following simplification:

CO2 forcing = AGW
Everything Else = Natural variation.


No, this is NOT what scientists think.  They look for patterns that emerge in the model ensembles with and without AGW (CO2) forcing and compare to observations.  Those observations that do NOT emerge with AGW forcing either indicate a flaw in the model or natural variation.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #313 on: April 11, 2017, 05:23:34 PM »
And they failed to take into account warming oceans and warm water incursions.  They also didn't include other greenhouse gases like methane and nitrous oxide, all of it anthropogenic.

So you can stuff your natural variability.

Occam's Razor.  The IPCC climate models didn't include any of these things, so they underestimated the melting. Simple as that.

All Ding's paper did was demonstrate the IPCC models were deficient.  Duh.  Their conclusions were not satisfied by their argument.   All they could really demonstrate was that 30% of the melting was unaccounted for by CO2 forcing in the IPCC models.

But we already knew what had been left out.  Not as if the IPCC models were the core dragon of the AGW argument which they had finally slain. 

« Last Edit: April 11, 2017, 06:27:52 PM by Cid_Yama »
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #314 on: April 11, 2017, 06:43:25 PM »
Effect of methane emission increases in East Asia on atmospheric circulation and ozone
Quote
Abstract

We used a fully coupled chemistry–climate model (version 3 of the Whole Atmosphere Community Climate Model, WACCM3) to investigate the effect of methane (CH4) emission increases, especially in East Asia and North America, on atmospheric temperature, circulation and ozone (O3). We show that CH4 emission increases strengthen westerly winds in the Northern Hemisphere midlatitudes, accelerate the Brewer–Dobson (BD) circulation, and cause an increase in the mass flux across the tropopause. However, the BD circulation in the tropics between 10°S and 10°N at 100 hPa weakens as CH4 emissions increase in East Asia and strengthens when CH4 emissions increase in North America. When CH4 emissions are increased by 50% in East Asia and 15% globally, the stratospheric temperature cools by up to 0.15 K, and the stratospheric O3 increases by 45 ppbv and 60 ppbv, respectively. A 50% increase of CH4 emissions in North America (with an amplitude of stratospheric O3 increases by 60 ppbv) has a greater influence on the stratospheric O3 than the same CH4 emissions increase in East Asia. CH4 emission increases in East Asia and North America reduce the concentration of tropospheric hydroxyl radicals (4% and 2%, respectively) and increase the concentration of mid-tropospheric O3 (5% and 4%, respectively) in the Northern Hemisphere midlatitudes. When CH4 emissions increase in East Asia, the increase in the tropospheric O3 concentration is largest in August. When CH4 emissions increase in North America, the increase in the O3 concentration is largest in July in the mid-troposphere, and in April in the upper troposphere.
https://link.springer.com/article/10.1007/s00376-015-5028-4


What most people don't get is it isn't just the warming.  It's also changes in atmospheric chemistry which have knock-on effects. 

« Last Edit: April 11, 2017, 06:53:02 PM by Cid_Yama »
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #315 on: April 11, 2017, 06:45:53 PM »
@  Archimid @ Cid_Yama

Why you are talking Bullshit? There is nothing wrong with the paper and all what you both said is totally wrong, they used the forced response of the models, this include not just co2, its also include ch4, sox, landuse, black-carbon... they also say, that some part of unforced atmosphere pattern could be a result of feedback to the ice loose itself, but they claim more to natural impact, as i shown here, it could be also not natural (in context of most) and this is the only point for critics to the paper, or in other words, there conclusion is not so confident that the last word would be spoken about it.

So, you both making the same shit, as the denials of global warming, you are also trapped in your own world, without any kind of open mind

AndrewB

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #316 on: April 11, 2017, 06:53:01 PM »
Here is a back of the envelope uncertainty analysis of the attribution claim in the 2017 Ding et al paper, for your comments.

From the abstract of the 2017 Ding et al paper: “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.” (lines 28-29)

By “internal variability” it is assumed the authors mean “natural climate variability”, in other words, non-anthropogenic forcing.

This preposterous (i.e. against logic and common sense) claim contradicts previously published papers on Arctic sea ice decline, for example the previously mentioned 2016 Notz and Stroeve paper that evidences a linear relationship between the rise in cumulative CO2 emissions from the burning of underground fossil carbon and the decline in Arctic sea ice volume (see my previous posts).

The claim that the unprecedented decline in Arctic sea ice may be in a large part attributable to natural climate variability defies logic and common sense when we take a look at the exponential trend in Arctic sea ice volume loss evidenced by 38 years or so of satellite data. Note that not only September sea ice follows an exponential trend; all months do so, indicating that the Arctic will be essentially ice free all year round, and this probably decades before the end of the century.

As someone put it in the Stoat blog, nearly 40 years of one-sided “natural variability” seems unlikely.

I asked Dr Ding how confident he was about this claim, in other words, would he be willing to quantify the “may” in “… may be responsible...” in the attribution claim in the abstract. In other words, is there a 90% chance that “30-50% of the overall decline in September sea ice since 1979” is attributable to natural climate variability, in which case the apparently preposterous claim should be taken seriously by policy makers that previously were concerned about the disappearance of Arctic sea ice as a serious indicator that radical emissions reduction policies should be put in place ASAP? Or is it the case that the authors are only 10% confident about this particular claim (and so it should not be found in the abstract in the first place)?

The problem is that the 2017 Ding et al paper lacks any uncertainty analysis of this particular claim. The “30-50%” range in attribution to natural variability is derived in the paper from two different sets of reanalysis products (NCEP2 and MERRA2) that indicate very different trends in GL-Z200. This in detailed in lines 253-261 of the paper:
“The impact of observational uncertainties on our conclusions can be estimated by linearly scaling the results from Exp-6 by the GL-Z00 trends extracted from different reanalyses products. The atmospheric circulation contribution to sea ice loss ranges from 48% (NCEP-2) to 75% (MERRA-2). Using the 70% contribution of internal forcing to the circulation variability established above, we can attribute 30-50% of sea ice loss to internal variability.
Reanalysis products are reliable representations of the observed circulation, humidity and temperature. The reanalysis data probably also reliably represent the variability in total cloud cover in the satellite era, particularly in summer.”

As we can see, the “30-50%” range already relies on a series of mostly unwarranted assumptions, even before we question the skill of the model used in Exp-6.
Let’s list just a couple of these assumptions:
1) It is assumed that the two different sets of reanalysis products (NCEP2 and MERRA2) represent the extremes for the range of atmospheric circulation contribution to sea ice loss ranges. This is an extremely important assumption and yet there is absolutely no reason for this to be true.
2) The assumption that reanalysis data for the period 1979-2014 for GL-Z200 closely represents the reality of atmospheric circulation over the entire Arctic region. This is an essential assumption in the paper and yet it is inherently questionable, specially when we know that reanalysis data for GL-Z200 is derived from observations from a limited number of meteorological stations along the coast of Greenland. Just looking at a map of the Arctic one realizes that generalizing the weather or atmospheric circulation over the southern coast of Greenland to the whole Arctic region is more of a leap of faith than a scientifically justifiable assumption (see attached map).

If we roughly estimate the uncertainty in the reanalysis product data at +/- 15% (with 95% confidence), and the uncertainty over the generalization of GL-Z200 to the entire Arctic region at +/- 25% (again with 95% confidence), we can rewrite the original attribution claim as follows:

“Internal variability dominates the Arctic summer circulation trend and may be responsible (with 95% confidence) for about 0-80% of the overall decline in September sea ice since 1979.”

Now, of course this still assumes the sea ice model (POP2+CICE4) used by Ding et al in Exp-5 and Exp-6 to be perfectly skillful, but we know this is not the case since none of the existing sea ice models correctly predict the decline of Arctic sea ice, as indicated in the Notz and Stroeve paper.
And also note that whatever error/uncertainty added by the POP2+CICE4 model used by Ding et al must be doubled when stating the attribution claim, which is derived from the difference between two model runs with different sets of data.

Let’s roughly estimate the uncertainty in the POP2+CICE4 model at +/- 20% (with 95% confidence). We must now rewrite the original attribution claim in a final form:

“Internal variability dominates the Arctic summer circulation trend and may be responsible (with 95% confidence) for about -40 to +120% of the overall decline in September sea ice since 1979.”

Which of course it is a totally meaningless claim, and would expose the eleven co-authors, including Ding himself, to ridicule.

I am not claiming my back of the envelope uncertainty analysis is correct, but unfortunately the Ding et al is lacking in this area (despite the numerous caveats), which makes it quite useless as a basis for policy makers, and in my not so humble opinion, of little if any scientific value.

jai mitchell

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #317 on: April 11, 2017, 07:20:41 PM »
@  Archimid @ Cid_Yama

Why you are talking Bullshit? There is nothing wrong with the paper and all what you both said is totally wrong, they used the forced response of the models, this include not just co2, its also include ch4, sox, landuse, black-carbon... they also say, that some part of unforced atmosphere pattern could be a result of feedback to the ice loose itself, but they claim more to natural impact, as i shown here, it could be also not natural (in context of most) and this is the only point for critics to the paper, or in other words, there conclusion is not so confident that the last word would be spoken about it.

So, you both making the same shit, as the denials of global warming, you are also trapped in your own world, without any kind of open mind


1.  The term 'natural variability' is assigned to global atmospheric circulation patterns that are largely driven by the tropical pacific surface water temperature cycles (ENSO)

2.  Recent studies have confirmed that the REGIONAL impacts of point-source SOx emissions (and volcanoes) drove the 'natural variability' cycles in the tropical pacific.  see:  http://www.nature.com/nclimate/journal/v6/n10/full/nclimate3058.html

Quote
Our results suggest that a slowdown in GMST trends could have been predicted in advance, and that future reduction of anthropogenic aerosol emissions, particularly from China, would promote a positive PDO and increased GMST trends over the coming years.

3. The key period identified in the Ding et al paper was the shift to +IPO in the period between 2003 and 2005 (prior to the 2007 'black swan' ice loss and then again in 2012.  In their analysis they DID NOT INCLUDE REGIONAL SO2 FORCING AS A DRIVER.

The key point of the problem is revealed when one looks at the actual chinese rampup and drawdown of SO2 emissions for power generation during this period. 



now that china has shut down its high-sulfur coal production and shifting to cleaner sources of power generation, we are now seeing the wider impacts of these aerosol emissions in ways that are apart from global forcing and directly impact atmospheric circulation patterns that have previously been ascribed as 'natural variability'.

1.  The sea ice is melting out 40 years ahead of the models
2.  slightly more than 1/2 of the total GMST warming since the industrial era is currently being offset by SOx emissions
3.  When the Arctic melts out changes in albedo alone will increase GMST by over 0.5C
4.  the IPCC did not include permafrost emissions in their RCP emission scenarios.
5.  Without a national (U.S.) mobilization utilizing non-market forces to transform our economy away from fossil fuels on a single decade timescale, we will be unable to prevent +4C and global warming will kill your children.
6.  We need to stop allowing our scientific body to act like these things are not real and currently happening.  we need to address this technical issue now and not dilly-dally about magical +1.5C emission scenarios as though they exist.
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seaicesailor

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #318 on: April 11, 2017, 07:38:57 PM »
6.  We need to stop allowing our scientific body to...
Didn't the last POTUS tweet start along similar phrasing?
Why don't we let the scientists alone do their fine good job?

seaicesailor

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #319 on: April 11, 2017, 07:43:20 PM »
Actually, why don-'t we LEAVE SCIENTISTS ALONE now that they are being actively prosecuted, buried, insulted by Trump????????????????????????????????????????

jai mitchell

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #320 on: April 11, 2017, 07:47:16 PM »
6.  We need to stop allowing our scientific body to...
Didn't the last POTUS tweet start along similar phrasing?
Why don't we let the scientists alone do their fine good job?

Individual science work is vital and necessary and good.  As a collective body, working within political frameworks, the IPCC has done a great disservice to humanity and there should be selection for lead author contribution to a mea culpa that will act as the preamble to the IPCC 2017 Summary for Policymakers.

https://www.theguardian.com/environment/earth-insight/2014/may/15/ipcc-un-climate-reports-diluted-protect-fossil-fuel-interests

IPCC reports 'diluted' under 'political pressure' to protect fossil fuel interests
Saudi-led coalition sought to make policy summaries as vague as possible to minimise climate action
Quote
Far from being too alarmist, these criticisms suggest that the IPCC's summary reports are too conservative. Like Wasdell, Broome describes how "a coalition of countries led by Saudi Arabia" at the April approval session in Berlin "insisted" that all "figures" depicting increases of greenhouse gas emissions in countries classified by 'income group' "should be deleted."

Saudi Arabia, he said, also "wanted to delete all references to any part of the main report that mentioned income groups… in the end Saudi Arabia got its way completely."

Quote
Global Warming will kill your children
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Archimid

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #321 on: April 11, 2017, 08:06:40 PM »

No, this is NOT what scientists think.  They look for patterns that emerge in the model ensembles with and without AGW (CO2) forcing and compare to observations.  Those observations that do NOT emerge with AGW forcing either indicate a flaw in the model or natural variation.

I believe that what you said is exactly what they think. There is a good logic to it. Their elaborate and continuously updated and tested models can predict with very good accuracy certain aspect the climate system. They can be very insightful tools.  I can agree that withing the limits of the models, attributing up to 60% of Arctic sea ice loss to the natural variation of the models maybe acceptable.

However, when seen under other lines of evidence the claim that what they found is due to natural variability does not hold.

First, Arctic recent history. The evidence I have seen clearly indicate that the arctic was pretty much a constant size since 1850. See the first image , taken from what I think is the best article on Arctic Recent history here:
https://www.carbonbrief.org/guest-post-piecing-together-arctic-sea-ice-history-1850


I see no 60 year / 100 year or any type of cycle visible that would account for 60% sea ice loss.


Then when I look at the 20,000 year temperature record, (second image) it is obvious that for the last 500 years the world was much colder than the 20th century, so it is not a stretch to assume that the Arctic was as nice and healthy as it was during the 20th century.

image URL: https://tamino.files.wordpress.com/2013/03/shakun_marcott_hadcrut4_a1b_eng.png

Then there is the beginning of the Holocene which was about as warm as it is now but for thousands of years. That's the only time there could have been and ice free arctic that I would attribute to natural variation.

So the evidence points at something other than natural variation for the Arctic sea ice loss. The evidence clearly points at anthropogenic forces being responsible for not only the 40 % due to CO2 forcing and other modeled phenomena, but also for much of the 60% forcing that the random noise of the models point to.

That is the reason I attack the conclusion that up to 60% of Arctic sea ice loss is due to natural variability. It is 100% due to human influence. That the Atmosphere may be a bigger driver than other AGW attributable things, I don't doubt it for a second. That the atmospheric variations are due to natural variation? I don't believe it for a second.



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

Neven

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #322 on: April 11, 2017, 09:18:40 PM »
Folks, let's not do the re-run of this show, okay?
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #323 on: April 11, 2017, 09:22:03 PM »
Commentary in response to the Ding et al. [2017] paper:

Climate variability: Natural causes of Arctic sea-ice loss [Swart N., 2017]
http://www.nature.com/nclimate/journal/v7/n4/full/nclimate3254.html
Currently: Postdoctoral Research Associate - Princeton University & NOAA GFDL - Atmospheric and Oceanic Sciences
UC Irvine - Earth System Science Ph.D., M.Sc.
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Random_Weather

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #324 on: April 11, 2017, 09:23:27 PM »
Archimid,

"1.  The sea ice is melting out 40 years ahead of the models"

Not correct at all, because as i shown, the models had different model sea ice states, the model with the most realistic model sea ice state, has no problem to loose much ice as we saw in observation

"2.  slightly more than 1/2 of the total GMST warming since the industrial era is currently being offset by SOx emissions"

Speculation on the upper Band, its not clear yet  how much, its arround -0.2K up to-0.8K

"3.  When the Arctic melts out changes in albedo alone will increase GMST by over 0.5C"

And deep water formation also change, which cools, never foreget, the atlatic site is always warmer because of MOC, would ice be gone, melt of Greenland intens, MOC would slow down and cancel some warming out.. what about increase of albedo on landside in the arctic, more greening means more albedo also increase in cloudcover and and and

"4.  the IPCC did not include permafrost emissions in their RCP emission scenarios."

Why should, dont you understand that this is a model output, not a imput, the model physics make it up how much is released

"5.  Without a national (U.S.) mobilization utilizing non-market forces to transform our economy away from fossil fuels on a single decade timescale, we will be unable to prevent +4C and global warming will kill your children."

Yeah, sounds confident by someone who is not knowing about imputs and outputs in models :-)

"6.  We need to stop allowing our scientific body to act like these things are not real and currently happening.  we need to address this technical issue now and not dilly-dally about magical +1.5C emission scenarios as though they exist."

The really first thing to do is, tpo wipe out people who deny climate change is real and people who always say we unable to prevent it (as you)

Random_Weather

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #325 on: April 11, 2017, 10:41:07 PM »
Neven,

"Folks, let's not do the re-run of this show, okay?"

Soory, cant let this stand so, some claims here about the paper are so far away from reality that it hurts

sidd

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #326 on: April 11, 2017, 11:35:15 PM »
Heres a paper that may be relevant: doi:10.5194/tc-2017-39

From the abstract:

" Downward longwave radiation is an essential element for sea ice reduction, but can only be sustained by excessive upward heat flux from the sea surface exposed to air in the region of sea ice loss. The increased turbulent heat flux is used to increase air temperature and specific humidity in the lower troposphere, which in turn increases downward longwave radiation ... A quantitative assessment reveals that this feedback process is amplifying at the rate of ~ 8.9 % every year during 1979–2016. Based on this estimate, sea ice will completely disappear in the Barents and Kara Seas by around 2025. Availability of excessive heat flux is necessary for the maintenance of this feedback process; a similar mechanism of sea ice loss is expected to take place over the sea-ice covered polar region when sea ice is not fully recovered in winter."

Open access. Read all about it:

http://www.the-cryosphere-discuss.net/tc-2017-39/

sidd

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #327 on: April 11, 2017, 11:45:53 PM »
Neven,

"Folks, let's not do the re-run of this show, okay?"

Sorry, cant let this stand so, some claims here about the paper are so far away from reality that it hurts

Random_Weather    +1

Zach Labe - thanks for the link to the Neil Swart comment that appeared in NATURE CLIMATE CHANGE.  Here are the paragraphs that matter:

Quote
The challenge, until now, is that there has been no clear understanding of the relative contributions of human-induced warming versus internal variability to the observed long-term decline in Arctic sea ice.

Ding et al. make a significant advance in this area by estimating the contribution of internal variability to the observed long-term sea-ice decline. Beginning with a statistical analysis, they show that observed September near-surface warming and seaice loss are strongly correlated with changes in the upper-level atmospheric circulation centered over Greenland. To determine the causality of these changes, the authors conduct a novel series of model simulations that show that the circulation change is indeed a driver of, not a response to, the sea-ice loss. Remarkably, their simulations suggest that the large-scale atmospheric circulation changes could be responsible for up to 60% of observed summer-time Arctic sea-ice loss since 1979.

If the circulation changes are caused by anthropogenic greenhouse warming (or other human or natural external forcings such as ozone depletion, aerosol emissions, or solar activity) this pattern of atmospheric change should emerge as a clear signature when averaging together many climate model simulations of this period. Averaging together many simulations effectively cancels out all random internally generated fluctuations seen in individual climate simulations, leaving behind the model response to external forcings, such as increasing greenhouse gases. Using this approach, Ding et al. find that external forcing accounts for very little of the observed circulation changes, and therefore attribute the changes predominantly to internally generated variability. The result is surprising, in that it attributes a multidecadal atmospheric circulation anomaly to internal variability. Typically, internal variability is most prominent at shorter timescales — from months to years — and accounts for less of the observed variability as one extends to longer and longer timescales. The simulation-averaging approach they use to make this attribution is common, but it relies on the assumptions that the models have been supplied with the correct forcing, and are faithfully replicating the real world response to that forcing — assumptions that are always open to question. Nonetheless,multi-decadal-scale internal variability does exist, most often relying on the longerterm memory of the ocean. For example, tropical Pacific sea surface temperature(SST) variability has been shown to have a strong connection with atmospheric circulation anomalies over Greenland and Arctic sea ice . Thus, there is a plausible link between tropical SST variability and Arctic sea-ice decline, but firmly establishing this relationship would require further work. 
« Last Edit: April 12, 2017, 12:30:32 AM by ktonine »

Jim Williams

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #328 on: April 11, 2017, 11:49:18 PM »
My only complaint about the "alarmists" viewpoint is the claim that we need to do anything.  First I think it is too late to do anything, and second I think that trying to do anything is likely to lead to an even worse result.

We screwed up the climate with the Industrial Revolution.  End of story.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #329 on: April 12, 2017, 12:36:47 AM »
A quick commentary on the commentary by Neil Swart.
Quote from: Neil Swart
The challenge, until now, is that there has been no clear understanding of the relative contributions of human-induced warming versus internal variability to the observed long-term decline in Arctic sea ice.

I don't think this has been the challenge. I think the challenge is that sea ice models until now have failed to explain the rapid decline in Arctic sea ice, as stated in the Notz and Stroeve 2016 article which I have mentioned in one of my previous comments.

Quote from: Neil Swart
Ding et al. make a significant advance in this area by estimating the contribution of internal variability to the observed long-term sea-ice decline. Beginning with a statistical analysis, they show that observed September near-surface warming and sea ice loss are strongly correlated with changes in the upper-level atmospheric circulation centered over Greenland. To determine the causality of these changes, the authors conduct a novel series of model simulations that show that the circulation change is indeed a driver of, not a response to, the sea-ice loss. Remarkably, their simulations suggest that the large-scale atmospheric circulation changes could be responsible for up to 60% of observed summer-time Arctic sea-ice loss since 1979.

Is that really that remarkable? There are only two physical mechanisms by which heat from the tropics can be carried to the Arctic, namely atmospheric circulation or oceanic currents. And we know already that intrusions of warm, moist air from the tropics in the Arctic during summer will result in extra melt and lower sea ice extent in September.

The fact is that these intrusions of warm, moist air from the tropics did not seem to occur before, and now they do. And that's where the attribution question arises.

Quote from: Neil Swart
If the circulation changes are caused by anthropogenic greenhouse warming (or other human or natural external forcings such as ozone depletion, aerosol emissions, or solar activity) this pattern of atmospheric change should emerge as a clear signature when averaging together many climate model simulations of this period. Averaging together many simulations effectively cancels out all random internally generated fluctuations seen in individual climate simulations, leaving behind the model response to external forcings, such as increasing greenhouse gases. Using this approach, Ding et al. find ...

There is no mention in the Ding et al paper that they "average together many simulations". They don't use this method, actually what they do is run the POP2+CICE4 model with two sets of data, and subtract the results from one run from the results from the other run.

Quote from: Neil Swart
...
that external forcing accounts for very little of the observed circulation changes, and therefore attribute the changes predominantly to internally generated variability. The result is surprising, in that it attributes a multidecadal atmospheric circulation anomaly to internal variability. Typically, internal variability is most prominent at shorter timescales — from months to years — and accounts for less of the observed variability as one extends to longer and longer timescales.
(emphasis mine) That's the objection that many have stated here in many different ways, but in a few words: nearly 40 years of one-sided variability seems unlikely.

Quote from: Neil Swart
...
The simulation-averaging approach they use to make this attribution is common,...

Again, Ding et al don't use a simulation-averaging approach.

Quote from: Neil Swart
...
but it relies on the assumptions that the models have been supplied with the correct forcing, and are faithfully replicating the real world response to that forcing — assumptions that are always open to question.

That is exactly my objection above that they didn't properly quantify the uncertainties associated with the reanalysis data that they fed their POP2+CICE4 model in Exp-5 and Exp-6.

Quote from: Neil Swart
...
Nonetheless,multi-decadal-scale internal variability does exist, most often relying on the longer term memory of the ocean. For example, tropical Pacific sea surface temperature(SST) variability has been shown to have a strong connection with atmospheric circulation anomalies over Greenland and Arctic sea ice . Thus, there is a plausible link between tropical SST variability and Arctic sea-ice decline, but firmly establishing this relationship would require further work. 

This latter question is purely of academic interest.

jai mitchell

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #330 on: April 12, 2017, 01:51:22 AM »
Quote
If the circulation changes are caused by anthropogenic greenhouse warming (or other human or natural external forcings such as ozone depletion, aerosol emissions, or solar activity) this pattern of atmospheric change should emerge as a clear signature when averaging together many climate model simulations of this period.

Unfortunately. . .

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0362.1

Indirect Aerosol Effect Increases CMIP5 Models’ Projected Arctic Warming

Petr Chylek et al.

Abstract:  Phase 5 of the Coupled Model Intercomparison Project (CMIP5) climate models’ projections of the 2014–2100 Arctic warming under radiative forcing from representative concentration pathway 4.5 (RCP4.5) vary from 0.9° to 6.7°C. Climate models with or without a full indirect aerosol effect are both equally successful in reproducing the observed (1900–2014) Arctic warming and its trends. However, the 2014–2100 Arctic warming and the warming trends projected by models that include a full indirect aerosol effect (denoted here as AA models) are significantly higher (mean projected Arctic warming is about 1.5°C higher) than those projected by models without a full indirect aerosol effect (denoted here as NAA models). The suggestion is that, within models including full indirect aerosol effects, those projecting stronger future changes are not necessarily distinguishable historically because any stronger past warming may have been partially offset by stronger historical aerosol cooling. The CMIP5 models that include a full indirect aerosol effect follow an inverse radiative forcing to equilibrium climate sensitivity relationship, while models without it do not.

----------------------------

even IF they used an average, the average between the models shows inherent internal bias AGAINST exposing the new apparent mechanism of tropical SST impacts from SE Asian aerosols since this effect is NOT represented in most of the CMIP5 models.

. . .so it must be 'natural variability'.
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Rob Dekker

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #331 on: April 12, 2017, 04:25:40 AM »
Thanks Ktonine, for quoting from the Swart paper.
Swart also adds :
Quote
Robustly establishing that such a large fraction of observed Arctic summer-time sea-ice loss can be attributed to internal variability will need independent observational corroboration.
Can’t argue with that…:o)

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Rob Dekker

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #332 on: April 12, 2017, 04:29:23 AM »
ktonine wrote :
Quote
Obviously they've gone over the models dozens of times trying to figure out why they don't match observations.  At some point (Ding et al) someone was bound to come up with the rational idea that maybe it's not being entirely forced, but simply natural variation.

Interesting is Swart’s graph from the Canadian Earth System Model version 2 model runs, which pretty nicely match observations.
So your argument may not hold ground.

The point is, some CMIP5 models are bad and some CMIP5 models are good.
You can't use the bad models (or the mean) as an argument that the lack of match with observations is caused by 'internal variability'.

As Michael Mann wrote :
https://twitter.com/MichaelEMann/status/841362467603255298
Quote
But misfit relative to CMIP5 mean doesn't imply internal variability!
CMIP5 mean likely does NOT capture true forced trend.
« Last Edit: April 12, 2017, 05:11:21 AM by Rob Dekker »
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jai mitchell

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #333 on: April 12, 2017, 04:32:33 AM »
Archimid,

"1.  The sea ice is melting out 40 years ahead of the models"

. . .

That was my post, not archimids,

1.  I was referring to the current CMIP5 ensemble used in the IPCC projections for future arctic sea ice loss.  The most aggressive model does show sea ice loss (effective september minimum) at about the right time (next 2-5 years).

2. Even the band of 0.2K to 0.8K produced by the CMIP5 model ensemble is understating since they do not include water vapor and lapse rate feedbacks produced by SOx emissions reductions.  In addition, the known issue of indirect cloud effects being poorly modeled (and even absent from about 1/2 of the CMIP5 ensemble) shows that the actual range is 0.5K to 1.3K being currently offset by anthropogenic SO2 emissions

3.  The albedo effect of an ice-free arctic is well studied and a 0.5K increase in GMST is actually a conservative figure.  I assert that we are actually well on our way to have JUNE 21st ice free conditions in the total absence of SO2 emissions and BAU global carbon emissions for the next 10 years.  (I project this summer solstice ice free state to occur sometime around 2065).  This will produce over 1.5C of GMST warming in pure albedo with over 70w/m^2 annual shortwave additional forcing over the Arctic ocean - this is verified by NASA satellite analysis of the Bearing Sea published in 2014.

4.  The IPCC included other carbon cycle feedbacks in their CMIP5 ensemble, including a projection of Atmospheric Fraction.  To not include this massive feedback is to severely understate our current climate crisis.   Leading to policy directions that do not serve to meet the existential crisis that is global warming.

5.  I know that even with a WWII mobilization effort we may not be able to prevent +4C in globally averaged warming and we will likely be forced to engage in global dimming geoengineering.

6.  I do not say we are unable to prevent it, I am saying that we have already surpassed the +3.5C CO2e abundance levels if we include the following feedbacks that are not included in the CMIP5 model ensemble.

Quote
early sea ice loss albedo
increase in arctic algae bloom further increasing albedo loss
Near persistent +IPO leading to collapse of the Amazon Rainforest
Rapid collapse of arctic permafrost
collapse of the boreal forest system due to heat stress/drought
ocean acidification causing a long-term loss of the production of Dimethyl Sulfide
reduction in far-infrared emission from the Arctic ocean as sea ice is lost
much greater warming soils carbon feedback (not frozen soils) than contained in the current model ensemble


« Last Edit: April 12, 2017, 09:03:16 PM by jai mitchell »
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Rob Dekker

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #334 on: April 12, 2017, 05:30:41 AM »
Qinghua Ding was kind enough to reply to my post regarding the 'attribution' experiment (Exp 7/8), in a private email, explaining this experiment in more detail :
Quote
In our Exp7 and 8, we repeated our exp2 ( in which we specified the observed winds everywhere in the model)  but removed the CO2 forced wind changes (1979 to 2014) from the observed winds. The CO2 forced winds were derived from CMIP5/LENS runs that were only forced by anthropogenic forcing. In other words, we wanted to see how much atmospheric warming would be left in the Arctic if we could remove any winds that is due to CO2 forcing. We found that there are still 70% to 90% of atmospheric warming left in Exp7 and 8 ( compared with Exp2).  This is how we dealt with that attribution. I don't think the method you described is similar to what we did in Exp7 and 8. 
It seems to me that if you want to tease out the 'anthropogenic' part of the warming trend, that you should not just eliminate the "CO2 forced wind changes", but you should also include the much more obvious "CO2 forced" factor : Temperature !

This is my main criticism of the Ding et al 2017 paper : At no point (neither in the 'causation' (Exp.5/6) nor in the 'attribution' part (Exp 7/8) did they even attempt to address the influence of AGW, the KEY 'anthropogenic' factor in this game.
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ktonine

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #335 on: April 12, 2017, 05:41:22 AM »
Interesting is Swart’s graph from the Canadian Earth System Model version 2 model runs, which pretty nicely match observations.
So your argument may not hold ground.

The point is, some CMIP5 models are bad and some CMIP5 models are good.
You can't use the bad models (or the mean) as an argument that the lack of match with observations is caused by 'internal variability'.

Rob - don't get blinded again.  Whether a particular model does or does not "match observations" isn't the key point. The key point is does it match observations *because* the AGW forcing also creates the key atmospheric pattern?  If it matches observations but doesn't match the circulation pattern, then it's probably just coincidence or particular attention was paid to "tuning" parameters where possible to better match observations.

I think it highly, highly unlikely that Ding or Swart haven't already considered and evaluated this to some degree.  You'd expect Swart as a noted climate modeler, and of a model that *does* reproduce observations well, to take the *opposite* view of Ding et al.

The ensemble mean is still the best guess unless it can be shown that excluded models all suffer some physical flaw.  Hansen's tour de force "Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous" was impressive because they *did* find and fix several flaws they found in the model they were using - notably I recall they were able to fix the model so that Antarctic Bottom Water formation took place in the correct geographical location.

In any event, believing a paper is or isn't completely correct isn't what I objected to - I'm agnostic on Ding et al.   The rude, asinine, and flatout character assassination of the Ding et al authors by some here (not you) is what riled me up. 

ktonine

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #336 on: April 12, 2017, 05:50:52 AM »
This is my main criticism of the Ding et al 2017 paper : At no point (neither in the 'causation' (Exp.5/6) nor in the 'attribution' part (Exp 7/8) did they even attempt to address the influence of AGW, the KEY 'anthropogenic' factor in this game.

We're going down the rabbit hole again. From Ding et al, METHODS Exp-6: "Given a strong correlation between circulation and surface winds, temperature, specific humidity, sea-level pressure, and downwelling long wave radiation in the Arctic,variability and trends in these six variables that are associated with Z200GL are processed and removed from the forcing.

Darvince

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #337 on: April 12, 2017, 07:01:30 AM »
A quick commentary on the commentary by Neil Swart.
Quote from: Neil Swart
The challenge, until now, is that there has been no clear understanding of the relative contributions of human-induced warming versus internal variability to the observed long-term decline in Arctic sea ice.

I don't think this has been the challenge. I think the challenge is that sea ice models until now have failed to explain the rapid decline in Arctic sea ice, as stated in the Notz and Stroeve 2016 article which I have mentioned in one of my previous comments.
Um, both are completely connected and interdependent on one another. If 30-60% of the sea ice loss trend is naturally forced, then wouldn't the model mean fail to show the sea ice loss trend that was observed? This directly happened with the small rise in Antarctic sea ice when models predicted a small loss over the past 40 years. Does this mean the models were bad? No, it means that trends elsewhere in the world unconnected to climate warming caused the sea ice gain in the south. In fact, posted in two placed by AbruptSLR he links papers which show that the gain in Antarctic sea ice over the last decade and a half was due to the IPO climate oscillation (and, apparently, the more rapid loss of Arctic sea ice since ~2000):

http://forum.arctic-sea-ice.net/index.php/topic,1053.msg94192.html#msg94192
http://forum.arctic-sea-ice.net/index.php/topic,724.msg82561.html#msg82561

Now, what can actually make the finding by Ding et al. irrelevant would be showing that the recent negative phase of the IPO was directly due to anthropogenic sources.

jai mitchell

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #338 on: April 12, 2017, 07:23:16 AM »
Now, what can actually make the finding by Ding et al. irrelevant would be showing that the recent negative phase of the IPO was directly due to anthropogenic sources.

http://www.nature.com/nclimate/journal/v6/n10/full/nclimate3058.html

Role of volcanic and anthropogenic aerosols in the recent global surface warming slowdown

Doug M. Smith et al.

The rate of global mean surface temperature (GMST) warming has slowed this century despite the increasing concentrations of greenhouse gases. Climate model experiments1, 2, 3, 4 show that this slowdown was largely driven by a negative phase of the Pacific Decadal Oscillation (PDO), with a smaller external contribution from solar variability, and volcanic and anthropogenic aerosols5, 6. The prevailing view is that this negative PDO occurred through internal variability7, 8, 9, 10, 11. However, here we show that coupled models from the Fifth Coupled Model Intercomparison Project robustly simulate a negative PDO in response to anthropogenic aerosols implying a potentially important role for external human influences. The recovery from the eruption of Mount Pinatubo in 1991 also contributed to the slowdown in GMST trends. Our results suggest that a slowdown in GMST trends could have been predicted in advance, and that future reduction of anthropogenic aerosol emissions, particularly from China, would promote a positive PDO and increased GMST trends over the coming years. Furthermore, the overestimation of the magnitude of recent warming by models is substantially reduced by using detection and attribution analysis to rescale their response to external factors, especially cooling following volcanic eruptions. Improved understanding of external influences on climate is therefore crucial to constrain near-term climate predictions.
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Rob Dekker

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #339 on: April 12, 2017, 08:00:12 AM »
This is my main criticism of the Ding et al 2017 paper : At no point (neither in the 'causation' (Exp.5/6) nor in the 'attribution' part (Exp 7/8) did they even attempt to address the influence of AGW, the KEY 'anthropogenic' factor in this game.

We're going down the rabbit hole again. From Ding et al, METHODS Exp-6: "Given a strong correlation between circulation and surface winds, temperature, specific humidity, sea-level pressure, and downwelling long wave radiation in the Arctic,variability and trends in these six variables that are associated with Z200GL are processed and removed from the forcing.

My point exactly.
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Rob Dekker

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #340 on: April 12, 2017, 08:11:06 AM »
Interesting is Swart’s graph from the Canadian Earth System Model version 2 model runs, which pretty nicely match observations.
So your argument may not hold ground.

The point is, some CMIP5 models are bad and some CMIP5 models are good.
You can't use the bad models (or the mean) as an argument that the lack of match with observations is caused by 'internal variability'.

Rob - don't get blinded again.  Whether a particular model does or does not "match observations" isn't the key point. The key point is does it match observations *because* the AGW forcing also creates the key atmospheric pattern?  If it matches observations but doesn't match the circulation pattern, then it's probably just coincidence or particular attention was paid to "tuning" parameters where possible to better match observations.

Mmm. Are you suggesting that Swart's Canadian Earth System Model version 2 model was " "tuning" parameters where possible to better match observations" ?
Or could it just be a better model ?
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #341 on: April 12, 2017, 10:39:19 AM »
A quick commentary on the commentary by Neil Swart.
Quote from: Neil Swart
The challenge, until now, is that there has been no clear understanding of the relative contributions of human-induced warming versus internal variability to the observed long-term decline in Arctic sea ice.

I don't think this has been the challenge. I think the challenge is that sea ice models until now have failed to explain the rapid decline in Arctic sea ice, as stated in the Notz and Stroeve 2016 article which I have mentioned in one of my previous comments.
Um, both are completely connected and interdependent on one another. If 30-60% of the sea ice loss trend is naturally forced, then wouldn't the model mean fail to show the sea ice loss trend that was observed?
There are many possible reasons why the model mean could fail to explain the observed Arctic sea ice decline. For example:
- Lack of sufficiently accurate weather data over the Arctic ocean during the period considered.
- Most models not including some positive or negative feedbacks that have only recently been uncovered.
- The particular complexity of the Arctic climate system and how it interacts with the global climate system may not be captured by the model mean.

Ding et al instead chose to stroll down "natural climate variability" argument path, but that was because they had already done so in their 2014 paper about warming in the eastern Canada and Greenland region. As I wrote in one of my previous comments, the 2017 Ding et al paper makes similar assumptions, uses a similar methodology and reaches a similar conclusion, as the Ding et al 2014 paper. It doesn't mean that both papers are correct.

Quote from: Darvince
This directly happened with the small rise in Antarctic sea ice when models predicted a small loss over the past 40 years. Does this mean the models were bad? No, it means that trends elsewhere in the world unconnected to climate warming caused the sea ice gain in the south. In fact, posted in two placed by AbruptSLR he links papers which show that the gain in Antarctic sea ice over the last decade and a half was due to the IPO climate oscillation (and, apparently, the more rapid loss of Arctic sea ice since ~2000):

http://forum.arctic-sea-ice.net/index.php/topic,1053.msg94192.html#msg94192
http://forum.arctic-sea-ice.net/index.php/topic,724.msg82561.html#msg82561

Now, what can actually make the finding by Ding et al. irrelevant would be showing that the recent negative phase of the IPO was directly due to anthropogenic sources.

In the second part of my first question to Dr. Ding, I asked him exactly that: what scientific experiment or physical evidence would prove his "natural variability" attribution claim wrong.

ktonine

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #342 on: April 12, 2017, 06:13:59 PM »
My point exactly.
Rob - you're not making sense.  When they ran the same simulations with and without AGW influence how can that possibly be characterized as not trying to determine the effects of AGW?  That's what Exp-5/6 were about. 

You may not like the specific design. OK, all that sounds like is I'm smarter than them and would have designed the experiment differently.

Mmm. Are you suggesting that Swart's Canadian Earth System Model version 2 model was " "tuning" parameters where possible to better match observations" ?
Or could it just be a better model ?
[/quote]

Of course it *could* just be a better model. Assume that it is.  Then Dr Swart should be critical of the Ding et al results if he bought into your objections - not complimenting them.

Qinghua ding

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #343 on: April 12, 2017, 06:24:55 PM »
So many interesting discussions!
 
Just a quick answer to AndrewB. I will have more to add this weekend.

If you can show me an ensemble mean ( more than 10 to 20+ realizations) of multiple models forced by anthropogenic forcing ( whatever you like to add in the models, Co2, aerosol, land surface use and ozone etc ) that can well capture the observed circulation change in the past 40 years. I think this would be a good evidence that my argument is wrong. If not, we have to say that a portion of observed circulation change is due to a natural source and this part of natural source can melt sea ice through a dynamical impact rather than the greenhouse effect.
 
Please read our papers in 2014 (fig. 4) and 2017(fig.4) . We checked all available models to do this analysis and we couldn't find a similarity. 
« Last Edit: April 12, 2017, 06:31:21 PM by Qinghua ding »

Qinghua ding

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #344 on: April 12, 2017, 06:29:21 PM »
This is also a very interesting article from Dr. Swart published in 2015.

Swart, N. C., Fyfe, J. C., Hawkins, E., Kay, J. E. & Jahn, A. Influence of internal variability on Arctic sea-ice trends. Nat. Clim. Change 5, 86–89 (2015).

Random_Weather

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #345 on: April 12, 2017, 08:08:39 PM »
Dr. Ding

So many interesting discussions!
 
If you can show me an ensemble mean ( more than 10 to 20+ realizations) of multiple models forced by anthropogenic forcing ( whatever you like to add in the models, Co2, aerosol, land surface use and ozone etc ) that can well capture the observed circulation change in the past 40 years.

In my opinion this is overconfidence in models, on global scale i would agree but in arctic i would be carefully and it seem not to be a problem of forcing representation, but more in the models(the mean of it) state of cyrosphere. In fact, if we looking for september sea ice concentration we get this: (SIC for 70-90N)

http://fs5.directupload.net/images/170328/hq2ruz53.png

Over the complete Hindcast, the mean of models have to less ice concentration in september against observation, also lower trend, this is a result (look also Q. Shu 2015: Assessment of sea ice simulations in the CMIP5) of that the models have complete different states of sea ice Annual Extent, Aplitude and Trend, as shown above the mean of the models is totaly different to the observation, also shown is MPI-ESM-MR and it works well with observation. So whats different,  MPI-ESM-MR has the most realitic sea ice state untill 2005(Annual-Extent, Aplitude and Trend) and therefore in forecast also the best. In forecast, we see that the ups and downs are different, which imply a different phase of internal variability. So i would tend to say, still if physics of models were perfect, they are not able the produce the real world aplification of regional climate system because of the lack of representation of cyrosphere state in the hindcast.

Under the line, it seem not confident to me to claim it would be more natural source, because of the lack of cyrosphere representation in models. Also to say, if you test z200 JJA CIMP5 and JJA SIC CIMP5 you will get R^2= 0.925 (1979 to 2016), which imply that SIC in JJA and z200 JJA are strongly connected, since the models undereastimate the Trend, they will also undereastimate z200 Trend for JJA


To make a clear point:
I would not say your Paper is wrong or any kind of it, but the results(in magnitude) seem to me not so confident and there is more research needed

Edit:
Sources:
KMNI-Explorer SIC NSIDC between 70-90N
KMNI-Explorer SIC CMIP5 mean between 70-90N
KMNI-Explorer SIC MPI-ESM-MR between 70-90N
KMNI-Explorer z200 CMIP5 mean between 70-90N (JJA)
KMNI-Explorer SIC CMIP5 mean between 70-90N (JJA)

« Last Edit: April 12, 2017, 08:30:26 PM by Random_Weather »

Qinghua ding

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #346 on: April 12, 2017, 08:33:32 PM »
Thanks. My quick answer to Random_Weather is that I realize many people here really like to use a domain mean or a global mean plot. In my view, that could be misleading to some extents. Some models could get the correct sign of a change due to a wrong reason. So I believe I need to see the spatial pattern first ( not only sea ice ) and then make a conclusion.  I will show you more evidences why I say so this weekend once I find some time.
 

Random_Weather

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #347 on: April 12, 2017, 08:49:02 PM »
Dr. Ding, Thanks for fast reply

"So I believe I need to see the spatial pattern first"

This would also change the spatial pattern, in your Paper you show CIMP5 in average and the atmosphere modul of MPI-ESM-MR and it show clear the same spatial pattern like in observation just a bit weaker, but CIMP5-mean is fail to reproduce the pattern. It brings me to the question, why the model MPI-ESM-MR can produce it and have one of the best representations in Hindcast of cyrosphere state (Annual-Extent, Trend and Aplitude). A coincidence? I dont belive in it, so i looking for reasons.

So again, i am unwillig to say there is something wrong, but i also unwillig to see a coincidence that the model with near observed sea ice state in Hindcast, produce nearly same spatial pattern and sea ice concentration in September in forecast

PS:
I do test the domains Greenland(as decribed in your Paper) vs. Arctic (70-90N) MPI-ESM-MR and found for 200z Trend-Conditions: JJA in 1979-2016

MPI-ESM-MR
(Arctic:Greenland)
1.00:1.34

NCEP-Reanalysis
1.00:1.73
This would imply that they both do have a stronger trend in z200 on Greenland which is in contrast to CMIP5-mean

PPS: On Tropical domain, MPI-ESM-MR increase (T2m) near double strong as in Observation
« Last Edit: April 12, 2017, 11:09:08 PM by Random_Weather »

jai mitchell

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #348 on: April 12, 2017, 09:51:53 PM »
-- why the model MPI-ESM-MR can produce it and have one of the best representations in Hindcast of cyrosphere state (Annual-Extent, Trend and Aplitude). --

good question,

my reading of it is that they do not have aerosol-cloud interactions but they do have a strong cloud-effect positive forcing parameter and just happen to under represent tropical upper troposphere temps by about 1K.

in effect, while indirect cloud aerosol interactions are not expressly described, increases in upper troposphere humidity and cooling under aerosol loading and cloud expansion under a reduction in aerosols as well as observed Tropical variability are represented well which happens to work as a good proxy for the interactive effects of high-troposphere aerosols - though again, it appears to be an artifact of the model and not directly aerosol-forced paramaterization.

though this is not strictly expressed in the model description.  it fits.
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Rob Dekker

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #349 on: April 13, 2017, 06:02:49 AM »
My point exactly.
Rob - you're not making sense.  When they ran the same simulations with and without AGW influence how can that possibly be characterized as not trying to determine the effects of AGW?  That's what Exp-5/6 were about. 

ktonine, you misunderstand Exp-5/6.
These experiments do NOT try to determine the effects of AGW.
They try to determine the effect of 'atmospheric circulation' and specifically the effect of Z200GL (geopotential height over Greenland). Ding et al 2017 uses a regression method to find out how much the other variables (including the most important one : temperature) may have been affected by Z200GL. As a result, the method knocks out 2/3rd of the Arctic temperature trend, effectively assigning it to 'atmospheric circulation' as the cause.
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