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Rob Dekker

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #500 on: April 20, 2017, 07:07:00 AM »
Thanks for the links Jai.
Give me some time to read these papers.
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Rob Dekker

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #501 on: April 20, 2017, 07:52:07 AM »
I read the Booth paper quickly and it does suggest that HADGEM2-ES explains a part (but not all) of the 'bump' in temperature in the 30's-40's. Also, I understand that their HADGEM2-ES run is mostly driven by indirect (not direct) aerosol forcing. If I understand that correctly, it makes assumptions about cloud coverage affected by aerosols.

Now I'm not sure yet how important their findings are, but I do see that this paper (Booth et al) draws criticism in the scientific literature.

For example, here, by Zhang et al 2012 responds to Booth et al :
Quote
However, here it is shown that there are major discrepancies between the HadGEM2-ES simulations and observations in the North Atlantic upper-ocean heat content, in the spatial pattern of multidecadal SST changes within and outside the North Atlantic, and in the subpolar North Atlantic sea surface salinity. These discrepancies may be strongly influenced by, and indeed in large part caused by, aerosol effects. It is also shown that the aerosol effects simulated in HadGEM2-ES cannot account for the observed anticorrelation between detrended multidecadal surface and subsurface temperature variations in the tropical North Atlantic. These discrepancies cast considerable doubt on the claim that aerosol forcing drives the bulk of this multidecadal
variability
.
http://journals.ametsoc.org/doi/abs/10.1175/JAS-D-12-0331.1

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« Last Edit: April 20, 2017, 08:07:19 AM by Rob Dekker »
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jdallen

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #502 on: April 20, 2017, 08:09:27 AM »
I read the Booth paper quickly and it does suggest that HADGEM2-ES explains a part (but not all) of the 'bump' in temperature in the 30's-40's. Also, I understand that their HADGEM2-ES run is mostly driven by indirect (not direct) aerosol forcing. If I understand that correctly, it makes assumptions about cloud coverage affected by aerosols.

Now I'm not sure yet how important their findings are, but I do see that this paper (Booth et al) draws criticism in the scientific literature.

For example, here, by Zhang et al 2012 responds to Booth et al :
Quote
However, here it is shown that there are major discrepancies between the HadGEM2-ES simulations and observations in the North Atlantic upper-ocean heat content, in the spatial pattern of multidecadal SST changes within and outside the North Atlantic, and in the subpolar North Atlantic sea surface salinity. These discrepancies may be strongly influenced by, and indeed in large part caused by, aerosol effects. It is also shown that the aerosol effects simulated in HadGEM2-ES cannot account for the observed anticorrelation between detrended multidecadal surface and subsurface temperature variations in the tropical North Atlantic. These discrepancies cast considerable doubt on the claim that aerosol forcing drives the bulk of this multidecadal
variability
.

Don't you just LOVE science and the scientific process ?
Indeed; that said, it causes me to question somewhat the reference to that warming period as an indication of base-line "natural" increases driving Ding et. al.'s  conclusion, even if not responsible for *most* of the increase.

How would we eliminate human-sourced aerosols from baseline calculations of natural variability?
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Rob Dekker

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #503 on: April 20, 2017, 08:28:42 AM »
Jai, your second paper (Bellomo et al 2016) seems to deal mostly with cloud effects over the tropics:

Quote
From these experiments we conclude that cloud feedbacks can account for 10% to 31% of the observed SST anomalies associated with the AMO over the tropics.

I'm not sure yet how much that has to do with aerosols and the 30's-40's temperature bump in the Arctic.
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Rob Dekker

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #504 on: April 20, 2017, 08:35:30 AM »
Indeed; that said, it causes me to question somewhat the reference to that warming period as an indication of base-line "natural" increases driving Ding et. al.'s  conclusion, even if not responsible for *most* of the increase.

That is a good point, but please note that Ding et al 2017 does not take the temperature bump in the 30's and 40's as any form of 'base-line' for natural variability. In fact, they don't even mention it in the paper. Only Qinghua did in the comment section of this very forum.

In the paper, Ding et al 2017 uses a statistical method to 'tease out' the effect of 'atmospheric circulation', but in that process they knock out 65 % of the temperature trend (and trends in other variables) in the Arctic and assign it to 'atmospheric circulation'. And at attribution time, they do not compensate for any global warming (temperature) signal in these trends at all. Only 'high latitude winds'.

That's why I don't like Ding et al 2017. At all.
« Last Edit: April 20, 2017, 08:59:49 AM by Rob Dekker »
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #505 on: April 20, 2017, 01:58:06 PM »
Maybe it was a combination of AMO and lack of aerosols?
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ktonine

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #506 on: April 20, 2017, 06:22:57 PM »
Quote from: Rob Dekker on 4/18
Also, I find it interesting that on the ASIF Qinghua proposed a “70 year” cycle in the Arctic climate, although there is very little evidence to support that.

I doubt that the 30s-40s temperature bump had much to do with aerosols.
The AMO is a much more likely candidate.
After all, Delworth and Mann 2000 extracted (approx. 70 year) AMO cycles back 400 years from climate proxy data, including this one from the 30s-40s :


jai mitchell

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #507 on: April 20, 2017, 06:24:56 PM »
Jai, your second paper (Bellomo et al 2016) seems to deal mostly with cloud effects over the tropics:

Quote
From these experiments we conclude that cloud feedbacks can account for 10% to 31% of the observed SST anomalies associated with the AMO over the tropics.

I'm not sure yet how much that has to do with aerosols and the 30's-40's temperature bump in the Arctic.

The Ding paper does not mention this bump because they assume that it is natural variability, as does the IPCC.

The translation of tropical circulation impacts in the arctic is the fundamental work of the paper.  There are also many other papers that indicate the linkage between aerosol emissions and tropical water vapor, high troposphere humidity, PDO, NAO and even AMOC circulation changes.  In addition, the sudden drop in sea levels at that time (1920-1928 see image below) also indicates a significant increase in tropical precipitation on land. 



This paper from 2002

http://journals.ametsoc.org/doi/full/10.1175/1520-0442(2002)015%3C2103:TRTATI%3E2.0.CO%3B2

Quote
The present results, combined with this earlier finding, suggest that the indirect effects of anthropogenic sulfate may have contributed to the Sahelian drying trend. More generally, it is concluded that spatially varying aerosol-related forcing (both direct and indirect) can substantially alter low-latitude circulation and rainfall.

This paper in 2016

http://journals.ametsoc.org/doi/full/10.1175/JCLI-D-15-0174.1

Quote
For the sstClimAerosol simulation, the cloud albedo effect contributes significantly to the changes in land surface temperature and precipitation pattern (Fig S6).

Note: TL in the image below shows changes in tropic land precipitation expected for a large increase in aerosols.



Also attached image S6 from the supplementary information showing full aerosol modeling with extreme reductions in tropic land rainfall due to an increase in Aerosols (and by reason a large relative increase from a reduction in aerosols).
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jai mitchell

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #508 on: April 20, 2017, 06:37:51 PM »
http://www.meteo.psu.edu/holocene/public_html/Mann/articles/articles/MannEtAlGRLPreprint.pdf

Quote
For example, Mann and Emanuel [2006]
show that such a procedure misattributes at least part of the forced cooling of the NH
by anthropogenic aerosols during the 1950s-1970s (especially over parts of the North
Atlantic) to the purported down-swing of an internal “AMO” oscillation. A number of
climate modeling studies support their finding [Santer et al, 2006; Booth et al, 2012;
©2014 American Geophysical Union. All rights reserved.
Evan, 2012; Dunstone et al, 2013], though the precise role that anthropogenic
aerosols have played in recent decades continues to be debated in the literature [Koch
et al, 2011; Carslaw et al, 2013; Stevens, 2013].

When they detrended forcing for AMO oscillation using CMIP5 they used a model mean that largely did not include secondary cloud effects.

thus their AMO trend below still fits the anthropogenic aerosol emission curve very well.

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ktonine

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #509 on: April 20, 2017, 07:27:57 PM »
http://www.meteo.psu.edu/holocene/public_html/Mann/articles/articles/MannEtAlGRLPreprint.pdf

When they detrended forcing for AMO oscillation using CMIP5 they used a model mean that largely did not include secondary cloud effects.

thus their AMO trend below still fits the anthropogenic aerosol emission curve very well.

Huh??

The "true AMO" graphs and the emissions graphs look nothing alike.  The timing and amplitude variances are completely different.





ktonine

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #510 on: April 20, 2017, 07:43:15 PM »
Merging the emissions graph and Mann et al's "true AMO" graph yields:


jai mitchell

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #511 on: April 20, 2017, 07:54:14 PM »
Merging the emissions graph and Mann et al's "true AMO" graph yields:



Why do you suppose that the intensity of the 1930 change in aerosols would have the same effect in 1978?  The effect is driven by RELATIVE forcing compared to the GHG forcing component, not absolute.  In addition, the use of this graph must be framed within a dynamic fluid system that has inertia of forcing impacts  So the scale of the emissions is not as important as the breakpoints as shown below.

In addition, the AMOC curve is using multiple models to derive AMO from northern hemisphere temperature changes, there are average values that smooth the curve over decadal scales, so the break points are not clearly defined but it is clear that they fit the emission profile breakpoints very well (as do the other metrics that I posted above).
« Last Edit: April 20, 2017, 08:52:46 PM by jai mitchell »
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ktonine

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #512 on: April 20, 2017, 08:22:40 PM »
(note: never mind, I see that you do not have a science education background)

Hmmm....I did attend MIT.  I do work as a metrologist.  Otherwise, spot on.

Please tell us the regression statistics.  You're just willy nilly drawing arbitrary lines and they really don't match up ..... or perhaps you're unable to.  Shoulld I do it for you - oh, wait, I don't have a science background. LOL.

jai mitchell

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #513 on: April 20, 2017, 08:53:22 PM »
my apologies
I thought you came from an MBA background and worked in manufacturing
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jai mitchell

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #514 on: April 20, 2017, 09:14:18 PM »
(note: never mind, I see that you do not have a science education background)

Please tell us the regression statistics. 

I already told you you have to adjust for relative forcing with impact of SO2 on tropical circulation (not simply a function of global forcing as regional impacts and high-altitude impacts appear to have much more weight).  This would be consistent with a simple model that shows relative impact of short-term aerosol emissions on the global system through the industrial period.  In addition, to accurately assess these impacts one would have to identify an overshoot effect from these short term changes based on the previous forcing history.  for example, shifts to positive AMO look to occur when SO2 emissions slow, revealing a strong signal that is being suppressed by aerosol emissions, however the break back to a negative AMO appears to happen quite suddenly when emissions begin to rise significantly - indicating a very large SO2 emission 'control knob' on the AMO function - as a function of relative forcing and energy imbalance and within a regional impact scale.

The lines are not arbitrary they are break points in both graphs and within the period of smoothing for the AMO using multiple models and Within the scale of emissions, they actually line up much better than I would expect.

for example, in the first graph, the 1920 line is actually 1917 (if you apply a grid function to determine the actual date instead of eyeballing it like I did)  and the 1935 graph line could reasonably be shifted to 1942 since this was when the emissions actually started to increase again (driving the shift in the AMO graph).
« Last Edit: April 20, 2017, 09:22:56 PM by jai mitchell »
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ktonine

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #515 on: April 20, 2017, 09:41:37 PM »
for example, in the first graph, the 1920 line is actually 1917 (if you apply a grid function to determine the actual date instead of eyeballing it like I did)  and the 1935 graph line could reasonably be shifted to 1942 since this was when the emissions actually started to increase again (driving the shift in the AMO graph).

And since Mann et all detected a 70 yr cycle going back 400 years are you really serious or just so tied into a pet theory that you can't see the silliness of it??

Besides how is it we don't see a change when MT Agung or MT Pinatubo erupted?  Is this only forced by anthropogenic aerosols and ignores natural emissions??  Funny how the atoms and molecules must be zipping around with little origin tags on them.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #516 on: April 20, 2017, 09:51:45 PM »
for example, in the first graph, the 1920 line is actually 1917 (if you apply a grid function to determine the actual date instead of eyeballing it like I did)  and the 1935 graph line could reasonably be shifted to 1942 since this was when the emissions actually started to increase again (driving the shift in the AMO graph).


Besides how is it we don't see a change when MT Agung or MT Pinatubo erupted? 


Rainfall and cloud patterns are a Tropospheric loading effect with larger impacts from upper troposphere loading.  Stratospheric impacts act more like GHG.  What can you tell me about secondary cloud effects of tropospheric aerosols?

Actual AMO series below:

https://www.esrl.noaa.gov/psd/data/correlation/amon.us.long.data
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #517 on: April 20, 2017, 09:52:18 PM »
jai - another factor you've completely ignored is the completely different spatial/geographical distributions; high emissions in the early and mid-20th century would have been from Eurpope and North America. In recent decades those areas have seen reduced emissions while Asia/China have greatly accelerated.  Expecting the same forcing patter from completely different geographical distributions would seem a bit over-reaching - to put it charitably.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #518 on: April 20, 2017, 10:00:11 PM »
jai - another factor you've completely ignored is the completely different spatial/geographical distributions; high emissions in the early and mid-20th century would have been from Eurpope and North America. In recent decades those areas have seen reduced emissions while Asia/China have greatly accelerated.  Expecting the same forcing patter from completely different geographical distributions would seem a bit over-reaching - to put it charitably.

why don't you quote me where I did this.

wrt Mann's 70 year AMO cycle analysis is this the paper you refer to?  perhaps you want to back up your assertions with credible links to peer reviewed papers as I have?

https://pdfs.semanticscholar.org/24e9/6c16772d5d38dd1f0e759514fc6d2523dc1c.pdf
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ktonine

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #519 on: April 20, 2017, 10:32:56 PM »
wrt Mann's 70 year AMO cycle analysis is this the paper you refer to?  perhaps you want to back up your assertions with credible links to peer reviewed papers as I have?

https://pdfs.semanticscholar.org/24e9/6c16772d5d38dd1f0e759514fc6d2523dc1c.pdf

The Mann paper was already previously cited upthread with link.

And actually the record now goes back over 600 years: Amplification of the Atlantic Multidecadal Oscillation associated with the onset of the industrial-era warming, G. W. K. Moore, J. Halfar, H. Majeed, W. Adey & A. Kronz, 2017

Quote
The reconstruction that captures the centennial timescale variability explains ~25% of the variance in the time series (Fig. 3a). The mode has a local maximum during the 15th century that was followed by an ~400 year period of near constant values that ended in the early part of the 19th century after which there was a trend towards higher values. Indeed, values in the late 20th century were the highest over the 643-year long record. This behaviour is broadly consistent with the piecewise linear fit to the time series shown in Fig. 1.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #520 on: April 21, 2017, 12:05:35 AM »
so basically, your contention of there not being a significant aerosol component to the 1930's trend is justified by the following long-series?

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nukefix

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #521 on: April 21, 2017, 12:43:11 AM »
Interesting, does the AMO-reconstruction show the abrupt end of the LIA, or something else?

Rob Dekker

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #522 on: April 21, 2017, 03:57:05 AM »
Quote from: Rob Dekker on 4/18
Also, I find it interesting that on the ASIF Qinghua proposed a “70 year” cycle in the Arctic climate, although there is very little evidence to support that.

I doubt that the 30s-40s temperature bump had much to do with aerosols.
The AMO is a much more likely candidate.
After all, Delworth and Mann 2000 extracted (approx. 70 year) AMO cycles back 400 years from climate proxy data, including this one from the 30s-40s :

Yeah. That kind of did not come out the way I wanted and requires some explanation :D

The first comment was in response to Qinghua's statements suggesting a 70 year cycle that originated in "atmospheric circulation" and is significant enough to explain a large part of the recent multi-decadal ice decline (50% in his paper). The same sort of significance that Qinghua uses to predict that the real big melt will be 50 - 100 years from now. And the same sort of significance that Qinghua believes there was in the 30's and 40's.

What I wanted to point out is that there is no evidence for such a strong signal.

There only is the AMO, a 70 year cycle which has a very limited effect on NH warming (about 0.1 C as Mann pointed out; with 0.4 C in the Northern Atlantic, maybe a bit more in the Arctic) and a limited effect on sea ice retreat as Walsh pointed out for the 30's-40's period, and as Kinnard et al 2011 showed in the reconstruction of 1450 years of Arctic sea ice.
« Last Edit: April 21, 2017, 06:04:40 AM by Rob Dekker »
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #523 on: April 21, 2017, 04:28:50 AM »
for example, in the first graph, the 1920 line is actually 1917 (if you apply a grid function to determine the actual date instead of eyeballing it like I did)  and the 1935 graph line could reasonably be shifted to 1942 since this was when the emissions actually started to increase again (driving the shift in the AMO graph).

And since Mann et all detected a 70 yr cycle going back 400 years are you really serious or just so tied into a pet theory that you can't see the silliness of it??

Besides how is it we don't see a change when MT Agung or MT Pinatubo erupted?  Is this only forced by anthropogenic aerosols and ignores natural emissions??  Funny how the atoms and molecules must be zipping around with little origin tags on them.
https://en.wikipedia.org/wiki/Kondratiev_wave

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #524 on: April 21, 2017, 07:02:52 AM »
u know bbr that was my first thought too but realized it would be impossible to show that the economic cycle drove the emission trend or if the temperature trend drove the economic cycle.  (I suspect the former)  It is interesting though that the KWave has shifted to a longer period than in the 1800s ( it used to be a 50 year cycle.
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #525 on: April 21, 2017, 07:54:01 AM »
u know bbr that was my first thought too but realized it would be impossible to show that the economic cycle drove the emission trend or if the temperature trend drove the economic cycle.  (I suspect the former)  It is interesting though that the KWave has shifted to a longer period than in the 1800s ( it used to be a 50 year cycle.
I would think it is most definitely that economic cycles drive emission trends. I think this began with the dawn of agriculture, when albedo feedbacks (as well as primitive emissions) would have started the see-saw that continues to this day, where economic prosperity drives climactic changes, which demand innovation & economic re-organization (i.e. periods of recession/depression), and then the cycle continues.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #526 on: April 21, 2017, 05:14:22 PM »
It would be very difficult to expect an aerosol forcing component in the historical trend based on agricultural cycles.

however

there is more than a number of papers that have determined that the late period cycle could (Edit:) NOT be driven by natural variability without a strong aerosol cloud effect in the tropics.

for example:

http://onlinelibrary.wiley.com/doi/10.1002/2016GL071337/abstract

Quote
we conclude that models need external forcing to explain the magnitude, timing, and apparent multidecadal frequency of the observed twentieth century AMO variability.

« Last Edit: April 21, 2017, 06:16:32 PM by jai mitchell »
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #527 on: April 21, 2017, 06:01:49 PM »
It would be very difficult to expect an aerosol forcing component in the historical trend based on agricultural cycles.

however

there is more than a number of papers that have determined that the late period cycle could be driven by natural variability without a strong aerosol cloud effect in the tropics.

for example:

http://onlinelibrary.wiley.com/doi/10.1002/2016GL071337/abstract

Quote
we conclude that models need external forcing to explain the magnitude, timing, and apparent multidecadal frequency of the observed twentieth century AMO variability.
Well, aerosols would not have been the primary driver initially, it would have been albedo changes (forest -> cropland over the Middle East, Eastern Asia, Southern Europe, and parts of the Americas).

Perhaps slash and burn techniques would have contributed some token amount of aerosols, but that does not mean that temperature trends/climactic variability were not impacted, creating the initial see-saw mechanism that persists to this day.

I would think that aerosols further amplified the existing changes as primitive industrialization began ~4000-3000BC (look at the Pyramids!) with corresponding heavy industry that was very inefficient in terms of raw materials -> output (which pushed large amounts of aerosols into the atmosphere). This peaked with the Romans & Chinese in the first millennium AD, with those numbers only reached again ~1800-1850. While raw output may have been higher post-1800, emissions were still roughly equivalent until about 200 years ago due to the dirtiness of industry way back when.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #528 on: April 21, 2017, 06:18:46 PM »
please see my edit above:

It is impossible to determine these things without a strong explanation of the scale of early ag emission cycles.
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #529 on: May 31, 2017, 01:16:28 PM »
I saw this article today on Phys.org that reminded me of this thread:

Quote
Researchers uncover a cause for early 20th century Arctic warming

Is a warmer Arctic a canary of global warming? Since the 1970s the northern polar region has warmed faster than global averages by a factor or two or more, in a process of 'Arctic amplification' which is linked to a drastic reduction in sea ice.

But then how to explain a similar rapid warming that occurred during the early 20th century, when the effects of greenhouse gases were considerably weaker than today? And what can we prove about the period, given the scarcity of usable data and observations prior to the 1950s?

Now scientists from Kyoto University and UC San Diego have discovered that this phenomenon occurred when the warming phase—'interdecadal variability mode'—of both the Pacific and Atlantic Oceans coincided. The team's findings appeared recently in the journal PNAS.

"We found that early 20th century sea surface temperatures in the tropical Pacific and North Atlantic had warmed much more than previously thought," explains lead author Hiroki Tokinaga of Kyoto.

"Using observations and model simulations, we've demonstrated that rising Pacific-Atlantic temperatures were the major driver of rapid Arctic warming in the early 20th century."

Previous explanations for early Arctic warming have including decreased volcanic aerosols and increased solar radiation, but none of these have been able to simulate observed conditions from the period.

Tokinaga's team found that when the interdecadal rise in sea surface temperatures was included in simulation calculations, the results properly reflected early Arctic conditions.

"Coupled ocean-atmosphere simulations also support the intensification of Arctic warming," continues Shang-Ping Xie of UCSD, "which was caused by a concurrent, cold-to-warm phase shift of Pacific and Atlantic interdecadal modes."

The researchers explain that these new findings can help constrain model climate projections over the Arctic region.

"It is likely that temperatures in the Arctic will continue to rise due to anthropogenic global warming," concludes Tokinaga. "Our study does not deny this. We are rather suggesting that Arctic warming could accelerate or decelerate due to internal variability of the Pacific and the Atlantic."

"It is a challenge to accurately predict when the next big swing of multidecadal variability will occur. Careful monitoring is essential, given the enormous impact on the Arctic climate."

Obviously the same Atlantic-Pacific simultaneous interdecadal variability mode hasn't been positive in the past 30-40 years, or we'd be hearing all about it. So, what happens when it does go positive?

Sorry, rhetorical question.  ;)
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epiphyte

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #530 on: June 02, 2017, 06:36:39 AM »

The most intriguing part of that event is that warming exhibited a pretty large scale feature in the Arctic and the area was warmed by something very fast from 1920s to 1930s.  So causes  of this fast warming rate has puzzled me for a long time.

Reduction in global SO2 emissions


So the early 20th-Century UK initiatives to clean up the "Dark, Satanic Mills" and to banish the London "smog" could now be interpreted as having unintended consequences?

Don't let the Dirty-Coal lobby get wind of that one. Next thing you know DT will be tweeting that the librul tree-huggers _caused_ global warming.




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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #531 on: June 02, 2017, 07:04:32 AM »

The most intriguing part of that event is that warming exhibited a pretty large scale feature in the Arctic and the area was warmed by something very fast from 1920s to 1930s.  So causes  of this fast warming rate has puzzled me for a long time.

Reduction in global SO2 emissions


So the early 20th-Century UK initiatives to clean up the "Dark, Satanic Mills" and to banish the London "smog" could now be interpreted as having unintended consequences?

Don't let the Dirty-Coal lobby get wind of that one. Next thing you know DT will be tweeting that the librul tree-huggers _caused_ global warming.

I thought the coal-lobbyists lead by US government already did this? At least I've seen some comments claiming this. The best way to attack these assholes would be to pour sulfuric and nitrous acids to their yards and spray their houses with the stuff as they want the good old 1970s back, but as this is still illegal, we'd need to find something else for these asshats. Severe their US made cars and Ddos attack their servers? Still illegal, but less conspicuous.
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #532 on: June 02, 2017, 07:26:15 AM »
This is fitting given current events

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #533 on: June 02, 2017, 01:05:41 PM »
Guys, I completely agree with your comments--but please be mindful of the thread you're in, and try to stay on topic. Thanks!

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #534 on: June 02, 2017, 08:43:39 PM »
I saw this article today on Phys.org that reminded me of this thread:



And I saw your thread post and it reminded me of this article ;-)

onlinelibrary.wiley.com/doi/10.1002/2017GL073480/full

Trajectories toward the 1.5°C Paris target: Modulation by the Interdecadal Pacific Oscillation

article here:
https://www.theguardian.com/environment/planet-oz/2017/may/09/planet-could-breach-15c-warming-limit-within-10-years-but-be-aware-of-caveats

Planet could breach 1.5C warming limit within 10 years, but be aware of caveats

Quote
But new research published in a leading scientific journal suggests that just eight years after that report is published, the world might have already reached that 1.5C target – or at least one definition of it (some senior scientists disagree with some of the assumptions in the paper – read on for those important caveats).


Global warming 'hiatus' doesn't change long term climate predictions – study
Published in the journal Geophysical Research Letters, the research looks closely at the influence of a mechanism in the climate known as the Interdecadal Pacific Oscillation (IPO).

“The IPO is like the long-term version of El Niño – it’s like El Niño’s uncle,” says Ben Henley of the University of Melbourne and the research’s lead author.

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Iceismylife

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #535 on: March 24, 2018, 12:44:35 AM »
nice thread. I will read it through and through.  This comment is just so I can find it again.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #536 on: March 24, 2018, 03:38:54 PM »
Neven & folks, there is a potential weakness in the reasoning above in that interesting paper about early 20th century Arctic warming. That warming was apparently brought on naturally by concurrent warm phases in the north Atlantic and north Pacific. But they do not eliminate the possibility that human caused GHG forcing could bring on concurrent warmth in the north Atlantic and north Pacific. There was a period in the 1960's when sulfate aerosols cooled the north Atlantic masking the effects of increasing GHGs. Now aerosol levels are high above the seas near China and India.

Because the southern hemisphere has a continent at the pole surrounded by the vast southern ocean it will tend to warm more slowly than the north after a positive forcing event because the Antarctic Circumpolar Current prevents warm subtropical water from getting close to the continent at any place other than the Antarctic peninsula.  Gulf stream water, however gets into the Arctic ocean at 300m to 600m depth. And Rossby wave teleconnections cause atmospheric heating in the Arctic when the equatorial west Pacific gets warmer than normal and has very strong convection like it did this NH winter.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #537 on: November 05, 2018, 07:41:42 PM »
New paper by Ding et al.:

Fingerprints of internal drivers of Arctic sea ice loss in observations and model simulations

https://www.nature.com/articles/s41561-018-0256-8


Abstract:
Quote
The relative contribution and physical drivers of internal variability in recent Arctic sea ice loss remain open questions, leaving up for debate whether global climate models used for climate projection lack sufficient sensitivity in the Arctic to climate forcing.  Here, through analysis of large ensembles of fully coupled climate model simulations with historical radiative forcing, we present an important internal mechanism arising from low-frequency Arctic atmospheric variability in models that can cause substantial summer sea ice melting in addition to that due to anthropogenic forcing. 

This simulated internal variability shows a strong similarity to the observed Arctic atmospheric change in the past 37 years.  Through a fingerprint pattern matching method, we estimate that this internal variability contributes to about 40–50% of observed multi-decadal decline in Arctic sea ice.

Our study also suggests that global climate models may not actually underestimate sea ice sensitivities in the Arctic, but have trouble fully replicating an observed linkage between the Arctic and lower latitudes in recent decades.  Further improvements in simulating the observed Arctic–global linkage are thus necessary before the Arctic’s sensitivity to global warming in models can be quantified with confidence.

Paper is paywalled, but the full text can also be found at sci-hub.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #538 on: November 05, 2018, 11:55:00 PM »
I'm going to need to read that.  I have a hard time swallowing that 40-50% figure.  I'd like to see supporting evidence from historical data and physical evidence suggesting cycles tied to a driving mechanism.
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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #539 on: November 06, 2018, 01:10:38 PM »
Looks good to me. The "hiatus" in Sept extent since 2012 has some time to run yet. It would be interesting to know if there are similar things going on in other seasons and whether they correlate e.g. if we can expect a continuing run of winter records but no summer records, but they've only done the analysis for the summer weather and September extent.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #540 on: November 06, 2018, 02:32:59 PM »
It is incredibly distressing to me to see the author use "arctic sea ice" and "arctic sea ice area" interchangeably. Arctic sea ice area or extent are terribly important measures, but they DO NOT measure the ice in the arctic, only the surface area the ice occupies. Sea ice is frozen sea water, a 3 dimensional object.

When the author says 50% of the current losses are due to "internal variability", how does he determined if internal variability changed due to climate change?

Does this mean he expects a 50% recovery soon? When does this "natural cycle ends"?

Also, what's up with figure 1.E? Why are the models way below observations during the earlier decades and then match observations in the recent decades?

I think the intentions of the author are very good, and I wouldn't dare to challenge the math, but I also think that some necesary assumptions for this analysis are wrong, in particular using sea ice area as proxy for sea ice and calling random variability "natural" when the variability itself probably changed and will change more as the climate changes.
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Richard Rathbone

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #541 on: November 06, 2018, 06:03:28 PM »
It is incredibly distressing to me to see the author use "arctic sea ice" and "arctic sea ice area" interchangeably. Arctic sea ice area or extent are terribly important measures, but they DO NOT measure the ice in the arctic, only the surface area the ice occupies. Sea ice is frozen sea water, a 3 dimensional object.

When the author says 50% of the current losses are due to "internal variability", how does he determined if internal variability changed due to climate change?

Does this mean he expects a 50% recovery soon? When does this "natural cycle ends"?

Also, what's up with figure 1.E? Why are the models way below observations during the earlier decades and then match observations in the recent decades?

I think the intentions of the author are very good, and I wouldn't dare to challenge the math, but I also think that some necesary assumptions for this analysis are wrong, in particular using sea ice area as proxy for sea ice and calling random variability "natural" when the variability itself probably changed and will change more as the climate changes.

The various mentions of sea ice and sea ice area almost always refer to Sept extent.

The fingerprinting is how the variability is attributed. The same fingerprint is seen in the control runs as the runs under historical forcing and the historical observations. The same fingerprint in all 3 is good evidence that the mechanism of the variability hasn't changed much and that much of the Sept 2012 record can be attributed to it.

The models bounce all over the place in 1e because internal variability is high. The increasing spread of the grey area with time does suggest that the variability has increased, but the fingerprint correspondences are good evidence that the models are representing it decently.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #542 on: November 06, 2018, 08:43:36 PM »
Continuing Archmid's thought, the paper in contrast highlights the view some of us have, which is volume rather than extent and area is the key metric for ice and by extension, arctic system "health".

Area and extent both will become far more volatile as volume decreases.

As such,  they will become far less useful metrics to use in assessing the state of the system, or for skillfully determine change and direction in the system.
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Archimid

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #543 on: November 06, 2018, 10:12:25 PM »
Thanks for the answers. They bring clarity and more questions.

Quote
The various mentions of sea ice and sea ice area almost always refer to Sept extent.

Yeah, this is common practice in most climate papers I've read and maybe even in ASIF. I'm probably guilty of it on occasion.  It is distressing to me because area is such an incomplete measure. Area and extent seems like pillars of ASI science when volume with shape information should be the pillar. I understand that volume is a much more difficult measure and area has  larger, more agile set, but still. I believe it is wrong to use them as equivalent because it may lead to fundamental mistakes in the science.

Quote
The fingerprinting is how the variability is attributed. The same fingerprint is seen in the control runs as the runs under historical forcing and the historical observations.

This is what the paper says about the fingerprint:

Quote
Internal variability is determined from a long (1,800 years) control run of CESM1 with constant pre-industrial forcing (‘PI’ hereafter), as well as by the deviations of each ensemble member in 40-Forced from the ensemble mean.

 After re-reading the paper (and failing to fully comprehend it) my questions increased.

This is my understanding of the experiment. They take a series of models, run them and calculate mean ASI area loss as a result of forcing. The ensamble (a sort of mean of the models) under predict the ASI area lost. Thus the difference between the ensemble and the observations must be "internal" variability.

I can agree with that if two assumptions hold. The author is beholden to the truth enough ( gotta love science) to say it more clearly than I could:

Quote
This approach makes the assumption that sea ice sensitivity can be observed without contamination by internal variability and that models appropriately capture the linkage between Arctic sea ice loss and global temperatures.

I'm convinced that neither of these assumptions hold, but that is based on my mental model of the Arctic. I will know over the next few years. If the Arctic recovers then it was internal variability. If it doesn't then we are in deep trouble.
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Richard Rathbone

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #544 on: November 06, 2018, 11:24:01 PM »
Thanks for the answers. They bring clarity and more questions.


This is what the paper says about the fingerprint:

Quote
Internal variability is determined from a long (1,800 years) control run of CESM1 with constant pre-industrial forcing (‘PI’ hereafter), as well as by the deviations of each ensemble member in 40-Forced from the ensemble mean.

 After re-reading the paper (and failing to fully comprehend it) my questions increased.

This is my understanding of the experiment. They take a series of models, run them and calculate mean ASI area loss as a result of forcing. The ensamble (a sort of mean of the models) under predict the ASI area lost. Thus the difference between the ensemble and the observations must be "internal" variability.



The fingerprint is the particular pressure pattern in the Arctic summer in high loss years and the weather patterns that connect it to particular temperature variations in the Pacific. The same pattern is seen in the control run, and the historically forced runs and the data.

The internal variability isn't the difference between the historical data and the ensemble mean, its the spread of the ensemble. Look at the band of grey lines in 1e. The internal variability is the difference between the top of that band and the bottom of that band.

There's not enough historic data to pull the variability from it alone. Thats one of the key points from this paper. In 30 years time it might be possible to assess the variability from the historic data, but the record is still too short to properly characterise the climate.

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #545 on: November 06, 2018, 11:46:52 PM »

Quote
The various mentions of sea ice and sea ice area almost always refer to Sept extent.

I understand that volume is a much more difficult measure and area has  larger, more agile set, but still. I believe it is wrong to use them as equivalent because it may lead to fundamental mistakes in the science.
I believe that concentrating on minimum (just one day in the year) is not good enough.

Area to me is very important as the less area of ice there is means the greater area of open water with consequent major change to the climate / weather where it is happening. How one distinguishes a "natural variation" from a feedback from climate change caused by an icy sea becoming an open water sea I have not the foggiest idea.

That is why I developed an analysis of open water vs sea ice for each of the 14 seas to track the change in each sea (1980 to 2018) from icy deserts to maritime open ocean at various periods of the year and the entire year. I think I will give them another airing on the sea ice extent thread sometime this month and definitely at the year end.

Volume alone surely also is not the answer, as volume is thickness x the area covered, and loss of area surely changes the climate ?

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oren

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #546 on: November 07, 2018, 03:11:04 AM »
I've read it, it's an impressive piece but I am not very convinced of the bottom line. I doubt the system can be modeled effectively enough to draw such conclusions.
A few questions floated in mind as I read:
* Do we expect sea ice to recover nearly 50% of the loss since 1979 when the JJA200 high pressure flips to low pressure? I personally find it very hard to believe.
* How often does this pressure regime flip occur in the control simulations? How long does it last?
* Can the models replicate winter sea ice reduction as has been occurring in the last few years (lower max)? I agree with gerontocrat that focusing on one day of the year is not enough.
* Can the models replicate volume loss and strong reduction of older MYI? Do the models go down to such level of detail?
* I notice that the area data used was up to 2015. But in 2016 there was another very low point of sea ice area at min. Does 2016 fit the pressure pattern of the study?

Richard Rathbone

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #547 on: November 07, 2018, 01:59:56 PM »
I've read it, it's an impressive piece but I am not very convinced of the bottom line. I doubt the system can be modeled effectively enough to draw such conclusions.
A few questions floated in mind as I read:
* Do we expect sea ice to recover nearly 50% of the loss since 1979 when the JJA200 high pressure flips to low pressure? I personally find it very hard to believe.
* How often does this pressure regime flip occur in the control simulations? How long does it last?
* Can the models replicate winter sea ice reduction as has been occurring in the last few years (lower max)? I agree with gerontocrat that focusing on one day of the year is not enough.
* Can the models replicate volume loss and strong reduction of older MYI? Do the models go down to such level of detail?
* I notice that the area data used was up to 2015. But in 2016 there was another very low point of sea ice area at min. Does 2016 fit the pressure pattern of the study?

It already has. Check what happened between 2012 and 2013.
The earlier paper claims a 70 year oscillation, the current one merely that 30 years of data can
 have seriously biassed trends in it. That could be due to a 70 year oscillation, but they don't make the case that it is.
2016 was still higher than 2007 and there's a decade of trend between them too.
These models can't replicate anything on a timescale of a few years. This paper says 60 years of data is needed before you can get decently reliable results from it and that if you look at shorter timescales the internal variability is quite likely to be fooling you.
Volume is in the models, but they aren't all that good at extent, let alone volume. This paper has good evidence for the ensemble spread being down to real variability on long timescales, but the ensemble mean still has significant bias in it. (that bias is why the left and right hand scales on 1e are offset, the match with observations isn't as good as it looks if you don't notice the bias has been removed in that figure)

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #548 on: November 08, 2018, 07:37:15 AM »
Jim Pettit's graph and data from the UW applied physics laboratory summarizes my difficulty accepting the author's conclusions:

http://iwantsomeproof.com/extimg/siv_annual_max_loss_and_ice_remaining.png

Can we find *any* pre-industrial evidence to suggest built-in variability dropped volume to near or under 10,000KM3 and then returned it to greater than 15,000KM3 at summer minimum?

Also contributing... The changes that have taken place in the last 20 years have dramatically altered the system's dynamics.  The energy mechanics of 1980 are nothing like those in 2000 which are nothing like those now.  How can you comfortably attribute 50% of system variability to "natural" variability when the fundamental mechanics of the system itself have changed?
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Richard Rathbone

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Re: Arctic sea ice changes: Natural variation vs human influence
« Reply #549 on: November 09, 2018, 01:43:36 PM »
Jim Pettit's graph and data from the UW applied physics laboratory summarizes my difficulty accepting the author's conclusions:

http://iwantsomeproof.com/extimg/siv_annual_max_loss_and_ice_remaining.png

Can we find *any* pre-industrial evidence to suggest built-in variability dropped volume to near or under 10,000KM3 and then returned it to greater than 15,000KM3 at summer minimum?

Also contributing... The changes that have taken place in the last 20 years have dramatically altered the system's dynamics.  The energy mechanics of 1980 are nothing like those in 2000 which are nothing like those now.  How can you comfortably attribute 50% of system variability to "natural" variability when the fundamental mechanics of the system itself have changed?

We know full well that extent and volume have behaved differently during the historical period. This paper provides strong evidence that conclusions drawn from a data span as short as the historical period are biassed. A plot of volume from the historical period only is doubly biassed, first because the period considered is too short to capture the range of variability and second because its volume rather than extent.

The fundamental mechanics haven't changed. Heat is still being transferred by radiation, conduction and convection. Ice still melts and water freezes according to imbalances in energy transfer at the phase interfaces. Air and water are still moving in response to pressure gradients. The Navier Stokes equation is as valid then as it is now.

The way ice moves in response to the stresses exerted on it by air and water is not well understood and its quite possible that the equations used for it and the parameters fitted to them work better in an Arctic dominated by MYI, but its also possible they work better in an Arctic dominated by FYI and the models are actually representing that aspect better.

There's strong evidence in this paper that the high melt years in 2007-2012 are at the extremes of melt below the trend and 2013 is on trend, and the reason that isn't obvious from the historical record is that the historical record is too short.

We have a historical temperature record with multiple El-Ninos in it so its obvious when a misleading trend line is drawn in it by picking El-Nino/La Nina endpoints. If we only had one half of an ENSO period in the historical data it would be extremely difficult to get a reliable trend from it. Thats the situation we are in with regard to ice extent in the Arctic. The historical period is too short and trends in it are liable to substantial bias.