Begin by reading Role for Eurasian Arctic shelf sea ice in a secularly varying hemispheric climate signal during the 20th century? That post offers some snarks on the paper, and some indications why you might distrust it, but no really substantive criticism. I'll try to do that here but I won't fully succeed because (just like Wyatt and Curry) I don't really understand MSSA. I'm hoping that someone how does know it will do a proper analysis.
Where's the meat?
If you look through the paper to find the core substance, you won't. There are layers of mush and piles of words but precious little hard matter. Figure 12 is about the closest they come to a mechanism, but its just a pile of words arranged in a picture; there's no maths here. So really, we're reduced to figure 2 and similar as being the only vaguely convincing bits.
And... well, it looks good, doesn't it? All those nice smooth wave-like lines showing clear evidence of "propagation". What more could you want? Weeellll...
First of all, the smoothness is because all the indices have been heavily filtered into a spectral band (update: Eli has a nice post showing quite how heavy the filtering is. Note that this isn't fatal of itself - the ACW was also heavily filtered - but). Not precisely this, because its been done via MSSA, but effectively so. Unfortunately they don't show this in spectral space somehow, which I think would have been helpful. However, they do show you the proportion or power of the original signal that remains in this band, and this is really very revealing.
As ever, click on the image for a larger version. Note that I've cropped the caption. Ignore the ovals drawn on, instead note the fraction of variance for NINO in the range - about 1%. That makes sense: we all know that NINO is quasi-periodic at ~5 year, so you expect little left over at very slow periods. But this means, in turn, that NINO is irrelevant at their timescales of interest - as, very likely, we could have guessed at the outset. So whatever their MSSA has done, it certainly hasn't allowed them to filter out variables that contribute little to the pattern.
But then why is the black line in figure 2 of about the same amplitude as all the others? Because they've all been normalised. A more representative version of this picture would renormalise the lines by some-version-of-variance; in which case the black NINO line would be essentially flat.
Once you realise that, you can see that EIE, NAOw, and ALPI, all with less than 10% variance in band, are also negligible at this scale. EIE is "East Ice Extent" of the East Eurasian Seas; even W+C note that its negigible at this scale, and its not in fig 2, so we'll forget it. NAOw is NAO in winter; since they don't provide a pic for it I'll have to assume that NAO, too, has negligible variance in-band and it too should be ignored. ALPI is the Aleutian Low Pressure Index.
Then I thought: but hold on, NHT is the hemispheric temperature index; it can't propagate. Removing this, along with the other three that have essentially no in-band variance, leaves me with this crudely retouched version of their figure 2 a. Its now much less obviously a wave; its just three (four really, but two essentially overlay) different lines filtered to within an inch of their lives into a 60-year-ish band.
I think that's about it, really. All the stuff about exploding sardines is just fluff and can be ignored. The "mechanisms" is an extended exercise in self-delusion.
[Update: Michael E. Mann, Byron A. Steinman and Sonya K. Miller, "On forced temperature changes, internal variability,
and the AMO" say:
. Using the synthetic temperature histories, we also show that certain procedures used in past studies to estimate internal variability, and in particular, an internal multidecadal oscillation termed the “Atlantic Multidecadal Oscillation” or “AMO”, fail to isolate the true internal variability when it is a priori known. Such procedures yield an AMO signal with an inflated amplitude and biased phase, attributing some of the recent NH mean temperature rise to the AMO. The true AMO signal, instead, appears likely to have been in a cooling phase in recent decades, offsetting some of the anthropogenic warming. Claims of multidecadal“stadium wave”patterns of variation across multiple climate indices are also shown to likely be an artifact of this flawed procedure for isolating putative climate oscillations.
Weirdly enough, MW doesn't like it.]
Refs
* ZOMG! Not everyone is arrogant enough to create a website to showcase one not-very-good-paper, but then Wyatt isn't everyone.
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I thought it might help to track down a description of M-SSA
http://en.wikipedia.org/wiki/Singular_spectrum_analysis#Multivariate_ex…
But no, not really.
Are you really saying that your understanding of natural internal variability has not been transformed? But how can that be?
to get a handle on M-SSA I had to first read ADVANCED SPECTRAL METHODS FOR CLIMATIC TIME SERIES by Ghil et al (including one M.E.Mann), then Multivariate singular spectrum analysis and the road to phase synchronization by Groth & Ghil, and reviewed some material from one stats package - KSpectra Toolkit. *IF* I understand half of what I read, and then look at their Figure 2a, the only question I have is, "AND?"
Via Curry and Wyat we learn that it was warm in the 1930s and again in the 1990s. Hence there's probably a 64 year cycle involved. Though it varies in "amplitude and tempo" - so it might be a 50 year cycle or an 80 year cycle. It might not even be a cycle at all. Yeah. That's pretty much BREAKING NEWS!
We also learn that climate in one part of the world contains a clue (sometimes a really, really small clue) as to climate in other parts of the world. Fascinating. IOW, what happens in the tropics doesn't stay in the tropics. Who would a thunk it - other than everybody?
Some of the phase relationships (via Fig 2) are interesting, but the area I find most interesting is the period between 1950 and 1970 where we see anomalous relationships. Some of the indices move on unperturbed, others wander around a bit. Close examination of this period might *actually* provide some insights, but I didn't find anything in the paper that attempted to do so. I was scanning it pretty quickly, so maybe that's my fault as a reader.
I came away underwhelmed.
From my understanding of the report, it depends on periodic fluctuations of Arctic sea ice (notice the capital A). I know sediment core samples contain evidence of the past and can determine if sea ice was present or not, ergo, such periodicity would show itself. The chronology of the recent past can be easily found in areas experiencing rapid sedimentation and determined to the year. Such sedimentary core samples from the Arctic exist on Earth, but I don't have access to such things, needed to refute or confirm the claims in that report. The proof is mostly in the hands of the fossil fuel industries trying to harvest the Arctic and that makes me wonder why haven't they confirmed the WUWT author's findings?
From my understanding of the report, it depends on periodic fluctuations of Arctic sea ice (notice the capital A). I know sediment core samples contain evidence of the past and can determine if sea ice was present or not, ergo, such periodicity would show itself. The chronology of the recent past can be easily found in areas experiencing rapid sedimentation and determined to the year. Such sedimentary core samples from the Arctic exist on Earth, but I don't have access to such things, needed to refute or confirm the claims in that report. The proof is mostly in the hands of the fossil fuel industries trying to harvest the Arctic and that makes me wonder why haven't they confirmed the WUWT author's findings?
[If there was a good way to extend the arctic sea ice record back, people would be doing it. But for the pre-satellite era its very hard. Just look at the "records" for winter ice before 1950, or even after that - it flatlines (e.g. http://www.ipcc.ch/publications_and_data/ar4/wg1/en/figure-4-10.html - I know that's AR4, but its not getting any better -W]
I pointed out the same thing on Curry's blog that the NINO component was very small, while we all know that it has a huge effect on subdecadal fluctuations, enough to compensate for "the pause".
This is my take on applying one of Curry's Stadium Wave components, the LOD - length-of-day characteristic, which likely does have some correlation to long-term decadal fluctuations (according to Dickey of NASA JPL).
http://entroplet.com/context_salt_model/navigate
The battle continues in the comments section of the Stadium Wave posting. The strategy is that if the skeptics give you something, use it and then shove it back in their face.
The phase relationships in Curry and Wyatt Figure 2 are not what we'd expect after reading NAO implicated as a predictor of Northern Hemisphere mean temperature multidecadal variability by Jianping Li, Cheng Sun, and Fei-Fei Jin
Li et al make no mention of waves; neither propagating nor stadium. They say nothing about secular cycles with varying amplitude and tempo. Instead they seem to rely on actual physical processes and testable predictions. The nerve of some people :)
[I wasn't all that happy with Li et al. either, ter be honest, and there's not much physics in it either -W]
'Stadium wave'? ...no, it's a hand wave.
Delusions of grandeur by Curry fanboys such as the Chief Hydrologist:
"Marcia certainly assembled the A team of American climate dynamicists in her thesis committee. That’s pretty impressive by itself. I expect that there will be Nobel Prizes in due course."
[Welcome. The trouble is, these people have no reputation - I mean the people writing this drivel about Nobel prizes. I do so wish there was some way of forcing them to live up to the drivel they've written in the past. I also wonder why they bother -W]
It is not only worse than you think, it is worse than you can think. So bad that even Willard Tony knows better
They've made a prediction and now we'll have to wait decades to assess. Just like all the other climate hypotheses. Who's deluded? My money's on Stout. Not that I think that this particular paper has "nailed it".
If some poor individual were to ask me, I'd tell them that I think the reason for the apparent ~60yr cycle is due to inertia in the oceans, but what do I know. Maybe northern polar cyclical activity is the driving force. Check back in 30 years.
Did I mention the Stoat is delusional? Perhaps that's too harsh. DK might be more appropriate.
[No: we don't assess the quality of science by saying "its a prediction; we'll wait". The first thing we need to do is actually read the science, something I don't see a lot of people doing.
But if you're keen on predictions, you could also read part I, where I discuss some bizarre "predictions" about sea ice they made that have already falsified -W]
Of course the Stoat suffers from DK! It's not like he has ever published any scientific papers about climate before!
Sorry? He has? Many, you say? Surely then AJ will show us he is an accomplished climate scientist himself. If not, AJ has clearly failed to remove the mirror when he used terms like "delusional" and "DK".
Most are focusing on figure 2 but that actually comes directly from Wyatt's previous paper (open access). Figure 1 in that paper shows the same thing but also shows the details of the MSSA processing. The nominal purpose of this new paper was to hypothesise a mechanism for the previously-identified stadium wave behaviour.
[I didn't realise it was avaialable online. Now I'm forced to look again, I find fig 1(a) suspicious: the outstandingness of components 1 and 2 is odd. Also odd is now little something as important as El Nino appears in the analysis -W]
As far as I can tell this 60-year cycle business is a bit of a red herring (though the authors appear to have ill-advisedly promoted the herring through their "predictions" which are literally derived by next peak/trough = last peak/trough + 60). I can't see any reason their proposed mechanism would necessarily produce a 60-year cycle, or even any cycle of regular periodicity. Perhaps they're thinking of a restoring force wave situation where the next oscillation is likely to have a similar wavelength to the previous one, but prediction on that basis fundamentally ignores the impacts of anthropogenic forcing on the processes involved in their stadium wave. With that in mind I wonder what the authors think is actually meant when they say: “The stadium wave signal predicts that the current pause in global warming could extend into the 2030s."
The Li et al. reference is interesting because they suggest NAO prefigures AMO and NHT evolution. In W+C Figure 2 the NHT and AMO curves have been inverted for some reason. I don't think it would be too disruptive for the stadium wave visage for them to appear unflipped so does this choice reflect their belief concerning the direction of causation, contradicting Li et al.?
[The curves drawn in W+C fig 2 are like PCA components; you're entitled to draw them any way up you like; negating them merely requires you to negate the corresponding eigenfunction / MSSA pattern -W]
W - (re: Li, ..." there's not much physics in it either..."
I guess if you're looking for 'new' physics, you'd be correct. I simply read it as using the existing known physics of the NAO/AMO oceanic processes as being sufficient for their purposes. The 3rd and 4th pages of their RESULTS summarize the physics with numerous references.
I came away from Li et al with the impression they've taken known physical processes with their associated indices and devised an application to provide a 15-year window on the probable future of NHT internal variability. This seems like a fairly sizeable leap forward as opposed to just wondering what natural variation might be like over the coming decade.
[I didn't really mean new physics. I had another look when I read your first comment, but I'm not rechecking now, but: what I meant was that the paper is largely based around data; anomalies from trends, drawing graphs, correlations, and writing words about those graphs. What physics there is comes from talking about it. But there's no "wave" in the sense of a wave equation, or anything like it -W]
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The Li et al. reference is interesting because they suggest NAO prefigures AMO and NHT evolution. In W+C Figure 2 the NHT and AMO curves have been inverted for some reason. I don’t think it would be too disruptive for the stadium wave visage for them to appear unflipped so does this choice reflect their belief concerning the direction of causation, contradicting Li et al.?
[The curves drawn in W+C fig 2 are like PCA components; you're entitled to draw them any way up you like; negating them merely requires you to negate the corresponding eigenfunction / MSSA pattern -W]
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TILJANDER!!! TILJANDER!!!
Did Curry come up with the 'stadium wave'-metaphor? If so, I find that interesting, psychologically speaking.
I think the paper is supposed to have some relevance regarding internal variability of the climate (?), so I would have thought that the authors would want to remove the effects of external forcings as far as possible.
Nearly all of the stats goes above my head, and maybe this is a minor point given the issues already pointed out, but I’m intrigued by the use of linear de-trending of northern hemisphere temperature (NHT). Is this an adequate method for removing the effects of external forcings? I had a feeling there might be some published evidence available to support better methods. (Would this make much difference to the overall results?)
Given that the sun has a small 60 year cycle (? see Scafetta or Landscheidt), at least over the last 120 years, and that solar insolation is an external forcing, well no. It is just them being that way
To try to clarify what I said in #13...(Leaving aside the point that NHT can't propogate) NHT is one of the things that allegedly is exhibiting (or is affected by? or predicted by ?) 'stadium wave' behaviour; but if the shape of the linearly de-trended and smoothed NHT record used in Wyatt & Curry's paper (W&C) is already explainable by external forcings or other known factors then inclusion of NHT as part of the hypothesised ‘stadium wave’ wouldn’t seem like a good idea to me.
I suppose I’m asking: Is there enough certainty about the contributions of various causes of the NHT trend in the 20th century (forcings, feedbacks & known causes of short-term variation such as ENSO) that we could say that the assumption that [linear-detrending and smoothing of 20th century NHT as done by W&C leaves us with the temperature changes caused by internal climate variability] is false, and therefore the fitting of NHT into the hypothesised ‘stadium wave’ is spurious? Apologies if this is a silly question.
[The trouble is that without a mechanism, who can know? However, it really isn't clear why detrending NHT to remove external forcing is a good idea: if the NHT were some part of this wave, how would the other bits of the wave know to ignore the bit that is caused by external forcing, and only respond to the anomaly component? I think the detrending is voodoo by W+C: its what people do in most circumstances, so it must be OK here, appears to be their unstatd assumption -W]
Thanks for your helpful inline response to #15. I've been assuming that W&C see the de-trended variability in NHT as an effect of their stadium wave and not as a cause of the other components. However, I don't see my assumption backed up anywhere in their paper.
[Again, its hard to tell. If you look at the top figure I've in-lined, NHT is there along with all the others, cutely forming the wave. As an experiment I just tried re-reading the paper, searching for NHT, but all I found was words -W]