Please don't force me to write another of these, I'll run out of "oh dear"s.
The issue is RP Jr venturing into areas of climate science he doesn't understand (see losing the plot for the last one I remember) and dragging Cruel Mistress along behind, though to be fair CM doesn't fully commit herself.
AndrewT has already expalined the truth to Roger, but it doesn't look like he wants to know it :-(.
And I still haven't written up Larklight or Saturn's Children.
[While I'm here, and since I can: HH on foxes -W]
[Update: you may want to know about my comment policy. Please put any tedious whines about censorship in there. Or go read DenialDepot -W]
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Is the point that Mann's method finds a corelation between local cooling and global warming, so that the same proxy can simultaneously record both?
[The proxy is correlated against the instrumental record before being amalgamated into the global record. So T_glob = avg(Proxy_i * corr(Proxy_i, T_ins)) (it isn't, but its like that. Avg() is over i, corr is over the period of the instrumental record, the proxy series is assumed to run over a longer period). So if you reverse the sign of Procy_i, it makes no difference at all to T_glob -W]
Andrew over there wrote:
"... it does not ask whether such an arrangement makes physical sense. So, if you have a series like the one in question that suddenly spikes in the twentieth century in a manner that would normally indicate cooling...."
In the original papers there are comments about the phase of the climate switching.
I think, and posted somewhere, that it seems to me that they are talking about the climate changing from a cold-dusty-dry to a warm-and-wet climate -- which would do exactly this, change the time of maximum runoff and more organic material in the sediment layer to a different _season_.
In which case, you'd expect the material in the layers to also switch the same way.
It seemed so simple when I glimpsed it.
Can anyone help with a sanity check?
Huh, RPjr sez:
Mann said:
The actual accusation is that Mann flipped flipped the sign of the data. The "upside down" description is, shall we say, a somewhat sensationalist attempt to make him look dumb to those who perhaps aren't numerically literate.
Mann's comment makes perfect sense to me. Is Roger missing what "insensitive to the sign of the predictors" means?
[There are two possibilities here. The charitiable one is that Roger just didn't understand what is going on. The rather less attractive possbility is that he did understand (the third, that I'm wrong, can of course not credibly be entertained). I'm going to go with the first until proved otherwise. I think by now it is rather likely that he does understand that his original post was a mistake but that he will refuse to admit error -W]
It is telling that the true AGW propagandists... [cut. I'm not interested in the usual back-and-forth on this. Stick to the issue of the relevance of the sign of the proxy or have your comments deleted -W]
I don't know... this post by Roger doesn't bother me nearly as much as, for example, his "helpful undergrad Megan" post where he displayed (and stubbornly defended) a stunning ignorance of statistics. Here, I think there is a legitimate point to be made that the standard method has a danger of making correlations that don't necessarily make intuitive sense, and that Mann's response could have been more informative about this. (and yes, I understand that a proxy could match global warming even when there is local cooling if either the proxy is detecting precip or some other larger-scale influenced variable, or for some reason local cooling is actually a result of global warming... but I'd be cautious about assuming that such a relationship is as robust as a proxy from a region with local warming matching global warming, and I think it would be worth highlighting those proxies that did have such a "inverse" relationship)
(And just for people who didn't enjoy this the first time around:
http://sciencepolicy.colorado.edu/prometheus/archives/prediction_and_fo… )
-Marcus
["response could have been more informative about this" - could be, but he was writing for a journal and not the general public. For a journal, he is just stating the bleedin' obvious -W]
The Tijlander varve series that Mann used was contaminated by farming run off. It has a pronounced hockey stick in varve thickness since about 1800 as a result of this. The data after 1800 is of no use in climate studies.
[This, if true, would be a valid objection to the use of the series in reconstruction. You do understand, though, that it is irrelevant to the point at hand, which is the "upside down" stuff? -W]
Prior to 1800, a low thickness varve is evidence of a warm spring or at least this is the interpretation that Tijlnder and other researchers in the area gave to it. Mann chose the opposite with a thick varve indicating a warm spring. Mann gave an interpretation to this proxy that was inverse given to it by specialists in the field..
[Ah, and this is why it is "upside down"? You realise this is irrelevant to the reconstruction, don't you? -W]
I suddenly regret using the name "Cruel Mistress" for my blog. I guess I don't really mind gender-bending, but for some reason, the pronoun startles me.
At any rate, I think my point is only that if there's a correction to be had, and that correction somehow appears in the peer-reviewed lit, I'm cool accepting that it's legit.
[Your "only" point is somewhat unclear. If you're saying, peer-review is the right place to fight this out, then I agree. But your post appeared to assert that the issue was settled, and Roger certainly thinks it is settled, in which case the question would be: on which side do you think it has been settled? As I see it, there has been a paper, and a comment, and a reply to the comment. So if you adopt the last-word-wins, then Mann et al. win. If you don't, then how do you think it is or will be settled? -W]
There were two methods in Mann08, each were equally bad but EIV is the multivariate method which by 'bizarre insensitivity' will automatically flip the data for best correlation. It's RegEM so I know a bit about it. CPS however has a pre-assigned sign and it was inverted. In addition some data was used in a positive position in part of the reconstruction and a negative orientation in another.
[Trivia cut]
OK, this looks like the first serious objection - that there are two methods, and for one (CPS) it matters. Thank you. Now I'll have to actually read the paper :-(
Which is: http://www.pnas.org/content/105/36/13252.full
And it says: Reconstructions were performed based on both the âfullâ proxy data network and on a âscreenedâ network (Table S1) consisting of only those proxies that pass a screening process for a local surface-temperature signal. The screening process requires a statistically significant (P < 0.10) correlation with local instrumental surface-temperature data during the calibration interval. Where the sign of the correlation could a priori be specified (positive for tree-ring data, ice-core oxygen isotopes, lake sediments, and historical documents, and negative for coral oxygen-isotope records), a one-sided significance criterion was used. Otherwise, a two-sided significance criterion was used. Further details of the screening procedure are provided in SI Text.
This looks to me quite important - I hope that you too have read it. It states quite clearly that there are two different sorts of proxies, some whose sign of variation against temperature is known, and some whose sign is unknown. Now it does put the lake sediments into the known category, but I don't think this affects the clear implication that the method works with proxies whose correlation-against-temperature-sign is not known in advance.
The paper then moves onto results without explaining the details of CPS, leaving that to ref 10, http://www.agu.org/pubs/crossref/2004/2003RG000143.shtml. So at some point I'll have to read that. However, at the moment it isn't clear why you're sure that CPS requires knowledge of the sign. Can you give more detail? -W]
I'm a lay person who was intrigued by Roger Pielke's account and the discussion in his comments. I pulled the Mann et al. (2008) PNAS paper and Supporting Information, which led to a some questions, and considerable puzzlement. I posted them as a two-part comment over there, #35 and #37.
To me, the heart of the matter seems to be this. Mann et al. used a series of 15 time-series data sets (Fig. S9) to derive a "Temperature Anomaly vs. Time" graph for the Northern Hemisphere (Figs. 2 and 3). It turns out (Mcintyre claims that) that Mann et al. made an error in handling one of the 15 proxies (Tiljander's X-Ray Diffraction measures of the Lake Korttajarvi varve series). Mann et al. assumed that lower XRD values signify cooler temperatures, whereas Tiljander and others assign lower XRDs to warmer temperatures.
[OK, yes. This is the assertion that the series is "upside down". Mann et al. (and I) claim this doesn't matter -W]
In addition, Tiljander states that the four Lake Korttajarvi records (XRD and three other varve characteristics) are unreliable after about 1720 because of nearby human activity. Peat ditch-cutting in 1930 and bridge construction in 1967 are the causes of the most prominent recent variances in three of the four records, clearly visible in Fig. S9.
[This is a different - though important in its own right - matter. It may be peripherally related -W]
How is it possible to remove these four records (and three others), leaving eight proxy series for the Northern Hemisphere, and end up with a Temperature Anomaly reconstruction that is indistinguishable from the one constructed from all fifteen proxy series (Fig. S8a, green vs. black line)?
[That would require various bits of analysis which I can't readily do to answer. But I can offer a hand-wavy answer. Suppose the lake sediments have been so affected by recent (non-climatic) changes that they are just random noise. then their correlation against recent temperature will be essentially zero. So their contribution to the reconstruction will be very small. You can (I speculate) extend this argument to a large number of proxies: you can throw in any number of series with no idea of their correlation to temperature, and the method will (on average) sort them all out. Of course, if *none* of your records usefullly records temperature you won't get anything interesting out -W]
Mann seems to be saying that reversing one of the fifteen proxies (mistakenly correlating higher XRD with higher instead of lower temperature) doesn't alter the temperature reconstruction. How can this be? If the varve XRD proxy is inconsequential, why include it at all?
[No, you've misunderstood. Its not that its inconsequential, just insensitive to sign. See my helpful formula in one of the comments higher up -W]
Could any of the other 14 proxies have their polarity reversed without effect? How about two? three?...
[All -W]
This doesn't make sense to me.
[And yet it is not that difficult. Maybe I need to blog this -W]
AMac,
I suggest you take a look at figure 1 in the actual paper. This shows the distribution of proxies in the data he used. It was over 1200 in total more than 400 passed the local temperature screen. Dropping 4 or even 8 series from this (series which Mann admits in the SI to be problematic) reconstruction would obviously have little effect on it, contrary to McI blowing this up into some case which should be heard in the war crimes court at the Hague.
As far as how the two recons are virtually identical, in the modern period hundreds of proxies are in use and so the effect of these problematic proxies is small. The larger effect is probably seen in the error bars associated with values in the 9th and earlier centuries, take a look at Figure S10 which shows the effects better due to the expanded scales used.
[I'd rather this didn't broaden out into the usual discussion of the validity of the reconstructions. This should focus on the narrow point: does the sign of the proxies matter. So far the only serious objection I've seen is "it doesn't matter for Regem but does for CPS". Anyone with an informed view on that is welcome to comment -W]
Thanks, Rattus Norvegicus! I see that I'm asking about a smaller issue (the 15 screened proxies available for the NH CPS reconstruction back to the 9th century and earlier, end of pg. 13255 ff). Your point on the broader issue is that there are much, much larger numbers of proxies available for more recent times (red symbols in Fig. 1).
McIntyre claims that all four of the Lake Korttajarvi varve proxies had their signs reversed in Mann et al (2008), not just the XRD one.
Thus, I remain perplexed by Fig. S8a. That depicts the NH Land Temperature Anomaly reconstructions, performed (1) with the full proxy network (green line), and then (2) with the eight proxies remaining after the removal of seven potentially problematic series (black line).
The full proxy network would be the fifteen NH proxy records that pass the screening procedure back to AD 818 or earlier, shown on Fig. S9. Of the seven removed for the black line, four are the four flipped-around Lake Korttajarvi series. Yet the two reconstructions look almost identical, from 200 AD through to 2000 AD.
With so few proxy series, shouldn't this removal have led to a very different-looking curve?
(I'll cross-post this at Pielke's blog.)
AMac, yes if a method is insensitive to sign, you should be able to reverse the polarity of any or all of the inputs and the output should remain unchanged. As Marcus says above, this does seem to raise other questions - which sadly you might actually need to know something about paleoclimatology to consider.
In truth I was more fascinated by Roger wading into paleoclimatology after his recent railing that the professionally-unqualified should not be debating his work.
Why doesn't RP Jr just stop?
When RP Jr doesn't understand something or is entirely careless, he always seems to err strongly on the contrarian side. Why might that be? Is he not skeptical of skeptics?
andrewt, thanks.
> if a method is insensitive to sign, you should be able to reverse the polarity of any or all of the inputs and the output should remain unchanged.
As a general statement, this is certainly true, and it seems to apply to the four upside-down Lake Korttajarvi varve proxies and the reconstruction in Figure S8a. But that's what puzzles me: what, exactly, does Figure S8a show?
[Cut. Sorry, perfectly sensible comment, but not on the (restricted) topic -W]
You guys are missing the point here.
1) Yes, the sign going into a multivariate regression doesn't matter. But the sign coming out certainly does. And if the correlation coming out has a sign opposite to the a priori physical meaning, then we have a problem. That means the correlation is aphysical and spurious.
[The sign going in is the point at issue here. If the sign going in is wrong, then the correlation has the same absolute value but the wrong sign, which means the series gets added back in to the reconstruction with the sign wrong twice, ie correctly. If by "the correlation is aphysical" you mean, of the wrong sign, then you are correct. BUt this is irrelevant -W]
2) The CPS method used by Mann (one of two methods he used) is not a multivariate regression. As described by CA "CPS is little more than averaging and shouldn't take more than a few lines of code. You standardize the network - one line; take an average - one more line; and then re-scale to match the mean and standard deviation of your target - one more line."
So, the sign clearly does matter.
[If they do it as CA says, then yes. However, I'm not going to take CA's word that Mann et al. did it this way - certainly, from the above, it doesn't look like they actually know -W]
Guys, this one is a no-brainer,
[I'm unsure what you mean by that. You're clearly wrong on your point 1 - are you applying this "no-brainer" comment to yourself? On point 2 there is unclarity, but simply relying on CA to tell you the truth seems unwise -W]
Point #15 clears this up quite nicely. Since Kaufman has issued a Corrigendum in which the upside down series is acknowledged, is he wrong or is Mann?
[He is right and Mann is right -W]
#8 William,
CA has replicated the whole CPS portion of the study. In the case of CPS the ambiguous proxy is flipped according positive or negative correlation. I'll dig through the code later if I get a chance and point to the exact line where the flipping occurs or doesn't. When CPS is finished you have a multiplier vector 'a' times array 'Ta' for each proxy. The sum of the array after multiplication times a is the result - flipped proxy!
In the case of EIV the process is a 'best fit' of proxies to the temp record - iterative multivariate regression through expectation maximization.
If you took 100 downslope tiljanders + a small amount of noise and fit them to an upslope temp record, they would mostly flip upside down matching the temp rise with a probability that some were used upside right. The net sum would give a best match to the temperature upslope even though 100 percent of the data had the original Tiljander downslope initially.
Of course despite the match to instrumental records, the important historic result would have very little to do with temperature and were the proxy related to temperature, the historic portion would represent anti-Tiljander temperature after averaging.
It's really a very very dead issue.
"If by "the correlation is aphysical" you mean, of the wrong sign, then you are correct. BUt this is irrelevant -W"
How can it be irrelevant that a proxy reconstruction is inverting constituent proxies with a known (or presumed) physical correlation to that which the reconstruction is attempting to reconstruct ?
[Cut. Answer: read the stuff above -W]
William, are you seriously defending Mann's use of Tijander with the given orientation?
[Trimmed. If you've read what I've written before, you know the answer to that -W]
Imagine you only have two temperature records, one from the northern and one from the southern hemisphere. Neglecting the sign these turn out to be perfectly correlated. This can correspond to two situations:
1. The the temperature varies in sync so both of the represent the global temperature.
2. The temperature varies like a see-saw between the hemispheres while the global average is constant.
An algorithm that ignores the sign of the temperature series is not going to be able to distinguish between these radically different situations. This seems troublesome to me.
[Agreed. This would be a problem if you were using global temperature as the thing you train against. But (I believe) you train against the local temperature -W]
You might want to give some thought to what the phrase "insensitive to" actually means in this context.
In other deep mysteries in the universe, -1 * -1 = 1 * 1.
The only issue is whether or not the CA crowd is correct about the CPS methodology being sensitive to sign.
"Where the sign of the correlation could a priori be specified (positive for tree-ring data, ice-core oxygen isotopes, lake sediments, and historical documents, and negative for coral oxygen-isotope records), a one-sided significance criterion was used."
Is it possible to clarify what this means?
[Well, I can repeat it :-). What they mean is, they want to see if the correlation of the proxy against temperature is significant. If you don't know the sign, you need a two-sided test. If you do know the sign, then you can use a one-sided test. Is that any clearer? -W]
If, as I am inclined to, accept Williams double negative explanation of the insensitive to sign:
If it was put into the group where positive correlation is expected but the correct correlation is negative then I would expect this proxy would fail the one sided significance criterion so you would end up discarding or heavily underweighting the proxy?
[I would expect so -W]
Do we know this proxy did get included in the reconstruction? If the data is upside down would this be through a fluke counter correlation due to human effects on the proxy during the instrumental temperature record period? If so, does this affect the weighting of the use of this proxy?
[My understanding is that the claim is that the thin-thinness of the proxy was interpreted the wrong way round for the expected temperature effects. But on top of that, there are non-climatic artefacts. Non-clim artefacts would generally be expected to de-weight the proxy -W]
If a one sided significance criterion is used, is it still plausible that the insensitive to sign still applies to the reconstruction part while the significance test is supposed to sensitive to the sign (if you put it in that group)?
[Depends what you do with the sig test -W]
Anyway it seems to me that it might be true that the reconstruction calculation part is insensitive to sign but this may not be sufficient to say there is not a mistake and the correlation weighting could still be messed up. Could it be that the insensitive to sign is true but that this is far from the whole truth of whether it affects the reconstruction?
[Rumour has it that regression vs CPS might matter. Sadly no-one who knows is bothering with such detail -W]
The validation period for the 15 screened NH CPS proxy series was 1850-1995 (pg. 13254). Tiljander states that natural signals in the Lake Korttajarvi varve proxies are disrupted after ~1720 by nearby human activities (SI, pg. 2). Thick, mineral-rich varves due to ditch-cutting in 1930 and bridge-building in 1967 are prominent in Fig. S9.
The CPS method was applied in three different ways. Full CPS (calibration 1850-1995), Early (1850-1949) Calibration [Validation 1950-1995], and Late (1896-1995) Calibration [Validation 1850-1895] (pg. 13254).
The Full, Early, and Late 15-proxy reconstructions have the same general shape from 400 to 1850, though there are periods of divergence prior to 1700 (Fig. S11a).
For the varve proxy series, all three CPS calibration approaches appear to have led to the correlation of the deposition of thick, mineral-rich varves with higher temperatures.
Thus, it would appear that the four Lake Korttajarvi proxies contributed a "warmer" signal to the 400-1850 CPS reconstructions in the decades when varves were thicker and more mineral-rich. And a "cooler" signal when varves were thinner and included more organic material. (See orientation of Tiljander proxy plots in Fig. S9, and CPS curves in Figs. 2, 3, S7, S8, S10, & S11.)
This appears to be the opposite interpretation to the one offered by Tiljander, who correlates thinner, more organic-rich varves with higher temperatures. Kaufman accepts Tiljander in his 10/9/09 correction.
If this description is correct, it would appear that there is a "sensitivity to sign" in the CPS method of analyzing climate proxies to derive reconstructions of hemispheric temperature anomalies.
Hey, PJr. is suggesting that you're on the verge of "doing the right thing". What's that all about?
[Haven't got a clue. I think he means "say that RP was right all along" which, since he is wrong, isn't likely. I think I've worked one thing out though: Roger doesn't understand the difference between and individual proxy and the overall reconstruction -W]
Commenting on my own post... how gauche. Anyway, over at CM is an intersting and perhaps enlightening comment by Bender, which may indicate that the entire debate is shifting. I don't know if this is merely B's viewpoint, or if the CA types have realised that the "upside down" charge in its original form won't fly. I'll copy my reply, which I think quotes B's main points:
The substantive issue is how does Mannâs code treat a proxy when its relationship with temperature changes as you move from the calibration phase into the reeconstruction phase. Aha! Thank you. This is the first time someone has made a coherent arguement over this (perhaps it has been said before but lost in the noise, if so my apologies for missing it).
I would answer that such a proxy is simply useless. Getting the sign of the overall series right would not make it useful. A proxy with the properties you describe should not be used.
And itâs not a statistical issue; itâs a coding issue I disagree. It is a data-source issue.
Mann should have investigated more thoroughly once heâd seen the McIntyre complaint â not sure about that. McIâs complaint (assuming weâre talking about the same text) was: âTheir non-dendro network uses some data with the axes upside down, e.g., Korttajarvi sediments, which are also compromised by agricultural impact (M. Tiljander, personal communication), and uses data not qualified as temperature proxies (e.g., speleothem δ13C). â If he meant what you said, he could and should have said so.
Incidentally, âwhich are also compromised by agricultural impact (M. Tiljander, personal communication)â is an interesting phrase â this appears to imply that the compromise wasnât clear without pers comm.
William, you're missing the basic point here.
A temperature reconstruction is _supposed_ to be a logical argument which shows that, as long as a certain set of assumptions hold, past temperatures may be characterized by a calculated curve.
The problem with Tiljander is not that Mann somehow miscalculated. The problem is that the basic assumptions which give Mann's calculations meaning have been violated.
Mann's logical argument assumes that the relationship between Tiljander and local temperature has been uniform during the period for which its signal has been used. This is plainly (and in this case spectacularly) false.
During the period for which we have instrumental temperature readings, the Tiljander signal is dominated by non-temperature related anthropogenic activity (building bridges, etc.). During earlier periods it is believed (by the people who collected the data) to be correlated with temperature in the opposite direction of what Mann has used.
The end result, is that warmer MWP temperatures in Finland cause Mann's temperature reconstruction to go down, and visa versa.
To the extent that Mann would attempt to use his reconstruction to make arguments about current temperatures compared to MWP temperatures (unprecedented in the last 2000 years kind of arguments), his argument is logically flawed.
In summary, the people who are saying that the proxy is upside down are NOT saying that Mann made an arithmetic error. They are saying that, due to modern artifacts, several (heavily weighted) components of Mann's calculation have a negative correlation with temperature.
If Mann's curve does not represent past temperature, then its not a temperature reconstruction.
Wow! I've just read comment 25. (I started writing my previous comment last night but never submitted it).
McIntyre was crystal clear on this issue from the first moment it was discussed (http://www.climateaudit.org/?p=3967). A great many people substantially less intelligent that you "got it".
Rereading this thread, you seem to have been determined not to understand.
William, you wroter:
"The proxy is correlated against the instrumental record before being amalgamated into the global record. So T_glob = avg(Proxy_i * corr(Proxy_i, T_ins)) (it isn't, but its like that. Avg() is over i, corr is over the period of the instrumental record, the proxy series is assumed to run over a longer period). So if you reverse the sign of Procy_i, it makes no difference at all to T_glob"
Given your articulation of the calculation, you are correct only if the corr(Proxy_i, T_ins) is moreorless constant through the full time period covered by Proxy_i.
[No, you've misunderstood. That corr is a single number, and is thus constant by definition. Were you under the impression that it was some kind of time-dependent running correlation? -W]
Since Tiljander clearly indicates that the true relationship is swamped and in fact reversed by local non-temperature related activities in the recent period then (a) Mann should have excluded this proxy and (b) using it produces as spurious and as misleading a relationship as using the annual consumption of firewood in Finland over the last 500 years. It is simply a gross error and Mann (and you) should simply acknowledge it.
[If the proxy represents non-climate information then it shouldn't be used. But I've already said that, so I'm not sure why you want me to say it again. But now I have - are you hap-hap-happy? -W]
I don't think that anybody claims that the multivariate regression analysis Mann did would come out differently if the Tiljander data were flipped in sign.
This raises the question, though, of why flip it at all?
The question people have is about the wider topic of whether the Mann results accurately approximate past temperatures. That is, about teleconnection, trees as thermometers, the alleged spuriousness of the correlation, and so on.
A quick question.
AMac, you assert that in Finland colder temps lead to greater snowpack, however warmer air tends to hold more moisture and result in greater precipitation. For example, here in Montana we get our heaviest snowfalls when temps are just below freezing. When temps lower into the teens, even in the midst of a storm, snowfall amounts are typically less and the water content of said snow is nil. Since we live in a rather dry continental area this relationship might not hold true in Finland, but given what I know about snowfall and snowpack in Montana I would hazard that warmer winters might lead to greater snowpack and a larger snowmelt. There are also some confounding factors associated with late spring (or runoff season) temps. A good hot streak can cause rapid snowmelt which really loads up the rivers around here with sediment and shortens the runoff season. More normal temps during snowmelt extend the runoff season and the rivers have a lower sediment load. Of course these observations are strictly local in nature, but around here my guess would be that warmer temps would be indicated by thicker lake bed sediment deposition and colder temps by less deposition. Are you sure that you are correct about the way that Tiljander interpreted the thickness proxy and not the non-organic/organic matter proxies?
#25, You have to give McIntyre some room in his reply to PNAS the study had many flaws and everything had to fit inside 250 words.
Mann realized that the proxy was used upside down. I understand bender's comment but it seems simple enough to me that when you invert the scale on your thermometer it ain't temp anymore. Explaining the reason for the inversion was due to local environmental factors (which were pointed out by the Tiljander authors) and careless use of algorithms is another issue entirely.
Flipping an alleged temperature curve upside down and averaging with other alleged temperature curves is an obvious mistake...
#29, In the CPS method the orientation of the data does make a difference. In the EIV method it does not. Therefore, it does make a difference in the final result of the CPS method for certain, however we would need to see the resulting weight factors of EIV to determine if it was inverted there.
Now with all that said, EIV is trying to find the best fit. Since we have to invert tiljander to achieve an upslope and positive correlation it's highly likely that EIV also created the same problem.
Rattus Norvegicus wrote (1:36pm) --
> [AMac], Are you sure that you are correct about the way that Tiljander interpreted the thickness proxy and not the non-organic/organic matter proxies?
I'm certainly not sure that I'm correct about Tiljander's interpretation! In fact, I have wondered the same thing. I'm a lay person (who was a long-ago geology major). I've never even been to Scandanavia.
However, I paraphrased Tiljander's interpretation of the data, which McIntyre reports has been supported by other Finnish scientists working in this area, and now by Kaufman.
It seems to me that the burden falls on Mann et al to explicitly state and defend a contrarian interpretation, if they are going to base reconstructions on it.
Read Mann et al's SI Methods treatment of the possible psot-1720 unreliability of the varve record. They don't raise this issue, and imply (in my opinion) that they follow the standard interpretation.
I find it very unlikely that Mann et al realized that their algorithm imposed the opposite interpretation on the varve data. If they had, I think they would have dropped the varve proxies.
William:
This is your site and you can clearly moderate it as you see fit.
[Yes, I certainly can and will. Read the comment policy if you're in doubt -W]
[Snip]
Let me repeat...
[Snip. No, please don't. Bandwidth is precious - don't waste it -W]
...corr(Proxy_i,T_ins).
I understand that for a given period it is a constant number. Tiljander's explanation (and as acknowledged by Kaufman) is that this number reflects an incorrect interpretation of the way this varve varies with temperature if the calibration includes post-1930 temperature data.
[No, you've garbled this, I believe. this number reflects an incorrect interpretation of the way this varve varies with temperature is meaningless. T says that non-climatic signals dominate the recent record (some have claimed since 1760-odd; why don't you provide a link instead of a paraphrse? -W]
I find it very interesting that the discussion is focusing on the sign of the proxy which is being discussed. It seems bizarre that this is viewed as the substantive issue when it does appear fairly clear that the proxy is not suitable for use due to contamination of the modern period - a fact which seems to be quite plain once the sign and coefficient of the proxy's contribution to the reconstruction are known (or guessed).
Is this a game of semantic point scoring, or is a discussion of the validity of this proxy in this specific method relevant here?
[This post, as the title rather suggests, was written in response to RP's confusion. The main aspect of that appeared to be his misunderstanding of the "upside down" issue. The issue of whether this particular proxy is of any use or not is another matter, doubtless fascinating in itself -W]
Courtesy Roger I notice I've been anonymously elevated to "the Team" at SM's blog. Not sure why as I don't know the first thing about climate - hopefully its a good thing as its apparently hard to get off "the Team". I see William is still on "the Team" despite quitting climate science for software.
SM's repeated use of a collective noun to denote a nebulous group of people supposedly opposing him, is hopefully some sort of lame joke and just giving the appearance of paranoia.
After wading through SM's post I couldn't tell why he quoted me - presumably he disagrees but I couldn't actually tell.
2 issues with Tiljander [cut; you want this post -W]
@andrewt
I see William is still on "the Team" despite quitting climate science for software.
They never truly leave.
"Is this a game of semantic point scoring, or is a discussion of the validity of this proxy in this specific method relevant here?"
This comment strikes me a dead on. The essence of SM's point is that Mann's algorithm misused the proxy by orienting it during the reconstruction period in a manner opposite of the physical theory that justifies its use as a temperature proxy. That is what SM meant by saying it was used "upside down" and I think that he certainly makes this clear on his blog, but perhaps less so in his published comment with its space limits. I also understand that "multivariate regression methods are insensitive to the sign of predictors." The statement is true and entirely beside the point of SM's criticism.
I've read Pielke's post and it is clear to me that he understands SM's argument. He may have been confused by the statement, "Multivariate regression methods are insensitive to the sign of predictors." I can also understand why his "confusion" arose, because I was similarly confused at first. He likely thought, as I did intitially, that the statement was responsive to SM's criticism, whereas it is actually a dodge, perhaps made intentionally or quite possibly based on a misinterpretation of SM's brief published comment.
The bottom line, however, is that I think it is unfair to criticize Pielke when he accurately understood the major point of the controversy, although he may have been a little confused on a technical statistical issue that is ultimately irrelevant.
[You're welcome to your opinion, of course, but I see nothing in Pielke's post that suggests he has a clue. What makes you think he "accurately understood the major point of the controversy"? As for "may have been a little confused on a technical statistical issue " I think you're being very generous -W]
A totally neutral, non-climate realted, example of why regression analysis is indifferent to the sign of the input.
http://sabermetricresearch.blogspot.com/2009/10/dont-use-regression-to-…
Here the input is "hitting triples" in baseball and the output is "runs scored" and the result is "upside down" from the logical inference.
"[Agreed. This would be a problem if you were using global temperature as the thing you train against. But (I believe) you train against the local temperature -W]"
No, if you are a climatologist then you actually train against global temperature and when someone rightfully objects you claim teleconnect.
BTW, just because a method is insensitive to sign doesn't mean it cannot produce spurious correlation. Especially when training is only done for a small portion of the length of the proxy. Just because the tail end of some proxy data correlates with known global "averages" doesn't mean the rest of it does. There is the question of whether trees make good thermometers in the first place.
William,
Besides you got the whole point of McIntyres original article backwards.
[No I didn't. I didn't read McI's original article and wasn't commenting on it -W]
[Cuts] The sediment proxy data was actually contaminated over the period used for calibration.[Yes yes, we've said all this already. Why are you repeating things? -W]
Just read Williams comment 25 where he finally understood the flaw that was pointed out from the beginning by McIntyre. He even admits, "(perhaps it has been said before but lost in the noise, if so my apologies for missing it)."
But then he backtracks: "If he meant what you said, he could and should have said so." He'll have to clarify why, but I think he never read the original article by McIntyre, because he clearly states:
"By flipping the data opposite to the interpretation of Tiljander et al, Mann shows the Little Ice Age in Finland as being warmer than the MWP, 100% opposite to the interpretation of the authors and the paleoclimate evidence. The flipping is done because the increase in varve thickness due to construction and agricultural activities is interpreted by Mann et al as a "nonlocal statistical relationship" or "teleconnection" to world climate. " - McIntyre Oct 2nd 2008
He not only stated it he drew pictures. I don't know how anyone who read the article and is math savvy could miss the point. Did you read the original article William, or did you depend on others misinterpretions of it?
[Cuts. Of course not. I was reading the PNAS comment, which is supposedly a clear expostiion of the problem - no? -W]
SM's gripe as I recall was that MM in his PNAS Reply had only replied to what SM wrote in his PNAS Comment, but that MM had failed in his Reply to respond to something that wasn't in the Comment but was blogged about.
William - AndrewT writes in the comment you linked to: "Now if the mathematical interpretation placed on the data by their methods conflict with physical information from other sources, it does raise questions". Has anybody expanded on that yet?
[Yes, just about everyone has said the same blindingly obvious things -W]
Furthermore...does the fact that "multivariate regression methods are insensitive to the sign of predictors" mean that if by mistake somebody would throw in proxy data from a different planet that were undergoing global cooling, those proxies would reinforce Mann et al.'s conclusions?
[No -W]
Beats me William - why not?
And yes I am just asking...as that's the way I interpreted your answer to comment #1. Duh?
[If you'd pause for a minute and think how the method works, you'd be able to answer your own question. The Mea method correlates the roxy over a training period, usually the instrumental record, and uses that to determine sign and weight for the regression step. What your hypothetical other planet record would "tell" you about, say, the MWP would depend on the relation of its "MWP" signal to its present day signal, just like any other proxy -W]
I guess we can summarize it like this?
1) Sign doesn't matter when the data goes into the algorithm. You can flip data and the end result is similar.
2) However, if the data has problems, see (3), then inside the algorithm it can get a wrong sign, just before averaging. This is another kind of flipping than flipping in the (1) sense. This results in a wrong result.
3) Problems here being contamination during the thermometer period, from which the sign inside the algorithm (see 2) is calculated.
4) Mann replied on flipping in the first sense (1) while McIntyre et al had complained about flipping in the second sense (2). It would have been clearer if they had been more specific but...
5) I've read from Korhola's blog that the comment was seriously short of space, and have translated that bit over at Grumbine's here.
http://moregrumbinescience.blogspot.com/2009/10/sound-and-fury-at-wuwt…
6) End result: In my (weak and incomplete) understanding, these proxies should not have been used.
7) Meta comment on talking about this: people should specify if they are talking about flipping in the first sense (1) or flipping in the second sense (2).
I think this is largely correct, but I disagree slightly with 7 and 4, in the sense that the true problem appears to be the contamination of the proxy during the instrumental period. That would be a problem *even if the proxy didn't get flipped* - so the entire "flipping" issue is a red herring. If the proxy is so contaminated during the instrumental period that it ends up flipped, then the scaling pre-instrumental will be wrong. If the proxy was just as contaminated, but that contamination happened to be in a sense that didn't flip it, then the pre-instrumental scaling would still be wrong -W]
Well, if McI had complained that problems with the data over the last couple of hundred years (influenced by human factors) had led to a spurious correlation and that the proxy should not have been used then:
1. Mann would not have responded to the "sign flip problem" claim by pointing out the insensitivity of multivariate regression to sign.
2. Mann could've responded, "well, yeah, we pointed out potential problems right in the paper and therefore ran reconstructions with and without the problematic proxy data, thank you for confirming that our concerns were well-justified".
Of course, McI and crowd would've asserted fraud, incompetence, agenda-driven analysis, etc anyway. But "confirmed the authors fears" isn't exactly controversial nor proof of incompetence, fraud, etc so one can understand why it wasn't presented in such a straighforward, inconsequential manner.
Given McI and the CA crowd's checkered history when it comes to such claims, I recommended waiting until what the people doing science say.
WIth or without, you get essentially the same "hockey stick", so it's possible it's going to get the "big deal (shrug)" treatment it deserves.
I was going to write that we are pretty much in agreement now I think, but then having read your later posts and the PNAS stuff (didn't know it was available for free) it seems I had some wrong information - the way McI's comment is worded, it really now seems the claim is of the upsidedownness in the first sense, if I may use my self-defined terms... :)
I'm a bit tired but I appreciate the efforts of people digging to the end of this, logically.