Over the past few days, it has become clear to me that the entire issue of "flipping" or "upside-down-ness" of the Tiljander proxy is a red-herring.
Here's why:
Imagine a climate proxy, accurate over the last 2kyr, that shows (for example, let us suppose) a warm period around 1000 AD and which, undisturbed, would show the recent warming. Further suppose for definiteness that this proxy is of such a nature that increases in the proxy value represent increases in temperature. Imagine this proxy is contaminated with non-climatic signal over the last 200 years, enough that the climatic signal is overwhelmed. Suppose that this contamination is of such a nature that it leads to a strong decrease in the values of the proxy over the last 200 years. Such a proxy (call it A), fed into the Mea algorithm, will be flipped over (due to its negative correlation with recent instrumental temperature) and will contribute a net cold influence around 1000 AD. How much it contributes will depend on how well it correlates to recent times.
Now imagine a similar proxy, except the nature of the non-climatic contamination is such as to add a strong increase over the last 200 years. We'll call it B. This time, the proxy won't be flipped over, because its correlation to recent times will be positive. But the variance into the past will be strongly de-weighted (because we've just added an artificially large postiive trend). So it will imply not much change around AD 1000. But now we see this, we can see that the same problem applies to series A: unless, by bizarre co-incidence, the negative non-climate signal just happens to match the true positive instrumental signal, the variance in the past will be wrong. And since we've had to assume that the non-climate signal overwhelms the climate one, its likely that the recent variance will be too large, so the past will be de-weighted.
So in either case we can see that the real problem is the addition of the non-climate signal. The flipping is of little relevance.
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AMac,
I gave an example of how to search for papers on the general area that you say you don't know much about. Far more and better searches would be needed to learn the area.
I then gave an example of one paper from the many that one example search turns up.
You picked one picture given in that paper as an _example_ and are trying to do blog science on the example from the example from the example.
Shorter form: "Aaargh."
Image: http://i124.photobucket.com/albums/p13/NBerlatsky/enlightenment.jpg
Video: http://www.youtube.com/watch?v=sDW6vkuqGLg
These, too, are _examples_.
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So are you conceding that flipping has happened? That was the point all along. Producing a cold 1000 vs a warm 1000 is a huge difference, as the main point of the various hockey sticks is the comparison between current and past temperatures.
I still think you are missing one detail that I haven't yet confirmed: That the MEA algorithm will not flip the Tiljander proxy because of the way it is coded. I have been told this on ClimateAudit. If true, that would make Tiljander manually flipped.
The change in variance and deweighting of the past sums up the problem with the overall algorithm, that indeed is separate from the flipping issue. Jeff ID has demonstrated this in a post on CPS distortion. That when you select proxies that correlate with current temperature, you are likely to shrink past temperature values.
So what you're saying is that the flipping is a moot point because if you exclude the proxy because of the contamination, it is no longer there - flipped or otherwise. While that might be a neat way of tying up the loose ends, shouldn't we investigate the science behind the proxy's selection so that similar errors aren't made in the future.
Nice try, but unfortunately this is nothing but a horrible straw man. For starters: there does not exist such a thing as "the MEA algorith", and most (almost all) algorithm variations in Mea will not flip anything but disregard a proxy if it has wrong correlation sign.
Try to concentrate to the simplest issue of all: how are the code 4000 series (varve series, the code Tiljander series have) suppose to correlate with the instrumental data by the design of the screening in Mea? What interpretation that gives to those proxies?
W.,
Mea states:
In the vast majority of sediment proxies, varve thickness or density are presumed to be positively correlated with temperature. The Tiljander proxies are very much the exception. The authors posit a physical reasoning for this anomalous interpretation, and the presence of a moderate MWP could be considered to corroborate this.
On the other hand there is not a discernable LIA. And there is no way to calibrate or even test the sign of the correlation against the instrumental record, if the authors are correct as to the extent of human influence.
There are 1209 proxies in Mea. It is perhaps not practical to require an evaluation of "a priori" expected sign of correlation proxy by proxy. And such a procedure could be considered "opportunistic". Anyway, as far as I know, these are the only "one-sided" proxies that have been presumed by the original authors to have a relation with temperature inverse from the norm.
So there is certainly a strong case to be made that these particular sediment proxies should not be included at all. But Mann's sensitivity analysis demonstrates that their omission would have little effect on the overall reconstruction in any event.
Of course, this means that if there had been strong negative human influence, the Mea algorithm would have rejected the proxy.
But you're still right: No matter what, there is no discernable difference to the result. And the molehill is still a molehill.
DeepClimate,
"So there is certainly a strong case to be made that these particular sediment proxies should not be included at all. But Mann's sensitivity analysis demonstrates that their omission would have little effect on the overall reconstruction in any event."
Would that be the sensitivy test of S10 in the SI you are talking about ? ie where there are 15 proxies back to 750, _4_ of which are upside down Tiljanders, and the sensitivity test consisted of plotting the effect of removing 1 proxy at a time from the study ? (So for each "test" you'd have at least 3 of the Tiljanders included...)
[So, it would be S8 -W]
The sensitivity analysis for the overall reconstruction, with and without the 7 "potentially problematic" series, is Figure S8.
But you knew that already, didn't you.
This is getting pretty close to what Eli said several oh dears and Tijlanders ago
Anyone ever consider the proposition that Tiljander had it upside down? That may be what the reconstructions are saying. Just saying.
Tiljander's Mineral matter couplet thickness varve series
Three of the four Lake Korttajarvi varve series collected by Tiljander are archived here as a text file for years 0 to 1985. Tiljander stated that she believes that accumulation of mineral matter is the result of a harsher climate; i.e. there should be a correlation between lower temperatures and higher "mineral matter couplet thickness".
In addition, she believes that near-lake human activities have caused increasing deposition of mineral matter since ~1720.
From 0 AD to 1720 AD, the Mineral matter couplet thickness, averaged in 20-year intervals, gives values of 0.10 mm to 0.34 mm.
The sole exception is the 1321 to 1340 interval. That high average of 0.64 mm is due to the 1326 varve, which has a reading of 12.9 mm, seemingly the result of a one-off event.
From 1721 to 1860 (circa the beginning of the Mann et al calibration period of 1850-1995), mineral values rise from 0.16 mm to 0.53 mm, fairly steadily.
From 1861 to 1980 (approx. the Mann et al calibration period) mineral values rise from 0.43 mm to 1.59 mm. The five years 1981-1985 average to 2.14 mm. Human activities mentioned by Tijander are seen for 1930 (4.4 mm) and 1967 (4.6 mm).
A concrete instance of an "A"-type proxy
Thus the Lake Korttajarvi mineral varve proxy seems to fulfill the conditions of Proxy "A" as presented by WMC in the body of the post.
* Prior to ~1720, higher temperatures should correlate with lower values.
* During the 1850-1995 calibration period, human activity correlates with higher values.
* The Mann et al algorithm "flipped it over" such that higher values correlate with higher regional temperatures during the correlation. I believe (but am not certain) that this data was used by Mann et al to build the "tijander-2003-lightsum" trace seen in Fig. S9. (Note that the 1326 event can be identified in the raw data presented by Tijander in Fig. 9, but not in the Mann et al trace. The 1930 and 1967 events can be identified in both.)
(Note also that Tijander reproduces the local instrumental temperature record for the Lake Korttajarvi area, 1881-1993 in her Figure 2.)
Having these attributes of one of the Lake Korttajarvi varve proxy series to hand may help in discussing their use by Mann et al and others attempting paleoclimate reconstructions.
Estimating the effect of the proxy on temperature anomaly reconstruction
What follows is some back-of-the-envelope arithmetic. I claim no familiarity (much less competence) in temperature anomaly reconstruction methods. Still, this might give an approximate idea of the what sort of signal the tiljander-2003-lightsum proxy might have contributed to Mann et al's Fig. S8a, and others.
From Mann et al Fig. S4a, the Northern Hemisphere Temperature Anomaly was in the -0.4 C to -0.2 C range in 1850-1860. It stood at about +0.2 C in 1985. The varves' mineral thickness was ~0.6 mm in 1851-1860, and ~1.9 mm for 1976-1985, at the end of the series. That would seem to suggest a that a rise of 0.5 C correlates with an increased varve thickness of 1.3 mm. This is for the proxy in the "flipped over" orientation (with respect to Tiljander's interpretation) that Mann et al used.
On this basis, if used by itself in this way, here is what this proxy would yield over the 1 AD to 1850 time period.
The largest-magnitude temperature anomalies would be in the range of about -0.5 C for 1000 AD to 1300 AD (avg. mineral thickness 0.14 mm; the smallest 20-year averages are 0.10 mm for 1181-1200 and 1201-1220, and 0.11 mm for 1221-1240.)
Excluding the 1326 varve, this proxy would yield its smallest-magnitude temperature anomalies in the range of about -0.45 C for 581 AD to 800 AD, (avg. mineral thickness 0.27 mm; the largest 20-year average is 0.34 mm for 681-700.)
#7 Eli
I guess I raised the possibility in #4. To be fair, no one has actually raised that in the peer-reviewed literature, AFAIK. Still, you'd think the authors would address the fact that this inverse relationship is not the norm in these types of proxies. (My apologies if they did - in that case I missed it).
In the end though, I still agree with W. - the non-climatic influence is the real problem. And Mann did recognize that.
Graphs (small jpeg files) of the Lake Korttajarvi varve "mineral matter couplet" series discussed in the 11/4/09 8:37pm comment are available at Bitbucket.org.
...
You've gotta admit that Blog Science has all the bases covered ...
This does demonstrate a major problem one runs into when trying to counter so-called "debunking" arguments.
Would you care to show your back-of-the-envelope arithmetic showing that Mann's sensitivity test is wrong, apparently? Or should I just take your word for it?
Hmm, looking at Korttajärvi:
http://maps.google.fi/maps?f=q&source=s_q&hl=fi&q=Korttaj%C3%A4rvi,+411…
It's not far from the city of Jyväskylä and there are lots of fields around it. No doubt forestry and peat lifting as well in the basin. I'm certain that this has affected the sediments. Agriculture, peat and ditch making have made and are making have a huge impact at our summer cottage lake as well.
Tiljander's dissertation is available for free as a pdf for anyone interested in the subject:
https://oa.doria.fi/handle/10024/2702
I can think offhand of multiple mechanisms resulting in either a thicker or thinner sediment in warmer years. Things like more undergrowth reduces erosion, less snow (shorter winter) means less spring floods... But this is just ignorant speculation on my part.
The flipping proves you are adding non-climate proxies. It is a red-flag not a red-herring. The algorithm should be de-weighting non-climate proxies. But when the algorithm gets not only the magnitude but also the sign wrong, you know it is doing bad things. This has always been the point.
dhogaza says:
Rule #1: Whatever choice a paleoclimatology scientist makes, call it cherrypicking (unless it enhances MWP, of course).
dhogaza wrote at 11/5/09 8:28am --
Would you care to show your back-of-the-envelope arithmetic showing that Mann's sensitivity test is wrong, apparently? Or should I just take your word for it?
I'm unfamiliar with Mann's sensitivity test. In any case, I doubt I have the skill set to calculate it. I'd be interested in your interpretation of this test, or in a link that you feel describes it lucidly.
The back-of-envelope arithmetic is meant as an order-of-magnitude estimate of what "more minerals, warmer temperature" might mean, assuming that a simple linear relationship is ascribed to the 1850-1995 period and that there is no transformation of the data. I don't claim that this is an optimal way to handle varve data.
The 20-year averaged data for the three Tiljander varve series and some graphical views of them are now up at Bitbucket.org.
Arrrrrgh.
http://www.google.com/search?q=climate+mode+change+seasonal+varve+depos…
Look how the varve composition and structure abruptly change when the climate mode changes.
http://www.telesio-galilei.com/TGA%202008_Brauer_et_al.pdf
Now you are talking about the sensitivity test for Mann et al.
Mann's reply to Steve McIntyre's comment in PNAS that the accusation of upside-down usage was bizarre. The algorithm doesn't care about the sign of the predictor.
Do you now consider this to be an insufficient response?
Hank Roberts 11/5/09 10:48am --
When I look at Figs. 2b and 2c of the Brauer et al 2008 article that you link, I notice the Lake Meerfelder Maar varves getting thicker as the Younger Dryas cooling event takes hold, ~12,700 years ago.
Do you agree? Do you think an analogous {colder temps -> thicker varves} correlation likely holds true for Lake Korttajarvi as well? (Tiljander thought so.)
AMac, let me point out the obvious, for any highschooler writing a paper, I'm sure you're aware of these things.
You can't measure layers accurately from a printed page -- you're looking at the density of ink dots on paper, or pixels on a screen, not the actual core. You don't distinguish visible density from a change in grain size from composition. You can't determine the composition of the material.
Blog Science isn't.
Follow up the citing papers over the next few years to see what subsequent publications have referenced that one, and look for other papers using cores from the same lake and comparing them to other work.
Hank Roberts, thanks for the pointers. Still, my impression is that a journal like Nature Geoscience has figures because they can help readers to understand the ideas that the authors wish to present. Thus, it's reasonable to look at figures with that in mind.
Brauer et al are pointing out that lakebed varves became thicker in Lake Meerfelder Maar at the time that the Younger Dryas cooling began. The red trace in Figs. 2b and 2c don't refer to the composition of the sediments, although other traces do, and that's pursued in the text.
Many of the factors that Brauer et al show are important to the Lake Meerfelder Maar varve record -- changes in water level, mixing, anoxia at depth -- aren't discussed by Tiljander et al for Lake Korttajarvi. Is that why you commented, "Arrrrrgh"?
You show that Mann has a figure without the proxy, and therefore it doesn't matter if it was used upside-down.
However, if the proxy is used upside-down, then the sensitivity studies need to be redone. How do the OTHER charts look, when Tiljander proxies are placed in the right orientation, which in this case means removed entirely?
In other words, what if you remove the other proxies, and Tiljander is no loner used upside-down in those charts?
PS, why the enthusiasm? Perhaps it's because they're relying on that kind of work in part for this:
http://hatch.senate.gov/public/_files/ClimateChangeReconsidered.pdf
Yes, it's Singer and Isdos.
> Arrrrgh
AMac, I gave you an example of doing a search to learn about the science. From that result I gave you an example of a paper. That paper had a picture as an illustration of the material.
You are doing blog science on an illustration from an example out of an example.
Wrong direction. You need to learn the science first then work down to the specific detailed data -- not pick out a picture from an example and analyze that.
I think the end results would matter. From a little bit of sleuthing, AMac has confirmed and explained the upside-down usage of Tiljander, which was the topic of the posts to begin with. Pretty good job in my opinion. I wouldn't say it is worthy of saying he doesn't understand science.
Hank Roberts (11/6/09 11:47am), thank you for your patience, and for the considered response to my earlier comment. I think I understand your point now.
If I'm correct, you linked the Brauer et al paper to illustrate how difficult it is to understand how sediment series data relate to paleoclimate. In the case of the Younger Dryas, it's not profitable to wonder whether "thinner varves" or "thicker varves" correlate with cooling. Figures like Brauer's 2b and 2c are complicated, and thus too easily misinterpreted by non-specialists. Rather than focusing on an illustration from an example, I would do better to learn more about the larger picture of AGW, and then work down from there to analyses of specific detailed data.
Is that about right, do you think?
- - - - - - - - - -
The effect of removing the Lake Korttajarvi proxies from Mann et al's CPS calculations is compared to the 20-year averaged raw Lake Korttajarvi data in the Excel file "Tiljander-cf-Mann-CPS.xls", downloadable from BitBucket.
The corrected and expanded Fig. S8a is online at Mann's website. The expanded version (uploaded on Nov. 4, 2009) seems to address a major criticism leveled by some posters at Climate Audit (as I understand it). Mann et al now show the CPS reconstruction with tree rings entirely removed. The two new traces are "NH CPS w/o tree rings" and "NH CPS minus 7 w/o tree rings."
And guess what? Even when the 7 questionable series and the tree rings are remove you get the same result. This must be some nefarious scheme by nature to make McIntyre look like a fool. If she is, nature is doing a damn good job of it.
So AMac, are you willing to accept that Mann's results are substantially correct?
Rattus Norvegicus (11/6/09 5:43pm) --
> So AMac, are you willing to accept that Mann's results are substantially correct?
Our host may find my response off-topic; it may be snipped on that basis, which would be fair enough...
Before last week, I knew nothing about varves' use in paleoclimate reconstruction. I was broadly familiar with the conflicts between the large majority of scientists working on AGW (and their supporters), and the minority of technically-oriented AGW skeptics (and their supporters). (I exclude those with anti-AGW belief systems as uninteresting.)
I thought (and think) that the broad AGW argument is pretty compelling, but that unresolved issues persist.
Mann et al's use of varves seemed that it might offer insights into how the "pro-AGW" and "skeptical" camps handle controversy. The cutting edge is usually messy, so I didn't expect all the evidence would point one way or another.
Science thrives on the free exchange of ideas, and on handling appropriate challenges to the methods and logic used to obtain results.
In my opinion, the Mann group's handling of the Tiljander proxies is clearly in error, and uncorrected. PNAS's editors and the paleoclimatology community accept these outcomes.
As you point out, revised Fig S8a shows that Mann's calculation of the pre-instrumental northern hemisphere temperature anomaly is not greatly affected by the removal of both Tiljander and tree ring series.
Having looked closely at the Mann group's and the community's handling of a small methodological challenge, I am less confident of the correctness of Fig. S8a. Irrespective of whether these findings are "right" or "wrong," the take-away lesson for me is that error-correction mechanisms are not working properly in this field.
Thanks for asking.
AMac,
I beg to differ with your conclusion. The Tiljander proxies were known to be problematic, however they may have contained valuable information prior to the MCA. As I stated in a previous post for this reason the temptation to use the proxies was great, since there are damn few annually resolved proxies which stretch back to the days of Jesus F. Christ. However, Mann was aware of the problems with these 4 proxies, as well as 4 others that McI did not complain about, before the paper was published and did an analysis of the impacts of these 7 proxies (probably because he knew that McI was going to scream bloody murder).
Note that all of this was done before the paper was published. Did I say that loud enough? It was all done before the paper was published. And what were the results? No real difference, so he probably figured it was OK to leave them in. In or out, it doesn't make a lot of difference. Sitting here doing blog science, I might have made a different decision, but I can understand and accept Mann's decision. After all, it was at the bleeding edge.
The screaming, shit flinging monkey chorus over at CA started complaining about other proxies that Steve did not like over the last couple of months. What did Mann do? He generated an amended figure S8a which dropped tree ring proxies (because apparently using a tree ring proxy, which is well understood, as opposed to lake varves, which are not, is a cardinal sin in CA world). Guess what? Now that most of your data is gone -- because most highly resolved millennial scale proxies are tree rings -- you still get a pretty good recon except that in the earliest portion there is a lot of noise because most of the data is gone. The core of the reconstruction still stands though, it's gettin' hot out there.
So, unlike you, I think things are working out just fine. Whenever a researcher responds to the monkey troop and answers their complaints, they get substantially the same answer. It may not be the answer the monkeys want, but it is an answer to their complaints. The problem is that the monkeys are very practiced at moving goalposts. The minute one complaint is answered another is made. You can witness this in McI's and the monkeys response to Briffa's response going on at CA right now.
Rattus Norvegicus 11/6/09 11:20pm --
Thanks again for taking the time to respond.
I can't really comment on much of what you say because (1) I don't have a history with this issue, and (2) it would require looking into participants' hearts. Which would be Blog Psychology, I guess.
Notwithstanding (1) and (2): Anyone can stand at the back of the room, then ask a question at the end of the talk. "Why was the DNA that you recovered from the column 1,000 bases long, when the graph you showed in the previous slide implied that all input fragments were shorter than 200 bases?"
If that's a dumb question, it doesn't matter that the Chairman asked it. If that's a perceptive question, it's no less valuable because a first-year grad student posed it.
On review, Mann et al may conclude that the calibrations and orientations of the four Lake Korttajarvi proxies were justified. Then they should clearly state as much, and justify the departure from Tiljander. Or, they might conclude that one or more of the proxies were not correctly calibrated, or were mistakenly "flipped." Then they should do as Kaufman et al did, and correct their work.
My own view is that the prior paragraph should be unchanged by one's opinions of the various actors in this drama.
If these varves were about anything but paleoclimate, I think people would see the procedural issue with more clarity.
AMac, you're trying to make a point, stubbornly, where you say
> I would do better to learn more about the larger picture of
Good so far
> AGW,
Oops. Wrong.
Try reading _in_ the field of research -- the actual study of the layers of mud. Forget GW, A or not-A, for a while; learn how they're studying what's there in the mud. You have to be able to see what's there, before drawing conclusions.
Are you just assuming the scientists had AGW in mind and went looking for proof? That's how it sounds, and that's backwards. You see people on the blogs squabbling about whether the mud is right or wrong because it does or doesn't have some particular feature they associate with some period of time. That's backwards.
The mud is right. The trick is to learn how to read it, without prejudging it.
Hank,
The mud is right, but it speaks with a heavy accent. This makes it very hard to understand. Probably not a good climate proxy, even though Tiljander tried mightily to save it. One problem that I did not see addressed in the Boreas paper was the influence of increased precipitation in the 20th century on the hydrology of the catchment (see, I can talk like a scientist too!).
Because of this the increase in varve thickness during the 20th century might not be completely due to human influence. And of course, as you pointed out by referencing the Brauer paper, interpretation of varves is not as straightforward as say tree rings or ice cores.
Hank Roberts --
You might not be old enough to recall the image of Richard Feynman demonstrating the brittleness of cold O-Rings to the other members of the committee investigating the space shuttle Columbia disaster. Recap here.
Yes, complicated things shouldn't be oversimplified.
Simple things shouldn't be overcomplicated, either.
I can read Brauer and understand what they're showing in Figure 2b about how varve width changed in Lake Meerfelder Marr at the onset of the Younger Dryas. It's not lacustrine sedimentology mumbo-jumbo. In that instance, colder climate led to thicker varves.
Approach it with fresh eyes, and you'll see it, too.
They didn't. They said, up front, "we're not sure", then showed the results with and without the problematic proxies. Since there was no substantial difference between the reconstruction with and without the proxy, why not throw it out there with the appropriate caveats and let future work - by Mann et al or others - sort it out?
This isn't unusual in science, you know. The CA crowd - and you - totally ignore the caveats, the clear statement that the proxies in question are problematic, etc - in favor of "he's performing bias-driven science!!!!" Same with Mann's original "hockey stick" paper, which was full of caveats. The denialsphere did, and still does, pretend as though Mann et al in that first paper said "this is all cast in concrete, proven beyond reasonable doubt, above criticism" when the paper very clearly pointed out its innovative and exploratory nature.
Why do they ignore obvious qualifications like this? Obvious ... it's hard to scream "fraud" when someone acknowledges potential problems in the very paper itself if you acknowledge the fact.
Mann has obviously been following along. On 4 Nov 2009 he quietly corrected Figure S8 and reissued it:
"Another error was found in the corrected Supplementary figure S8a from December 2008 . . ."
http://www.meteo.psu.edu/~mann/supplements/MultiproxyMeans07/
Mann says: "Each of the various alternative versions where these sub-networks of proxy data have been excluded fall almost entirely within the uncertainties of the full reconstruction for at least the past 1100 years, while larger discrepancies are observed further back for the reconstruction without either tree-ring data or the 7 series in question, owing to the extreme sparseness of the resulting sub-network."
Another way to say "fall almost entirely within" is "does not fall within," so maybe they do matter an ittybitty bit.
Can we now conclude that the debates on these threads are not about whether Mann made errors, but whether those errors matter?
[I promised to be strict in apply the comment policy,and I failed. But its time now to start applying the "please don't just repeat yourself" part -W]
Re: my comment of 11/7/09 11:22am --
WMC, Please allow me to note that I dispute dhogaza's paraphrase of what I've written on the subject of Mann et al., in his comment of 11/7/09 10:01am (#33).
> Another way to say "fall almost entirely
> within" is "does not fall within,"
This is year by year.
Each year has an uncertainty band.
A few annual points don't fall within that; almost all of them do until you get far back in time. Noise happens.
Say you fall into the lake, all but a foot. Do you claim you're dry because one foot isn't wet?
Run goalposts run!
He tried to move on, but he's been sent back:
http://www.realclimate.org/index.php/archives/2009/11/the-cru-hack-cont…
And is saying he can't find the explanation for the updated figure:
http://www.meteo.psu.edu/~mann/supplements/MultiproxyMeans07/
Hint: it's "UPDATE 4 November 2009 ..."
Hank Roberts (11/23/09 7:15pm & 9:38pm) --
The first corrected Fig. S8a that I downloaded from the Penn State website after noting the 4 November 2009 Update showed that the Temperature Anomaly differed when the 7 problematic proxies were removed. That is at BitBucket as
Mann-S8a-PSUwebsite-circa091104.pdf
Compare "NH CPS minus 7" (black line) and "Original CPS minus 7" (green line). Note the divergence of black from green during 1020-1200, 1330-1390, and 1620-1660.
The second corrected version of Fig. S8a is currently in the Penn State directory you link, and also copied to the BitBucket directory as
Mann-S8a-PSUwebsite-circa091106.pdf
In this case, "NH CPS minus 7" (green line) and "Original CPS minus 7" (black line) are virtually superimposable from 400 through 1850.
This would explain Gavin's remark to me in Comment 204 at RealClimate:
"[Response: Your threshold for a significant difference is clearly different from mine. I don't see one if you remove the '7 problem' proxies. - gavin]"
Your 9:38pm comment here, "And [AMac] is saying he can't find the explanation for the updated figure" is a good paraphrase of my Comment 216.
Can you point me to text that explains when and why one Fig. S8a downloaded after the 4 November 2009 Update has been superseded by a different Fig. S8a?
Rather than an occasion for silliness, this strikes me as an illustration of how confusion can be avoided by keeping accompanying "readme" files up-to-date and complete.
> Can you point me to text that explains
You should inquire at the site. You know how to do this?
Hank Roberts --
You seem to propose "You should inquire at the site" as an appropriate standard for disclosures of corrections to the peer-reviewed literature.
If I recall correctly, your earlier counsel was "Hint: it's "UPDATE 4 November 2009 ..."
I am just a military trained nuclear engineer.
But after reviewing what the "Tiljander" data is, I have a few doubts about the validity of this data after the 20th century.
[You are correct. Thre appears to be near-universal agreement that the Tiljander dataset is not a good climate proxy during the 20th century. This is not news -W]
Since the ratio of organic material to inorganic material is done by testing for the X-ray tenth thickness of each layer
( Larger tenth-thickness means more organic )
How does Mann compensate for agricultural fertilizer and detergents ?
[If anyone were to be doing such corrections, it would be Tiljander -W]
Both of these would dramatically increase the organic life in a lake and artificially increase the organic material deposited on the lake bed.
How was this handled?
[Why aren't you asking Tiljander? -W]
1.Was any research done to track contamination of fertilizers during the 20th century and what impact this would have on sediment layers?
[Ditto -W]
2.Was Tiljander after a certain date simply excluded?
[Is it really too much to ask a simple nuclear engineer to actually read the paper in question before commenting? -W]
And if so how was the value of past layers "calibrated*" since recent layers from when we have actual temp readings is artificially inflated by fertilizers.
(*I know this isn't the correct term but I am just a layman.)
It would seem to me that if there was no effort to compensate for fertilizer the Hiljander data would weigh the data to a colder average than actual prior to the 20th century.
[In which case it would appear that you are proving the point of this post -W]
3.How heavily does the Hiljander data weigh in the overall result?
[Why not read the paper and find out? -W]
Less than 1% ?
Less than 10% ?
If it is removed as a proxy does the graph change noticeably?
[Gosh. What an interesting thought. You are clever and original - I bet no-one else has thought of that, and certainly not the original authors.
Sigh. You *are* trying to be ironic and prove my post correct, aren't you? Please tell me you are -W]
I would appreciate it if someone could give me any answers or show me where to find the answers to my questions.
[Search for "Tiljander" on this site. And don't be lazy -W]
Hank Roberts --
I checked this comment I made on 11/3/09; that is the date that I downloaded Mann et al's once-modified Fig. S8a--one day before the 11/4/09 update. That figure (uploaded by Dr. Mann on 12/1/08, I believe) is still up at his website, though labeled as Fig. 7. This is not reflected in the directory's ReadMe file.
Apologies for the mistake in my recollection, in my comment of Nov. 23, 2009 @ 11:10pm.
I think this argument has a weakness that needs to be addressed. The conclusion depends on a pair of statements made about the relative strengths of the non climate signal to the instrumental signal.
1. âIt would be bizarre if the non climate signal matched the true positve instrumental signal.â
2. âIts likely that the recent variance will be too large.â
I can go along with point 1 but I canât see a reason to accept point 2 without further justification. Why is the possibility of it being too small not considered?
For example if the non climate signal was say 150% stronger than the climate signal it would result in a residual of -50%.This is weaker and of opposite sign thus resulting in both flipping and increased weighting in the past.
[I don't think I'm following you. The *problem* with the Tiljander series is asserted to be that the recent contamination with non-climate information is large. If it isn't clear, "variance" at this point doesn't mean inter-annual -W]
I thought the problem with Tiljander was the sign and not the magnitude.
[Sigh. Yes, that is a mistake that many people have made. This post is pointing out why a possible sign error in the use of Tiljander is not the problem. You need to read what I've actually written -W]
I'll try to be clearer. You started your argument using hypothetical proxies that you called A and B that have only the following specifications; that they have non climate signal of opposite signs, magnitude greater than climate, scale not further specified. That was the line of reasoning I was taking on in my comment.
Are you now saying the Tiljander series are proxy A, if so why not just call them that in the first place?
[I don't know. I haven't studied it in enugh detail -W]
By all means let's use the real data and drop the hypotheticals but that is how you started this whole page.
Allow me to go back to my original criticism and clarify it by putting some numbers in to make it more specific. Iâll consider the case where the non-climate signal is of the opposite sign to the climate signal and categorise the relative strengths of climate and non-climate into a number of rough bands and consider each separately:
For reference climate signal strength = 100
Non Climate signal strength My comment
0 to 10 No problem, this would be an excelent proxy
10 to 50 Not too bad, proxy still pretty useful
50 to 99 Proxy not much use climate signal almost wiped out
100 Perfect cancellation, truly bizarre coincedence (agreed)
101 to 200 "Danger Zoneâ â Non climate dominates and weighting increased
200 to 300 âHigh riskâ â Non climate dominates and small de-weighting
300 to infinity Proxy will be strongly deweighted (your original point, agreed)
My point is that non climate signal strength in the danger and high risk zones would lead to a strong decrease in the proxy value over the last 200 years as you specified but would not result in significant deweighting.
Your argument works fine but only in the upper range so itâs not generally applicable. Before one can agree to applicability of your argument one needs to know that the non climate signal is in the extreme upper range.
Now Iâll raise a second objection. This objection applies even if the first objection can be overcome. The objection is this; inappropriate deweighting is not harmless.
Iâll elaborate. If indeed you show that in all likely cases a modern contaminant will deweight past variance to nought then you have shown that this processes is like a big steam roller; any variance due past warm or cool period will be obliterated for this proxyâs contribution to the analysis. If we retain this proxy in the multivariate analysis the past variance will be incorrectly reduced which is still a serious error by any measure.
The second link I posted at 16 above
http://www.telesio-galilei.com/TGA%202008_Brauer_et_al.pdf
appears to have gone bad.
I check back after noticing (at KK's only-the-messenger and hot climate chat emporium) a recent septic comment about 'upside down' varves from some guy that made clear he had no idea what 'upside down' refers to.
It's not a picture flipped up and printed upside down to fool people.
Duh.
That term refers to a change in the sequence of sandy vs. clay sediment in the annual bands -- one tied to the development of agriculture, which breaks up ground during the growing season and causes runoff carrying different material at a different time of the year, so the varve layers are 'upside down' compared to the sequence of material in the years before agriculture started.
This will find some of the same studies describing what "upside down" means in the paleo lake sediment papers:
http://scholar.google.com/scholar?hl=en&q=Brauer+sediment+varve+galile
Ah, found it:
http://www.telesio-galilei.com/tg/images/stories/documents/Academy_News…
See the picture of the difference in varves as climate changed: "Figure 3 Photomicrographs of varves before and after the onset of the Younger Dryas event."