Michael Mann's errors

[UPDATE July 1, 2010: Penn State just today issued a final report on their investigation into allegations of misconduct by Dr. Mann. Note their criteria for misconduct were as follows:

(1) fabrication, falsification, plagiarism or other practices that seriously deviate from accepted practices within the academic community for proposing, conducting, or reporting research or other scholarly activities;
(2) callous disregard for requirements that ensure the protection of researchers, human participants, or the public; or for ensuring the welfare of laboratory animals;
(3) failure to disclose significant financial and business interest as defined by Penn State Policy RA20, Individual Conflict of Interest;
(4) failure to comply with other applicable legal requirements governing research or other scholarly activities.
where "research misconduct does not include disputes regarding honest error or honest differences in interpretations or judgments of data, and is not intended to resolve bona fide scientific disagreement or debate."

The report concludes "there is no substance to the allegation against Dr. Michael E. Mann"; the worst they could say was that he was somewhat "careless" in sharing unpublished manuscripts with colleagues. However, this was a pretty high-level review, and seems it did not get into the "Tiljander" issue. So we'll see where that goes here.]

Deep Climate has a new post up concerning the IPCC TAR Figure 2.21 "hockey stick" curves prepared by lead author Michael Mann for the 2001 report. This follows up on my post looking into similar questions regarding the AR4 Figure 6.10b "hockey sticks" in the latest (2007) report. Despite Steven Mosher's claims that the same rather subtle "trick" of padding the Briffa curve with instrumental temperatures was used in both figures, my analysis showed it could not have been in the AR4 case. Deep Climate has now shown that it's possible this padding was used for the Briffa curve in the TAR figure, but it makes essentially no difference (0.01 degrees over about 10 years, almost imperceptible in the full graph). The Mann curve in the TAR figure ("MBH") clearly was padded from 1980 with instrumental temperatures in the end-point smoothing, while the Jones curve in that figure clearly was not. The details of Mosher's (and McIntyre's, in this case) accusations about Mann and Briffa also seem to be contradicted by the actual record as DeepClimate shows, but that's another matter.

In any case, there definitely was an issue with the way Michael Mann was doing end-point smoothing in several of his early published papers, and in at least one of the curves in this IPCC report. As noted in the previous discussion, Mann admitted to this several years ago and indicated it wouldn't happen again, and it doesn't seem to have. So, an error, with minor impact on a couple of curves, since repented of.

In my last post, I called for the best examples of anything close to fraud by climate scientists, in particular Mann. There certainly are a number of cases where he has made similar errors that seem to have not substantially effected the results, but still were indicative of a certain carelessness, and sometimes stubbornness in recognizing the problem. And there are other examples of minor errors by other groups, for example several glitches in the GISS instrumental temperature analysis over the years that caused minor shifts in historical temperature numbers, particularly regionally.

Of course the worst case of unacknowledged errors in climate science was probably the UAH satellite analysis, which for 26 years was substantially under-reporting warming due to an algebra error in the analysis.

People make mistakes; as long as they correct them when the error is detected, it's really not such a big deal. The question I raised in my "Where's the fraud?" post was whether there was any substantive error of some sort that had not been admitted or corrected after exposure.

The strongest case seems to be the Tiljander proxy issue in a 2008 paper, as outlined by AMac in comments on my last post, and reference links there. Since nobody has proposed anything stronger, I plan to look into it in some further detail to make sure I understand the alleged error myself in its proper context. Here's how I understand it from my reading so far of the case (which hasn't yet included looking at any of the scientific papers or data involved, merely reading comments from others):

* Several data series were published by Tiljander et al which they believed could act as a temperature proxy (in ways they described) but only up to about 1720; for more recent years the authors believed the data were contaminated by human influences that masked any temperature signal

* Michael Mann and coauthors included the Tiljander series in a 2008 reconstruction paper. They were apparently aware of the possible contamination issue and made note of it in supplemental material that included a graph comparing the reconstruction with and without the Tiljander (and a few other suspect) series

* What Mann apparently was not aware of, or did not acknowledge, was that the contamination, for at least some of the Tiljander series, was bad enough to reverse the correlation between temperature and their data, so that Mann's calibration method would spuriously turn some of the Tiljander temperature proxies upside down in the pre-1720 period (at least if Tiljander's temperature correlation claims are correct). Mann's calibration method was regression-based and so didn't care whether the input was "upside down" or the right way up, it would determine a linear coefficient of whatever sign made the modern temperature correlation work.

* Kaufman published a similar reconstruction in 2009, using a different calibration method that really did care about sign but didn't use modern-period calibration; since some of the Tiljander proxies in that case were truncated to the earlier period that would have made sense, except that that method depended on having the right sign. A correction was published when this was discovered.

* McIntyre and McKitrick published a comment on Mann 2008 making the "upside down" accusation, but not being clear that the issue was a twisting of the correlation in Tiljander itself

* Mann's reply indicated he didn't understand the twist either.

* There's been a lot of blogosphere discussion of this, but one side seems to keep saying "upside down" while the other side says "it doesn't matter to the reconstruction", ie. the usual people talking past each other. The real problem is the twist in the data, which nobody seems to talk about.

Open questions to me are:

(1) Is the "twist" real - was the original Tiljander paper correct in assignment of certain temperature correlations which reversed in the modern period?

(2) Should Mann and friends have figured out the twist from the blogosphere discussion, the M&M comment, and Kaufman's correction, rather than interpreting "upside down" literally and not understanding it, as their reply and various defenses since suggest?

(3) Is it possible, despite the one figure showing no substantive difference to the reconstruction, that use of Tiljander did make a material difference to some of the conclusions of Mann 2008 (and apparently later papers using the same data)?

If the answer to these 3 questions is "Yes", then that adds up to a somewhat damning allegation against Mann's work on this. Evidently he's made some minor errors in the past, if those are true then I agree this one was a bit worse.

So, I'll spend a bit of time looking into these; references and help welcome in the comments, thanks.

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TCO, admitting being wrong is

TCO, admitting being wrong is not easy for anyone.... still Mike Mann has published his share of corrigenda in journals, and less formal corrections on his own web site. He will acknowledge real mistakes. A mann's gotta do what a mann's gotta do :-)

About being unrepentant about errors, I don't see the problem with that. Sin belongs in church, and the only way not to make errors is to not do anything, and certainly not anything for the first time ever.

About "it doesn't matter": that's very, very often the right question to ask. "All models are wrong", remember? Ask if the wrongness matters. And get the order of magnitude right. One problem I see with McIntyre is a lack of intuition on the influence of various "wrongnesses" in data and statistical procedures that he goes on about. That broke him up in the Yamal spat too. Strange for someone with the reputation of being a skilled statistician.

Note, as usual I've been

Note, as usual I've been getting lots of spam, and since comment levels have slowed down considerably, it's a bit of a tough job to filter - I know I deleted at least one person's comments here inadvertently while cleaning out a ton of spam. Sorry about that - if you have a copy or can remember what you wrote, please repost, thanks.

That must have been mine in

That must have been mine in reponse to MikeN's contention (referring to some CA conversation) that Mann et al.'s EIV code would be 'a mess'. Having actually looked at the code, I can tell that it is not. It is heavily based on Tapio Schneider's RegEM code, which is widely used elsewhere and if wrong, Mann would not be the only one in trouble. The only added code is two small main programs calling the RegEM code.

He was specifically asked

He was specifically asked about Tiljander, and responds that the algorithm is blind.

And he was clearly correct, for both cases, EIV and CPS. The regression algorithm is blind. The pre-screening is a different story... that's preprocessing, logically separate from the regression algorithm.

Several commenters went off of this and thought that a proxy would be flipped back if it was entered upside-down.

Those commenters were a bit quick perhaps... the flipping back only happens in the case of CPS: this is what the sign() operator does. For EIV, there is no "flipping", and yet that algorithm too is "blind" to proxy orientation. So, flipping is a bit of a red herring.

This "blindness" is a well known property of regression methods of this kind. I cannot think of a valid algorithm where this is not so. Shouldn't even be controversial... I can see where Mann's "bizarre" comes from.

>The regression algorithm is

>The regression algorithm is blind. The pre-screening is a different story... that's preprocessing, logically separate from the regression algorithm.

So he gives a response that is irrelevant to the issue. The output of the code is not based on the algorithm alone.

> The output of the code is

> The output of the code is not based on the algorithm alone.

Mike, he never claimed differently!

Mann's reply was

Multivariate regression methods are insensitive to the sign of predictors. Screening, when used, employed one-sided tests only when a definite sign could be a priori reasoned on physical grounds.

My italics. Two separate statements on two distinct parts of the processing chain. Both responsive to what was said in McI's comment, and both factually correct.

Do we agree that this is what the code does?

With respect to the use of

With respect to the use of the Tiljander proxies in Mann08, McIntyre's and McKitrick's Comment had this to say, in toto:

Their 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)

(Note that "pers. comm." is superfluous, as modern non-climate impacts are discussed in Tiljander03, Tiljander's thesis (2005), and in the Methods of Mann08.)

Mann, Bradley, and Hughes' response on this point was, in toto,

The claim that “upside down” data were used is bizarre. Multivariate regression methods are insensitive to the sign of predictors. Screening, when used, employed one-sided tests only when a definite sign could be a priori reasoned on physical grounds. Potential nonclimatic influences on the Tiljander and other proxies were discussed in the SI, which showed that none of our central conclusions relied on their use.

As MikeN noted upthread, this answer is nonresponsive to the issue that was raised.

In this recent comment, Martin Vermeer offers an informed opinion on the use of the Tiljander proxies in Mann08. Distasteful though it may be to some, Martin's interpretation maps to McIntyre's ("Their non-dendro network uses some data with the axes upside down, e.g., Korttajarvi sediments"), and is inconsistent with Mann's ("The claim that “upside down” data were used is bizarre.")

As I have stated previously -- without informed arguments suggesting otherwise -- "upside down" is a consequence of the Tiljander proxies being uncalibratable to the instrumental temperature record, 1850-1995. This is due to their contamination by non-climate-related factors during that time.

For the authors of Mann08 to respond meaningfully to McIntyre's Comment on Tiljander, they would need to address this point. To my knowledge, they have not done so.

AMac, I disagree strongly for

AMac, I disagree strongly for reasons that should be clear to any reasonable reader by now. Mann's reply was fully responsive to the statement as made by McIntyre in the Comment. He could not be expected to engage in mind reading, or to follow, or even be aware of, discussions on fringe blogs. I am disappointed that you continue to fail to see this, AMac, and have nothing further to add.

[Mann] could not be expected

[Mann] could not be expected to engage in mind reading, or to follow, or even be aware of, discussions on fringe blogs.

At Collide-a-scape, Prof. Mann's RealClimate.org co-blogger Gavin Schmidt wrote,

The original supplementary material included reconstructions with and without the Tijlander proxies (addressing Amac's point). The additional test (removing tree rings and Tijlander at the same time) was added later (addressing willis's point), after claims (from CA and repeated here) that this was somehow a deliberate omission.

"The additional test" refers to the third revision of Mann08's Fig. S8a, linked by Dr. Schmidt earlier in that thread.

This passage strongly suggests that Mann08's authors were aware in late 2008 of McIntyre's critiques concerning the Tiljander proxies, as posted at his ClimateAudit website. And as noted earlier, the question of the calibration of these proxies is just not that complicated.

Tiljander has taught me about the difficulty of discussing a technical controversy with adherents to the AGW Consensus, as well as with dissenters from it. All too often, members of one party refuse to address and (perhaps) resolve questions with the normal tools of science (e.g. logic, maths, physical understanding, evidence from prior publications, reductionist inquiry). Instead, the controversies seem to loom largest as signifiers of tribal membership. In certain cases (e.g. Tiljander), Consensus adherents take this stance (no matter how untenable), while in others (e.g. ChiefIO's temperature analyses), skeptics take that one (no matter how untenable). Soldiers, hold your ground! Don't yield an inch!

The points I made above in "With respect to the use of" were limited, and carefully stated. I see nothing in that comment that should be withdrawn.

It is disappointing but not surprising that modest areas of agreement between Martin Vermeer and me turn out to have been fleeting.

The contamination issues are

The contamination issues are known to Mann as can be seen in the paper.
Steve McIntyre says they have used the proxy upside-down, referring to upside-down axes.
In fact, regardless of the contamination issue, the axes are upside-down, with a failure to flip.

Now if there is a response that says accusation of upside-down use is bizarre, the followon statement is supposed to explain why it is bizarre. Perhaps that the axes are not used upside-down, but instead they responded with:

Multivariate regression methods are insensitive to the sign of predictors. Screening, when used, employed one-sided tests only when a definite sign could be a priori reasoned on physical grounds.

Now, as you say both sentences are accurate, but not in the context of what the reader is expecting. If this is an explanation of why the accusation is bizarre, then Mann is saying, in the first sentence, it doesn't matter if you turn things upside-down the algorithm will flip them, man is that McIntyre an idiot, and indeed that is how many defenders interpreted this response.

The second sentence is more interesting, and brings me to another detail I just noticed. He says screening, when used,...
Why mention the screening and one-sided tests? It should have been sufficient to say, upside-usage accusation is bizarre, Tiljander was oriented correctly.

Right after that first sentence, I think Mann is saying that Tiljander did not go through screening, a definite sign could not be reasoned on physical grounds. His statement is a shorter version of saying:

Multivariate regression is blind to the sign of the predictor. The only exception to this case is when screening is used. The one-sided test used during screening is only for those proxies when it can be determined ahead of time which is the correct orientation. Tiljander is not such a proxy.

Except, it I understand the

Except, it I understand the paper correctly, that screening was only used for CPS and not EIV. I'll admit that Tljander is a problematic proxy, but the Boreas paper is not the greatest. For example the Boreas paper never tried to calibrate to local temperature, the entire paper was qualitative. She never tried to actually sort out the postulated non-climatic anthropogenic effects, much like Idso, who I suspect was mostly responsible for this, and Graybill and the CO2 fertilization of P. Longavea. Subsequent work has shown this to be unlikely.

However, Mann did a sensitivity analysis and explained his reason for including the proxy. You might agree or disagree with his choice, and it was a choice, but the sensitivity analysis showed that there was no significant impact on the analysis. Also note that the analysis in the SI was done before the paper was published. However, I can't imagine that Mann is not sensitive to the criticisms of the CA crowd. It seems to be necessary for most scrutinized paleo people (Briffa and others too) to head off the silly criticisms launched by CA (oh, but you didn't do a sensitivity analysis of no tree rings and no Tiljander). I suppose this is a cost of working in an area of science which is "post normal", but the post normalcy is mostly due to CA and "scientists" like S. Fred and others whose opinions seem to be for sale (it only seems this way, S. Fred seems to be heavily influenced by his ideological opinions).

AMac, you are flogging a dead horse here. You might disagree with the choice made, but a thoroughly documented and explained choice does not invalidate a study. Show how this choice makes a material difference in the conclusion in Mann 2008 or better yet how it makes a difference in Mann 2009 and you might have something. Until then, you are just pissing in the wind.

> screening was only used for

> screening was only used for CPS and not EIV.

Screening is not the issue, use is.

> I'll admit that Tljander is a problematic proxy,

What is that adjective (and that phrase) meant to mean?

> but the Boreas paper is not the greatest... Mann did a sensitivity analysis and explained his reason for including the proxy. You might agree or disagree with his choice, and it was a choice...

Mann08's authors -- Kaufman09's authors too -- are of course free to propose original interpretations of others' earlier findings. The requirement in non-postmodern science is for authors to explicitly explain their choices in such cases. This line of reasoning was explored in an earilier exchange upthread; start at "Steve Bloom, let us stipulate".

> the Boreas paper never tried to calibrate to local temperature

Of course not. According to Tiljander et al's interpretation, the varve data are uncalibratable to the instrumental temperature record. Still, they do present the temperature and precipitation records of the nearest weather station from the 1880's to the 1990's. Per Mann08, I extracted the calculated temperature anomaly from the relevant 5 degree by 5 degree gridcell and graphed it against XRD in this post. Visual inspection reveals a correlation that is consistent with Mann08's SF9 and SI methods.

> the sensitivity analysis showed that there was no significant impact on the analysis.

This is a sensible and germane point. See my comment "Here's some strong evidence" and my post "Tiljander Proxies' Modest Effects on Mann08 Estimates... probably".

> Also note that the analysis in the SI was done before the paper was published.

The analysis is in the third revision of Fig. S8a, not submitted to PNAS for peer review, but posted two fourteen months later on Prof. Mann's website. At Collide-a-scape, Gavin Schmidt claimed that version 3's analyses were done in response to post-publication criticisms of the paper.

> but a thoroughly documented and explained choice does not invalidate a study.

Per the cited exchange with Steve Bloom, please explain how the actual choices in respect to the calibration and use of the Tiljander proxies were thoroughly documented and explained.

> Show how this choice makes a material difference in the conclusion in Mann 2008...

This will require my learning R, so it will take some time. As noted earlier, the effect on the spaghetti trace is likely modest. Per the discussion in Gavin Schmidt's Collide-a-scape thread, it is not negligible. I suspect that a larger impact may be on the calculated error bars and their interpretation. To the broader point: in post-normal science, there is a stringent standard concerning "making a difference" for one's adversaries, and a much laxer one for one's allies. With respect to acknowledgement and correction of errors, I think all authors of peer-reviewed literature should strive to do as well as a bank employee who inadvertently miscalculated interest on a savings account.

> you are just pissing in the wind.

Thank you for sharing.

The issue isn't removing

The issue isn't removing Tiljander changes much. The issue isn't removing the tree rings which have been called into question changes much. The issue is removing both removes the hockey stick.

Mann's earlier work was called into question because its conclusions were based solely upon a few (questionable) proxies. If you took those out, the conclusion was changed. In response to this, his 2008 paper was lauded as using so many proxies. Unfortunately, all that changed is now you have two different sets of (questionable) proxies on which his conclusion can rely. As long as you keep one, you still get his hockey stick. Take out both, and again it vanishes.

Feel free to ignore all the issues about incorrect methodology, absurd defenses from Mann's supporters, and all the other side issues. Just focus on one thing. For over a decade, Mann's hockey stick has depended entirely upon a small subset of data (of questionable validity). Nothing has changed, save the way in which this has been hidden.

But it doesn't remove the

But it doesn't remove the hockey stick. You are sadly mistaken.

John Sully, you provide no

John Sully, you provide no evidence that Brandon Shollenberger is sadly mistaken. Presumably your confidence is wholly based on interpreting the twice-corrected, non-peer-reviewed version of Fig. S8a posted at Prof. Mann's PSU website.

This has been covered in this thread. See "Here's some strong evidence", which links to a post of Jeff Id's that supports that interpretation.

Even if that is correct -- and it might be -- the Tiljander argument still matters. "The Tiljander argument".

On the other hand, it may not be right. Steve McIntyre's emulation in 2008 of Mann08's code produced a no-treering-no-Tiljander spaghetti trace that did not resemble any of the traces in twice-revised SF8a.

I note that McIntyre has a new post up today, "Make a stick, make a stick", in which he works through such an emulation of SF8a, step by step.

It does not inspire confidence in the fidelity of any of the versions of Fig. S8a to what they are stated to represent.

AMac, the problem is worse

AMac, the problem is worse than even what you say. John Sully isn't basing his comment (I presume) on that figure, but rather on Gavin Schmidt's description of the figure. Gavin claimed that figure shows a hockey stick survives the removal. This is untrue.

There is no doubt the figure ends in an uptick as the original hockey stick ended. However, a hockey stick consists of more than just an uptick at the end. To be a hockey stick, the figure has to have a flat "shaft" for the earlier portion. Figure S8a does not have such. The elevated temperatures in the earlier portion of the figure mean the figure does not show a hockey stick. For a visual analogy, imagine trying to play field hockey with a boomerang.

Gavin got called out when he claimed the hockey stick could be found in that figure. He responded by not responding (he didn't post on the site again). His claim was pure misinformation.

It is absurd when something obviously untrue can be stated as fact, then accepted without question.

It is important to provide

It is important to provide links and citations, so that other people can see for themselves what the basis of our claims are.

Gavin Schmidt has commented further on the use of the Tiljander proxies in the Mann group's paleoclimate reconstructions, this time via his in-line responses to comments at RealClimate. At Comment #525 in Tamino's thread "The Montford Delusion," Gavin writes,

Since the no-dendro CPS version only validates until 1500 AD (Mann et al (2008) ), it is hardly likely that the no-dendro/no-Tijl CPS version will validate any further back... Note too that while the EIV no-dendro version does validate to 1000 AD, the no-dendro/no-Tijl only works going back to 1500 AD (Mann et al, 2009, SI)

In other words: the only part of Mann08's Fig. S8a that can be said to address the issue of whether the use of the Tiljander proxies "matters" runs from 1501 to 1849. With CPS, reconstructions prior to 1500 are, according to Gavin, unvalidated. With EIV, Gavin says that Mann09 shows that no-dendro validates to 1000, but no-dendro/no-Tilj fails to validate before 1500. If inclusion of Tiljander allows a reconstruction to pass validation tests for an additional 500 years, that would certainly seem to be significant!

Recall, that Gavin is bringing up this evidence in favor of the argument that inclusion of the Tiljander proxies in these reconstructions "doesn't matter."

As you highlighted, Gavin's

As you highlighted, Gavin's comment seems quite nonsensical. He originally claimed it doesn't matter if you include that data. He now says if you don't include the data, the reconstructions fail to validate for something like a quarter of the time covered. There is obviously a contradiction here.

On a bit of a tangent, the more I read from Gavin, the more it seems like he just doesn't understand what people are saying. The most recent inline responses at RealClimate are what make me think this, but a perfect example is found over at Collide-a-scape, where Gavin said it "doesn't matter" if you include that data. Read Gavin's comment at 29, then read lucia's comment at 60. There is such an obvious disconnect, and I don't understand how it is possible.

I hate to be "mean," it seems to me Gavin is just full of it.

It took awhile for me to

It took awhile for me to realize it, but it appears that Gavin doesn't understand the paleo stuff. He is a modeller, and deals with atmospheric physics. He is defending Mann because Mann is a co-founder of RealClimate, and naturally assumes correctness by his colleague.

AMac, the sensitivity

AMac, the sensitivity analysis for the effects of the Tiljander and other contaminated proxies was done in the SI as published at PNAS.

Yes, I understand that a

Yes, I understand that a sensitivity analysis was in the original peer-reviewed S8a, published in September 2008. In late 2009, Prof. Mann noted on his website that that figure contained errors, and was to be superseded by a corrected version on the website. Then in early November 2009, the corrected figure was further amended, again on the Penn State website and not at PNAS or the pnas.org website. It is this twice-amended Fig. S8a that contains the "no-Tiljander no-treerings" trace that Gavin Schmidt linked and discussed in the comments thread of his Collide-a-scape post (and again at RC at Tamino's review of "Hockey Stick Illusion").

I prefer a simple and true declarative statement over this variety of complex discourse.

"The Tiljander proxies cannot be calibrated to the instrumental temperature record."

This has all been covered before.

Amac, You will find similar

Amac,

You will find similar 'corrections' documented in the climategate files. Notably an error made by Lamb which CRU corrected in an obscure journal so as to spare Lamb embarasment.

You will also note that Arthur's standard WRT to my correction of my mistake included making a correction in the same place I made the error. One would think this standard would apply to science as well as blog comments, but we will see what kind of integrity folks have on these matters.

Arthur: It would appear that mann has corrected a figure in in PNAS SI, yet again. can you confirm that?

1. is it the case that the current figure in the SI has been updated elsewhere, namely on The Pennstate web site?
2. Is it the case that mann can update the PNAS SI?
3. Is it the case that a researcher who intends to use Mann's results will consider the SI at PNAS to be the most accurate statement of the science?
4. Should Mann update the SI so that it reflects what he publishes on the Penn State Site?
5. When McIntyre raises the issue of the sensitivity of reconstructions to the inclusion/exclusion of Tiljander, and when Mann continues to update the supplemental Information as a result of those questions, and when those results change in what appears to be a substantive way, should Mann Acknowledge McIntyre?

As Comment #512 (!) on

As Comment #512 (!) on Tamino's recent RealClimate post, Arthur Smith provides a careful overview of the Hockey Stick controversy.

It would seem to me that the topics covered in this thread, while narrow, are material to that discussion.

However, there is no mention of what Arthur may think of the use of the Tiljander proxies, or the adamant and unbending defense of those uses by the community of AGW Consensus scientists and advocates.

The community's posture of Inerrancy on this matter has done much to corrode my trust in their other Hockey-Stick-related pronouncamientos. Arthur is not similarly troubled: a good sign or a bad sign, depending on one's point of view.

Arthur, Would you be so kind

Arthur,

Would you be so kind to note that when I was shown to be in error I made a clear statement of my error. Answered your questions directly and completely. I have even given you credit for exposing the error. I think we agreed that was a proper protocal.

"(3) Is it possible, despite

"(3) Is it possible, despite the one figure showing no substantive difference to the reconstruction, that use of Tiljander did make a material difference to some of the conclusions of Mann 2008 (and apparently later papers using the same data)?"

"If the answer to these 3 questions is "Yes", then that adds up to a somewhat damning allegation against Mann's work on this. Evidently he's made some minor errors in the past, if those are true then I agree this one was a bit worse."

Can we start by listing the conclusions of Mann 2008.

1 Recent warmth appears anomalous for at least the past 1,300 years whether or not tree-ring data are used.

From RC:

Gavin,

So just to be clear with regard to your response to 525. Under either method (CPS or EIV) it is not possible to get a validated reconstruction to before 1500 without the use of tree rings, or the Tijlander sediments. I understand, of course, that as you remove proxies that the ability to project backward will naturally diminish.

[Response: That appears to be the case with the Mann et al 2008 network. Whether you can say more general things about medieval times using these and other proxies (cf osborn and briffa 2006) is another question. -gavin]

Not sure I understand where you stand on this Arthur, how do you read that?

If you recall, when I made a mistake about a graph in the FAR, we had quite a nice discussion about how one should go about correcting a mistake in a blog comment. Not that policy makers ever read blog comments, but others do and your ideas about how corrections should be made are most instructive. How should Mann go about correcting these things ( if you can admit that there is a mistake here) and should Mcintyre or others get credit?

Of course the worst case of

Of course the worst case of unacknowledged errors in climate science was probably the UAH satellite analysis, which for 26 years was substantially under-reporting warming due to an algebra error in the analysis.

Huh?

You had an UNFOUND error, that once it was found was corrected.

In Manns case ( with the precipitation proxies for example--- a case which you havent looked at) You have mistakes which were pointed out. Then repeated. Then pointed out AGAIN. then fixed and misrepresented with no acknowledgement to Mcintyre