Shollenberger's Technical Review of Mann's recent book

Readers may recall this posting A detailed review of Mann’s book: The Hockey Stick and the Climate Wars as it relates to the Wegman report to Congress. This post today is a continuation of that review, with more in-depth technical detail.

By Brandon Shollenberger

The Beginning

Earth Day, April 22, 1998, was the day the hockey stick was born. On that day, Michael Mann, and co-authors Ray Bradley and Malcolm Hughes published a paper in the scientific journal Nature (referred to as MBH98). This paper claimed to reconstruct northern hemispheric temperatures from the past 600 years by examining temperature “proxies” found in nature. The most important of these proxies were tree rings, the size (and density) of which can be influenced by temperatures.

The results of this paper were dramatic. The temperature reconstruction it contained showed relatively flat temperatures for approximately 500 years followed by a sharp increase in temperatures over the last hundred years. The sharp increase formed a curve, which when attached to the end of a relatively flat line created the image of a “hockey stick.” It told the viewer current temperatures were higher than anything seen in hundreds of years. Looking at it, it was almost impossible to think anything other than, “Humans are causing a dramatic change in temperature.”

Not only was the resulting image powerful, it was also extremely definitive. MBH98 claimed modern warmth was unprecedented in 600 years with “roughly a 99.7% level of certainty.” This high degree of confidence was only reinforced by the paper saying it’s conclusions weren’t based on a single type of proxy (such as tree rings), but rather:

the long-term trend in NH is relatively robust to the inclusion of dendroclimatic indicators in the network, suggesting that potential tree growth trend biases are not influential in the multiproxy climate reconstructions.

The authors said their conclusions were almost absolutely certain. They said their results were so certain, you could throw out tree ring data (dendroclimatic indicators), their largest source of data, and they’d still get the same results. The authors were full of it. On page 51 of Michael Mann’s book, he discusses an analysis he performed shortly after MBH98 was published:

The tests revealed that not all of the records were playing an equal role in our reconstructions. Certain proxy data appeared to be of critical importance in establishing the reliability of the reconstruction–in particular, one set of tree ring records spanning the boreal tree line of North America published by dendroclimatologists Gordon Jacoby and Rosanne D’Arrigo.

If “one set of tree ring records” was “of critical importance in establishing the reliability of the reconstruction,” the reconstruction could not have been “relatively robust to the inclusion of dendroclimatic indicators.” While Mann now casually admits the importance of such a small amount of data, neither he nor his co-authors ever made any effort to correct their paper on the point.

The next year, these authors published a new paper (MBH99), extending their hockey stick back another 400 years. In it, they concluded:

The 1990s was the warmest decade [of the last millennium], and 1998 the warmest year, at moderately high levels of confidence.

These two papers, collectively referred to as MBH, formed the basis for what is the most memorable image used in discussions of global warming. In 2000, Bill Clinton referenced it in his State of the Union Address. More importantly, in 2001, the International Panel on Climate Change (IPCC), an organization created by the United Nations to periodically release “assessments” of the state of knowledge on global warming, gave it prominent display. A summary made for government officials of its Third Assessment Report (TAR) even used MBH to conclude it likely “the 1990s has been the warmest decade and 1998 the warmest year of the millennium.” Out of hundreds of pages of documents, this image was selected to be the “public face” of global warming.

Controversy

Controversy began when Stephen McIntyre and Ross McKitrick collaborated on a paper published in the journal Energy & Environment in 2003. They concluded:

The particular “hockey stick” shape… is primarily an artefact of poor data handling, obsolete data and incorrect calculation of principal components.

In response to this conclusion, Mann fabricated a story about McIntyre and McKitrick’s results being based upon a faulty spreadsheet. However, he also said (page 123):

The paper’s dramatically different result from ours… was instead an artifact of the authors’ having inexplicably removed from our network two-thirds of the proxy data we had used for the critical fifteenth-sixteenth century period.46

This is untrue. McIntyre and McKitrick were forced to omit some data (but not two-thirds) because they couldn’t figure out certain undisclosed methodological choices Mann had made. When McIntyre asked Mann to disclose what he had done, Mann refused. Because it was impossible to know what Mann had actually done, McIntyre simply emulated the process as best he could. Despite what Mann claims, the difference in methodology didn’t affect any conclusions.

Peculiarly, the reference Mann gives says nothing about this claim. It says McIntyre and McKitrick were wrong, but gives totally different reasons.

This is especially strange as Mann wrote the article he references.

The Follow-Up

In this book, I attempt to tell the real story behind the hockey stick.

Michael Mann – Prologue

Over the next two years, both “sides” of the controversy tried to support their position. Most notably, Mann was forced to publish a corrigendum by Nature in order to correct errors pointed out in his work, though he claimed, “None of these errors affect our previously published results.”

During this period, Mann and some of his colleagues started a blog, RealClimate. McIntyre started a blog of his own, ClimateAudit, to respond to things posted on RealClimate. Many discussions and arguments were made on these two web sites, eventually leading McIntyre and McKitrick to publish another paper in the journal Geophysical Research Letters (GRL). Mann says of it (page 130):

McIntyre and McKitrick had quietly dropped their erroneous original assertion (in their 2003 paper discussed in chapter 8 that the hockey stick was an artifact of bad data. Their new, albeit equally erroneous, assertion was that the hockey stick was an artifact of the conventions used in applying principal component analysis (PCA) to certain tree ring networks…

While Mann claims the argument by McIntyre and McKitrick was new, it was one they had made in their first paper. The abstract of that paper states (emphasis added):

The particular “hockey stick” shape… is primarily an artefact of poor data handling, obsolete data and incorrect calculation of principal components.

This fact is even acknowledged by Mann in his book (emphasis added – note #45)

To be specific, they claimed that the hockey stick was an artifact of four supposed “categories of errors”: “collation errors,” “unjustified truncation and extrapolation,” “obsolete data,” and “calculation mistakes.”

McIntyre and McKitrick had always been aware there was a problem with how Mann did PC calculations, so this was not a “new” issue. All that was new was McIntyre and McKitrick had realized the data errors they had found were mostly irrelevant to the MBH results. Having realized that, they began to focus more on the main issue, the PC calculations. In regard to this, Mann says (page 137):

McIntyre and McKitrick used a different PCA convention in their 2005 paper. They centered the tree ring data over the long term (1400—1980). That’s fine—in fact, long-term centering is actually the traditional convention…

Clearly, Mann does not think they calculated their PCs incorrectly. Instead, he claims:

Applying our selection rule to these data, using a modern centering convention indicated that the leading two PC series should be retained…. By misapplying a selection rule derived for one convention (modern centering) to PCA results based on a different convention (long-term centering) [they] end up erroneously throwing out the proverbial baby with the bathwater.

Both groups kept two PCs for the North America tree ring network (NOAMER). Mann claims this is wrong, that McIntyre and McKitrick should have kept more. This fairly simple claim is Mann’s basis for dismissing the GRL paper:

In effect, McIntyre and McKitrick had “buried” or “hidden” the hockey stick. They had chosen to throw out a critical pattern in the data as if it were noise

In their GRL paper, McIntyre and McKitrick never said anything about how many PCs to keep. Instead, the paper is a discussion about how PCs were calculated with NOAMER being used as an example. Given Mann’s claim has no possible connection to this paper, it’s natural to try looking at another paper published by McIntyre and McKitrick that year. That paper was published in Energy and Environment (EE), and it did discuss how many PCs get kept:

If a centered PC calculation on the North American network is carried out (as we advocate), then MM-type results occur if the first 2 NOAMER PCs are used in the AD1400 network (the number as used in MBH98), while MBH-type results occur if the NOAMER network is expanded to 5 PCs in the AD1400 segment (as proposed in Mann et al., 2004b, 2004d). Specifically, MBH-type results occur as long as the PC4 is retained, while MM-type results occur in any combination which excludes the PC4. Hence their conclusion about the uniqueness of the late 20th century climate hinges on the inclusion of a low-order PC series that only accounts for 8 percent of the variance of one proxy roster.

Rather than simply “throw out” data based upon a “selection rule,” McIntyre and McKitrick carefully considered what happens based on how much data is used. Mann’s claim is exactly the opposite of the truth in relation to the EE paper (and is completely nonsensical in relation to the GRL paper). He continues this sort of misrepresentation (page 136):

We employed a standard, objective criterion for determining how many PCs should be kept for each region.

In the note he provides, he says the rule he used is called Preisendorfer’s Rule N. There is no evidence this rule was actually used on the tree ring networks. This claim first appeared years after the hockey stick was made, it wasn’t supported by any of the program code released my Mann, and the evidence says it couldn’t have been used.

Mann Seeks Support

During any controversy, people are bound to join in on the arguments. The hockey stick controversy is no different. Mann refers to one example of this when he discusses work by Eugene Wahl and Caspar Ammann (page 138):

Wahl and Ammann demonstrated that the hockey stick was not an artifact of PCA conventions and that the basic result is robust as long as key proxy records are not thrown out (either explicitly as in the original 2003 McIntyre and McKitrick paper, or implicitly through the use of erroneous selection rules, as in their 2005 paper).

Again, Mann repeats his misrepresentations of McIntyre and McKitrick’s work. More importantly, he says Wahl and Ammann find the MBH “result is robust as long as key proxy records are not thrown out.” This is the exact result observed by McIntyre and McKitrick. It is the exact result Mann admits in his book. Everyone agrees if you keep that particular set of tree ring records, you get a hockey stick. If you remove it, you don’t get a hockey stick.

Mann goes on to say Wahl and Ammann:

showed that, had McIntyre and McKitrick subjected their alternative reconstruction to the statistical validation tests stressed in MBH98 and MBH99 (and nearly all related studies), it would have failed these critical tests.

This is problematic in a number of ways. First, McIntyre and McKitrick never claimed to be offering an “alternative reconstruction.” They were merely testing what happened if certain changes were made. This serves the same purpose as running statistical validation tests. Both are ways of seeing how robust a paper’s results are.

Second, Mann raises the issue of statistical validation tests. There are a variety of such tests, the two most important of which are RE and r2. The closer the results of these tests are to one, the better the conclusion is. The problem is McIntyre had long criticized Mann for not publishing r2 verification scores which were practically 0 (very bad). Mann calculated these scores, but he never published the adverse results. When a committee formed by the United States House of Representatives asked Mann:

Did you calculate the R2 statistic for the temperature reconstruction, particularly for the 15th Century proxy record calculations and what were the results?

Mann simply avoided answering the question:

I assume that what is meant by the “R2” statistic is the squared Pearson dot-moment correlation, or r2 (i.e., the square of the simple linear correlation coefficient between two time series) over the 1856-1901 “verification” interval for our reconstruction. My colleagues and I did not rely on this statistic in our assessments of “skill”

He doesn’t admit or deny calculating the scores. He simply says he and his coauthors didn’t “rely” upon them. Whether or not they relied upon the scores, those scores are obviously relevant to anyone looking at the hockey stick. It would especially have been relevant to the IPCC which claimed Mann and co-authors (emphasis added):

estimated the Northern Hemisphere mean temperature back to AD 1400, a reconstruction which had significant skill in independent cross-validation tests.

Even worse, while the adverse results were hidden, Mann and his co-authors published r2 scores when they were helpful. Figure 3 of MBH98 shows r2 scores:

Figure 3 shows the spatial patterns of calibration b, and verification b and the squared correlation statistic r2, demonstrating highly significant reconstructive skill over widespread regions of the reconstructed spatial domain.

Given all this, it is difficult to understand why Mann would bring up statistical validation tests. He has long hidden the fact his own work fails such tests, and there is no reason failing such tests would matter for McIntyre and McKitrick’s results (they weren’t doing an alternative reconstruction).

To add to the oddness, Wahl and Ammann actually show the failing MBH r2 scores.

Congress

A second flood, a simple famine, plagues of locusts everywhere

Or a cataclysmic earthquake, I’d accept with some despair

But, no, you sent us Congress, good God, sir, was that fair?

Piddle, Twiddle and Resolve – 1776 (musical)

By this point, the United States Congress had already gotten involved in the hockey stick debate. In 2006, it increased its involvement by commissioning two reports to study the controversy, the National Academy of Science (NAS) Report and the Wegman Report.

The most important conclusion given by both of these reports deals with a methodological choice made by Mann involving principal component analysis (PCA). Mann used a non-standard implementation of PCA. His critics claimed this caused his method to “mine” for hockey sticks. If true, it would mean Mann’s methodology inherently gave undue influence to that particular shape. Both reports acknowledged this criticism. The NAS Report said:

As part of their statistical methods, Mann et al. used a type of principal component analysis that tends to bias the shape of the reconstructions.

The Wegman Report said:

The net effect of this decentering using the proxy data in MBH98 and MBH99 is to produce a “hockey stick” shape.

Both reports agree the original hockey stick was created by a biased methodology. It sought hockey sticks in the data and gave them undue significance. Despite this, Mann says (page 164):

The more extensive and authoritative NAS review, for example, had specifically dismissed the notion that PCA conventions had any substantial impact on our findings. As Bloomfield had put it at the NAS press conference, “the committee, while finding that the issues are real, [found] they had a minimal effect on the final reconstruction.”

Rather than quote the NAS Report, Mann quotes a comment made in a press conference which isn’t supported by the report. He does quote the report on page 161:

The basic conclusion of Mann et al. (1998, 1999) that the late 20th century warmth in the Northern Hemisphere was unprecedented during at least the last 1,000 years has subsequently been supported by an array of evidence that includes both additional large-scale surface temperature reconstructions and pronounced changes in a variety of local proxy indicators

However, this merely supports the conclusion of MBH, not the methodology. Indeed, nothing in the NAS Report actually supports Mann’s work. Instead, it merely says other work reached the same conclusions. This cannot possibly address the merits of Mann’s work, a point expressed by Edward Wegman (the lead author of the report bearing his name):

Method Wrong + Answer Correct = Bad Science.

Despite this, Mann says:

The NAS report was widely reported to be an affirmation of our work.

Projection

Mann flagrantly misrepresents the NAS report in regards to “bristlecones,” the type of tree the all-important tree ring data was taken from. Mann says of it (emphasis added – page 190):

McIntyre also appealed to the conclusions of the 2006 NAS report to claim that our continued use of the very long bristlecone pine series was inappropriate. Yet this was a misrepresentation of what the NAS had concluded. The NAS panel expressed some concerns about so-called strip-bark tree ring records, which include many of the long-lived bristlecone pines. These trees grow at very high CO2-limited elevations, and there is the possibility that increases in growth over the past two centuries may not be driven entirely by climate, but also by the phenomenon of CO2 fertilization – something that had been called attention to and dealt with in MBH99 (see chapter 4). The NAS report simply recommended efforts to better understand any potential biases by “performing experimental studies on biophysical relationships between temperature and tree-ring parameters”.

This is a gross misrepresentation of the NAS report’s findings. From the very same page as the quote he offers (strip-bark is the type of bristlecones being discussed – page 52):

While “strip-bark” samples should be avoided for temperature reconstructions, attention should also be paid to the confounding effects of anthropogenic nitrogen deposition (Vitousek et al. 1997)…

McIntyre cited a conclusion from the very same page Mann was quoting from, yet Mann claims it was a misrepresentation. Clearly, the reverse is true. More importantly, it is clear bristlecones are a questionable data source. The NAS Report states this. It also acknowledges Mann’s hockey stick was dependent upon bristlecones:

For periods prior to the 16th century, the Mann et al. (1999) reconstruction that uses this particular principal component analysis technique is strongly dependent on data from the Great Basin region in the western United States.

There’s a final oddity to this issue. In a RealClimate post, Mann’s co-author Ray Bradley said:

One final note: bristlecone pines often have an unusual growth form known as “strip bark morphology” in which annual growth layers are restricted to only parts of a tree’s circumference. Some studies have suggested that such trees be avoided for paleoclimatic purposes, a point repeated in a recent National Academy of Sciences report (Surface temperature reconstructions for the last 2,000 years. NRC, 2006).

Mann even commented on that blog post (inline response to comment #7), yet he now completely misrepresents the finding his co-author referred to in it.

His treatment of the Wegman Report is little better (page 164):

The Wegman Report, commissioned by Joe Barton and published several weeks after the NAS report, seemed a transparent effort to further spread the attacks against our work. It uncritically repeated the old and tired McIntyre and McKitrick claim that the hockey stick was an artifact of the conventions used in a statistical (PCA) analysis…

The most important fact about the Wegman Report is not actually found in the Wegman Report. Instead, it was stated by Gerald North, the chair of the panel which wrote the NAS report:

CHAIRMAN BARTON. I understand that. It looks like my time is expired, so I want to ask one more question. Dr. North, do you dispute the conclusions or the methodology of Dr. Wegman’s report?

DR. NORTH. No, we don’t. We don’t disagree with their criticism. In fact, pretty much the same thing is said in our report.

The same point was reiterated by another member of the panel, Peter Bloomfield:

MR. BLOOMFIELD. Thank you. Yes, Peter Bloomfield. Our committee reviewed the methodology used by Dr. Mann and his coworkers and we felt that some of the choices they made were inappropriate. We had much the same misgivings about his work that was documented at much greater length by Dr. Wegman.

Mann claims the Wegman Report was just a repetition of McIntyre and McKitrick’s arguments. The NAS panel agreed with the criticisms found in the Wegman Report…

The Hockey Stick, Redux

Second verse, same as the first!”

I’m Henery the Eighth, I Am(song)

In 2008, Mann published a new hockey stick. Mann describes it (page 190):

With far more ice core and sediment records now available, we were able to obtain a meaningful reconstruction of the Northern Hemisphere average temperature for the past thirteen hundred years without using tree ring data at all. If tree ring data were used, the reconstruction could be extended, with some reservations, back over the past seventeen hundred years.

Mann’s critics claimed his original hockey stick was purely a product of a small amount of tree ring data. If his new reconstruction was free from that problem, it would be a major development. However, McIntyre almost immediately claimed to find problems with the new reconstruction:

Stephen McIntyre wasted little time in launching a series of attacks on the PNAS paper, employing–it would seem– the strategy of throwing as much mud against the wall as possible and hoping that some would stick. Teaming up with his former coauthor Ross McKitrick, he submitted a short letter to the editor of PNAS claiming that our reconstruction used “upside down proxy data.”52 That was nonsensical, as we pointed out in our response,53 one of our methods didn’t assume any orientation, while the other used an objective procedure for determining it.54

As Mann explains, two different methodologies were used, Composite Plus Scale (CPS) and Error-in-Variables (EIV). However, there is nothing “nonsensical” about saying data was used upside down. The CPS methodology screens proxy records by directly comparing them to the local instrumental records. If the two records are similar enough, the proxy record gets used. The problem is proxy records can increase without meaning temperatures increased. If one were measuring the accumulation of snow/ice, larger values would be expected for cooling, not warming. This increase would be compared to an increase in instrumental temperatures, and thus the CPS methodology would treat the cooling as warming. This would cause the series to be used upside down.

EIV is similar to this, though it doesn’t screen proxy series. Instead, it compares each proxy series to the temperature record and determines how similar the two are. If it finds a similar trend, but in the opposite direction, it “flips” the series upside down. This means both methodologies used by Mann are capable of using proxy series upside down despite the fact he claims such is “nonsensical.”

McIntyre settled then on a more specific avenue of attack: our use of a small group of sediment records from Lake Korttajarvi in central Finland. But this was quite inconsequential and, ironically, we were the ones who had raised concerns about these particular data in the first place, not McIntyre. We had included them for consideration only to be complete in our survey of proxy records in the public domain.

The records Mann is referring to here are commonly called the Tiljander series. The four series are labeled Thickness, Lightsum, Darksum and XRD. Thickness and XRD are measured, but Lightsum and Darksum are derived from those measurements. This means using using all four series, which Mann did, results in double counting.

More importantly, these series were corrupted by human influence. The lake they were taken from began being influenced by farming and construction tn the 1700s. The impact from human influence completely overwhelmed any temperature signal there may have been in the data. The people who originally published the series noted this and cautioned people not to use the modern portion of the series as a temperature proxy.

Since Mann’s methodologies require calibrating proxy series to the instrumental record (1850-1995). it makes no sense to use series whose data has been corrupted in the modern periods. Any correlation which may be found is spurious, not caused by the proxy actually responding to temperature. Since the correlation is spurious, it could not have any connection to the temperature response the series were supposed to have before being corrupted. This is what caused two of the Tiljander series to be used with the opposite correlation as that suggested by the original authors.

Mann’s Nonsense

In the online supplementary information accompanying publication of our PNAS article, we had both noted the potential problems with these records and showed that eliminating them made absolutely no difference to the resulting reconstruction.57 McIntyre had thus attempted to fabricate yet another false controversy

Mann acknowledged the authors warning not to use the data as he did, yet used it anyway. The reasoning he offers for such makes no sense: he says there is “no difference” if he uses the series. If there is no difference, why include them? The answer is simple. Using them makes a huge difference.

The main temperature reconstruction is barely affected by removing the Tiljander series because it includes the tree-ring data which was essential for Mann’s original hockey stick. Mann’s paper claims not to need that data to get a hockey stick, but that is only true if he includes the Tiljander series. If you remove both the Tiljander and tree ring series, there is no longer a hockey stick.

This point is confirmed by Gavin Schmidt, a coauthor of Mann’s at RealClimate:

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

A commenter at RealClimate noticed this remark and asked:

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 Tiljander sediments.

Schmidt responded:

That appears to be the case with the Mann et al 2008 network.

Mann himself has acknowledged this. From the Supplementary Information for a later paper:

Additional significance tests that we have performed indicate that the NH land+ocean Had reconstruction with all tree-ring data and 7 potential “problem” proxies removed (see original Supp Info where this reconstruction is shown) yields a reconstruction that passes RE at just below the 95% level (approximately 94% level) back to AD 1300 and the 90% level back to AD 1100 (they pass CE at similar respective levels).

The test used by Mann required his reconstruction pass at a 95% confidence level, and he acknowledges it can only do so by including either the tree ring data or the (nonsensically used) Tiljander series. The “false controversy” he claims McIntyre raised actually repudiates a central claim of Mann’s paper:

With far more ice core and sediment records now available, we were able to obtain a meaningful reconstruction of the Northern Hemisphere average temperature for the past thirteen hundred years without using tree ring data at all.

Nobody Agrees With Mann

Mann continues to spread disinformation (page 198):

When Science in early September 2009 published an article by Darrell Kaufman and his colleagues showing the most dramatic hockey stick yet–a two-thousand-year reconstruction of Arctic temperature changes19–Stephen McIntyre and his forces went on the attack on the Internet,20 immediately trumpeting the false claim that the work was compromised by bad data, despite the fact that whether or not the authors used the data in question made no difference to the result they obtained.

The “data in question” are the Tiljander series which were once again used upside down. Despite Mann’s claims, McIntyre never said this was the source of the Kaufman hockey stick (he primarily blamed another series, Yamal). Beyond that, a few months after the Kaufman paper came out, a corrigendum was published. Included in it was this line:

Record 20 was corrected to reflect the original interpretation of Tiljander et al. (S32) that X-ray density is related inversely to temperature.

Mann claims McIntyre raised a “false claim” to attack a paper, yet the authors of that paper acknowledged his claim was correct. Even stranger, Ray Bradley was a coauthor on both Mann’s 2008 paper and the Kaufman paper. Both papers made the same mistake, but only the Kaufman group admitted it.

A Simple Point

For all the “technical” issues in Mann’s papers, the controversy is actually very simple. Mann’s papers give undue focus to a small amount of data. Even he and his supporters admit his original hockey stick was based entirely upon a small amount of tree ring data (which the NAS says should not be used to measure temperature). His latest hockey stick was the same, save he added upside down data which he couldn’t possibly calibrate to temperature.

Denouement

If you want a happy ending, that depends, of course, on where you stop your story.”

Orson Welles

One of the most common defenses offered for Mann’s hockey stick is other papers get the same result. The idea is if Mann got the right answer, criticisms of his work don’t matter. This is a dumbfounding position, and the best response is that given above by Wegman:

Method Wrong + Answer Correct = Bad Science.

Mann’s work has been highly publicized. If the glaring problems in it are overlooked, how can anyone trust other papers reaching the same conclusions? What is to stop those other papers from being just as flawed? Nothing. They cannot be ignored or dismissed because of flaws in Mann’s work, but they should all be carefully examined rather than accepted on faith. Unfortunately, the same basic criticisms are leveled against practically every one of those reconstructions.

General Issues

It would be impossible to discuss every paper showing a hockey stick. However, two general problems found in them can be covered. The first problem has already been shown, namely, mistakes don’t get admitted. Mann’s PC1 (the source of his hockey stick) was created with a biased methodology, and it was made up of data the National Academy of Scientists said should be avoided. Despite this, it was included in the latest IPCC report.

Related to the above, papers with hockey sticks tend to rely on the same data. In addition to bristlecones, a commonly used series is called Yamal. Mann discusses it (page 198):

A more vicious attack was reserved for later that month. The matter concerned a tree ring temperature reconstruction for Russia’s Yamal region that Keith Briffa and colleagues had published some years earlier; it once again showed recent warmth to be anomalous in a two-thousand-year context. At a time when Briffa was known to be seriously ill and not in a position to respond to any allegations, McIntyre publicly accused him of having intentionally cherry-picked tree ring records to get a particular result…

To support his “cherry picking” allegation, McIntyre had produced his own composite reconstruction–which happened to lack the prominent recent warming evident in Briffa’s reconstruction.

McIntyre didn’t accuse Briffa of cherry-picking, and he didn’t make “his own… reconstruction.” He simply did a sensitivity test. Testing to see what happens when you make a change is not the same as saying that change is “right.”

How did he accomplish this? By deleting tree ring records of Briffa’s he didn’t seem to like, and replacing them with other tree ring data he had found on the Internet, which were inappropriate for use in a long-term temperature reconstruction

Mann claims the data added was “inappropriate for use in a long-term temperature reconstruction,” but it was no different than the data McIntyre removed. Mann also claims the data was “data he had found on the Internet.” Surprisingly, that’s true. McIntyre found the data on the internet web page for the International Tree Ring Data Bank, the single largest repository for tree ring records… As for the “tree ring records… he didn’t seem to like,” they were 12 cores (tree rings measurements), a rather low amount. McIntyre removed them to see what would happen if a different site’s data was used instead. This new site had 34 cores, a far better number, and it was from the same area. More importantly, McIntyre then added the 12 cores back in and got the same result.

Put simply, McIntyre showed a series with a prominent hockey stick lost it’s hockey stick shape if a little data from the same area was added. This series has been used in a dozen reconstructions. Is it any surprise those reconstructions got the same result as Mann got? All this shows is if you give a small amount of questionable data undue focus, you can get the same results Mann got by giving a small amount of questionable data undue focus.

The hockey stick was originally accepted without anyone verifying it. That was a mistake. Newer hockey sticks were accepted without anyone verifying them. That was a mistake. Will the same mistake be made with Mann’s book?

Advertisements

  Subscribe  
newest oldest most voted
Notify of
pat

To any rationale person, Mann’s work seems not so much science as opinion. I simply find it hard to believe that governments make policy on such ephemeral, ambiguous ‘data’.

A great review that also constitutes a great summary of the “Hockey Stick” controversy.
One of the important things of the controversy is this: why can’t MBH et al produce a temperature reconstruction that lacks the flaws that everyone admits exist but Mann?

Keith W.

Very good summation, Brandon.

Nerd

The hockey stick won’t go very easily. Just look at cholesterol and saturated fat consumption causing theory… It has been proven wrong many times but the theory is still being used anyway to attack steak, eggs, etc.

John W. Garrett

Marvelous. Bravo!

Richard S Courtney

Brandon Shollenberger:
Thankyou for this fine assessment of Mann’s assertions in his book.
You end it by asking;
“The hockey stick was originally accepted without anyone verifying it. That was a mistake. Newer hockey sticks were accepted without anyone verifying them. That was a mistake. Will the same mistake be made with Mann’s book?”
Of course, your question is rhetorical. However, newcomers to this subject may not recognise that, so I state the following answer.
Yes, deliberate mistakes are often repeated, and the deliberate mistake of not verifying Mann’s work will certainly be made with Mann’s book by the same people who deliberately failed to verify his work.
Richard

Peter B

“For all the “technical” issues in Mann’s papers, the controversy is actually very simple. Mann’s papers give undue focus to a small amount of data.”
Yes, and there’s something very odd going on when so many supposed scientists don’t see this.

I knew the paper was bad from day one.It contradicted decades of research in several fields such as Geology,History and Biology.

Grumpy Old Man

Why do they keep using the word methodology when the word method will suffice? Methodology sounds ‘scientific’. It actually means the science or study of method. If you see the word methodology in an article or report, it’s pretty fair bet you are reading B*S.

RE: Piddle, Twiddle…. you sent us Congress; was that fair?
How Ironic. Mann compares his plight to John Adams’,
The main character of 1776, who as Jefferson sings:
“Mr. Adams, damn you, Mr. Adams,
You’re obnoxious and disliked, that cannot be denied…..”

tl;dr
Looks like Mann uses a hockey stick like an out of control Detroit Redwings forward

Dodgy Geezer

Two ‘usings’ in “The Hockey Stick, Redux” section (Third para from the bottom of the section)

“The records Mann is referring to here are commonly called the Tiljander series. The four series are labeled Thickness, Lightsum, Darksum and XRD. Thickness and XRD are measured, but Lightsum and Darksum are derived from those measurements. This means using using all four series, which Mann did, results in double counting.
More importantly, these series were corrupted by human influence. The lake they were taken from began being influenced by farming and construction tn the 1700s. The impact from human influence completely overwhelmed any temperature signal there may have been in the data. The people who originally published the series noted this and cautioned people not to use the modern portion of the series as a temperature proxy.”
This is a perfect example on how shoddy his work is.He goes out of his way to introduce bias in his paper.A deliberate effort for the purpose of advancing a particular belief that does not exist.
He is a perfect example of a pseudo-scientist.

Reed Coray

After reading Shollenberger’s Technical Review of Mann’s recent book, I ask myself: How can anyone in the scientific community put any faith whatsoever in the scientific findings of Dr. Michael Mann? The only answer I came up with was: Fear of repurcussions. Does anyone have a different answer?

Michael Larkin

Brandon,
I’ve always had a hard time understanding the intricacies of the arguments about the hockey stick, not least because I’m challenged by the maths/stats. This is the clearest exposition for a layman that I have seen. I thank and congratulate you for it.

artwest

Thanks Brandon, a very concise and readable summary.
If only a few politicians would read it. I am sure that, among the charlatans, that there are many more who are guilty of ignorance.
I suspect most people would be shocked at how little data was being manipulated to justify the wrecking of economies.
On a related note, I’d love to see a TV channel going out on the street and asking people by how much they think the planet has supposedly warmed over the last century. Given all the hysteria, I am sure that in some cases peoples guesses would be out by ten degrees or more.

neill

Mann, the log balancer.

Latitude

First off….to believe in the Hockey Stick……someone would have to believe the climate was freakishly stable for 1000 years…………

Allan MacRae

Mann’s 1998 “hockey stick” eliminated from the historic record both the Medieval Warm Period and the Little Ice Age. This was a bold falsehood, that was then promoted by the IPCC to scare the public about global warming. The IPCC has since quietly dropped the Mann hockey stick.
Furthermore, it took eight more years before the “Divergence Problem” was revealed. Mann grafted modern surface temperature data onto older tree ring temperature proxies to produce his upward-sloping “hockey stick” graph. Grafting together two different datasets is usually NOT good scientific practice.
Why did Mann do this? Because if he had exclusively used tree-ring data, the blade of the hockey stick, instead of showing scary warming in the last decades of the 20th Century, would have shown COOLING.
This was later referred to in the Climategate emails as “Mike’s Nature trick” to “hide the decline”. Oops!
The scientific conclusion, in my opinion, is that using tree rings as a proxy for temperatures is not sufficiently accurate for the major conclusions that were drawn from the Mann study.
Mann and the IPCC were clearly wrong about the hockey stick – the only remaining question is not one of scientific error, it is one of deliberate fraud.
For more on the Divergence Problem, see
http://www.climateaudit.org/?p=1530
and
http://www.climateaudit.org/?p=899

Camburn

Prof Mann knows he is wrong in his theory and the results he finds.
He has made more reconstructions, and all of them lack scientific merit.
What is most sad is that a few of the louder supporters of his theory seem to continue to have opportunity via the press.
Prof Mann is not well respected in the geological nor biologicall fields of science because of his shoddy works.

Brandon Shollenberger

Keith W:

Very good summation, Brandon.

John W. Garrett:

Marvelous. Bravo!

Michael Larkin:

I’ve always had a hard time understanding the intricacies of the arguments about the hockey stick, not least because I’m challenged by the maths/stats. This is the clearest exposition for a layman that I have seen. I thank and congratulate you for it.

Thanks guys! I’m happy to see it’s helpful for people.
Dodgy Geezer:

Two ‘usings’ in “The Hockey Stick, Redux” section (Third para from the bottom of the section)

D’oh. That makes two typos people have found in it so far (AMac pointed out I used it’s instead of its at one point). I guess that’s what I get for self-editing. Oh well. Thanks for pointing it out to me.
Grumpy Old Man:

Why do they keep using the word methodology when the word method will suffice? Methodology sounds ‘scientific’. It actually means the science or study of method. If you see the word methodology in an article or report, it’s pretty fair bet you are reading B*S.

This isn’t true at all. Method and methodology are two different things. In fact, a methodology will generally encompass a number of methods. You can’t just switch the two at will.
Stephen Rasey:

How Ironic. Mann compares his plight to John Adams’,

Actually, I was the one who put that quote there. It was more clear in the PDF version, but basically, I put a quote at the start of each section (aside from the first).

More of this insidiously stupid posit that anyone can tell what the temps are with tree rings. This may be tiresome for many, but I’ll keep repeating this until this vapid posit gets removed as a question of science.
The trees in question are samples taken from high latitude or high altitude places. They only grow (tree rings) from about 6 to 8 weeks a year. There is absolutely no way to pick up an annual signal from these rings. They won’t grow in extreme heat, and they don’t grow in the cold. The hockey stick graph which eliminated the MWP and the LIA is because they don’t respond to extremes. The handle is an artifact of the rings themselves.
Even if you can extract a temp signal from the tree rings, (which one can not) it only gives us data for 2 months out of the year. Was it a mild or very cold winter? There is absolutely no way to tell when the ring doesn’t respond to either. So, pretending that we can say the rings tell us it averaged 60° F in the summer for any particular location. So what? Does that mean the winter averaged 10° F or -20°F? The trees don’t grow in either. So what is the average annual temp? Somewhere between 20° and 35° ? That’s tea leaf reading. That’s as stupid as phrenology. What’s the decadal average? More stupidity akin to numerology.
All of the papers regarding temp-dendrochonology particularly from the cores in question needs thrown out of science. It is not a valid concept. It doesn’t matter is one particular core sampling hinged on the results or not. It doesn’t matter what statistical approach was used. It is the same as arguing over how many angels can dance on the head of a needle.
Can anyone show the work of science that circumvents the fact that the rings have no cold or extreme hot signal? I’ve looked and I can not find it. Where is the proof that this approach even theoretically works?

DirkH

Reed Coray says:
March 11, 2012 at 9:54 am
“After reading Shollenberger’s Technical Review of Mann’s recent book, I ask myself: How can anyone in the scientific community put any faith whatsoever in the scientific findings of Dr. Michael Mann? The only answer I came up with was: Fear of repurcussions. Does anyone have a different answer?”
Of course. CO2AGW was a grant-sucking fra*d from day one; all that the CO2AGW consensus scientists want is stay in the sweet spot where their dull incompetent made-up papers enjoy undeserved prominency. Mann is useful for this purpose.
In what other scientific field can you sit back in front of a computer simulation, and the moment one of the curves shows some wiggle, write a paper about how concerned you are about that wiggle, get it published presto and add one more reference to your CV?

TFNJ

About 40 years ago the pop group M Mann had a hit with “Ha, Ha, Said the Clown”.
Prescient, or whar?

Here we have a perfect example of someone (Mann) who believes HIS version of the facts as he remembers them and seems to think that everyone else will too. Does it not occur to him that, like any scientist or author, he is required to check his facts before publication, and that if he doesn’t others will. Talk about “when you are in a hole, stop digging”.

jaypan

As welcome as the Hockeystick seemed to be for certain circles, the question arises if it was created by sloppy scientific work or by careful work, based on something like “if you could show that …”.

I too am very glad to read this summary, since the whole MBH controversy was well before I ‘saw the light’ on climate stuff, so the details have rather tended to elude me. Thank you Brandon.

JFD

This was a difficult review to write, so my thanks to the author. This hockey stick question needs to be elevated to a level that pays people to do the work. This treatise provides enough meat to raise serious technical questions about Mann’s et al hockey sticks. At first blush, it seems to me that a set of data tests could be performed to prove/disprove the impact of including the datasets and statistics at issue. I have lost some faith in the National Academy of Science in recent years so cannot suggest that they supervise the work. I do know that Stephen McIntyre should be involved in the supervision.
Perhaps the work should be done in the UK where they have different treatment of technical issues in legal proceedings. The technical experts for the two sides have to agree on the work and interpretation of the results. I have done enough work in recent years on technical, geological, historical and archeological data sets to have real concern about carbon dioxide being the root cause of the global warming seen from about 1978 to 1998. It is time to take the hockey stick problem away from the scientists and give it to the statisticians, geologists and process engineers who work for money, not power and prestige. That probably means involving the lawyers in a court setting.
JFD

Interstellar Bill

This same hand-waving fakery is rampant throughout the entire AGW movement,
for it is totally hollow, founded on a false premise of IR insulation by CO2.
Though CO2 levels are higher, the CO2 window of the Earth’s IR emission is no colder than 30 years ago. In spite of spectroscopic theory, there has been no CO2 forcing and there will be no AGW. Though Earth may have been CO2-sensitive in its geological past, its current sensitivity is very low, whereas its sensitivity to solar influences is high.
This is why they have to fake all their data — CO2 seems literally to be a paper tiger.

John Bills

Lets see how many times Mann’s work is mentioned in AR5………..

Latitude

James Sexton says:
March 11, 2012 at 10:20 am
———————-
100% correct…you can only get temps from splicing actual temps on to the end…. 😉
Also important, trees can’t tell you when that 2 month period was…..was it May/June…because there was a warmer winter, or cold winter started sooner…..or Sept/Oct because it followed a long cold hard winter, or because the following winter started later and was milder………etc

This is starting to look like shooting fish in a barrel. Not much sport to it, but someone’s gotta roll up his sleeves put an end to this misery.
Recommended title for an upcoming Brandon Shollenberger book, The Mannslaughter Diaries or Sticking the Hockey Stick Shtik.

Steve from Rockwood

I wonder how many books he has sold thus far?

Steve (Paris)

What a wonder is a sharp mind at work.

John another

The vegetation being revealed by receding ice in the Antarctic Peninsula, northern Canada and Russia all seem to date back to the MWP (and we are still nowhere near the temp necessary for the reformation of such plant life). We also know that Sweden was able to march it’s army straight to Denmark during the LIA. But of course, the Hockey Stick tells me this simply could not have happened
It would be nice to know the exact temperature during these events but that number would not alter these facts.

Ian

An interesting and detailed review. This should be posted on Amazon, so potential purchasers know what they are actually looking at buying.

GeoLurking

Steve from Rockwood [March 11, 2012 at 10:44 am]
“I wonder how many books he has sold thus far?”
Doesn’t really matter. The books will be gobbled up by a ‘benefactor’ in order to legally shuttle money to him. Then they will either be given away as swag or donated to a library.

Brandon Shollenberger

Reed Coray:

After reading Shollenberger’s Technical Review of Mann’s recent book, I ask myself: How can anyone in the scientific community put any faith whatsoever in the scientific findings of Dr. Michael Mann? The only answer I came up with was: Fear of repurcussions. Does anyone have a different answer?

I think a large part of it is just that people believe the conclusion behind the hockey stick, and thus, they don’t look closely at the things which support it. It’s a common form of confirmation bias.
John Bills:

Lets see how many times Mann’s work is mentioned in AR5………..

When some of the Zero Order Drafts were leaked, I downloaded the section on paleoclimatology. Mann’s original hockey stick was used in one of the graphs. The caption for it included the line:

new reconstructions need to be included, and perhaps MBH99 dropped if considered to be superceded by Mann et al. (2008).

I have no idea what’s in the First Order Draft now, but that line made me expect the worst.

Peter Whale

Brandon thanks for an elucidating essay it tells exactly what has occurred in the hockey stick fiasco, unfortunately you are dealing with serial liars and obfuscation of the first order. Mann’s apologists will never argue the facts but will attack your motives.Mann will not reply because he has no argument.They issue statements and op eds always without discussion. Replication is only ever done with their own team, without disclosure of raw data and method, so that no other person can check the veracity of their conclusions. Just keep arguing the scientific method, once enough scientists,physicists, statisticians and engineers enter the fray the argument will be truly explored.

Brandon may be starting an industry. A title for a compendium of critiques: The One-Legged Mann and the Arse-Kicking Contest. Yes, yes, I can all but see the eye-rolling and hear the groans, but I’m on a roll, baby!

Phil Clarke

Too many unsupported assertions and half truths to list in detail. Here’s just one example of rather selective quotation, from the NAS report:-
“As part of their statistical methods, Mann et al. used a type of principal component analysis that tends to bias the shape of the reconstructions. ”
The next section being carefully ommitted:
“In practice, this method, though not recommended, does not appear to unduly influence reconstructions of hemispheric mean temperature; reconstructions performed without using principal component analysis are qualitatively similar to the original curves presented by Mann et al.
So despite all the noise expended on it, the whole PCA question is moot, as indeed Wahl and Amman and and von Storch et al (2005) demonstrated.
Clearly, Mr Schollenberg is not being entirely candid with his readers.

[SNIP: Yes, it is OT. Please submit to Tips and Notes. -REP]

Good thing for Mann that books don’t have to be peer reviewed before publication!
The Mann’s entire career is founded on shonky stats. He’ll probably convince himself this steaming pile will be a bestseller with some clever way of counting the sales reciepts.

Alan S. Blue

It’s worth noting the work of Mann’s own graduate student Dr Abadneh.
The fundamental, core claim is that a very limited set of trees (those picked by Mann’s methods) are a very heavy fraction of the entire global temperature reconstruction. Since they line up well with instrumental results for 1900-1960, we assume they line up well outside of that period… and continue constructing a reconstruction into the non-instrumental periods.
Dr. Abadneh remeasured some of the exact same trees, as well as a wide swath of other trees in the vicinity. The basic goal was (obviously) to see if the tree series could be brought up to date.
These same trees – which are enshrined as being reasonable predictors of pre-instrumental period temperatures for wide swaths of time – do not line up with current instrumental readings. This is “the decline”.
It is not shocking that there is a proxy that doesn’t agree – Mann’s reconstruction uses (and essentially discards) -hundreds- of proxies that don’t agree. It’s fundamentally a filtering method that discards everything it doesn’t agree with by the hundreds. Plenty of true proxies are probably discarded already for insufficient agreement with the flawed estimated of surface temperature called ‘the instrumental period’.
But these are the crucial trees. And – they don’t agree. So now, over the period of instrumental measurement, you’ve got a proxy that lines up -well- for half … and not at all for half of the period. The ‘not at all’ half is discarded, yet the claim that these same trees have always been good temperature proxies for the pre-instrumental period remains. Somehow.

Hawkwood

Badanov-“Looks like Mann uses a hockey stick like an out of control Detroit Red Wings forward”
Actually looks more like an out of control Toronto Maple Leaf ie. perennial losers

Robert Austin

Wegman called it “decentering”, I recall Steve McIntyre called it “short centering” and Mann calls it “modern centering”. As if centering over the full extent of the record is an out of date concept instead of being the proper statistical technique. What a charlatan! Mann’s centering technique should be properly called “post-modern centering”.

Ian

Phil:
This, however, goes back to the point that Mann’s work, even if it accidentally got the correct answer (and there is lots of other evidence to suggest that it did not), was poorly conducted. That is the relevant point, and there is nothing in your quote that supports the idea that Mann’s work was correctly conducted. Brandon’s review correctly notes that other, similar studies – many using the same, suspect bristlecone pines – arrived at similar conclusions. That is not an endorsement of Mann’s use his novel, hockey-stick forming PCA. Brandon also notes that each of the subsequent papers needs careful examination as well.
In addition, the phrase from NAS – “qualitatively similar” – is deliberately vague and leaves a gap big enough to take a truckload of bristecone pines through. It was the best North could do to salvage something for Mann.
How, indeed, do you deal with North’s later testimony to Congress and his agreement with Wegman?

DirkH

Phil Clarke says:
March 11, 2012 at 11:06 am
“So despite all the noise expended on it, the whole PCA question is moot, as indeed Wahl and Amman and and von Storch et al (2005) demonstrated.”
No, far from it, whatever NAS says. Wahl and Amman of Jesus paper fame?
http://bishophill.squarespace.com/blog/2008/8/11/caspar-and-the-jesus-paper.html
von Storch, German proponent of post-normal science?
Some fine fellows you have selected there.

William Astley

In reply to JFD’s comment:
“JFD says:
March 11, 2012 at 10:38 am
It is time to take the hockey stick problem away from the scientists and give it to the statisticians, geologists and process engineers who work for money, not power and prestige. That probably means involving the lawyers in a court setting.”
I would hope eventually this issue will be settled definitively at a scientific level, rather than in a court.
The paleoclimatic record shows cycles of warming and cooling that correlate changes of cosmogenic isotopes. The cosmogenic isotope changes are known to have been caused by changes to the solar magnetic cycle.
Mann’s paper removed the cycles of warming and cooling to create the hockey stick. Truth is truth. The past cycles and abrupt climate change events occurred for a reason. Mann’s paper only affected people beliefs.
There has been no warming for 17 years. A significant interruption to the solar magnetic cycle is underway. There have been roughly a hundred published papers which try to explain the mechanisms by which solar changes and geomagnetic field changes cause cyclic and abrupt climate change.
Based on the paleoclimatic record the planet is about to cool. One would assume there will be public requests for an explanation as to physical cause when there is cooling.
There are quite obvious cycles of warming and cooling in this graph (See this link figure 3.) which is an analysis of the Greenland Ice sheet core to determine ice sheet temperature over the last 12,000 year. Note the ice sheet temperature warms and cools cyclically. Interesting there is no correlation of the cyclic warming and cooling with CO2 changes and there is no correlation of the temperature changes with changes to ocean currents.
“Fig.3. The upper panel shows the air temperature at the summit of the Greenland Ice Sheet, reconstructed by Alley (2000) from GISP2 ice core data. The time scale shows years before modern time, which is shown at the right hand side of the diagram. The rapid temperature rise to the left indicate the final part of the even more pronounced temperature increase following the last ice age. The temperature scale at the right hand side of the upper panel suggests a very approximate comparison with the global average temperature (see comment below).”
http://www.climate4you.com/
http://arxiv.org/abs/1009.0784v1
Long-term Evolution of Sunspot Magnetic Fields
Independent of the normal solar cycle, a decrease in the sunspot magnetic field strength has been observed using the Zeeman-split 1564.8nm Fe I spectral line at the NSO Kitt Peak McMath-Pierce telescope. Corresponding changes in sunspot brightness and the strength of molecular absorption lines were also seen. This trend was seen to continue in observations of the first sunspots of the new solar Cycle 24, and extrapolating a linear fit to this trend would lead to only half the number of spots in Cycle 24 compared to Cycle 23, and imply virtually no sunspots in Cycle 25.
http://www.hindawi.com/journals/amet/aip/543146.pdf
Solar activity and Svalbard temperatures
The long temperature series at Svalbard (Longyearbyen) show large variations and a positive trend since its start in 1912. During this period solar activity has increased, as indicated by shorter solar cycles. The temperature at Svalbard is negatively correlated with the length of the solar cycle. The strongest negative correlation is found with lags 10–12 years. The relations between the length of a solar cycle and the mean temperature in the following cycle are used to model Svalbard annual mean temperature and seasonal temperature variations.
These models can be applied as forecasting models. We predict an annual mean temperature decrease for Svalbard of 3.5 to 2oC from solar cycle 23 to solar cycle 24 (2009–‐20) and a decrease in the winter temperature of ≈6 oC.
http://www.agu.org/pubs/crossref/2002/2000PA000571.shtml
On the 1470-year pacing of Dansgaard-Oeschger warm events
The oxygen isotope record from the Greenland Ice Sheet Project 2 (GISP2) ice core was reanalyzed in the frequency and time domains. The prominent 1470-year spectral peak, which has been associated with the occurrence of Dansgaard-Oeschger interstadial events, is solely caused by Dansgaard-Oeschger events 5, 6, and 7. This result emphasizes the nonstationary character of the oxygen isotope time series. Nevertheless, a fundamental pacing period of ∼1470 years seems to control the timing of the onset of the Dansgaard-Oeschger events. A trapezoidal time series model is introduced which provides a template for the pacing of the Dansgaard-Oeschger events. Statistical analysis indicates only a ≤3% probability that the number of matches between observed and template-derived onsets of Dansgaard-Oeschger events between 13 and 46 kyr B.P. resulted by chance. During this interval the spacing of the Dansgaard-Oeschger onsets varied by ±20% around the fundamental 1470-year period and multiples thereof. The pacing seems unaffected by variations in the strength of North Atlantic Deep Water formation, suggesting that the thermohaline circulation was not the primary controlling factor of the pacing period.
http://www.agu.org/pubs/crossref/2003/2003GL017115.shtml
Timing of abrupt climate change: A precise clock by Stefan Rahmstorf
Many paleoclimatic data reveal a approx. 1,500 year cyclicity of unknown origin. A crucial question is how stable and regular this cycle is. An analysis of the GISP2 ice core record from Greenland reveals that abrupt climate events appear to be paced by a 1,470-year cycle with a period that is probably stable to within a few percent; with 95% confidence the period is maintained to better than 12% over at least 23 cycles. This highly precise clock points to an origin outside the Earth system; oscillatory modes within the Earth system can be expected to be far more irregular in period.

KnR

Mann’s Hockey Stick work is not a piece of research that is open to challenge and review as would be normal scientific prat ice, but an icon of ‘the cause’ that like all religions icons cannot be challenge nor reviewed. And for Mann its been the passport to fame and fortune , the IPCC adoption of this for its political purposes made Mann and without it his effectively gone. So he has no choice but to defended to his last breath. It that means lying , then so be it .