Kaufman’s grudging acknowledgement (see their draft Corrigendum) that they used the Tiljander proxies upside down has not convinced the Team that the identical orientation of the Tiljander proxies in Mann et al 2008 was also upside down.
There has been an active new round of debate in the blogs, with William Connolley endorsing Upside Down Mann. It seems that we are facing not simply an Upside Down Mann, but an Upside Down Team.
Roger Pielke Jr had opined hopefully that this concession would finally settle at least one small point in paleoclimate. Pielke said that “it looks like this dispute will in fact be resolved unequivocally through the peer-reviewed literature, which for all of its faults, is the media of record for scientific claims and counterclaims”. Pielke was obviously aware of the role of blogs (both Climate Audit and in Finland) in this dispute and was here focusing more on the fact that Kaufman was admitting the upside down use in a formal venue, rather than the role of the journals in extracting the admission from Kaufman. This point was misconstrued by Ben Hale here who interpreted Roger’s post as evidence that the Kaufman error had been detected and resolved by journal peer review and due diligence, when that’s not what happened at all. (I posted a comment at Hale’s to this effect.)
The debate over the relationship of blogs and Peer Reviewed Literature is one that Andy Revkin raised recently as well. And it’s one that’s playing out in a very interesting way in the recent Briffa commentary on Yamal, which, regardless of how this issue plays out, is, in my opinion, a more substantive and interesting bit of work of than any of his recent articles in the Peer Reviewed Literature, because it is accompanied on time by DATA, is technical and makes no effort at faux “originality”. (Obviously much more on this in the next week or two.)
Had matters been left with blogs debating the relative contributions of blogs and Peer Reviewed Literature in the settling of this small point, that would seem like the logical denouement of this sorry little episode.
But this under-estimated the propensity of the Team to engage in prolonged trench warfare on the most elementary and seemingly unwinnable points. A Pielke commenter argued that, under Mann’s methods, the “data can’t be upside-down”, adding that neither Pielke nor I were qualified to engage in such a debate anyway:
“Multivariate regression methods are insensitive to the sign of predictors”. Mann et al seem to be saying their methods are invariant to the data’s orientation – perhaps to linear translation? – anyway it means the data can’t be upside-down. Now if the mathematical interpretation placed on the data by their methods conflict with physical information from other sources, it does raise questions. Presumably the next sentences in Mann et al’s reply l refer to this, I can’t see anything in Kaufman et al that illuminates this and it would seem to require detailed knowledge of the field to judge the importance of these issues. And as you said, we (you, me, Steve McIntyre,…) are not professionally qualified to engage in the substance of such a debate.
Despite the worries of Pielke’s reader as to whether Pielke or I were sufficiently qualified to determine whether a series is going up or going down, I can assure the reader that I have enough experience in the stock market (both painful and otherwise) that I know the difference between whether things are going up or down, and I believe that even readers uninitiated into the mysteries of RegEM are capable of understanding the difference.
This comment at Pielke’s was praised by William Connolley, the Team’s representative at Wikipedia, in a recent post decrying Pielke. Connolley then vigorously supported Upside Down Mann in comments at both Pielke Jr and Ben Hale, where the matter has been discussed relatively briskly.
Mann’s use of the Tiljander sediments was originally discussed here on Oct 2, 2008, a post which discussed the multiple problems with Mann’s use of these proxies, summarized as follows:
In Mann et al 2008, there is a truly remarkable example of opportunistic after-the-fact sign selection, which, in addition, beautifully illustrates the concept of spurious regression, a concept that seems to baffle signal mining paleoclimatologists.
The issue with Mann’s use of the Tiljander proxies isn’t just that he used them upside down (which he did). The problem is worse than that. The Tiljander sediments are the combination of two unrelated processes: a presumably climatically driven process in which narrow sediments are interpreted by the authors as “warm” and thick sediments as “cold” and a nonclimatic process in which sediments are produced by ditches, bridges and farming.
Although the following point is not well understood by climate scientists (including, apparently, Connolley and Mann), a “reconstruction” at the end of the day is a linear combination of the proxies. While Peer Reviewed Literature does not require climate scientists to report these weights, in our dissections of reconstruction methodologies, this is the sort of thing that we keep track of.
Leaving CPS aside for a moment, Mann and his defenders say that, in a multiple regression setting, it doesn’t “matter” what the orientation of the series is going in to the meatgrinder. However, this ignores the relevant issue of what the orientation of the series is coming out of the meatgrinder. Connolley and Mann and others seem to assume that the meatgrinder can’t get it wrong. But this is not the case either in principle or in the particular case of the Tiljander sediments.
By examining the code to keep track of weights (as Jean S, UC and myself have done), it is possible to track the orientation of the Tiljander sediments into the final reconstruction and see whether the contribution of the Tiljander sediments to the reconstruction is inverse to the interpretation of the original authors or not. It is definitely and incontrovertibly upside down.
The reason why it is upside down is the spurious correlation between the nonclimatic sediments from bridges and farming and temperature, which confuses the Mannian meatgrinder algorithm. While I confirmed my understanding of the sediment interpretation by email with Tiljander, this is also clearly reported in the original article (See my original note on this).
As I’ve recounted at CA (most recently here), we reported these and other problems in our PNAS Comment. These comments are limited to 250 words, 5 references and no figures. This is far less detail than available in any blog post. Connolley’s most recent argument is that our PNAS Comment was insufficiently clear.
Perhaps Connolley is gradually realizing that the problem is not just the upside down proxy, but a package of issues including modern contamination and spurious regression. Needless to say, Connolley doesn’t blame Mann for making the errors, but blames me for not expressing these points clearly enough that even a climate scientist could understand them.
If he meant what you said, he could and should have said so.
Quite frankly, I’m baffled at what else I could have said. The issues seem very elementary to me and I don’t understand why they seem to difficult for climate scientists. Let me try one more analogy. As noted above, the Tiljander sediments are in a sense a “compound” of a climatic and nonclimatic process.
Consider a series defined as the difference between the incidence of the name Gavin (which increases strongly in the 20th century) and the Central England temperature (scaled to keep on the same page) and feed this into a Mannian meatgrinder. The Mannian algorithm will detect a strong correlation between the compound series and world temperature during the 20th century. In the “reconstruction” period when the Gavin effect wears off and is at a very low level, the compound series is the inverted temperature (upside down). The spurious regression results in the series being upside down in the reconstruction period.
As I said above, it’s not just that the series is used upside down; there’s a combination of problems, ones that, in my opinion, were fully described in posts on the topic (posts that are easily located merely by googling “Upside Down Mann” and following the links.)
It’s Saturday Night Live (Oct 2, 2008)
When you’re trading in puts and calls (or derivatives), it’s important to know the sign of the relationship between the value of the derivative and the market. Short positions will go up in value as the market goes down. And, unfortunately, you don’t get to decide afterwards whether you wanted to be short or long. Proxies in climate can, in a sense, either be “short” or “long”, in the sense that the values of some proxies (e.g. coral dO18) are said to go down with higher temperatures, while the values of other proxies (e.g. ice core dO18) are said to go up with higher temperatures.
One feels that it is not asking too much of paleoclimatologists to know the expected sign of a proxy derivative. Traders would like to decide on the sign of a proxy derivative after the fact, by taking a correlation to market performance, but this luxury is denied to them, as it should be denied to climate scientists.
In Mann et al 2008, there is a truly remarkable example of opportunistic after-the-fact sign selection, which, in addition, beautifully illustrates the concept of spurious regression, a concept that seems to baffle signal mining paleoclimatologists. For this example, we turn to the highly HS-shaped Finnish sediment series of Tiljander et al 2003.
Tiljander et al cored varved sediments from Lake Korttajarvi, Finland, going back through most of the Holocene. In Tiljander et al 2003, they distinguished the amount of mineral and organic matter in each varve. The basis for using mineral and organic matter as climate proxies is set out as follows:
The amounts of inorganic and organic matter, form the basis of the climate interpretations. Periods rich in organic matter indicate favourable climate conditions, when less snow accumulates in winter by diminished precipitation and/or increased thawing, causing weaker spring flow and formation of a thin mineral layer. In addition, a long growing season thickens the organic matter. More severe climate conditions occur with higher winter precipitation, a longer cold period and rapid melting at spring, shown as thicker mineral matter within a varve.
The caption to their Figure 5 reports the following link between X-ray density and their climate mechanism:
High X-ray density corresponds to high amount of mineral matter (light grey value tints in X-ray film) and low X-ray density corresponds to dark grey values caused by a higher proportion of organic matter.
Putting the two paragraphs together: warmer climate favors more organic material and thus a low X-ray density. In order to show warm values at the top of a graph, you need to invert the plot (i.e. you have to pay attention to the sign of your climate derivative.)
In the figure below, on the left, I show an excerpt from their Figure 5 which they show vertically (only the X-ray density is shown here – consult the original paper for the other plots.) The left portion of their Figure 5 shows an organic-rich period in the MWP, about which they say:
An organic rich period from AD 980 to 1250 in the Lake Korttajarvi record is chronologically comparable with the well-known ‘Medieval Warm Period’ (e.g. Lamb 1965; Grove & Switsur 1994; Broecker 2001). The sediment structure changes, less mineral material accumulates on the lake bottom than at any other time in the 3000 years sequence analysed and the sediment is quite organic rich (LOI ~20%). Thus, the winter snow cover must have been negligible, if it existed at all, and spring floods must have been of considerably lower magnitude than during the instrumental period (since AD 1881). According to the scenarios presented by Solantie & Drebs (2001), a 2°C increase in winter temperature would decrease the amount of snow in southern Finland significantly. Under such conditions, winter snow accumulation and intense spring floods would be rare events….
The Lake Korttajarvi record also indicates a climatically more severe period in the 17th century. Two periods, AD 1580–1630 and AD 1650–1710, are marked by an increase in both sedimentation (varve thickness) and mineral matter accumulation (relative Xray density). Also, magnetic susceptibility values are high between AD 1650 and 1710, indicating increasing mineral matter input into the lake.
They cite literature, including Hulden 2001, showing mild conditions in Finland in the MWP.
On the right, I’ve plotted the corresponding data so that “warm” grey values are on the top. I’ve also highlighted the (MWP) period identified as having elevated values of organic matter. If you squint, you can satisfy yourself that the left-hand and right-hand panels are showing the same data.
Fig. 1. Left from Tiljander et al 2003 Figure 5; right – plot of X-ray density (inverted).
Plotted according to the climatic interpretation offered by Tjilander et al, the modern warm period shows as colder than the Little Ice Age, something which makes no sense if this data is to be used as a climate proxy. Tiljander et al provide a plausible interpretation of the “divergence” of the proxy from its climatic interpretation as a result of agricultural and construction disturbance to sediment patterns, actually tying several especially thick varves to ditch and bridge construction:
This recent increase in thickness is due to the clay-rich varves caused by intensive cultivation in the late 20th century. …
There are two exceptionally thick clay-silt layers caused by man. The thick layer of AD 1930 resulted from peat ditching and forest clearance (information from a local farmer in 1999) and the thick layer of AD 1967 originated due to the rebuilding of the bridge in the vicinity of the lake’s southern corner (information from the Finnish Road Administration).
Now let’s see what Mann et al did with this data. All of the 20th century values of varve thickness, X-ray density etc go up like crazy with the agricultural and construction activities as shown below for 2 of the 4 series (the other two are similar). Instead of using the climatic interpretation of the data described by Tiljander et al, Mann correlates the increases in varve thickness and changes in density and color, originating from local construction and farming, to world climate.
Figure 2. Two of 4 versions used in Mann et al 2008
By flipping the data opposite to the interpretation of Tiljander et al, Mann shows the Little Ice Age in Finland as being warmer than the MWP, 100% opposite to the interpretation of the authors and the paleoclimate evidence. The flipping is done because the increase in varve thickness due to construction and agricultural activities is interpreted by Mann et al as a “nonlocal statistical relationship” or “teleconnection” to world climate. Mann:
the EIV approach, which makes use of nonlocal statistical relationships, allowing temperature changes over distant regions to be effectively represented through their covariance with climatic changes recorded by the network
A more convincing example of spurious regression in “peer reviewed” literature will be hard to find. After reading through this, I keep expecting someone to say:
Live from New York, it’s Saturday Night.
H/t to Howard Wiseman: http://www.youtube.com/watch?v=M1owcncKCHg
TILJANDER, MIA, M. SAARNISTO, AEK OJALA, and T. SAARINEN. 2003. A 3000-year palaeoenvironmental record from annually laminated sediment of Lake Korttajarvi, central Finland. Boreas 32, no. 4: 566-577.