Posted by Ari Jokimäki on June 28, 2010
Note (September 8, 2016): The article below contains some false statements. I have overlined the false parts. See the discussion below for further information.
Arthur Smith wrote about the Mann/Tiljander issue. For months I have had a draft about this issue waiting for me to finish and publish it. As Arthur Smith asks comments on this issue and as I do seem to have something relevant to say on this issue, it is time for me to finish this thing.
Mann et al. (2008, from hereafter I will call this paper “MEA”, proper references with links are given at the end of this article) used Lake Korttajärvi dataseries from Tiljander et al. (2003, from hereafter “TEA”) as temperature proxies in their reconstruction. There has been lot of different claims about Tiljander series being upside-down in MEA. McIntyre & McKitrick (2009, from hereafter “M&M”) wrote a comment to PNAS on MEA and on the Tiljander issue they said:
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),…
To this, Mann et al. (2009) responded:
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.
McIntyre has also presented some claims relating to this before in his website. Here’s to my knowledge the first of his posts on the issue, saying:
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.
Is the TEA data upside-down in MEA?
One of the four dataseries in TEA is the relative X-ray density. This dataseries is presented in TEA Figure 5. MEA presents it (among some other proxies) in their Supporting Information Figure S9. Mann website has the data and the codes for their reconstruction available. The relative X-ray density dataseries is there in the “data” section as tiljander_2003_xraydenseave.ppd. I have made a graph out of this data presented in Figure 1. It is easy to see by comparing the values in X-axis and Y-axis to those in TEA Figure 5 that the data is in the ppd-file exactly same way as it is presented in TEA.
Now that it is established that the data in MEA input (in the ppd-file) is in same way as in TEA, I shall now look at the reconstruction codes a little. The ppd-file is read among other proxy files and written to a data-matrix. TEA data is not handled in any special way compared to other proxies before it is entered to the matrix, so TEA data is not turned upside-down at this stage.
Data is then read from the data-matrix to perform the reconstruction (there are several steps involved in this but it is not important here). There’s nothing special done on TEA data at this point either compared to other proxies, so the data seems to stay the same way throughout the reconstruction. So, the Tiljander data clearly is not flipped upside-down there.
That doesn’t mean the Tiljander data is handled correctly there. Tiljander data is actually handled upside-down there. It is because the data is given in TEA so that higher values of relative X-ray density correspond to lower temperature values, so MEA should have turned the data upside-down before using it in their analysis. Seeing the real situation with this issue, it seems that MEA did an honest mistake, which of course should be corrected. There has been some claims that MEA would have done this deliberately, and/or that they have refused to correct the mistake. I don’t see any proof here that they would have done it deliberately. The thing about correcting the mistake has more to do with M&M description of the situation than MEA attitude, in my opinion. The way M&M descibed this problem is bizarre, just like Mann et al. (2009) put it. M&M comment to me seems so misleading that I don’t see how it could be considered as informing the situation to MEA.
Are McIntyre’s claims about the issue correct?
Looking at McIntyre’s claims on this and the real situation descibed above shows that McIntyre’s claims are false. Just look at the graphs McIntyre presented. In all graphs there the values in X- and Y-axes give matching values, and yet McIntyre shows them as they would show the mistake. The graphs he presents just show how the data is in the TEA and in the input of the MEA reconstruction so basically those graphs just show that MEA have not flipped the data upside-down before feeding it to their analysis, which is exactly the opposite that McIntyre claims to be the case. He claims that MEA have flipped the data, while in real world the problem is that they haven’t flipped the data.
McIntyre’s role in this is very strange. Even when the basic claim is correct, i.e. the claim that the data is used upside-down in MEA, McIntyre still cannot make correct claims about it. It makes one wonder. If a person is aware of this problem, then why make false claims about it?
Mann, Michael E., Zhihua Zhang, Malcolm K. Hughes, Raymond S. Bradley, Sonya K. Miller, Scott Rutherford, and Fenbiao Ni, PNAS September 9, 2008 vol. 105 no. 36 13252-13257, doi: 10.1073/pnas.0805721105. [abstract, full text, supporting information]
Mann, Michael E., Raymond S. Bradley and Malcolm K. Hughes, Reply to McIntyre and McKitrick: Proxy-based temperature reconstructions are robust, PNAS February 10, 2009 vol. 106 no. 6 E11, doi: 10.1073/pnas.0812936106. [Full text]
McIntyre, Stephen, and Ross McKitrick, PNAS February 10, 2009 vol. 106 no. 6 E10, doi: 10.1073/pnas.0812509106. [Full text]
Tiljander, Mia, Matti Saarnisto, Antti Ojala, Timo Saarinen, A 3000-year palaeoenvironmental record from annually laminated sediment of Lake Korttajärvi, central Finland, Boreas, Volume 32, Number 4, December 2003 , pp. 566-577(12). [abstract, full text]
Appendix – Tiljander relative X-ray density against local temperature
UPDATE (June 29, 2010): I decided to add this section as there’s a question relating to this by AMac in the comment section.
I have also looked at the relative X-ray density series of TEA against the local temperature record. The closest temperature measurement site in GISS database is Jyväskylä (which is quite close to the Lake Korttajärvi – about 10 km). Here’s the link to the GISS-data of the Jyväskylä temperature measurements. Jyväskylä temperature series start only from 1950, so there’s not much overlap between the two series. I inverted the Tiljander series and plotted the two in the same graph. Here’s the result:
The linear correlation between the two series is only about -0.12, so the relative X-ray density is not very good temperature proxy. It is, however, interesting to see that this series (when inverted) tracks temperature somewhat even if there were strong human influence to 20th century part of the series (according to TEA).