We keeping hearing the incantation from the Team that all the reconstructions on the Jesuit Index show a warmer modern than medieval period. I reported that I recently obtained a digital version of Grudd’s revised Tornetrask reconstruction and I’ve been anxious to test out its impact on the Jones et al 1998 reconstruction (together with the impact of the Polar Urals update.) I’d experimented a little with this previously using my own unwinding of Briffa’s “adjusting” of the Tornetrask series, but this analysis is obviously much stronger using Grudd’s version.
In doing so, I took the opportunity to re-visit and tidy my emulation of the Jones 1998 reconstruction methodology, which includes an implementation of the “variance adjustment” procedure of Briffa and Osborn (Dendrochronologia 1999), the eminent statistical successors of Sir Ronald Fisher (J Royal Statistical Society). Previously, I’d been able to directionally replicate these results – most of the series overlapped with MBH and I used the MBH versions in my emulation where available. However the replication was not nearly as precisely as I wanted; I asked Jones for a copy of the data as used (which was never archived) in order to try to reconcile results. Jones (“we have 25 years invested in this”) refused.
I caught a little break when Juckes et al was published. Although Jones had refused to provide me with the data as used in Jones et al 1998, it turned out that he was willing to provide the data as used to other Team members (though not to potential critics.) When Juckes archived his data, I noticed that the version of the Greenland dO18 data was different than the MBH version and so I was also interested in seeing the impact of changing these versions on my replication.
If you’ll bear with me, I want to document a couple of these points, before showing the impact of the new series versions. The black series in the top panel shows the difference between the archived reconstruction and my emulation. As you see, the early portion is pretty much bang on up to rounding, while the later portion isn’t bad, but the change in variance indicates that I’ve probably introduced the wrong version of one of the series. Looking closely, the change in amplitude occurs around 1659, when the Central England series (MBH annual version) was introduced.
As some of you may recall, the Central England version was an issue in MM03 and the MBH Corrigendum, as it turned out that, instead of using annual data as they had said in their original SI, they used a summer version starting in 1730, previously used in Bradley and Jones 1993 (though the truncation was also unreported there.) I substituted the MBH truncated JJA version and re-ran with the results shown below, this time matching before 1659 and after 1750. My guess is that there is another version of this data around somewhere, probably a summer version which coincides with the MBH version after 1730, and starts in 1659, suggesting that the explanation of the inconsistency in the Corrigendum was itself incorrect. The reconciliation is now pretty good in any event.
I then made two updates to this data set: 1) replacing the Briffa version of Tornetrask, where, as discussed elsewhere, Briffa bodily adjusted the 20th century results to match his expectations; 2) using the updated Polar Urals chronology from Esper et al 2002. Using the same methodology, this yields the following result. (I have not substituted the Yamal series for Polar Urals, as Briffa did, as I am unaware of any report showing any defects in the Polar Urals update. While the Team didn’t like the results, in my opinion, that is insufficient reason to withhold the results.)