One point that Wahl and Ammann and ourselves agree on, but which Juckes appears to contest, is that principal components methodologies applied to AD1400 MBH98 networks result in upweighting or downweighting of bristlecones. Their Scenario 6 shows reconstruction results without bristlecones for covariance, correlation and Mannian PCs. I have no dispute with these calculations although I would characterize the situation differently.
The Figure below shows results for the key cases for WA Scenario 6 (no bristlecones) as compared to their Scenario 5. Understanding this graphic goes a long way towards understanding the oceans of words on this topic. Pink shows results with 2 covariance PCs; red with Mannian PCs; blue – 2 correlation PCs and 5 covariance PCs; orange – Mann’s unreplicated archived results, which are lower in the 15th century than any replication.
The left graphic is identical to what was either illustrated or discussed in MM05(EE); I have no major disagreement with the calculations in WA Scenario 5 – only with their failure to acknowledge that their results were equivalent to the MM05 (EE) results. Wahl and Ammann Scenario 6 – without bristlecones – yields results that are essentially equivalent to results with 2 covariance PCs in the left panel (what people call the “MM” results, though they are really just MBH with lower bristlecone weight.) If there are no bristlecones in the network (as in the right panel), then the different standardization procedures don’t “matter”. But the methodology makes a difference to the final reconstruction if bristlecones are in the system.
This diagram also illustrates rather clearly the lack of substance to Juckes’ complaint that using 2 covariance PCs “effectively eliminates” much of the data. This is not correct. The results using 2 covariance PCs are essentially identical to results without bristlecones. It is simply false that “much” of the data is “effectively eliminated” using 2 covariance PCs. The only data whose downweighting is material are the bristlecones.
Figure 1. MBH98-style NH Temperature Reconstructions. Left – WA Scenario 5 as previously described. Right – WA Scenario 6 with bristlecone series excluded. Orange – MBH98 for reference. Red – with two Mannian PCs; magenta – with 2 covariance PCs; blue – one graph with 2 correlation PCs; one graph with 5 covariance PCs. All smoothed with 21-year gaussian filter. wahl.c11.gif
This direct connection between bristlecones and PC methodology (mentioned in MM05 articles) was acknowledged by Wahl and Ammann as follows:
Restricting the PCs in MM05a/b to only the first two (5d) indirectly omits the information carried by the bristlecone/foxtail pine records and thereby leads to a non-meaningful reconstruction. (33)
Now Ross and I categorically agree with Wahl and Ammann that an MBH-style reconstruction without bristlecones is non-meaningful. Our point of difference is that we assert that an MBH98-style reconstruction with bristlecones is also non-meaningful. This is a different issue than whether the 15th century values of the reconstruction are higher than 20th century values.
If the reconstruction isn’t meaningful, it doesn’t matter whether the 15th century portion is higher or lower than the 20th century. (However, if it is higher using Mannian methods, then that is a rather neat refutation of the claim that 20th century uniqueness has been established with Mannian data and methods – regardless of whether the reconstruction is meaningful or not. This logic is a nuance of our approach that many controversialists lose sight of.)
In my recent European presentations (including at KNMi to Mitrie coauthor Nanne Weber), I summarized our position post-NAS panel and post-Wahl and Ammann as follows:
1) Wahl and Ammann and ourselves agree that an MBH98-type reconstruction without bristlecones is non-meaningful.
2) the NAS panel agreed that strip-bark sites (which include all the relevant bristlecone, foxtail and even a couple of limber pine sites) should be avoided in temperature reconstructions for a variety of reasons.
I see no remaining wiggle room for MBH supporters. However rather than squarely facing up to the bristlecone problem, Juckes simply avoided any discussion of the impact of bristlecones, even though this was squarely in the middle of the agenda, both as a result of our work and even of Wahl and Ammann. Instead, as we’ve seen here, Juckes reverted to realclimate code words, “effective elimination of much of the data”, rather than careful analysis distinguishing between bristlecones and everything else.