Obviously there’s been a lot of discussion in the last few days about the difference between the CRU 12 and the Schweingruber 34. In making such comparisons, it’s always a good idea to look at the data in detail – something that obviously should have been done by Briffa and the Team before the widespread use of the Yamal proxy in so many reconstructions, rather than this late date, over 9 years since its original use in Briffa 2000.
In a previous thread, I showed a plot of the actual ring widths of the 10 CRU trees ending in 1990. Today I’m going to show a similar plot of the “dimensionless index” for the same 10 trees. It is the “dimensionless index” that is averaged to make the “chronology”.
Recall that in RCS, a “standard” is established for the decline in ring width with age – the decline is assumed to be a negative exponential curve plus a constant (“generalized negative exponential”) and the index is the observed ring width divided by the “age standard” ring width for the age of the given tree in that year.
For comparison, I’m going to do a similar plot for 18 Schweingruber trees (17 sampled in 1990 plus one). The plots are shown on a uniform vertical scale (0,9) and a uniform horizontal scale (1850,2000). I’ve marked 1990 with a vertical red line and a horizontal line at 1 (the overall mean ratio.)
First, here is the plot for the 18 Schweingruber trees. Probably your first reaction is: why did he choose such a squished vertical scale for this graphic – we can’t see this as clearly as we’d like. Your second reaction is probably – well, if there’s a stick in there, it would take something like Mannian principal components to dig it out.
Next here is the corresponding plot for the CRU 10. Without doing any sort of fancy statistical test, one can readily see a difference. None of the YAD** trees on the right are especially old – the graph shows their full history – all start after AD1800. However, instead of the standard negative exponential declining growth, these particular trees started off very slowly, like old trees, and then got a burst of virility when they got to be 100 years old. Benjamin Button trees so to speak. Because of the one size fits all RCS standardization, this post-100 growth pulse is divided by a small standard denominator – YAD06 reaches 8 sigma and is the most influential tree in the world. YAD06 does not always drink beer, but when it does, it drinks Dos Equis. Stay thirsty, my friends.
UPDATE: Oct 1. Tom P in a comment below asserts:
These plots explain why it would be extremely difficult to extract a centennial signal from the live cores of Schweingruber series. Most are under 100 years old! The Schweingruber series is therefore of very limited utility for a valid comparison with the much longer-lived trees of the CRU archive. Your earlier sensitivity test is comparing a signal to noise.
I agree 100% that it “would be extremely difficult to extract a centennial signal” when “most [of the cores] are under 100 years!”. However, I disagree that the trees in the CRU archive are “much longer-lived”, other than the trees selected for the modern comparison. The following graphic shows the average of tree by year in the CRU archive, the average age in the “Schweingruber variation” in which russ035w is used instead of the CRU12 to represent living cores. Prior to around 1800, the average age of the tree in a given year was around the 100-year mark that Tom complains about. There is a profound inhomogeneity in the age composition of the living trees in the CRU archive relative to the subfossil archive, which is much reduced in the Schweingruber Variation. Does the age inhomogeneity in the CRU version “matter”? It’s the sort of thing that should have been reported and discussed in a site report, prior to using this chronology in multiproxy studies.