journal resistance to Jim Bouldin’s criticisms of certain methods in dendroclimatology

]]>On looking back at this thread, it appears that the “pith offset” mentioned by Giano on Sept. 30 is the issue I raised on Oct. 8 over on the “Yamal and the divergence Problem” thread, here:

I’m afraid I haven’t kept up with all the comments on every Yamal thread, so please forgive me if this question has already been answered:

How do we know how old the trees are in Briffa’s newly released Yamal data file at http://www.cru.uea.ac.uk/cru/people/melvin/PhilTrans2008/YamalADring.raw?

Each core in the file has a start date and an end date, but do we know the core reached the oldest part of the tree? The person taking the core presumably aimed for the center, but often trees grow lopsided. Even the relatively symmetrical tree round held by Michael Mann in the photo on his webpage has off-center heartwood.

Evidently age is the critical factor in the RCS standardization that is central to much of this discussion. For example, our friend YAD06 had an admittedly hunking 28.70 mm ring in 1993, which is astonishing for any species that is not bamboo! But skimming through the Yamal file, lots of trees had similar rings throughout the past 2000 years. In 1611, during the LIA no less, tree L15581 actually had a 41.30 mm ring!

YAD06’s record went back to 1803, or 190 years before its big ring, while L15581’s went back to 1574, only 37 years before its big ring, so maybe there was an age difference that means we should interpret these growth spurts differently. But how do we know how old L15581 was in 1574 when its record started?

Even if dendros can measure the increasing curvature of the rings as the bottom of the core is approached, and can extrapolate to where the true center would be, where is this estimate recorded in the Briffa file?

Of course, to the extent that these “day in the sun” growth spurts are just due to competing neighbors being taken down by old age or tornadoes, the median age-adjusted ring size must be a more representative indicator of local climate than the mean, provided the sample size is large enough to be representative.

So do we know the “pith offset” for the new Briffa Yamal data? Is it safe to assume that Briffa would have just set these to 0 for each tree? Any common pith offset would just change the cofficients, but leave the anomalies the same, so this only makes a difference if different trees might have different offsets.

If Briffa did use non-zero offsets, but didn’t include these in his file, he still hasn’t complied with TRSB’s requirement that he make his data available.

]]>]]>I was hoping to find a similar exposition for RCS in R.

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With PCA, you can determine an effective weight of an individual input pretty directly.

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Can something similar be done with RCS? Or is it meaningless?

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Reconstructing PCA was outlined in detail, and I was hoping to find a similar exposition for RCS in R. ]]>

Can someone who is hitting this thread say hello and comment on their interest?

]]>I havent had much success with it, but maybe you will have more luck!

It can be found at: http://web.utk.edu/~grissino/software.htm ]]>

It seems that with RCS the initial estimate of the date function is unity and this is used to give an estimate of the age function which in turn yields an estimate of the date function.

Why stop there. You now have a better estimate of the date function to use to get a better estimate of the age function.

Try forgetting everything you know about the way trees grow (not difficult in my case) and just let the data pick both functions for you.

This would be indicated whenever you have “sensitive” trees as the initial assumption that the date function is unity is going to be more troublesome than for non “sensitive” trees.

I have given it a go for about the first twenty trees in the Yamal archive and the iteration is stable and converging and gives results similar but not quite the same as Steve’s resuls above.

Alex

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