We’ve all been looking at the Yamal (Steve Mosher named)treemometer ring width data. Yamal is a tree ring series with a huge hockey stick blade used in and likely to be highly influential in a lot of serious studies which demonstrate the unprecedentedness of recent temperatures. When Steve McIntyre replaced 12 of the hockey stick creating proxies (the dirty dozen) with equally valid schweingruber proxies the blade of the hockey stick disappears along with the unprecedentedness. Of course the boys at “Real” Climate made a big stink about it but notably missed any specific criticism of the methods or data chosen. However, in this post I looked at the methods of RCS standardization and the effects it has on the series.

RCS is a method for correcting the ring widths of trees based on the age. For instance, we would expect that a young tree would have thicker rings at its core. As it grew thinner rings would form with diameter and eventually the diameter would become basically a non-factor. So dendro guys figure that they should fit an exponential decay function to tree rings and that will give a basic correction factor for total width.

The function is of the form

correction = A + B * e ^ -(C * age)

Don’t worry too much if that’s not a familiar equation to you, you’ll figure it out either way. I’m sure it is to many of my readers though. This equation is fit to 100% of the data simultaneously in Yamal. The assumption is:

1 – All the trees in the same conditions grow at the same rates.

2 – Fitting the equation to all trees together will average out over all the variable climates and despite different conditions, we can achieve a similar result to #1.

There is a problem with these assumptions which occurs at the endpoints of dendroclimatology reconstructions in that the most recent trees are still alive and therefore on average going to have a skewed age – either younger because they are equal and haven’t died or older (as is the case here) because trees that are long lived are easier to find than partially fossilized mud bound trees.

What it means is that the assumption fails for trees existing in vastly different conditions.

Now what I wanted to see was first, what is the correction factor per year used and second how different is the correction factor when fit to the dirty dozen. After all, tree age, location, group and other conditions affect trees dramatically. So my question was – If we had only the 12 Yamal trees, how would the correction factor look.

Figure 1 - Correction factors

The dozen trees fit to the same function have a very different result when run alone – these trees are different! Now climatology in general may be tempted to call this plot bunk because these trees are chosen in a timeframe where we should see hockey stick temperatures and we have too few samples. However, I would remind climatology that these were the same 12 trees used to create the MASSIVE blade on a 200 plus core study.

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