dendro matching

thefordprefect:
September 29th, 2009 at 7:55 pm
Can I see if I have this correct?

1. We have a number of tree ring samples from different areas
2. Briffa has selected only rings that match valid local temperature records.
3. Briffa assumes that these trees stay in sync with temperature to an early time in their life.
4. Briffa matches older dead(?) trees to those that match local temperatures and says that these must therefore also be in sync with local temp.
5. repeat 4. and until tree rings are available at the required earliest age.
6. Statistics does not allow matching of tree ring temperature proxy to real temperature because this is cherry picking and will always produce a hockey stick

I agree that extending backwards from multiple overlapped records must produce greater deviations from reality.
I agree that a single tree ring record can deviate once away from the matched record.

However, thinking as an engineer trying to find an accurate reading of for example a time series of a voltage supply to a building monitored with inaccurate chart recorders over various lengths of cable (= added noise). if one recorder is known to have been calibrated (to national standards) over recent part of that record, then I would look at the other recorders over this calibrated period and throw out all the outlier readings (they are wrong now, and I do not know if they were ever correct so there is no reason to include them in my determination. Some of the more accurate recorders may have read high before the calibrated range and some may have read low. Some will be recording significant noise compared to the majority and so these could be ignored if sufficient others remain to determine this fact. I would then average the remainder and suggest that this average record is the most likely record of voltage.
As a statistician are you suggesting that all recorder outputs should be averaged including those reading zero and those reading full scale and those whose readings deviate grossly from the mean.
This seems wrong and certainly will give a invalid result. Am I wrong?

But then we need to look at the tree sampling.
Were the trees sampled totally at random - trees in water, trees in bogs, trees scraping by on a solid rock, trees near to death, young trees etc?
Were they at the tree line or sea level?
Were they all the same "make"?
Etc.

I would suggest that the actual sampling was not random. Altitude, health, species, etc. are all non randomly chosen (cherry picked)

If this is the case what is the point suggesting that they should not be further chosen to best represent temperature? what would be the point for example choosing a tree that fell over during its life but continued to grow with diminished root function? What would be the point in chosing a tree with growth limited by water/nutrients. What would be the point in including a tree 100skm further north than the rest? Would your statistical methods require that these be included in the sequence?


Steve McIntyre:
September 29th, 2009 at 9:28 pm
Re: thefordprefect (#244),

Some of your premises are not yet demonstrated. There are a couple of different levels of consolidation: at a "site", multiple cores are taken, usually within fairly close proximity to one another. These are composited into a "site chronology". Briffa unusually composites samples from areas not at all close to one another in Avam-Taimyr and Tornetrask-Finland. At Yamal, for some reason, he has not composited samples from Polar Urals, which is closer to Yamal than Avam is to Taimyr.

2. Briffa has selected only rings that match valid local temperature records.
[There are two issues: selection of trees at a site e.g. Yamal and selection of sites, e.g. Avam and a nearby Schweingruber site into Taimyr. The procedures are not described. It is not known how Yamal core selection decisions were made and which were made before CRU and which at CRU].

3. Briffa assumes that these trees stay in sync with temperature to an early time in their life.
[Not necessarily. WE don't know what was done. It is possible that trees with elevated growth rates were preferentially selected, but we don't know that for sure.]

4. Briffa matches older dead(?) trees to those that match local temperatures and says that these must therefore also be in sync with local temp.
[ no. crossdating is done by pattern matching.]

5. repeat 4. and until tree rings are available at the required earliest age.
6. Statistics does not allow matching of tree ring temperature proxy to real temperature because this is cherry picking and will always produce a hockey stick.
[this is a different issue.]

FP, I don't have time to provide personal education to everyone trying to get up to speed. I've asked people who don't have specialist viewpoints to comment on Unthreaded.