> Especially troubling is the way the current divergence is addressed. The argument looks to me like "we can use this data as a proxy for all periods except those where we have direct measurements to verify correlation" I find that weak at best.
+1
Yes, I know that "+1" a weak comment. But I wanted to draw attention to this particular point because I think it's really crucial, and so far I have not seen it well addressed.
Let's assume you have a sample from trees in one forest in say, Siberia, going back five thousand years. Do you know all of the environmental factors and how they've changed over that time period? Or do you just know how well the trees grew?
Assuming somehow you did know all of the environmental factors. Can you say with certainty how each of them affected ring width? Or are you relying on some sort of statistical correlation (which may be useful, but is NOT the same as causation)?
Let's assume that you know the micro-climate details and have established a very strong correlation between input factors and ring growth. With multiple or hundreds of factors I find that hard to swallow but let's say you did it. Now tell me, how many forests just like that do you need to sample to have some overall picture of global climate? Ten? A hundred? Does the data even exist in the numbers required? And how would you calculate the number required? It seems to me in order to be able to determine sample size you'd have to have a pretty good model of how the climate operated to begin with. And since this is the thing to be demonstrated, you can't also have this as a given -- that's circular logic.
As I understand the response to this, it relies heavily on statistical measurements and such. That's all fine and dandy, but it's a qualitatively different type of discussion than a theory-experiment-verify discussion. It's much more like a epidemiological study. And these are notorious for meaning much different things than researchers want them to. When all's said and done the only thing you may be proving is the statistical likelihood that certain trees will grow certain ways over the next few decades. Or you may have spent a lot of time proving or demonstrating nothing of any value at all, unfortunately.
+1
Yes, I know that "+1" a weak comment. But I wanted to draw attention to this particular point because I think it's really crucial, and so far I have not seen it well addressed.