Then I guess I just disagree with you. Scientists’ belief about the temperature pattern (P1) from 1850 to the present isn’t based on proxies—it’s based on measurements of the temperature which are much more reliable than any proxy. The best Bayesian estimate of the temperature since 1850 gives almost all of the weight to the measurements and very little weight to any other source of evidence (that is especially true over the past 50 years when measurements have been more rigorous, and that is the time period when P1 and P2 differ).
The tree ring proxy was filtered based on its agreement with the temperature measurements, and then used to estimate temperatures prior to 1850, when we don’t have measurements. If you want to think of it as substantiating something, it helped confirm the estimates made with other proxy data sets (other tree rings, ice cores, etc.), and it was not filtered based on its agreement with those other proxies. So I don’t think that the research has the kind of obvious flaw that you’re describing here.
I do think that the divergence problem raises questions which I haven’t seen answered adequately, but I’ve assumed that those questions were dealt with in the climate literature. The biggest issue I have is with using the tree ring proxy to support the claim that the temperatures of the past few decades are unprecedented (in the context of the past 1500 years or so) when that proxy hasn’t tracked the high temperatures over the past few decades. I thought you might have been referring to that with your “further substantiation” comment, and that either you knew enough about the literature to correct my mistaken assumption that it dealt with this problem, or you were overclaiming by that nobody in the field was concerned about this and we could at least get glimpses of the literature that dealt with it. (And I have gotten those glimpses over the past couple days—Wikipedia cites a paper that raises the possibility that tree rings don’t track temperatures above a certain threshold, and the paper I linked shows that they are trying to use proxies that don’t diverge.)
Then I guess I just disagree with you. Scientists’ belief about the temperature pattern (P1) from 1850 to the present isn’t based on proxies—it’s based on measurements of the temperature which are much more reliable than any proxy. The best Bayesian estimate of the temperature since 1850 gives almost all of the weight to the measurements and very little weight to any other source of evidence (that is especially true over the past 50 years when measurements have been more rigorous, and that is the time period when P1 and P2 differ).
The tree ring proxy was filtered based on its agreement with the temperature measurements, and then used to estimate temperatures prior to 1850, when we don’t have measurements. If you want to think of it as substantiating something, it helped confirm the estimates made with other proxy data sets (other tree rings, ice cores, etc.), and it was not filtered based on its agreement with those other proxies. So I don’t think that the research has the kind of obvious flaw that you’re describing here.
I do think that the divergence problem raises questions which I haven’t seen answered adequately, but I’ve assumed that those questions were dealt with in the climate literature. The biggest issue I have is with using the tree ring proxy to support the claim that the temperatures of the past few decades are unprecedented (in the context of the past 1500 years or so) when that proxy hasn’t tracked the high temperatures over the past few decades. I thought you might have been referring to that with your “further substantiation” comment, and that either you knew enough about the literature to correct my mistaken assumption that it dealt with this problem, or you were overclaiming by that nobody in the field was concerned about this and we could at least get glimpses of the literature that dealt with it. (And I have gotten those glimpses over the past couple days—Wikipedia cites a paper that raises the possibility that tree rings don’t track temperatures above a certain threshold, and the paper I linked shows that they are trying to use proxies that don’t diverge.)