I thought I'd set down my thoughts on one aspect of Eric Wolff's email to Neil Craig - namely the millennial temperature reconstructions. Eric has adopted what I called the "NAS defence" when I discussed it in the Hockey Stick Illusion. This is the idea that, whatever the failings of the Hockey Stick itself, a series of other temperature reconstructions have reached broadly the same conclusions - Mann may have used in appropriate data and a biased methodology but he still reached the correct conclusions.
Suffice it to say that I find this highly unsatisfactory.
In the spirit of Eric's "what we agree on" approach, I would have thought that we should be able to agree:
- that bristlecone pines and their ilk should not be used for temperature reconstructions
- that Mannian "short-centred" principal components analysis is biased.
These were the conclusions of the NAS panel (and Wegman too), so it is hard to see that there can be much argument on this score.
Can we agree that this is not a thermometer?If we can agree this, then I would hope that we can also agree that temperature reconstructions that feature either bristlecones or short-centred PCA cannot be cited as support for the idea that current temperatures are unprecedented.
I realise that this is not Eric's area and that he is probably therefore repeating the received wisdom - the IPCC line if you like - but it seems very clear to me that the IPCC line is insupportable on this count. I would have hoped that this area was somewhere where a measure of agreement could be reached.