from the latest CA article on PAGES2K-
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Discussion
Because of the heavy weighting of Kaufman et al 2009 proxies, the McKay and Kaufman conclusion that the “decadal-scale variability in the revised [PAGES2K] reconstruction is quite similar to that determined by Kaufman et al.” is, as advertised above, more of a tautology rather evidence of robustness of the result in the additional data.
At the end of the day, any proxy reconstruction is either a linear combination of the underlying proxies (or can be closely approximated by such a linear combination.) Over the years, I’ve consistently urged that the effective weights be shown for novel methods. Had this been done, I doubt that the above weights would have been the result, since it’s hard to believe that the Arctic2K authors intentionally adopted the above weights. Jean S has done some experiments and there are definitely alternative weighting schemes that can result from slightly varied implementations of paico.
As CA readers are aware,
I remain dubious that material benefits arise from putting relatively simple datasets into increasingly complicated and poorly understood multivariate methods and remain of the opinion that there are better opportunities for improving analysis by first comparing like proxies across regions and comparisons of unlike proxies within a region, prior to venturing into the assimilation of unlike proxies in different regions. But this recommendation has been mostly rejected by specialists in the field, who remain committed to dumping data into black boxes, but who get huffy when resulting defects are criticized.
Finally nearly all the difference between the PAGES2K-2013 and the revised result arises from a single proxy (Hvitarvatn, used upside down in the earlier version.)
Some readers have expressed surprise at the idea that specialists could use proxies upside down, observing that their interpretation as temperature proxies must be very tenuous if even specialists didn’t know which way was up. Particularly in a multi-author Nature article, subsequently relied upon by IPCC. I agree with this and have written numerous articles critical of
varvology, proxies that have become widely used in post-AR4 multiproxy studies. I think that there may well be usable information in this data, but as long as thick varves are interpreted by some specialists as evidence of cold and by other specialists as evidence of warmth, the first order of business for assessment is to reconcile varve thickness data before dumping the data into a multiproxy composite, rather than after.
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The Kaufman Tautology Climate Audit
yet crick and his ilk believe fully, believe deeply, that reconstructions are not only correct but precise.
