Steve McIntyre digs into more proxy hijinx from the usual suspects. This is a pretty good summary of what he tends to find, time and again in these studies:
The problem with these sorts of studies is that no class of proxy (tree ring, ice core isotopes) is unambiguously correlated to temperature and, over and over again, authors pick proxies that confirm their bias and discard proxies that do not. This problem is exacerbated by author pre-knowledge of what individual proxies look like, leading to biased selection of certain proxies over and over again into these sorts of studies.
The temperature proxy world seems to have developed into a mono-culture, with the same 10 guys creating new studies, doing peer review, and leading IPCC sub-groups. The most interesting issue McIntyre raises is that this new study again uses proxy’s “upside down.” I explained this issue more here and here, but a summary is:
Scientists are trying to reconstruct past climate variables like temperature and precipitation from proxies such as tree rings. They begin with a relationship they believe exists based on a physical understanding of a particular system – ie, for tree rings, trees grow faster when its warm so tree rings are wider in warm years. But as they manipulate the data over and over in their computers, they start to lose touch with this physical reality.
…. in one temperature reconstruction, scientists have changed the relationship opportunistically between the proxy and temperature, reversing their physical understanding of the process and how similar proxies are handled in the same study, all in order to get the result they want to get.