“Bring the proxies up to date” was the title of one of my earliest posts. Michael Mann had explained that doing so required the use of heavy equipment (like tree ring borers) and travel to out-of-the way sites such as Bishop, California or even Niwot Ridge, a full 45 minute drive from UCAR world headquarters in Boulder CO. As a result, Mann explained that few proxies were available after 1980 and it was therefore necessary to keep using bristlecone and other series ending in 1980 or so. [See next post in sequence.]
Obviously, given the warm temperatures in the 1990s and 2000s, up-to-date proxies reaching 1998 and later offer an ideal opportunity to test the validity of tree ring proxies out-of-sample. I’ve done a quick calculation of contributions to the North American tree ring data base at WDCP; I counted no fewer than 250 sites where there is data for 1998 or later.
The species with the most new sites is Douglas fir (PSME); there are also many new white spruce (PCGL) site – a species held to be a temperature proxy. There are 48 sites where new measurements have been archived, many due to the work of the Jacoby group in Alaska and northern Canada. Jacoby’s archiving is frustratingly incomplete however. Also presumably to be annoying, virtually none of the Jacoby chronologies are archived with the measurements. (This is the opposite of Briffa for Yamal, Taymir and the Tornetrask update, where the RCS chronologies are archived, but not the underlying measurement data.) The Team never makes it easy. In the new data, there are no bristlecone (PILO, PIAR) or foxtail (PIBA) sites with archived data for 1998 and later, although we know that Hughes carried out measurements at Sheep Mountain in 2002. (One of my standing predictions is that Sheep Mountain bristlecone ring widths did not go off the charts during the warm 1990s.)
Even without any Jacoby chronologies, there are still 14 PCGL chronologies reaching 1998 or later. The figure below shows the average of chronologies (the average of available chronologies.) I have trouble discerning a HS in this average. (I didn’t use Mannian principal components.)
Figure 1. Average of 14 North American PCGL chronologies
If the proxy hypothesis is that PCGL ring widths increase with increasing temperatures, I would say that these non-Jacoby chronologies are evidence against the hypothesis. Indeed, one might even be inclined to say that the average of these 14 chronologies is inversely related to temperature, as ring widths were low in the warm period in the late 1930s and increased to higher levels in the mid-1960s when temperatures were supposedly cooling.
Update: Rob Wilson and Mike Pisaric have observed that the Meko white spruce chronologies in northern Alberta are considered to be precipitation proxies rather than temperature proxies and argued that this post is “flawed!” In fairness, everything in this post is expressed conditionally: “if the proxy hypothesis is that PCGL ring widths increase with increasing temperatures”, then these particular updated chronologies are not evidence for that proposition. If they are not believed to be temperature proxies, then they are likewise not evidence for the proposition either. The logic may be a little subtle for a climatologist. I am quite prepared to accept their opinion that the white spruce chronologies from northern Alberta are not temperature proxies. However, as I point out in some subsequent point, applying the same logic requires dendroclimatologists to take a stand against some of the proxies used in multiproxy studies.
Update2: Discussion of Alberta sites by Meko here