A couple of days ago, I canvassed the ITRDB data bank for all tree ring series with values later than 1998, noting that there were many new series. Mann has justified the reliance on proxies not updated since 1980 and earlier, and thus not calibrated against recent warmth, on the basis that it is very expensive and time-consuming to do this – a justification which I believe to be laughable on its face. Since white spruce (PCGL) was used in treeline studies in the past, I did a quick collation of new PCGL series as a species identified previously as a temperature proxy to see whether ring widths for new contributions to the ITRDB data bank reflect recent warmth, as they should if tree ring widths were linearly correlated with temperature, as Mann and others have hypothesized.
I didn’t do any sub-analysis to see if the specific white spruce sites were “temperature sensitive” for which Mike Pisaric and Rob Wilson criticized me. My response – and that of other readers of those threads – was primarily to point out that this is what was done in MBH and other studies, which Pisaric and Wilson had never spoken against. Realistically, they aren’t going to speak out against Mann’s use of precipitation proxies in a temperature study so there’s not much point belaboring the matter further.
So let’s go back and re-visit their criticism of how I presented the information. They said that the PCGL series used in my average should not be used in an average because they are not “temperature” proxies but moisture proxies, as anyone can tell by looking at their location, and thus the average was meaningless. As an exercise, I’ve plotted the location of the PCGL proxies with post-1998 values in the map below, colored according to 5 author groups. I’ve also marked ( with a + sign) the 11 “treeline” sites of the original Jacoby and D’Arrigo 1989 study and joined all except the Gaspé site with a line (the Gaspé site is labelled both because it is anomalously located for both the Jacoby and D’Arrigo 1989 “treeline” study and heavily weighted in MBH98. There are many new Jacoby-D’Arrigo sites that have not been archived.
The Meko sites are shown in blue and, as Mike Pisaric says, are well away from latitudinal tree line. I’ve marked with smaller dots the location of all sites in the North American ITRDB data set (actually they go even further south), so you see that a PC1 taken from the MBH98 dataset includes almost no latitudinal treeline sites (and none earlier than about 1500). The Wilmking sites along the Brooks Range, Alaska look as though they must be pretty close to the latitudinal treeline, despite Rob Wilson’s caveats against Wilmking data. Sites in Alaska and along the Rockies may also be taken at altitudinal treelines so this has to be kept in mind when one looks at the map.
My objective was to see what relevant fresh data showed. Looking at this map, my conclusion is that the new Wilmking and Lloyd data from the Brooks Range, Alaska and the Jacoby site in Labrador are the only fresh data that are close to the latitudinal tree line and, accordingly, that examining this particular subset is the best implementation of the implicit Wilson-Pisaric criteria that can be done under current circumstances. There is a considerable amount of presumably relevant Jacoby-D’Arrigo data which is unarchived. But as long as it is unarchived, there’s not much that third parties can say about (and, in my opinion, until the data is archived, the study should not be cited by IPCC or others.)