After several years of trying, Briffa and Osborn have finally listed the sites used in Briffa et al 2001 and related publications. Briffa had reported results on large networks of over 300 sites collected by Schweingruber. Schweingruber had archived over 400 sites at WDCP.
However, it was impossible to tell exactly which sites had been used and up till now, Osborn and Briffa weren’t telling. While the webpage is obviously a huge improvement, there are some annoying problems. In some cases, the identification codes have typographical errors. I’ve noticed incorrect ids for adyboala, balyebda and lespiob in the data set for Briffa et al 2001.
Although Osborn says that all the sites are available at WDCP, most of the sites are there, but some are missing. I noticed 18 sites from the Tibetan Plateau. I’ve written Osborn to request that he remedy these things.
One of the first exercises that I carried out was to calculate a simple average of all the available ring width chronologies in the Briffa et al 2001 network (369 sites – 387 less the 18 unavailable sites.) In this case, I just used the Schweingruber chronologies without trying to re-do using RCS chronologies.
Here’s the result. As you see, there is a noticeable decline in the late 20th century – the “divergence problem.” If this is the average of a large sample of 369 sites, what are the odds that a random selection of say 8 sites has a sharp uptick in the late 20th century. Not very high.
Figure 1. Average of 369 available chronologies (as archived by Schweingruber) in the 387 site network of Briffa et al 2001.