No one will accuse me of arguing that Dulan junipers are a proxy for temperature. But twq has been to Dulan and says that they are. So let’s take twq’s assertion at face value and, a la O.J. Simpson, let’s reluctantly explore what happens if Dulan junipers were a temperature proxy as twq says. A post put up under duress, so to speak.
First here is a plot of the values of the Yang et al 2002 Dulan chronology. Again, I do not claim that this is a temperature reconstruction, but, you know, if it is, on twq’s say-so, I will reluctantly include it in reconstructions in place of (say) the Dunde data set. I noticed that there is a striking positive anomaly around the year 1000 – I wonder if anyone can come up with a good name for this period. Maybe Jonathan Overpeck can think of something.
Just so no one thinks that Yang et al 2002 is the only study to observe this strange phenomenon, here’s an excerpt from Figure 3 of Zhang et al 2003. The resemblance of the two chronologies is hardly accidental, since Zhang et al 2003 use 55 cores from Kang et al 1997, which was relied upon in the Dulan chronology used in Yang et al 2002.
Excerpt from Figure 3 of Zhang et al 2003. Original caption: The 2326-year ring-width chronology of Sabina przewalskii Kom. and the number of samples for each year in Dulan area of eastern Qinghai-Tibetan Plateau. The smoothed curve superimposed on the chronology is derived after filtering to emphasize long-term fluctuations (the filter is a cubic spline passing 50% of the variance in a sine function with a wavelength of 64 years).
So, reluctant as I am to consider these ring width chronologies as temperature proxies, since we’re so easy to get along with here at climateaudit, we’ll give twq the benefit of the doubt – this time only.
Now twq thought that he’d try to compare the low-frequency variations of Dulan tree rings to the low-frequency Dunde variations. To assist him in this process, I’ve collated various Dunde versions below over the same period as shown for Dulan juniper chronologies above. The IPCC SPM told us that “additional data” from mulitple indicators showed “coherent behavior”; Lonnie Thompson’s ice core data is one of the most important such indicators, featured prominently in Inconvenient Truth. The Dunde ice core chronology (chronologies?) represents one of the triumphs of modern climate science. In a field fraught with dendroclimatological uncertainty, here is a data set where one can find firm ground under one’s feet so to speak.
Indeed, if one uses the Dunde data for statistical analysis, multiple linear regression takes on a whole new meaning, as here twq has the opportunity to perform multiple linear regressions on just one data set and, following dendro precedent, pick the version that he likes the best. Western dendroclimatologists call this sort of procedure “robust” and “rigorous”; I’m sure that there is a mot juste in Chinese.