Yamal III: Summary and Update
A fair number of people have been visiting this humble blog in the last few days, presumably not for my excellent tips on where to find the best huevos rancheros in the world. My previous posts on Yamal are long and perhaps technical in places, so I wanted to provide a quick summary.
in Yamal I, I emulated the modifications of the Yamal chronology by Steve McIntyre. As I noted in that post:
Adding the Khadyta River series reduces the the level of the chronology though the 1970s and 1980s and into the early 1990s, when those data end. But if one includes both data sets, the series terminates similarly to the original Yamal chronology, of course (because the last few years are only present in the modern trees from Yamal). These changes are potentially important, and the actual scientific questions are interesting
I also noted that the manner in which the series are low pass filtered can change the impression of the impact of these changes. Smoothing and filtering series — particularly dealing with end points — is a complicated issue, so care is always necessary when designing, deploying, and subsequently interpreting smoothed series.
In doing the emulation, I noted that there are differences in the archived Yamal, McIntyre emulation, and my own. These probably arise due to the different curve fitting techniques (time varying spline for Yamal, nonlinear least squares for McIntyre’s R code, and standard spline or Supersmoother fitting for my emulation). In terms of identifying relative differences due to adding the Khadyta River data, though, these don’t seem to matter too much. Apparently, McIntyre noted that his RCS routine created a greater rise than the archived Yamal chronology (again, this is probably differences in curve fitting, if I had to guess), but I can’t locate the statement now.
I also see, via Deep Climate, that McIntyre has posted graphs showing the chronology from the full data set (including the complete set of trees from Yamal and Khadyta River). We seem to differ on showing the period from 1991 to 1996, apparently — I think if you are going to make rather strong statements about using all the data, you should use all the data, but I don’t expect us to agree on this.
So, more interesting perhaps is my second post, Yamal II, where I looked at the raw data from Yamal and Khadyta River. Here, I concluded:
Khadyta River does display the divergence problem, in that it ceases to track temperatures as it did from 1883 to the 1960s.
Relatively little more can be said about the specific case of Yamal at this point — I’ll leave that to the scientists working in this part of the world — but even my quick review of these data here shows that including Khadyta River raw data in the Yamal chronology does not result in a more accurate nor precise understanding of past temperatures in the region. This isn’t to say that some time in the past that Yamal didn’t experience divergence (this after all is a large part of the concern about divergence), but we can clearly see that Khadyta River does exhibit modern divergence.
That’s where I stand now, and I’m not sure what further insights will come from solely the data at hand. However, reading blog posts about this topic, I’ve become aware that there persist misunderstandings in how field and lab dendrochronology is actually done. So, hopefully there will a post about this from me in the near future.