In March last year, I was intrigued by the following statement in the then recent IPCC Summary for Policymakers which stated:
“Studies since the TAR draw increased confidence from additional data showing coherent behaviour across multiple indicators in different parts of the world”
What exactly was the “additional data” since the TAR? At the time, AR4 had not been published. Even now, if you re-visit chapter 6, there is negligible support for this statement. Yes, AR4 lists many Team multiproxy studies, but, for the most part, these regurgitate pre-TAR data. Note that Mann et al 2008 will be of no help in this respect as it almost entirely relies on pre-TAR data as well.
Anyway, I was stimulated enough in March 2007 by this comment to re-canvass North American tree ring in the ITRDB for new additions. I noticed a recent addition of spruce chronologies from northern Alberta and did a post on Mar 19, 2007 showing a quick average of these chronologies to see if they supported the IPCC claim. I observed that, if these were temperature proxies (carefully expressing the matter in conditional terms), these did not evidence the SPM claim.
This post prompted a number of posts from angry/frustrated dendros and a discussion of what to do about CA at the dendro listserv.
Rob Wilson, a welcome and occasional visitor here, sharply criticized me for simply grabbing sites from ITRDB without determining that they had been sampled as temperature proxies, pointing out that Meko, the author of the majority of these particular chronologies, was known primarily for moisture studies:
For readers of this blog, PLEASE understand that one cannot randomly sample trees from any location and expect there to be a valid climate signal (temperature or precipitation)….
Dendrochronology is NOT just a study of climate. Tree-rings are used to study fire history, geomorphological processes and ecological aspects of tree growth (e.g. stand dynamics, insect attacks, pollution effects etc). Therefore, one cannot assume that ALL tree-ring data in the “North American tree ring data base at WDCP” was sampled with a climate related question in mind. Therefore, a simple average of 14 sites, without knowing why they were sampled in the first place, is arguably a meaningless exercise.
Mike Pisaric, another dendro, joined in the criticism, stating that my analysis was “flawed!”, that ITRDB chronologies had been collected for a multitude of purposes and that you could not assume that they contained a climate signal.
As Rob points out in 3 and 28, Steve’s analysis is flawed!… The ITRDB contains tree ring chronologies that have been used for a multitude of purposes and not just paleoclimatology. So no, you would not expect all tree ring chronologies from the ITRDB to contain a valid climate signal.
So – should I (we) ignore this Blog? … Personally, I cannot do this. Although some of the criticisms and commentary are valid, some of it is simply wrong and misinformed, and in my mind, it is dangerous to let such things go. .. Overall, this is a matter of outreach. I believe that tree-rings are one of the most powerful palaeo proxies available. However, we cannot allow the discipline to be muddied by a few ‘loud’ individuals who’s motives may be suspect.
I responded to this criticism in a post The Dendrochronologists are Angry , stating that I had no interest in spreading misinformation and would undertake to promptly correct any such misinformation, opening up a thread for dendros to respond without any obligation to deal with CA readers. This did not result in much of a response.
I challenged the Dendro Truth Squad to root out the use of precipitation proxies, highlighting Dulan junipers as an example, a chronology used (either directly or indirectly in a number of multiproxy studies). One angry dendro replied via Rob Wilson (see here),
Those in the know, who really know the science, know not to use that chronology and know who still use that chronology. The work that uses that chronology for a temperature reconstruction is less-respected than others.
He accused me of ignoring “recent work that surpasses all others.“. I expressed my desire to visit this particular shrine and requested the identity of this work that “surpasses” all others , but no one was able to identify it for me. Perhaps the angry dendro had a draft version of Mann et al 2008.
There were about 10 posts at the time both on this dispute and on the more general question of North American treeline proxies, listed in this category.
As so often, my principal disappointment and frustration was on the one hand at the lack of substance in the dendro interventions and, on the other hand, at their inconsistency.
The inconsistency was particularly frustrating. While I didn’t think that I particularly deserved the criticism leveled at me for merely calculating an average of the 14 PCGL chronologies, I would have readily accepted the criticism if this led to the articulation of an industry-wide standard that dendros would apply to multiproxy standards. (In this light, I criticized dendros for feeling that it was important to speak out about an incidental post at CA, while remaining silent on MBH98-99 and similar studies.)
History repeats itself. If Peter Brown, Mike Pisaric, Rob Wilson and other dendros were outraged at my calculating the average of 14 Alberta PCGL chronologies, then how can they stand idly by while Mann et al 2008 essentially scavenges the ITRDB like a garbage picker? If they felt so strongly about my post last year, then they must be outraged about the total failure of Mann et al to assess “Location, location, location”.
Let’s go back to the questions asked at the dendro listserv and see which, if any, of the following applies to Mann et al:
So – should I (we) ignore this ? …
Although some of the criticisms and commentary are valid, some of it is simply wrong and misinformed, and in my mind, it is dangerous to let such things go…
I believe that tree-rings are one of the most powerful palaeo proxies available. However, we cannot allow the discipline to be muddied by a few ‘loud’ individuals who’s motives may be suspect.
What’s sauce for the goose is sauce for the gander.