The Sheep Mountain CA bristlecone site is the most important proxy in MBH and the MBH98 reconstruction actually doesn’t differ very much from the Sheep Mountain tree ring chronology (other than it ends in 1980 at pretty much the peak of the Sheep Mt chronology and doesn’t include the downtick in the 1980s.) Various efforts by Mann and his associates to show that they can “get” a HS using various salvage methods do little more than present the bristlecone ring width chronologies up to 1980 in various wigs (borrowing Hu McCulloch’s apt phrase).
A few months ago, I reported that Linah Ababneh’s thesis contained an updated Sheep Mountain chronology which cast the matter in a provocative new light – in which even MBH wigs were of no avail. Here is the comparison that I posted up at the time showing the remarkable “divergence” between the updated Ababneh chronology and the Graybill chronology used in MBH98 (and other studies as well either directly or via the Mann PC1: Crowley and Lowery 2000; IPCC 2001; Mann and Jones 2003; Osborn and Briffa 2006; Hegerl et al 2006; Rutherford et al 2005; Mann et al 2007; IPCC 2007.) Obviously the distinctive HS shape of the Graybill chronology is not replicated in the recent Ababneh chronology. You can view a version of the original Ababneh graphic in this post
if you wish to verify that my plot here (from Hans Erren’s digitization) correctly implements the Ababneh version in her thesis.
Figure 1. Ababneh and Graybill chronologies. Ababneh-black; Graybill -red.
I was doing some calculations to show the Divergence Problem in relation to these chronologies and did a short-segment Mannian standardization of these two series (on the period 1902-1980), yielding the following interesting result. In this perspective, instead of diverging in the period from 1850 on, the two chronologies match rather closely! Despite the seemingly different appearance of post-1840 values in the first plot, they are very similar after 1840 if re-scaled.
So we have a real puzzle? In Figure 1, the Ababneh and Graybill chronologies track each other closely up to about 1840. In Figure 2 (after re-scaling), the Ababneh and Graybill chronologies track each other closely after 1840. Here’s what happens: after 1840, the Graybill chronology is dilated about 186% relative to the Ababneh chronology. It’s almost a linear transformation!
This is really weird, even for dendro. What explains it? I can really only guess. However, it is surely unacceptable in any professional science to have unexplained differences like this – especially in an important series in MBH98 (and one which is even illustrated in IPCC AR4 – based on the Graybill version, of course).
We can eliminate one “explanation” pretty easily: it isn’t CO2 fertilization, since we’re talking ring width measurements at the same site presumably with many of the same trees.
One possibility is that Ababneh screwed up her chronology calculations. This seems unlikely as these calculations are pretty much canned calculations given the measurement data. These results were presented as the major part of her PhD thesis and in a recent “peer reviewed” journal article. Did anyone on her thesis committee at the University of Arizona (including Malcolm Hughes) check her calculations? While one doesn’t expect mistakes to be made with canned programs, things happen. Checking would only take about 20 minutes to do given the measurement data. Or maybe calculations aren’t checked in University of Arizona PhD theses. In her thesis, she says that she will archive her data at ITRDB, but nothing has been archived so far. I guess the dendros didn’t check that either. The University of Arizona claims not to have the data.
I have no reason to believe that her calculations are incorrect, but that leaves the dilation relative to the Graybill chronology unexplained. Should the thesis committee have asked for this to be explained in her thesis? This occurred to me immediately. Malcolm Hughes knows the Sheep Mountain chronology – it was an issue in our MBH criticisms. Why didn’t he ask that she deal with this. But, hey, it’s climate science.
The most likely difference is due to populations. Ababneh used 100 trees in her calculation – which is larger sample than that which Graybill archived. Maybe the Graybill sample was not representative. At Almagre, we found that Graybill did not archive all of the measured trees – only a subset. Nobody ever mentioned this in any literature. Is the Graybill chronology based on a specially tailored subset? This is possible: Graybill was looking for data to support his theory of CO2 fertilization and in Graybill and Idso 1993, he said that they selected strip bark trees. Maybe this explains the difference. Or maybe the Graybill sample was simply too small. Who knows? There’s no proper data archiving, no proper analysis. It’s a typical MBH mess.
What we do know is that we have inconsistent versions of the Sheep Mountain chronology – versions that are different on the key issue of medieval-modern relationships. In the Graybill version (as applied by Mann), the California “sweet spot” had bitter cold in the MWP; for whatever reason, Ababneh didn’t replicate this result.
Until the University of Arizona provides a proper explanation of the present fiasco in their Sheep Mountain records, I do not believe that any of these chronologies can be validly used in a temperature reconstruction. End of story. All calculations using Graybill’s Sheep Mountain (and Campito Mountain etc.) chronologies should be frozen and put on the sidelines until the matter is resolved – just the way a professional organization would do it.
Sure Mann can claim till he’s blue in the face that he can “get” a HS from Graybill chronologies and the rest of the MBH network using RegEM or whatever, but, as Mann himself observed some time ago, “Garbage In, Garbage Out”. If the Graybill chronologies are garbage – and until the difference with Ababneh chronologies is resolved and the Graybill chronologies validated, they must be treated as though they were garbage – MBH98, (Rutherford et al 2005, Mann et al 2007, etc.) calculations using Graybill chronologies are also unusable. Or to use Mann’s term, “garbage”.
UPDATE: Here’s an interesting figure which shows the Ababneh reconstruction scaled to match the Graybill reconstruction in the Mannian calibraiton period of 1902-1980, which vividly illustrates an interesting statistical point that I discussed in connection with Juckes – that you can have reconstructions that are virtually indistinguishable in their calibration and “verification” results with very different trajectories off in the earlier portion of the reconstruction, asking how can you objectively say that one is “right” and another “wrong”.
Here’s the Ababneh chronology rescaled to match the Graybill chronology in its recent history (I’ve used the early portion of the Graybill chronology to provide the “extension” to the Ababneh chronology.) As in Figure 2 (which is identical to Figure 3 in the latter portion), the Ababneh and Graybill chronologies are indistinguishable in terms of calibration (1902-1980) period appearance. But they are also virtually identical in the “verification period” back to 1850 – the divergence between the two series occurs either before 1840 (with Ababneh having a greater proportion of thick ring widths in the early history) or after 1840 (with Ababneh having a greater proportion of thin ring widths in the later history) – or some processing difference. Regardless of which chronology is “right”, for the multiproxy statistician – who is constrained by the “peer reviewed” time series squiggles emanating from the University of Arizona – there is no objective way of picking one version rather than the other.