Keith Briffa has a couple of posts today on Yamal – one discussing its impact in other multiproxy studies and the other on the Yamal chronology itself. His post on the Yamal chronology includes a careful consideration of various issues involved in the development of the Yamal chronology and is accompanied by an extensive archive of original data. The concurrent inclusion of data is to be commended.
It will take a little while to consider this as there’s a lot of data to assimilate. First, let me discuss the post on the impact, which I can do quite quickly.
Briffa considers three aspects of Yamal use: (1) in Osborn and Briffa 2006; (2) in IPCC 2007; and (3) in other multiproxy studies. He concludes:
Thus, with the exception of Briffa (2000), the reconstructions shown by the IPCC (Figure 6) either do not use the Yamal record or they combine the Yamal record with many others and this reduces their sensitivity to the inclusion of any individual records.
I disagree with this summary for several reasons outlined below.
I considered the impact of Yamal on other multiproxy studies in a CA post here, which is, unfortunately, not linked in the corresponding Briffa comment. There are many points of empirical agreement, but considerable differences in emphasis. The differences in emphasis are significant: I considered the use of both Yamal and strip-bark bristlecones/foxtails, identifying several “families” of reconstructions: a family in which strip bark bristlecones/foxtails were highly influential (but not Yamal); a family in which Yamal was highly influential (but not bristlecones); a belt-and-braces family in which both were used and which typically asserted “robustness” to removal of individual proxies; and a few odds-and-ends which were affected by other questionable proxies e.g. by the “cold” 11th century Polar Urals of Briffa et al 1995.
Yamal arose as an issue in the wake of our criticism of MBH, because of Team assertions that the Mann reconstruction was supported by various “independent” reconstructions. We observed (and this point has been also observed by Briffa in the past) that the “independent” reconstructions are not, in fact, “independent” because of their re-use of the same proxies over and over, especially strip bark bristlecones/foxtails (both directly and as Mann’s PC1). Strip bark has been the more contentious issue; as I noted in my prior post ( a point also made in Wegman 2006), many of these supposedly “independent” reconstructions use strip bark bristlecones. However, not all of them do. Yamal became important as an issue because it is influential in reconstructions that do not use bristlecones (Briffa 200, D’Arrigo 2006, Kaufman 2009). To the considerable extent that Briffa’s response to Yamal impact is that they can “get” a stick using strip bark, the response is, shall we say in Mannian-speak, a little “disingenous”.
Briffa’s statement contradicts empirical observations at CA 7229 in only a couple of places and, in each case, I can demonstrate that Briffa is wrong. Both errors are relevant.
First, Briffa said that Hegerl et al (2006) did not use Yamal, while I said that they did. Hegerl et al (Nature 2006) url does not list the series that it uses; the companion Hegerl et al 2007 url states:
the west Siberia long composite involved Yamal and the west Urals composite.
Precisely how Yamal is “involved” in the west Siberia long composite is not reported. I’ve been trying to get the exact versions used by Hegerl since fall 2005 and despite many emails (mostly involving Crowley) have thus far been unsuccessful. (As I’ve mentioned elsewhere, my original attempts to get this data led to IPCC WG1 Chair Susan Solomon threatening to expel me as an IPCC reviewer.) On the empirical point of whether Hegerl et al used Yamal, given the explicit statement in Hegerl et al 2007, it is my opinion that Briffa is wrong.
Second, as regards d’Arrigo et al, Briffa said that Yamal was used, though “possibly labelled as Polar Urals”. To use a Mannian term, it is “disingenuous” to say that it was “possibly” labelled as Polar Urals. It is definitely labelled as Polar Urals. Briffa’s aware of the issue and has had an opportunity to check this out both by inspection of the article, where the labeling is evident and by asking the authors.
In my post on the impact, I identified the following reconstructions as ones which were “dependent” on Yamal, defining dependence as “equivalent calculation using plausible alternatives (e.g. Esper’s Polar Urals version instead of Briffa’s Yamal) yield different MWP-modern relationships”: Briffa 2000, the “closely related D’Arrigo et al 2006 and very recently, Kaufman et al 2009 (despite its first impression of a very different network)”.
Although the words “Polar Urals version” do not pass Briffa’s lips, he conceded the dependence in respect to Briffa 2000. He doesn’t consider Kaufman 2009, a recent reconstruction that we’ve discussed here and which can be seen to be dependent on Yamal in the above sense.
There is an empirical difference of opinion on the impact of Yamal on the D’Arrigo reconstruction. Here it is my opinion that use of Polar Urals rather than Yamal has a direct impact on the medieval-modern differential in the long D’Arrigo et al 2006 reconstruction. I’m not 100% sure of the size of the impact. I’ve been trying since 2005 to get the individual chronologies used in D’Arrigo et al 2006 in order to test precisely this sort of issue, but thus far have been unsuccessful. (I recently renewed this effort in the wake of present discussion.) The one that I am missing right now is their Coastal Alaska series. My surmise is based on the close relationship between the D’Arrigo series and the Briffa 2000 series. There are 6 series in the “long” D’Arrigo et al 2006 version (see their Figure 7) url are Yamal (labelled as “Polar Urals”), Tornetrask, Taimyr, Mongolia, Jasper (Icefields) and Jacoby-D’Arrigo’s Coastal Alaska. There are 7 series in the Briffa 2000 reconstruction: Yamal, Tornetrask, Taimyr, a shorter version of Mongolia (“Tarvagatory”), a slightly shorter version of Jasper (“Canadian Rockies”), the Jacoby-D’Arrigo NNorth America composite plus Yakutia(aka Indigirka River). My guess is that the it would alter the results materially, but I’m not 100% sure. Briffa guesses otherwise. We’ll see. (Obviously this shouldn’t be a matter of guessing. If D’Arrigo archived their data, then the guesswork would be eliminated.)
Briffa doesn’t mention strip bark bristlecones. Even the NAS Panel stated that strip bark should be “avoided” in temperature reconstructions. While these reconstructions are not affected by Yamal, neither can they be considered any longer to be relevant reconstructions without subtracting the strip bark series. In the case of MBH99, even Wahl and Ammann conceded that the MBH stick did not survive a sensitivity study without bristlecones. The IPCC did not squarely address the strip bark problem nor the sensitivity of multiple reconstructions to strip bark. Briffa should have addressed this point in his table. In my earlier post, I observed the following about this “family” of reconstructions (including, obviously MBH99).
One important “family” of spaghetti graph reconstructions are highly dependent on strip bark bristlecones/foxtails (a topic which has been much discussed here and elsewhere) but which do not use Yamal. These are “highly dependent” on strip bark bristlecones/foxtails in the sense that their methods do not yield a HS without them. Examples include MBH98-99, Crowley and Lowery 2000, Esper et al 2002 plus the re-statements of the MBH network in Rutherford et al 2005, Mann et al 2007 and Wahl and Ammann 2007.
In my earlier post, I pointed to recent reconstructions that used both strip bark (sometimes multiply) and Yamal as follows:
A third “family” of reconstructions wears both belt and braces – i.e. using both strip bark and Yamal. Key examples are Mann and Jones 2003, Mann et al (EOS 2003), Osborn and Briffa 2006, Hegerl et al 2007. The recent UNEP graphic uses the Mann and Jones 2003 version. A common stratagem in these studies is a leave one out sensitivity – where they show that they can “get” a similar result by leaving out any individual proxy. They can do so safely because they have both Yamal and bristlecones.
To this list, we can now add Tingley and Huybers (submitted Clim Chg). Briffa discusses the supposed “robustness” test of Osborn and Briffa 2006, the network used by Tingley and Huybers (submitted Clim Chg), upon which Clapton et al have already commented. In a network of only 14 proxies, Briffa used Yamal, Mann’s PC1 and strip bark foxtails as three of his 14 proxies. The trouble is that this sort of study has been data snooped: it doesn’t use Polar Urals, Indigirka River, Ababneh or Grudd’s Tornetrask.
In my earlier post, I pointed out that some spaghetti graph proxies didn’t go back to the MWP and were thus irrelevant to the MWP-modern comparison e.g. boreholes, Oerlemann, Briffa’s MXD reconstruction (the one where the “divergence problem” in the late 20th century was chopped off.) Briffa cites these as unaffected by Yamal, which is true but totally irrelevant to MWP-modern comparisons.
In my earlier post, I also noted that there were a few studies that were not materially affected by Yamal or strip bark bristlecones, but that these had their own problems, mentioning Jones et al 1998 and Moberg et al 2005 in this class.
There are a couple that are a bit sui generis, but these unfailingly have some serious problem. Jones et al 1998 uses neither Yamal nor bristlecones, but still has a slight modern-medieval differential. In its early portion, it uses only three series, two of which are early Briffa series (Tornetrask and Polar Urals pre-update). Both these series have serious problems – Briffa’s original Tornetrask series contains a gross manual adjustment to increase the 20th century relative to the MWP. See early CA posts on this.
Moberg uses both bristlecones and Yamal, but I view it as sui generis as well. Moberg used some unorthodox wavelet methods, that I’ve sort of emulated, but gave up trying to do so precisely. However, I can confirm that the bristlecone versions used in Moberg are not Graybill versions and don’t affect the result; they are merely fill. I’m not sure what impact Moberg’s filtering method will have on Yamal – I’ve not analyzed that in detail, but may do so some day. I’ve discussed Moberg problems in the past and, for present purposes, merely note that it is not a safe haven, but that it does not appear to stand or fall with Yamal and thus is not discussed further today.
I can guarantee 100% that the Jones et al 1998 reconstruction is materially affected by updates to Polar Urals (the Esper version) and updates to Tornetrask (Grudd). Briffa says that Moberg’s method removes all but the “high frequency” component of Yamal. No code is available for Moberg’s method; I can sort of emulate his results and will at some point examine the impact of Yamal. Moberg has some sui generis issues: e.g. its counterintuitive reliance on increased upwelling of cold water (subarctic G. Bulloides foraminifera in the Arabian Sea) as evidence of 20th century warming.
Revisiting Briffa’s table, I’ve added a column commenting on each reconstruction.
|Study||Briffa (2000) Yamal chronology|
|Jones et al. (1998)||Not used||Briffa 1995 Polar Urals.|
|Mann et al. (1999)||Not used||Strip bark bristlecone/foxtail. Briffa 1995 Polar Urals.|
|Briffa et al. (2001)||Not used||Short reconstruction. Divergent portion truncated.|
|Esper et al. (2002)||Not used||Strip bark bristlecone/foxtail|
|Briffa (2000)||Briffa (2000) Yamal was used||Yamal|
|Mann and Jones (2003)||Briffa (2000) Yamal was used in a composite of three ring-width chronologies from northern Eurasia||Yamal and bristlecone PC1|
|Rutherford et al. (2005)||Not used||Strip bark bristlecone/foxtail|
|Moberg et al. (2005)||Only high-frequency information from the Briffa (2000) Yamal chronology was used|
|D’Arrigo et al. (2006)||Briffa (2000) Yamal was used, though possibly labelled as Polar Urals||Yamal. It is definitely labelled as Polar Urals.|
|Hegerl et al. (2006)||Not used||"the west Siberia long composite involved Yamal and the west Urals composite."
|Pollack and Smerdon (2004)||Not used||Short reconstruction|
|Oerlemans (2005)||Not used||Short reconstruction|
|Kaufman et al (2009)||Yamal|
|Mann et al (EOS 2003)||Yamal and bristlecone PC1|
|Osborn and Briffa 2006||Yamal and 2 strip bark series (including Mann’s PC1)|
|UNEP graphic (Mann and Jones 2003)||Yamal and bristlecone PC1|
Briffa’s response provides a new bit of information about the IPCC spaghetti graph which even I was unaware of. He says:
In this analysis [IPCC 2007], the Yamal chronology was used cautiously because the series was truncated in 1985 for the purposes of constructing this Figure. Thus, the high recent values from Yamal were not shown in this Figure.
This truncation is nowhere mentioned in the graphic. Here is the figure showing the supposedly “cautious” use. The Yamal series is the one going off into the stratosphere at 4 sigma. To fully show Yamal in the version used by Kaufman, the height of the figure would have to be increased to 7 sigma! In my opinion, “cautious” use would mandate showing the actual data – all 6.97 sigma of it, so that readers could carefully consider the matter.
This is not the only instance of Briffa truncating data. As reported previously at CA, Briffa truncated the “divergent” portion of Briffa 2001 in IPCC TAR and, despite one IPCC reviewer insisting that this truncation not be repeated in IPCC AR4, did so once again.
Combining with Many Other Records
One of my major points of disagreement with Briffa and other Team authors is on whether “combining” Yamal and bristlecones with a lot of other records accomplishes the reduction in sensitivity that they assert using either CPS or Mannian methods. The graphic below, taken from a CA post here from a few years ago shows the impact of replacing all the “proxy” series in the MBH98 AD1400 network (other than Gaspe and the Mann PC1) by white noise. The reconstruction is virtually identical to the reconstruction with actual proxies. In actual reconstructions, most proxies are like the pills that Grace Slick’s mother gave her – they don’t do anything at all. In CPS and MBH-style methods is that the “white noise” “proxies” cancel out – the more “proxies”, the more effectively they cancel out under garden variety Central Limit Theorem considerations. In CPS and MBH methods, the average is not itself used. It is re-inflated to match the instrumental variance in the 20th century. If there are a couple of HS series lurking in the weeds (Yamal or the Mann PC1), they get re-inflated and you end up with the Mann PC1 plus a little static. That’s why the Mann reconstruction looks so much like the Mann PC1 (and the Graybill Sheep Mt series.) The same thing happens with CPS.
Thus, Briffa’s conclusion about the other studies: “they combine the Yamal record with many others and this reduces their sensitivity to the inclusion of any individual records” really doesn’t work as well he thinks. The “active ingredients” in study after study are strip bark and, secondarily, Yamal. Think of the screeching when sensitivities are done on MBH without strip bark – it’s as though the world had ended.