(This post is by Jean S.) A few days ago Steve discussed Raymond Bradley’s objection to use of the Yang Chinese composite reconstruction in the Mann et al Eos-response to Soon & Baliunas (2003). Bradley called the series “crap”, and demanded it to be removed from Figure 2 in the Eos article. It is not completely clear if Bradley was fully aware that the Yang composite was also brought in to the Figure 1 in the form of Mann and Jones (2003) (later MJ03) NH composite, which was substituted only 3 days earlier for Briffa’s long series (of the earlier draft) in an agreement made only between Mann and Jones. Nevertheless, Mann defended (#4207) the use of the Yang composite in MJ03 by saying it got “a moderate low weight” in the composite.
In our GRL article, Phil and I weighted the records we used with respect to their decadal correlations with the instrumental gridpoint surface temperature data for the same region (numbers in parentheses in attached figure 1 from the paper), so if a series is truly crap in an objectively determined sense, it got very low weight. The China series has a reasonable (r=0.22), but not great correlation–and it gets a moderate low weight.
Only a day later the weight was further downgraded form a “moderate low weight” to a “low weight” (CG1: 1056477710).
Phil and I have already discussed–we agree that the low weight given to the record in the Mann and Jones composite treats the record appropriately…
At the time it was impossible for Bradley and others to quantify what Mann’s “appropriate low weight” meant. Luckily, as pointed out by UC, the MJ03 code is available in #3499 (also CG1: 1092167224) and we can now calculate the weight of the Yang composite. Before doing that, let’s take a look at other proxies used in MJ03.
As Gavin observed there are “a few typos” in the Eos Figure 1.
I note there a few typos in the Eos figure 1 though (signs of fast turnaround perhaps). It should say 1856–1940 in the key for Briffa et al. for instance (as it is in Jones and Mann, 2004).
Another “typo” was, of course, calling MBH99 plus 0.5 sigma as “Crowley and Lowery” (yellow). I found a third “sign of fast turnaround” in the caption:
an extension back through the past 2000 years based on eight long reconstructions [Mann and Jones,2003].
The long NH reconstruction shown in Figure 1 is actually based only on six series as clearly stated in MJ03 (Figure 2a). There is also another NH series calculated in MJ03 based on eight series, but it only starts in AD553, and AFAIK it is not used anywhere. This shorter NH series has the same six proxies as the main reconstruction plus Jacoby’s Mongolia series (discussed by Steve yesterday) and Fisher’s West Greenland series, both shown in the Eos Figure 2.
A natural member of MJ03 portfolio is Mann’s own western North American PC1 shown on a top of Eos Figure 2 (“Western US”), and discussed by Steve here. This series is a splice of Mannomatic PC1 of six chronologies extending back to AD200 (up to 1700) and the infamous “fixed” Mannomatic PC1 (based on 27 chronologies) from AD1000 network in MBH99 (after 1700). How exactly the splicing was done, as far as I’m aware, remains a mystery today. However, it is interesting that Mann did not “extend” his “fixed” AD1000 PC1 by splicing the new PC1 (based on six chronologies) to the end (i.e., for 200-999 period), which would have been more inline with his stepwise approach in MBH9X. Instead, the cutting point was 1700. We’ll probably never find out the reason for this odd selection, and I only remark that “fixed” AD1000 PC1 has relatively high 11th century values compared to those in the extended AD200 PC1.
As a side note, around time of Steve’s MJ03 post (see comments) we began to understand the effect of this ridiculous “CO2-adjustment” (Mannkovitch Bodge) in MBH99: it adjusted the verification RE statistic and affected the 1000-1850 linear trend (“Milankovitch cooling”) as plotted in the Hockey Stick. It took two more years and ClimateGate files to fully understand what had been done, see Bishop Hill’s treatment for details.
[Update: Dec 5, 2011. Steve wrote me that it is likely that instead of the bodged Torneträsk series some type of mixture of Torneträsk, Taimyr and Yamal was used as the third series, see Fig. 1 in MJ03. However, Taimyr and Yamal are not used in Jones&Mann (2004) (see Fig. 1), which shares the code with MJ03, so it is hard to tell what exactly went in without actually seeing the file "torny.dat". Moreover, the decadal correlation value in the code (0.32) does not match either the one given (0.47) in Fig.1 of MJ03 or the one (0.54) in Table I of JM04 ...]
Third series in MJ03 is Briffa’s Torneträsk, again shown in the Eos Figure 2. I suppose only few even among regular CA readers know that also this series was “adjusted”, see Steve’s discussion of the topic from the early days of CA. Fourth series to enter the MJ03 portfolio is the Chesapeake Bay Mg/Ca proxy, also present in Figure 2. This series has declining temperatures since late 19th century. Finally, the last two components of MJ03 are rather surprising (not-so-suprisingly these are not plotted in the Eos Figure 2): two Greenland borehole reconstructions from Dahl-Jensen et al (1998) (pdf). Both D-J series have very high MWP values relative to the present (see Figure 4 in the article).
Now that we know the six proxies going in to MJ03 composite, we can return to the weighting issue. Recall that Mann claimed to Bradley (and others) that the weighting in MJ03 was done “objectively” by their decadal correlations to the local temperature, and that the Yang composite had a “reasonable (r=0.22), but not great correlation” and thus it obtained a “moderate low weight”. What Mann “forgot” to tell is that the weight in MJ03 is calculated not only based on correlation but also on the area.
Composite series were formed from weighted combinations of the individual standardized proxy series, employing weights on the individual records that account for the size of the region sampled, and the estimated reliability of the temperature signal as determined by comparison with the instrumental surface temperature record [Jones et al., 1999].
From the code it is seen that this areal weighting is actually cosine(latitude)*dof, where dof is an “estimated number of temperature gridpoints represented by record”. The total weight given to a proxy is then obtained by multiplying this area weight by the correlation. As the Yang composite has the highest dof (4) while both Dahl-Jensen series has 0.667, it is not hard to guess what the final weighting looks like…
…and here are the results of the relative weighting of MJ03 proxies:
extended NA PC1: 33%
Yang composite: 30%
D-J (DYE-3): 6%
D-J (GRIP): 4%
So in the end of the day, MJ03 composite so prominently presented in Eos Figure 1 is practically just an average of three series, “crappy” Yang composite, “extended” and “fixed” Mannomatic PC1, and Briffa’s “adjusted” Torneträsk. Also the definition of “low” in the Mannian dictionary is likely “anything below 1/3″.