Now that we know the abysmally low replication of the modern portion of Briffa’s Yamal chronology (something previously unknown to specialists), I’ve been backtracking through some earlier documents to see how this may have impacted past studies.
We’ve talked previously about how Briffa refused to provide measurement data to D’Arrigo et al 2006, resulting in them using Briffa’s Yamal chronology more or less blind.
For some inexplicable reason, their article worsens the situation by, in effect, conflating the two: they used the Yamal chronology, but, in the absence of Yamal core counts, used Polar Urals core counts! The NAS panel adopted this mishmash, also using the Yamal chronology together with Polar Urals core counts.
Here is an excerpt of NAS Panel Figure 4-2, taken from D’Arrigo et a 2006, showing 5 Eurasian RCS chronologies (North American RCS chronologies are shown in another portion of the original figure). Of the 5 chronologies in this figure, the only one which doesn’t have a “divergence problem” (i.e. going down in the latter part of the 20th century) is the one in the third panel labeled “POL”: the top part of the third panel shows the chronology, while the bottom part shows core counts. Look closely at both.
Figure 1. Excerpt from NAS Panel Figure 4-2. Original Caption: Results for individual regional composite chronologies for the sites shown in Figure 4-1. The time series have been loosely grouped according to latitude bands and normalized to the common period. The bottom two panels in the right column show grouped replication plots for both North America and Eurasia. SOURCE: D’Arrigo et al. (2006).
The caption to the above figure refers to the “sites shown in Figure 1″, which is shown below. While Polar Urals and Yamal are close to one another, the site marked as “POL” is located at the Polar Urals site (66N, 65E) and not at Yamal (67N, 70.5E).
Figure 2. NAS Panel Figure 4-1. Original Caption: Location map of individual sites (red) and regional composites (yellow boxes) used to reconstruct Northern Hemisphere surface temperatures for the past millennium. SOURCE: D’Arrigo et al. (2006).
Let’s pause for a moment and scratch our heads. The core counts illustrated in the panel come from the Polar Urals site (russ021+russ196). The visual appearance matches the Polar Urals core count graphic; the statistics for total number of cores and mean segment length in D’Arrigo et al 2006 Table 1 match the Polar Urals data set. The location is clearly Polar Urals.
There’s just one catch: the chronology doesn’t come from Polar Urals. It comes from Yamal!
I don’t want people to think that I was previously under the impression that D’Arrigo et al used Polar Urals in their RCS reconstruction. I spotted the distinctive Yamal shape right away and confirmed that they did in fact use Yamal – and we debated at CA whether there were valid decisions for using Yamal versus Polar Urals. We also knew at the time that D’Arrigo et al didn’t have Yamal core counts.
The question that I didn’t consider at the time – nor later when the NAS panel reported – was this: if D’Arrigo et al 2006 didn’t have core counts for their illustrated RCS chronology (Yamal), what was the basis for providing core counts for the illustrated RCS chronology?
With the clarity arising from the Phil Trans B archive showing the actual Yamal core counts, we can now clearly see that the panel is a total mishmash: they used the Yamal RCS chronology with the Polar Urals core count. Had they used the real Yamal core counts or the real Polar Urals chronology, this panel would have looked very different.
Just so there is no doubt: Rob Wilson was one of the authors of D’Arrigo et al 2006. While I disagree with him on statistical issues, his integrity is unimpeachable. The mishmash here is just the weird sort of cock-up that happens from time to time. In my opinion, the primary fault lies with Briffa for not providing the D’Arrigo authors with measurement data. Had Briffa done so, they would have identified the abysmal Yamal replication in 2005 and modified their article accordingly.
NOTE: Just in case anyone wants to doublecheck this claim, here is a script that retrieves Yamal and Polar Urals crn and measurement data and does the plot of the Yamal chronology and Urals core count in a similar style to the figure here.
urals.crn=get.crn("urals") ;tsp(urals.crn) # 778 1990
yamal=get.rwl("yamal_cru"); dim(yamal) #  40892 4
urals=get.rwl("pol", verbose="esper");dim(urals) #  25490 4
## DARRIGO FIGURE
#scale on 1686-1978 per D'Arrigo
temp= year>= 1686 & year< = 1978 #legend of Darrigo
plot(year,x,xlim=c(750,2005),xaxs="i",type="n",ylim=c(-2,5.5),ylab="SD Units 1686-1978",xlab="",axes=FALSE)
temp= x>0; x[!temp]=0
temp= x<0; x[!temp]=0