The three cores which account for 1032 being the "coldest" year of the millennium are 862450, 862470 and 862030. One other core (862460) is dated to the late 10th and early 11th century and contributes to early 11th century "coldness". The placement of these 4 cores has to be interpreted from the ring width information itself.
Figure 1 below shows the assigned start date versus identification – note that 862 is a site prefix and 0 is a suffix: thus the tree number is shown in digits 4 and 5. There is no information on sample locations or altitudes. This could easily be incorporated into WDCP records; being used to careful recording of geological information, I find the absence of this information to be very offputting. Doug Larson of the University of Guelph says that the assignment of identification numbers in field operations is nearly always connected with sample location: thus, cores with nearby sample numbers nearly always come from nearby locations. Note that 3 of the 4 critical trees: 862(45)0, 862(46)0 and 862(47)0 have highly anomalous dates relative to the implicit spatial arrangement of the identification numbers. (Presumably nearby) trees 40 and 41 have assigned start dates in the 17th century; conversely, the other trees assigned early dates have numbers below 10. Oddly, identification numbers 42, 43 and 44 are either not assigned or not reported.
FIGURE 1. Assigned Start Dates against Tree Identification Number. 862450, 862460 and 86470 are the anomalies.
The trees are dated by comparing ring width sequences to those of well-dated cores, building backwards in time from modern trees. The actual overlaps of these anomalous trees to well-dated trees are very tenuous, as summarized in Table 1. Tree 46 is dateable only with reference with trees 47 and 45: both of which dates are in question. Tree 47 is dateable only with reference to 2 (upstream) trees: 45 and 3. Trees 45 and 3 have more substantial overlaps, but quite different performance, as discussed below.
Table 1: Particulars of Early 11th Century Polar Urals Cores.
The next earliest trees (6 and 4 respectively) are dated to start in 1052 and 1059. Beginning in the second half of the 11th century, there is modest replication. Because most trees at the Polar Urals site are relatively short-lived in dendro terms (average of 128 years), arguably a higher degree of replication is needed to ensure crossdating success.
I mentioned yesterday that COFECHA quality control failed using the Polar Urals data set as archived. I have been able to get COFECHA reports by two different patches: 1) by deleting all records which do not meet COFECHA (or Larson) requirements i.e. ones with more than one break in the core and/or with long NA intervals; 2) by making a lot of new identification numbers so that each questionable core is split into subsegments with no more than one break and no long NA intervals.
I’ve archived the results of the RW run under the first method here [COFECHA run]. If you go to Part 5, you will see anomalously low correlation values for cores 862450, 862460 and 862470: no other cores in the entire record have correspondingly low correlations. (The same applies for the RW run under the second method.) In the crossdating information sent to me by Phil Jones, the correlation values for 862450, 862460 and 862470 were likewise substantially lower than for any other series. In statistical terms, if one took the correlations for the modern cores (31 of them) as being exactly dated and being a type of bootstrap sample for the distribution of correlations in correctly-dated cores, the correlations for each of these 3 cores fail a dating significance test at nearly a 99% degree of confidence.
I’ll illustrate these dating issues with some other calculations that I’ve made. As I understand it, COFECHA “slides” the undated series against a “master chronology” of dated series and calculates correlations. I’ve written up some programs to do this in R (and to give some additional information). A simple correlation statistic has end-effect disadvantages (when the overlap goes down to very low numbers), so I’ve done the same calculations with t-statistics, making N the period of overlap between the master chronology and the series to be dated. Figure 2 below shows the t-statistics (essentially the correlation adjusted for degree of overlap) for a well-dated modern core (862462). You can readily see a marked spike in both the RW and MXD series at a start date of 1858 — which is the start date in the archived series. There are over 1000 correlations taken here — so that a t-statistic with 95% is not sufficient. In fact, the correct t-statistic is 99.99% significant.
Figure 2. Sliding t-statistics for core 862462. Top — RW; middle — MXD; bottom — average.
What happens with the 4 cores in question: 862030, 862450, 862460 and 862470?
862030 has a very strong RW t-statistic and moderately strong MXD t-statistic at the assigned start date of 1015. It is also an in-sequence numbered core.
Figure 3. Sliding t-statistics for core 862030.
Now look at 862470 dated against all cores except the other 2 “undated” cores 862450 and 862460. There is no spike indicating a compelling start date and the t values fluctuate at levels quite similar to fluctuations for incorrect dates in the above correctly dated cores. This is one of the 3 cores used to show that 1032 is the “coldest” year of the millennium.
Figure 4. t-statistics for core 862470 (supposedly dated 966-1054).
Next, let’s look at core 862450, dated 914-1130. This overlaps most of the same cores as 862030. However, here there is no distinctive upspike. The t-statistic for the assigned start date of 914 is slightly elevated, but not to the significance of well-dated cores. One must conclude that the date of 862450 is simply unknown and cannot be used to assert that 1032 is the coldest year of the millennium.
Figure 5. t-statistics for core 862450 (supposedly dated 914-1130).
Finally core 862460 is a very short core, dated 936-1007, and dated only by reference to 862450 (against which the correlations are unremarkable). Against reasonably-dated cores, as shown below, no dating emerges.
Figure 6. t-statistics for core 862460 (supposedly dated 936-1007).
In inquiries about the dating, the answer from Phil Jones has been that the Swiss do not make errors on these things and that 1032 is a very distinctive year. What seems to have happened is that core 862030 (reasonably well dated) had a low density in 1032. Similar low densities are not unusual in the Polar Urals record and comparable examples occurred in the 1980s in individual trees. It looks to me like cores 862450 and 862470 (which also have a ring with low density) were dated by lining up their low density rings with the 1032 ring of 862030 and the impact on RW COFECHA or COFECHA-type results were simply disregarded. Now there were 3 out of 3 cores with extremely negative MXD values in 1032 and the "coldest" year of the millennium emerged.
For a year that 6 degrees C lower than normal (as claimed by Briffa et al [Nature 1995]), you would expect an impact in the RW series, but there is nothing odd there. You would expect it at other Russian sites, but 1032 passess unnoticed there.
It seems to me that the evidence is overwhelming that the Polar Urals site has inadequate replication in the 11th century and that the majority of cores used to claim that 1032 is the coldest year of the millennium (and to show a cold early 11th century) are misdated.