Briffa 2000 is one of the canonical “independent” reconstructions in the IPCC AR4 spaghetti graph, the Wikipedia spaghetti graph and similars. I’ve discussed it in the past, but I’m going to revisit this in light of the new information on Tornetrask and I’m going to run Brown’s inconsistency statistic on it.
Briffa used 7 series: Tornetrask, Taymir, Alberta (Jasper), the Jacoby North American composite, Yakutia, Mongolia and Yamal (replacing Polar Urals). Most of these series have been updated since Briffa 2000: indeed the updates were available. Tornetrask was updated in Grudd’s thesis; Taymir is relatively up-to-date; Rob Wilson updated Jasper, Alberta; Yakutia is updated – it;s the Indigirka River series in Moberg; Mongolia is updated; the Jacoby composite should be updated, but important series from D’Arrigo et al 2006 remain unarchived. Although there are hundreds of measurement data sets at ITRDB, these measurements are, for the most part, conspicuously absent: Tornetrask(other than a subset archived by Schweingruber); Taymir; Luckman’s Jasper, Alberta; Yakutia; Yamal. JAcoby’s Mongolia is archived and some of the Jacoby data.
The chronologies used in Briffa 2000 are available and I could exactly replicate the “normalized” composite as shown in the top panel below. The Briffa 2000 “reconstruction” was archived in connection with the Briffa et al 2001 but does not match the normalized composite, though the methodology is supposed to be only a linear transformation. When I reproduce the reported method, I get a somewhat different answer. I have no idea how Briffa got from his normalized series to the archived reconstruction. For replication purposes, I’ve used the replication algorithm that yielded the bottom panel, which is the best that I can do right now and works adequately enough for sensitivity.
For a sensitivity analysis of the impact of updating, I did the following updates (Taymir is pretty up-to-date. Only the Jacoby NOAMER series is not millennial. )
Tornetrask – the Grudd version;
Yakutia – the version used in Moberg, which extends to a millennium series;
Polar Urals – Esper’s Polar Urals update, rather than the Yamal substitution;
Mongolia – updated version used in Osborn and Briffa 2006
Alberta – Luckman-Wilson updated version used in Osborn and Briffa 2006
This yielded the following two panels – the top being the normalized composite in the same style as before and the bottom being the temperature reconstruction.
In this rendering, the maximum is in the 11th century, with an elevated modern period in the 1930s. The sensitivity version and the archived version are very close through the 19th century but their early trajectories increasingly diverge. Whereas the modern period was the warmest using older data, the 11th century is “warmer” here. This result is not “independent” of a similar result for the Jones series as key series overlap – but this non-independence existed already. Also the “divergence problem” is noticeable, especially recently where ring widths have not responded to very warm recent temperatures, raising questions about the ability of these proxies to record possible past warmth. Replacing the Polar Urals update with Yamal attenuates the MWP relative to the modern period.
Next here is a plot of Brown’s Inconsistency R(b) for the original Briffa network over the period of 100% representation (1601-1974). This shows rather dramatic inconsistency in the 19th century (and not so much in earlier periods). What does this signify? Dunno.
Next here is the same thing for the 6 series network of millennium series (here from 950 to 1990). Again this shows far more coherence in the modern period than in earlier periods. Prior to the 20th century, the inconsistency values are running at levels consistent with random data (the red line), with coherence existing only in the 20th century. Why is this? Dunno. These results certainly indicate that efforts to “reconstruct” past climate from this data are doomed, but I’m still feeling my way through this style of looking at the data.