Over the past 30 years, Finnish dendrochronologists have developed a “supra-long” tree ring chronology now stretching back (Helama et al 2008) to 7600BP, well into the Holocene Optimum. Earlier versions of this chronology have been reported in many articles (e.g. Helama et al 2002, Eronen et al 2002 and references back into the 1990s plus articles here. Among other things, the chronology has been used to date changes in the treeline, which, in turn, has been used to estimate past temperatures.
We discussed one such study (Kultti et al 2006) at CA here (which estimated MWP temperatures as 0.55 deg C higher than at present) in passing in 2006, but, because of the focus on studies relied upon by IPCC, we haven’t had occasion to consider this data at length.
Y’see, although the Finnish chronology is a long well-dated chronology that would seem to meet any reasonable selection criteria governing Tornetrask or Yamal or bristlecones, this data wasn’t used in any of the AR4 multiproxy studies, nor was it used in Mann et al 2008. Nor was it mentioned in IPCC AR4 (a point that I’ll return to in another post.) Given that Briffa was a co-author of Eronen et al 2002 (one of the key publications), its not as though he was unaware of this data. So its exclusion from earlier studies really requires a little explanation.
We re-encountered this data because it was (long overdue) included in Briffa et al 2008. After 6 months and repeated efforts by Phil Trans B, Briffa finally archived the first tranche of data (a merged version of Swedish and Finnish data.) Not making things easy, Briffa didn’t provide any metadata as to where anything came from. This led to a bit of head-scratching, but I think that we can now be sure that the first 430 items are from Finland (with a few from Norway via the Finnish authors) and the rest from Sweden.
With some effort, I was able to match a few series to archived versions (e.g. one beam form Sodankyla church). Jean S reminded us that Mauri Timonen, one of the architects of the chronology, had commented previously at CA. and urged me to contact him about questions regarding the Finnish component of Briffa et al 2008. This proved to be a very felicitous reminder. I sent an email to Mauri Timonen of METLA a few days ago and received a very cordial reply in which he sent greetings to CA readers and expressed satisfaction that the Finnish timberline pine chronology was being discussed. He mentioned that the 2010 World Dendro Conference was being held in Finland.
He sent me a lot of data, including a listing of the 1087 samples in the supra-long chronology (of which the 430 most recent were used in Briffa et al 2008). Of these 1087 samples, metadata (including UTM northing, easting and altitude) were provided for 1039 trees – there are 3 institutions involved in Finnish sampling: METLA, University of Joensuu (SAIMA) and University of Helsinki and I think that the exclusions pertain to data from other institutions (I’m clarifying this.) He also sent me measurement data for 342 cores, 71 of which were selected into the supra-long chronology. I don’t know who made the selection, why a subset was taken or the criteria for subsetting (I didn’t notice an explanation in Helama et al 2002 or Eronen et al 2002).
It’s nice to contrast the openness of Timonen and METLA, with the surly attitudes that bedevil so many operatives in this field (Santer, Mann, Briffa, Jones, Thompson, Hansen,…) I must say that it affects one’s attitude to the data (and I have to watch out for this), as one inevitably is more critical of data that you have to fight to get.
So I’m a bit swamped with fresh data right now and having a pleasant time with it. I have a couple of posts in the works, one of which will discuss their estimates for the MWP and Holocene Optimum; one will be on IPCC review comments, one on RCS.
Briffa, K. R., V. V. Shishov, T. M. Melvin, E. A. Vaganov, H. Grudd, R. M. Hantemirov, M. Eronen, and M. M. Naurzbaev. 2008. Trends in recent temperature and radial tree growth spanning 2000 years across northwest Eurasia. Philosophical Transactions of the Royal Society B: Biological Sciences 363: 2271-2284.
Eronen, M., P. Zetterberg, K. R. Briffa, M. Lindholm, J. Merilainen, and M. Timonen. 2002. The supra-long Scots pine tree-ring record for Finnish Lapland: Part 1, chronology construction and initial inferences. The Holocene 12, no. 6: 673.
Helama, S., M. Lindholm, M. Timonen, J. Merilainen, and M. Eronen. 2002. The supra-long Scots pine tree-ring record for Finnish Lapland: Part 2, interannual to centennial variability in summer temperatures for 7500 years. The Holocene 12, no. 6: 681.
Timonen, M. Lustia Dendrochronology Project. http://lustiag.pp.fi/.