At the Bishop Hill blog, the twisty-turny story of the bristlecone pine temperature reconstruction effort:
The story of Michael Mann’s Hockey Stick reconstruction, its statistical bias and the influence of the bristlecone pines is well known. Steve McIntyre’s research into the other reconstructions of the temperatures of the last millennium has received less publicity, however. The story of the Yamal chronology may change that.
The bristlecone pines that created the shape of the Hockey Stick graph are used in nearly every millennial temperature reconstruction around today, but there are also a handful of other tree ring series that are nearly as common and just as influential on the results. Back at the start of McIntyre’s research into the area of paleoclimate, one of the most significant of these was called Polar Urals, a chronology first published by Keith Briffa of the Climate Research Unit (CRU) at the University of East Anglia. At the time, it was used in pretty much every temperature reconstruction around. In his paper, Briffa made the startling claim that the coldest year of the millennium was AD 1032, a statement that, if true, would have completely overturned the idea of the Medieval Warm Period. It is not hard to see why paleoclimatologists found the series so alluring.
Yamal saves the day
Some of McIntyre’s research into Polar Urals deserves a story in its own right, but it is one that will have to wait for another day. We can pick up the narrative again in 2005, when McIntyre discovered that an update to the Polar Urals series had been collected in 1999. Through a contact he was able to obtain a copy of the revised series. Remarkably, in the update the eleventh century appeared to be much warmer than in the original — in fact it was higher even than the twentieth century. This must have been a severe blow to paleoclimatologists, a supposition that is borne out by what happened next, or rather what didn’t: the update to the Polar Urals was not published, it was not archived and it was almost never seen again.
With Polar Urals now unusable, paleclimatologists had a pressing need for a hockey stick shaped replacement and a solution appeared in the nick of time in the shape of a series from the nearby location of Yamal.
