Yamal: a divergence problem (click)Because Climate Audit is overloaded, here's the Google cache.
... a copy at Climate Audit (click)
The finding is very easy to describe. Briffa et al. (Science, published September 2009, see also Briffa et al., Philosophical Transactions 2008) offered another version of a "hockey stick graph", a would-be reconstruction of the temperatures in the last 2000 years that claimed to show a "sudden" warming in the later part of the 20th century, much like the discredited paper by Michael Mann et al.
Papers by Mann, Bradley, and Hughes in 1998 and 1999, included as a symbol of global warming into the previous IPCC report in 2001, indicated constant temperatures before 1900 and a dramatic warming afterwards. However, the papers have been proven wrong.
If you haven't heard about the lethal bug of the Mann methodology yet, the problem of the MBH98, MBH99 papers was that the algorithm preferred proxies - or trees (or their equivalents) - that showed a warming trend in the 20th century, assuming that this condition guaranteed that the trees were sensitive to temperature.