thanks Green Sand,
re: Briffa et al project on "The Dendroclimatic Divergence Phenomenon", this is worth close attention... is there a paper in submission yet? The May 2012 end date for the grant suggests they wanted something in time for AR5.... which is appropriate if done rigorously, i.e., of course scientists should try to prepare all relevant data and assessments in time for AR5, it's just that we have seen a lot of dubious behavior from "The Team" in the past so they always deserve our watchful attention (we don't need a careless rubber-stamp of The Team's work slipped into AR5).

===================================================================

The Dendroclimatic Divergence Phenomenon: reassessment of causes and implications for climate reconstruction

http://www.cru.uea.ac.uk/cru/research/

Keith Briffa (PI),
Tim Osborn,
Tom Melvin

12/09 – 05/12

"Palaeoclimate reconstructions extend our knowledge of how climate varied in times before expansive networks of measuring instruments became available. These reconstructions are founded on an understanding of theoretical and statistically-derived associations acquired by comparing the parallel behaviour of palaeoclimate proxies and measurements of varying climate. Inferences about variations in past climate, based on this understanding, necessarily assume that the associations we observe now hold true throughout the period for which reconstructions are made. This is the essence of the uniformitarian principle. In some northern areas of the world, recent observations of tree growth and measured temperature trends appear to have diverged in recent decades, the so called "divergence" phenomenon. There has been much speculation, and numerous theories proposed, to explain why the previous temperature sensitivity of tree growth in these areas is apparently breaking down. The existence of divergence casts doubt on the uniformitarian assumption that underpins a number of important tree-ring based (dendroclimatic) reconstructions. It suggests that the degree of warmth in certain periods in the past, particularly in medieval times, may be underestimated or at least subject to greater uncertainty than is currently accepted. The lack of a clear overview of this phenomenon and the lack of a generally accepted cause had led some to challenge the current scientific consensus, represented in the 2007 report of the IPCC on the likely unprecedented nature of late 20th century average hemispheric warmth when viewed in the context of proxy evidence (mostly from trees) for the last 1300 years. This project will seek to systematically reassess and quantify the evidence for divergence in many tree-ring data sets around the Northern Hemisphere. It will establish a much clearer understanding of the nature of the divergence phenomenon, characterising the spatial patterns and temporal evolution. Based on recent published and unpublished work by the proposers, it has become apparent that foremost amongst the possible explanations is the need to account for systematic bias potentially inherent in the methods used to build many tree-ring chronologies including many that are believed to exhibit this phenomenon."