Sunday, March 25, 2012


date: Wed Jul 29 16:56:48 2009
from: Tim Osborn <>
subject: Re: The Dendroclimatic Divergence Phenomenon NERC project
to: "Sheppard Sylv Miss \(SCI\)" <>

Hi Sylv,
there's no project website to link to. Here's a summary of the project:
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 Based on recent published and unpublished work by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.
At 10:52 29/07/2009, you wrote:

Hi Tim,

Ive received an RGN1 form for the above NERC project. Could you please send me a brief
description of the project to put up on the CRU website and a web link to the project if
there is one?


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