The tenth IMSC, Beijing, China, 2007 - International Meetings on ...

Linear and non-linear reconstruction from tree-ring series and written documents and the
problem of low frequencies and missing data
Speaker: Guiot, Joel
Guiot, Joel
CEREGE CNRS, Aix-en-Provence, France
guiot@cerege.fr
Nicault, Antoine
CEN, University of Laval, Quebec, Canada
Climatic reconstructions for the last millennium based on long tree-ring series and, when
available, on historical written documents, have several crucial problems related, to the
calibration (linear or non-linear methods, stationarity and range of the climatic variable), the
validation of the estimates (availability of independent data, method), the variability amplitude
of the extrapolation and the low frequency component of the reconstructed signal. Various
methods have been proposed as well for the pre-processing of the low frequency component
of the tree-ring series (standardization) than for the calibration method or the post-processing
of the reconstructions. We illustrate our discussion with examples taken from our own works
(reconstruction of temperature in Europe and summer PDSI in the Mediterranean region) that
we compare with approaches found in the recent literature (Mann et al, 2005; Rutherford et al,
2005; Burger et al, 2006 …). We will propose some solutions for the various problems pointed
out. So non linear calibration techniques such as analogues methods and artificial neural
network are useful for reconstructing the full range of the climatic variables and to perform in
presence of missing data (it is compared to the regularized expectation maximization (RegEM)
method). A combination of cross-validation and bootstrap technique is useful for a robust
validation. <strong>The</strong> treatment of the tree-ring series trend by using a flexible regional growth curve
is also a good solution for saving low frequencies in the reconstructed climatic series. Finally
we propose that, in the future, the use of inverted process models is an integrated approach
able to deal with most of the problems discussed in the talk.
<strong>The</strong> 'Hockey Stick' and the 1990s: A Statistical Perspective on Reconstructing Hemispheric
Temperatures
Speaker: Bo Li
Bo Li
National Center for Atmospheric Research
boli@ucar.edu
Douglas W. Nychka
National Center for Atmospheric Research
Caspar M. Ammann
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