Detecting instabilities in tree-ring proxy calibration 1Netherlands Environmental Assessment Agency (PBL), The Netherlands
2Swiss Federal Research Institute WSL, Birmensdorf, Switzerland
3Tree-Ring Laboratory, Lamont Doherty Earth Observatory, Palisades, New York, USA
4Centre for the Analysis of Time Series, London School of Economics and Political Science (LSE), London, UK
Received: 11 February 2010 – Published in Clim. Past Discuss.: 24 February 2010 Abstract. Evidence has been found for reduced sensitivity of tree growth to
temperature in a number of forests at high northern latitudes and alpine
locations. Furthermore, at some of these sites, emergent subpopulations of
trees show negative growth trends with rising temperature. These findings
are typically referred to as the "Divergence Problem" (DP). Given the high
relevance of paleoclimatic reconstructions for policy-related studies, it is
important for dendrochronologists to address this issue of potential model
uncertainties associated with the DP. Here we address this issue by
proposing a calibration technique, termed "stochastic response function"
(SRF), which allows the presence or absence of any instabilities in growth
response of trees (or any other climate proxy) to their calibration target
to be visualized and detected. Since this framework estimates confidence
limits and subsequently provides statistical significance tests, the
approach is also very well suited for proxy screening prior to the
generation of a climate-reconstruction network.
Revised: 31 May 2010 – Accepted: 05 June 2010 – Published: 15 June 2010
Two examples of tree growth/climate relationships are provided, one from the
North American Arctic treeline and the other from the upper treeline in the
European Alps. Instabilities were found to be present where stabilities were
reported in the literature, and vice versa, stabilities were found where
instabilities were reported. We advise to apply SRFs in future
proxy-screening schemes, next to the use of correlations and RE/CE
statistics. It will improve the strength of reconstruction hindcasts.
Citation: Visser, H., Büntgen, U., D'Arrigo, R., and Petersen, A. C.: Detecting instabilities in tree-ring proxy calibration, Clim. Past, 6, 367-377, doi:10.5194/cp-6-367-2010, 2010.