Climate of the Past www.clim-past.net 1814-9324 1814-9332 6 3 2010 10.5194/cp-6-367-2010 http://www.clim-past.net/6/367/2010/ http://www.clim-past.net/6/367/2010/cp-6-367-2010.html http://www.clim-past.net/6/367/2010/cp-6-367-2010.pdf 367 377 2010-06-15 Detecting instabilities in tree-ring proxy calibration H. Visser hans.visser@pbl.nl U. Büntgen R. D'Arrigo A. C. Petersen Netherlands Environmental Assessment Agency (PBL), The Netherlands Swiss Federal Research Institute WSL, Birmensdorf, Switzerland Tree-Ring Laboratory, Lamont Doherty Earth Observatory, Palisades, New York, USA Centre for the Analysis of Time Series, London School of Economics and Political Science (LSE), London, UK 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. <br><br> 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. 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