A critical evaluation of multi-proxy dendroclimatology in northern Finland

Twentieth-century summer (July-August) temperatures in northern Finland are reconstructed using ring widths, maximum density and stable carbon isotope ratios (delta C-13) of Scots pine tree rings, and using combinations of these proxies. Verification is based on the coefficient of determination (r(2)), reduction of error (RE) and coefficient of efficiency (CE) statistics. Of the individual proxies, delta C-13 performs best, followed by maximum density. Combining delta C-13 and maximum density strengthens the climate signal but adding ring widths leads to little improvement. Blue intensity, an inexpensive alternative to X-ray densitometry, is shown to perform similarly. Multi-proxy reconstruction of summer temperatures from a single site produces strong correlations with gridded climate data over most of northern Fennoscandia. Since relatively few trees are required (<15) the approach could be applied to long sub-fossil chronologies where replication may be episodically low. Copyright (C) 2010 John Wiley & Sons, Ltd.