Setting the tree-ring record straight

Josef Ludescher,Ulf Büntgen,Hans Joachim Schellnhuber,Armin Bunde

doi:10.1007/s00382-020-05433-w

Abstract

Tree-ring chronologies are the main source for annually resolved and absolutely dated temperature reconstructions of the last millennia and thus for studying the intriguing problem of climate impacts. Here we focus on central Europe and compare the tree-ring based temperature reconstruction with reconstructions from harvest dates, long meteorological measurements, and historical model data. We find that all data are long-term persistent, but in the tree-ring based reconstruction the strength of the persistence quantified by the Hurst exponent is remarkably larger (hcong 1.02) than in the other data (h= 0.52–0.69), indicating an unrealistic exaggeration of the historical temperature variations.We show how to correct the tree-ring based reconstruction by a mathematical transformation that adjusts the persistence and leads to reduced amplitudes of the warm and cold periods. The new transformed record agrees well with both the observational data and the harvest dates-based reconstructions and allows more realistic studies of climate impacts. It confirms that the present warming is unprecedented.

Highlights

One of the important questions in global change research is which impact the increase of the recent warming will have on societies and human beings (Stocker et al 2013)
We focus on central Europe, where the temperatures of the past can be obtained from tree-rings (Büntgen et al 2011), and from long meteorological measurements (1753-present) (Berkley Earth; Czech Hydrometeorological Institute) as well as from grape and rye harvests date records (Chuine et al 2004; Labbé and Gaveau 2011; Meier et al 2007; Wetter and Pfister 2011) that date back up to 1370 and from historical model data (850-1849) (Jungclaus et al 2010; Earth System Grid Federation)
We demonstrate that it is this overestimation of the long-term persistence that leads to the enormous climate variations in the tree-ring based reconstruction and discuss its potential origin

Summary

Introduction

One of the important questions in global change research is which impact the increase of the recent warming will have on societies and human beings (Stocker et al 2013). The main source for these kinds of data are treering chronologies that in some cases cover more than two Potsdam Institute for Climate Impact Research, 14473 Potsdam, Germany. We focus on central Europe, where the temperatures of the past can be obtained from tree-rings (Büntgen et al 2011), and from long meteorological measurements (1753-present) (Berkley Earth; Czech Hydrometeorological Institute) as well as from grape and rye harvests date records (Chuine et al 2004; Labbé and Gaveau 2011; Meier et al 2007; Wetter and Pfister 2011) that date back up to 1370 and from historical model data (850-1849) (Jungclaus et al 2010; Earth System Grid Federation)

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Conclusion