Revising midlatitude summer temperatures back to A.D. 600 based on a wood density network

Abstract

Annually resolved and millennium-long reconstructions of large-scale temperature variability are primarily composed of tree ring width (TRW) chronologies. Changes in ring width, however, have recently been shown to bias the ratio between low- and high-frequency signals. To overcome limitations in capturing the full spectrum of past temperature variability, we present a network of 15 maximum latewood density (MXD) chronologies distributed across the Northern Hemisphere extratropics. Independent subsets of continental-scale records consistently reveal high MXD before 1580 and after 1910, with below average values between these periods. Reconstructed extratropical summer temperatures reflect not only these long-term trends but also distinct cooling pulses after large volcanic eruptions. In contrast to TRW-dominated reconstructions, this MXD-based record indicates a delayed onset of the Little Ice Age by almost two centuries. The reduced memory inherent in MXD is likely responsible for the rapid recovery from volcanic-induced cooling in the fourteenth century and the continuation of warmer temperatures until ~1600.