Post‐industrial late summer warming recorded in tree‐ring density in the eastern Tibetan Plateau

Abstract

Tree‐ring density has been suggested to be a useful proxy for revealing long‐term late summer or growing season temperature variability on the Tibetan Plateau (TP). However, the current chronology length of tree‐ring density records on the TP is obviously shorter than both tree‐ring width and tree‐ring isotope records. This phenomenon implies the possibility of extending the current tree‐ring density record into earlier times and provides us with an opportunity to evaluate recent warming on a longer time scale. In this study, we present a 640‐year tree‐ring maximum latewood density (MXD) chronology of Balfour spruce back to 1,375 CE in the eastern TP. This tree‐ring MXD chronology is longer than the previous ones on the TP. Growth‐climate relationship analysis shows that the established MXD chronology correlates significantly and positively with August–September mean temperatures recorded at the nearest meteorological station over the common period of 1954–2014 (r = 0.66, effective degree of freedom [edf] = 62.7, p < 0.0001). Based on the growth‐climate response relationship, the August–September mean temperature was reconstructed from 1,625 to 2,014, which is the reliable period of the MXD chronology, with the expressed population signal (EPS) greater than 0.85. The reconstructed August–September temperatures show an increasing trend since the late 19th century, and this reconstruction suggests that the last 10‐, 30‐, 50‐ and 100‐year periods all appear to be the warmest over the past 390 years. Together with preciously published temperature reconstructions based on tree‐ring MXD near our study area, the results of this study demonstrate that the southeastern TP has experienced post‐industrial warming since the late 19th century.