Absence of late-summer warming trend over the past two and half centuries on the eastern Tibetan Plateau

Climate on the Tibetan Plateau is often considered sensitive to global changes, yet the degree of sensitivity in different spaces and seasons prior to instrumental records is not clear. In this paper, we studied tree-ring maximum latewood density (MXD) to examine the late-summer (August-September) temperature variation over the past two and half centuries on the eastern Tibetan Plateau. The MXD regional chronology was established from 109 tree-ring samples of Balfour spruce [Picea likiangensis var. balfouriana (Rehd. et Wils.)] at four high elevation sites. The chronology exhibited a high correlation (r = 0.82, n = 56, p < 0.001) with the mean August-September temperature. Using the tree-ring data, we reconstructed the late-summer temperature for the period A.D. 1765-2009. The reconstruction accounted for 71.4% of the variance in instrumental temperature in the period 1954-2009. The reconstructed temperature did not show a warming trend in the past 250 years, suggesting a unique characteristic of late-summer temperature variability in the study region of the Tibetan Plateau. Our tree-ring data are useful for further understanding of the plateau's thermal condition in late summer and its role in regulating southward retreat of the Southwest Asian monsoon.