Tree ring density-based warm-season temperature reconstruction since A.D. 1610 in the eastern Tibetan Plateau

• A new maximum latewood density chronology for purple cone spruce is presented.
• The density chronology is well correlated with April–September mean temperature.
• Eastern Tibetan Plateau warm-season temperature was reconstructed back to AD 1610.
• The reconstruction shows that the 20th century warming is unprecedented.

Tree-ring samples from purple cone spruce (Picea purpurea) were collected at four sites on the eastern Tibetan Plateau. Maximum latewood density (MXD) was measured by X-ray densitometry and a regional standard chronology was established from the four MXD chronologies using the Regional Curve Standardization (RCS) method. Based on significant correlation between the regional RCS chronology and mean April–September temperature, warm-season (April–September) temperature variability was reconstructed back to 1610 for the eastern Tibetan Plateau. The reconstruction explained 58.5% of the variance in the instrumental period (1961 to 2009). In the past 400 years, there were five cold periods with lower than average and four warm periods with higher than average. The temperature reconstruction captured the unprecedented warming in the 20th century, where the last ten years were the warmest decade in the last 400 years. The Ensemble Empirical Mode Decomposition (EEMD) was used to extract the multi-scale fluctuation of the temperature reconstruction. Four quasi-oscillations with periodicities of 2.2–2.7 years, 5.1–7.9 years, 11.9–15.4 years and 21.8–26.2 years indicated major fluctuations of original temperature. Agreement with other temperature proxies implied a high degree of confidence for our reconstruction and its large-scale spatial representation. The temperature reconstruction showed a warming trend on a longer time scale in the eastern Tibetan Plateau.