Summer mean temperature reconstruction based on tree-ring density over the past 440 years on the eastern Tibetan Plateau

Long climate records are very important to understand the past climate and assess the current status of climate variability compared with the long-term patterns. In this study, we developed a new tree-ring maximum density (MXD) chronology using 42 tree-ring cores from Balfour spruce on the eastern Tibetan Plateau (TP) to reconstruct the summer (July-September) mean temperature variability over the past 440 years. The results showed that the reconstruction explained 47.1% of the actual variances in summer temperature during the instrumental period from 1954 to 2009. The temperature reconstruction revealed three main cold periods and two main warm periods in the study area since 1570 CE. The reconstruction series captured unusual warming since the 1930s and indicated that the last twenty years (1990-2009) were the warmest period in the past 440 years. Strong agreements between the current reconstruction and other temperature reconstructions in the surrounding areas implied that our reconstruction exhibited high reliability and large spatial representation. Our temperature reconstruction also captured the cooling effects after fourteen major volcanic eruptions over the past 440 years. We found that the periodic cycle and decadal changes in temperature reconstruction were related to the influence of the El Nino-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO) and Atlantic Multi-decadal Oscillation (AMO). The study results could help understand the long-term temperature changes over the TP and provide an important reference for the detection and attribution of climate change.