中文摘要：

巴颜喀拉山地处青藏高原东缘，是长江和黄河上游的分水岭，其生态环境与气候背景变化对下游地区的生态安全具有重要影响，但较短的器测记录限制了对该地区气候变化历史和机制的认识。本文基于巴颜喀拉山东端青海云杉（Picea crassifolia）486年树轮宽度年表，重建了该地区376年的夏季（6月、7月和8月）平均气温变化。结果显示，研究区经历了2个冷期（1724~1789年、1864~1994年）和3个暖期（1637~1723年、1790~1863年和1995~2012年）。经集合经验模态分解（Ensemble Empirical Mode Decomposition，简称EEMD）发现，重建温度序列的年代际和多年代际信号与太平洋年代际涛动（Pacific Decadal Oscillation，简称PDO）和北大西洋涛动（North Atlantic Oscillation，简称NAO）的变化有较好的一致性，表明PDO和NAO可能对研究区夏季温度变化具有重要影响，但具体影响机制需要气候模式来进一步揭示。

英文摘要：

The Bayan Har Mountains are located in the water divide of upstream regions of the Yangtze and Yellow Rivers, China｜their ecological environment and climate change has important influences on ecological security of the downstream areas. Meanwhile, the Bayan Har Mountains are situated on the eastern margin of Qinghai-Tibetan Plateau and the climate transition zone from the alpine climate zone to the eastern subtropical monsoon zone. Thus, the climate variability in the study area is sensitive to the global climate change. However, the history and mechanism of climate variability in this region is poorly understood due to the scarcity of long-term instrumental data. In this paper, a 486-yr tree-ring width chronology of Picea crassifolia is established with 57 cores from 29 trees. The sampling site（YBG） is located on the eastern Bayan Har Mountains（32°37＇N, 101°34＇E｜3553 m a.s.l.）. The Subsample Signal Strength （SSS） of the standard tree-ring chronology was larger than 0.85 during the period from 1637 A.D.to 2012 A.D. The limited factor of the tree-ring growth in study area was considered as mean summer（June, July and August）temperature in the growth year, with a correlation coefficient of 0.59（p〈0.01）. Accordingly, we reconstructed summer mean temperature variability over the past 376 years. The equation of reconstruction was stable, sharing 34 % of the total variance of the observed data over the common period. The turning points of the accumulative anomaly series are illustrated that the reconstructed summer temperatures over the past 376 years included two cold periods（1724~1789A.D. and 1864~1994A.D.）and three warm periods（1637~1723A.D., 1790~1863A.D.and 1995~2012A.D.）. The Ensemble Empirical Mode Decomposition（EEMD）results show that the decadal and multi-decadal summer temperature variability is related to the Pacific Decadal Oscillation（PDO）and the North Atlantic Oscillation（NAO）. This indicates that the reconstructed summer temperature may be affected by the