Comparison of high-resolution climate proxies from the Tibetan Plateau and Scandinavia during the last millennium

In this preliminary study, we compare two tree-ring width chronologies from the Tibetan Plateau and Scandinavia. At their altitudinal limit of distribution Juniperus tibetica (Tibet) and Pinus sylvestris (Scandinavia) are sensitive to climate variability, and both chronologies cover the last 1000 years. We used regional curve standardization (RCS) of the tree-ring data, to reveal growth variability on annual to centennial timescales. Both records showed similar evolution in tree-growth variability, on decadal and longer time scales, between c. 1100 and 1550. However, the tree-ring data indicated a gradually varying climate in Tibet compared to the more frequent oscillations seen in the Scandinavian record. The impact of the Medieval Warm Period is not clearly evident at either site. Tree growth was reduced during the Little Ice Age (LIA) both in Tibet and Scandinavia, but the timing and magnitude of the LIA differ between the two regions. In Tibet, unfavourable climate was inferred mainly between c. 1400 and 1550 and in the mid-17th century, while in Scandinavia harsh growth conditions prevailed more or less from the late 16th century to the early 20th century. Around 1550 the two chronologies diverge, and it is suggested that this was caused by a strengthening of the Asian monsoon. Warming in the 20th century is more pronounced in Scandinavia. In Tibet, tree growth is declining, which may be a response to a strengthening of the Asian summer monsoon during the last four centuries.