Late Holocene variations in monsoon intensity in the Tibetan-Himalayan region -: Evidence from tree rings

The knowledge of past climate variability is of great relevance for understanding the dynamics of the climate system. We developed new reconstructions of the variation of summer monsoon intensity in High Asia during the past millennium from a network of tree-ring series from the Tibetan Plateau. We studied several wood parameters which contain information about different seasonal climate signals, i.e., ring width, maximum latewood density and stable carbon isotopes in wood cellulose. In central Tibet, periods of low pre-monsoon rainfall occurred during the second half of the 14(th) century, around 1600 AD, during the 1880's and the first half of the 20(th) century. High summer monsoon activity in eastern Tibet occurred between 1220 and 1400 AD and probably corresponds to the "Medieval Warm Period". Several minima in monsoon intensity occurred during the "Little Ice Age" between the first half of the 16(th) century and the second half of the 18(th) century. The monsoon intensity after 1980 AD is the highest since the first half of the 17(th) century. This finding is generally consistent with climate model predictions that suggest an intensification of the summer monsoon with ongoing climate warming. Thus, tree-ring networks can be used as an independent data source for the validation of climate models. The summer monsoon activity is presently still within the range of the natural variability documented during the past thousand years.