全球变化知识资源中心

Assessing paleo-climatic changes and the underlying driving mechanisms are an essential (and often poorly understood) first-step for understanding if natural variability in Earth's climate system from tectonic processes and orbital forcing could produce observed changes in surface processes. In this study, we take this first step of evaluating climate change in the Tibetan Plateau region for different distinct climate states. We do this using a high-resolution regional climate model parameterized for the Cenozoic rise of the Plateau and prominent Quaternary glacial and interglacial episodes. The main objective is to delimit the range of climate variability due to important natural drivers in the region by comparing climate changes during the main Cenozoic uplift period with climate anomalies during the last glacial maximum and the mid-Holocene optimum. This helps to interpret environmental changes documented by proxy data and to benchmark man-made climate changes expected during the 21st century. The innovative aspects of this study pertain to the use of a consistent high-resolution modeling framework and a multivariate statistical assessment of climate types and their shift during the various paleo-climatic episodes.

Reduced plateau elevation leads to regionally differentiated patterns of higher temperature and lower precipitation amounts on the plateau itself, whereas surrounding regions are subject to colder conditions. In particular, Central Asia receives much more precipitation prior to the uplift, mainly due to a shift of the stationary wave train over Eurasia. Cluster analysis indicates that the continental-desert type climate, which is widespread over Central Asia today, appears with the Tibetan Plateau reaching 50% of its present-day elevation.

The mid-Holocene is characterized by slightly colder temperatures, and the last glacial maximum by considerably colder conditions over most of central and southern Asia. Precipitation anomalies during these episodes are less pronounced and spatially heterogeneous over the Tibetan Plateau. The simulated changes are in good agreement with available paleo-climatic reconstructions from proxy data. The present-day climate classification is only slightly sensitive to the changed boundary conditions in the Quaternary. However, it is shown that in some regions of the Tibetan Plateau the climate anomalies during the Quaternary have been as strong as the changes occurring during the uplift period.