Understanding surface temperature changes over the Tibetan Plateau in the last millennium from a modeling perspective

To improve our understanding of temperature variations on the Tibetan Plateau (TP) and their response to external forcings, recent warming needs to be examined in a historical context during the last millennium. While reconstructions on the TP are well developed, less effort has been devoted to data-model comparisons and the physical mechanisms of TP temperature changes based on model simulations. Here, we investigate the TP temperature changes during the last millennium based on reconstructions and model simulations. Multiple reconstructions reveal obvious warm and cold fluctuations in the TP temperature, characterized by a warm period during 850-1250 CE and a cold interval during 1400-1850 CE, followed by the current warm period since 1850 CE. The CESM Last Millennium Ensemble simulation matches the reconstructions well. Multiple linear regression analysis based on model simulations indicates that external forcings account for 82% of the TP temperature variance at a multidecadal time scale during 850-2005 CE, among which volcanic forcing has a major contribution. Single-forcing experiments reveal that the colder climate observed during the Little Ice Age compared to the Medieval Climate Anomaly period is dominated by stronger and more frequent volcanic eruptions and an increased crop fraction. The warmer climate in the TP region after 1850 compared with that of the last millennium is mainly caused by increased greenhouse gas emissions, which are counteracted by ozone-aerosol forcing and land use-land cover changes. Our results have valuable implications for understanding the current TP climate change in the context of last millennium perspective.