Spatio-temporal patterns of centennial-scale climate change over the Tibetan Plateau during the past two millennia and their possible mechanisms

In order to project future changes in climate and their corresponding environmental and social impacts, it is of utmost importance to understand the spatiotemporal patterns of past climate changes on the Tibetan Plateau (TP). Although numerous records of late Holocene climate changes have been developed across the TP, the spatiotemporal patterns of changes in temperature and precipitation/moisture are unclear and a comprehensive review of this topic is urgently needed. Here, we present such a synthesis using currently available temperature and precipitation/moisture records from across the TP to understand spatial and temporal variations over the past two millennia. The main conclusions are as follows: 1) Temperature variations on the TP during the past two millennia are not homogeneous and show strong seasonality. Although patterns of mean annual temperature change on the TP during the past two millennia remain contradictory, summer temperature variations are generally consistent. The summer temperature reconstructions indicate that the warmest period during the past two millennia was in the middle ages, as opposed to the recent 20th century. 2) Precipitation/moisture patterns on the TP are spatially complex. The most striking feature is that an inverse pattern of precipitation/moisture variation can be detected over most parts of the TP between 600-1400 AD and 1400-1900 AD. Specifically, the eastern TP, southwestern TP, and part of the northeastern TP were generally wetter, whereas the southeastern TP, the southern TP, the northwestern TP, and part of the northeastern TP were generally drier during 600–1400 AD as compared to during 1400–1900 AD. However, such anti-phased hydroclimatic variability is not found in either the cold period of 1–600 AD or in the current warm period of the past century. This indicates that temperature and precipitation/moisture changes appear in multiple combinations. 3) Fluctuations in the intensity and seasonal movement of the westerlies and the Indian summer monsoon (ISM) over the Tibetan Plateau, as well as the associated climate variability modes (e.g., North Atlantic Oscillation (NAO), Indian Ocean dipole (IOD), ENSO, and Intertropical Convergence Zone (ITCZ)), might be responsible for the spatially complex patterns of climate anomalies over TP during the past 2000 years. 4) The results highlight the need for more high-quality paleoclimatic and paleoenvironmental reconstructions that span the past two millennia on the TP. Such reconstructions must have unambiguous climate significance, clear seasonality, site-specific calibration, and robust dating.