Temperature variations along the Silk Road over the past 2000 years: Integration and perspectives.

Reconstructing temperature changes along the Silk Road (SR) over the last two millennia can provide insights into past global changes and their impact on the rise and fall of ancient civilizations in this region. Numerous high-quality single-site paleotemperature records have been produced for the eastern part of the SR (mainly for the Xinjiang region and its surrounding areas), which provide the data basis for a comprehensive synthesis. In this study, we used objective criteria to select 10 high-quality ones from 30 temperature reconstructions derived from various geological archives including lacustrine sediments, ice cores, and tree rings in this region. Our aims are to summarize the pattern of temperature change over the past 2000 years, to provide a long-term viewpoint on the present warming, and to evaluate the impact of climate change on civilizations along the SR. The principal results are as follows: (1) The temperature variations over the last millennium are mutually consistent within these records. The study area experienced typical climate anomalies during the Medieval Warm Period (MWP, AD 1000–1250), the Little Ice Age (LIA, AD 1450–1850), and the Current Warm Period (CWP, AD 1850 to present); however, contrary to previous knowledge, the amplitude of climatic warming during the CWP did not exceed that during the MWP. (2) Fewer temperature records were available for the interval AD 1–1000, and there were large differences between them. For example, the reconstructed climate during both the Han Dynasty and the Sui-Tang Dynasties was either warm or cold, without prevailing consensus. (3) The warming during the MWP favored the rapid development of the SR route along the northern slopes of the Tianshan Mountains, and the cooling during the LIA contributed to the decline of the SR marked by the closure of the Jiayuguan Pass. Notably, the scarcity of temperature records and the discrepancies between them during AD 1–1000 in the eastern part of the SR have hindered our understanding of the hydroclimatic changes and their influence on the development of civilizations along the SR. Thus, it is important to obtain an increased number of high-quality reliable records spanning the past 2000 year, and to examine the occurrence of local signals of temperature changes during the period of AD 1–1000. On the other hand, the paleotemperature investigation on the western part of the SR over the last two millennia is wholly insufficient, and thus more high-quality single-site and integrated studies are needed, to facilitate more comprehensive insights into the coupled relationship between climate change and the rise and fall of civilizations along the entire length of the Silk Road. [ABSTRACT FROM AUTHOR]