Climatic changes during the past two millennia along the Ancient Silk Road

The Ancient Silk Road has a history of more than 2000 years and gave birth to the diversities of culture between East and West. Climate change may have played a crucial role in this process and in the flourishing and decline of civilizations. In this work, high-resolution temperature reconstructions covering more than 1000 years along the Ancient Silk Road are reviewed, and the main characteristics of temperature and hydroclimatic changes are summarized. Four warm stages occurred that included the 1st-3rd centuries, the late 7th century to the early 11th century, the mid-12th century to the mid-13th century, and since the 20th century, and three cold stages, including the 4th century to the early 7th century, the middle of the 11th century to the early 12th century, and the end of the 13th century to the mid-19th century, occurred. Within these various stages, regional differences existed in amplitudes and starting-ending years of the cold/warm phases. Wetness and dryness variabilities during the Medieval Climate Anomaly (MCA) were greater than during the Little Ice Age in Northwestern China. The climate was dry during the MCA in Central Asia, South Scandinavia, and North-central Europe. In addition, the climate backgrounds of several famous kingdoms flowering and social events that flourished during these times, such as the Roman Empire, the Loulan Kingdom, the Tibetan Kingdom, and the three unprecedented Mongol westward conquests, are discussed.