中文摘要：

13世纪上半叶蒙古帝国发动的3次西征极大地改变了欧亚大陆的政治格局和历史进程，成为世界最为重大历史事件之一；其发生原因一直是学术界关注的焦点，人们提出了各种假说，其中气候变化驱动说，即干旱或／和降温事件触发蒙古西征说最具影响力。文章依据古气候研究进展对蒙古西征的动因进行了重新研究，首先对蒙古西征各种假说进行了回顾，重点介绍和评述了气候变化驱动说，然后根据我国高分辨率气候重建资料，结合欧亚大陆其他地区的古气候重建成果，恢复了蒙古西征时期的气候背景；结果发现蒙古西征并非发生在传统上所认为的干旱或／和降温期，而是发生在相当于中世纪温暖期中的中后期，而且当时蒙古民族主要生活住居地区还比较湿润。研究结果对传统的气候驱动说提出了挑战，认为蒙古西征并非干旱或／和降温事件所触发，相反，当时温暖而湿润的气候环境为蒙古西征提供了良好的物质基础。研究结果较好地解释了蒙古当时征讨的重点地区为什么是西北方而不是东南方的印度和南宋地区之谜。

英文摘要：

The first half of the 13th century marks a significant period in the history of Eurasian continent, during which the unprecedented Mongol westward conquests were launched over the Eurasian continent by Chinggis Khan and his tribal members in 1219 - 1225A. D., 1235 - 1241A. D., and 1252 - 1258A. D. , respectively. These westward conquests not only altered the political structure but also affected the history courses of Eurasian continent, thus being regarded as a milestone and a turning point in the history of Eurasian. At present, many issues related to Mongol westward conquests have been resolved gradually. However,the causes of such massive drives still remains a mystery with some questions for further exploration. For instance,why did Mongol Empire launch three times of westward conquests？ Why did the Mongol westward conquests occur during the first half of 13^th century？ Why was the initial expansion launched towards to the steppe in the northwest rather than the tropic zone and subtropical zone in the southeast？ These questions have attracted numerous researchers for more than one hundred years, among which famous geographer Ells Worth Huntington, palaeoclimatologist H. Lamb and historian Arnold J. Toynbee are included. Various hypotheses on the causes of Mongol westward conquests have been put forward,however none could give a satisfactory explanation. Traditionally much more attentions were paid to the role of climatic deterioration（drought or cooling or both）. In recent decades,great progresses have been made on the high-resolution and precisely-dated climate change,which could provide a solid background for such historical events. In this paper,the possible role of climatic change in the Mongol westward conquests are reconsidered based on Chinese historical documents, as well as several high-resolved data such as ice-cores, tree ring, marine-core and stalagmite records, which could be correlated well with several highly resolved climatic records on other regions of the world. Our results in