中文摘要：

利用通用地球系统模式CESM过去1500年气候模拟试验结果,对比分析中世纪暖期南、北半球气候变化特征及成因,对认识南、北半球暖期气候变化规律及其与外强迫变化的关系有重要科学意义。结果表明：中世纪暖期全球及南、北半球总体是变暖的,但仍存在峰谷变化,高纬地区增温幅度大于低纬地区,北半球中世纪暖期比南半球更为明显,其距平变幅也大于南半球。全球降水距平基本为正,南、北半球降水变幅基本相当,降水变化显著区域集中于低纬地区。太阳辐射是影响中世纪暖期全球及半球气温变化最显著的因素,火山活动对北半球气温变化也有较显著的影响。从全球尺度来看,降水由太阳辐射和火山活动共同影响,其中太阳辐射影响最为显著,但从半球尺度来看,火山活动是影响半球降水的重要因素。

英文摘要：

The characteristics and causes of the climate change over Northern Hemisphere（NH） and Southern Hemisphere（SH） during the Medieval Warm Period（MWP） are analyzed in this paper, based on the climatic simulation results over the past 1500 years using the Community Earth System Model（CESM）. Moreover, the commonality and difference in the variations of temperature and precipitation between the NH and SH are also investigated. Six experiments are compared in this study, including Control experiment（Ctrl）, Total solar irradiation experiment（TSI）, Volcanic eruptions experiment（Vol）, Greenhouse gases experiment（GHGs）, Land use and land cover change experiment（LUCC） and All forcings experiment（All）. Based on the comparison of simulated results with observation and proxy records, the CESM＇s performance of simulating MWP is verified. The characteristics of the simulated temperature and precipitation by the CESM show similarity to the observation and reconstructions. The results show that the MWP is a global phenomenon. However, the MWP is not a steady and continuous warm period, and there are peak-valley oscillation in it. The global climate is warm and moist as a whole during the MWP. Both the NH temperature variations and the SH temperature variations are generally consistent with those of the whole globe.During the MWP, the NH warming is more obvious than the SH warming and the temperature anomaly amplitude in the NH is significantly larger than the SH counterpart, because the land area of NH is larger than that of SH, and the SH is mainly covered by ocean. The high heat capacity of the ocean leads to the smaller anomaly amplitude of temperature change in the SH compared to its NH counterpart. Besides, during the MWP, the warming in the high latitudes of the NH and SH is stronger than that in the low latitudes. For the precipitation variations, the global mean precipitation anomaly is basically positive. But unlike the temperature, the amplitude of precipitation anomaly in the NH i