我国“中世纪温暖期”气候的初步推断

根据历史文献中有关喜暖的亚热带作物苧麻、柑桔种植地点记录认为,13世纪中叶是一个典型的气候温暖期。由现代的作物种植气候区划资料推断,13世纪中叶我国中部地区年平均气温高于现代0.9—1.0℃,1月平均气温高于现代0.6℃以上,极端最低气温的多年平均值高于现代3.5℃。新近得出的南宋时代杭州春季终雪日期的资料比原先公布的日期一般提早7天。这项新资料的分析表明,南宋时代春季气温至少不低于现代,原先的有关南宋寒冷期的论断尚须更多的新资料进一步研讨。

A STUDY ON THE MEDIEVAL WARM PERIOD IN CHINA

Using the ancient record of plantings of Citrus tree and Boehmeria nivea (Ramie), an important fiber plant, some distribution maps of the two plants during the 8th, 11th and 13th centuries have been worked out. Comparing the historical planting distribution with the modern ones, it can be noted that the northern boundaries of Citrus tree and Boehmeria nivea in the 13th century laid to the north of the modern boundaries. The plant boundaries in the 13th century suggests that the climate during that dine might be the watrnest for the last 1 000 years. Based on the recent results of study on the climatic zoning of Citrus planting and on the climatic condition required by Boehmeria nivea for various cropping times, by using the historical records on the northern boundary of planting Citrus and the northernmost places where Boehmeria nivea could yield 3 crops a year in the 13th century, it can be estimated that the annual mean temperature in the 13th century might be 0.9—1.0℃ higher than that at present, the monthly mean temperature in January might be 0.6℃ higher than that at present, and the mean extreme minimum temperature might be 3.5℃ higher than that at present in the southern Henan Province. In addition, a new set of data for the date of the latest snowfall in spring in Hangzhou in the period of South Song dynasty obtained recently is generally 7—9 days earlier than that of the data set published previously. The statistics suggests that the average date of the latest snowfall for each decade between 1131—1264AD might be 5 days earlier than that at present in Hangzhou, and also earlier than that in Shanghai and Nanjing at present. Therefore, the previous conclusion that temperature in April in South Song dynasty was 1—2℃ lower than that of today should be revised.