Modern changes of the climate and glaciers in China's monsoonal temperate-glacier region

Abstract

Climatic data, ice core records, the tree ring index and recorded glacier variations have been used to reconstruct a history of climatic and glacial changes in the monsoonal temperate-glacier region of southwestern China during the last 400 years. All the results indicate that the temperature in the region increased in a fluctuating manner during the 20th century, after the two cold stages of the Little Ice Age during the 17th-19th centuries, with a corresponding retreat of most of the glaciers against a background of global warming. However, the amount, trend and amplitude of variation of precipitation have differed in different parts of the region. The climatic records in the Dasuopu ice core, from the Himalaya area in the western part of the region, show a decreasing trend of precipitation, the converse of the trend of temperature. In the Hengduan Mountains and other areas of the eastern part of the region, however, a rising trend of rainfall has accompanied increasing temperatures, as a result of the variable atmosphere circulations from different sources. The data indicate that the southwestern monsoon, which is the principal controlling factor in the Chinese monsoonal temperate-glacier region, can be classified into two parts. One is the Indian monsoon from the Arabian Sea, passing across the Indian Peninsula. This transports the vapour for precipitation in the Himalaya area, the western part of the monsoonal temperate-glacier region. The other part is the Bengal monsoon from the Bay of Bengal, passing over Bangladesh and Burma. This is the major source of precipitation in the Hengduan Mountains and other areas of the eastern part of the region. In addition, the eastern part is influenced by the southeast monsoon from the western Pacific, whilst the western part is affected by the southern branch of the westerly circulation in winter. This complex atmospheric situation results in different patterns of precipitation in the western and eastern zones.

通过对中国季风温冰川区的气候实测资料、冰芯记录、树木年轮指数和冰川进退记载等多种指标的综合分析,较详细地研究了400年以来本区气候与冰川变化。自17~19世纪小冰期的两个寒冷阶段以后,中国季风温冰川分布区气温普遍波动上升,与全球变暖的大背景一致, 大部分冰川正在后退,但降水量变化则比较复杂,达索普冰芯记录證明,本区西部的喜马拉雅山地区降水量表现为下降的趋势,与气温变化相反,而东部的横断山等地的降水则表现为上升的趋势,与气温变化同步,这主要是不同来源大气环流影响的结果。研究区主要盛行来源于印度洋的西南季风,此外,其东部还受来源于西太平洋东南季风的影响,西部受西风环流南支的影响,造成中国季风温冰川区东西部不均匀的降水分布和变化趋势。小冰期以后,我国的季风温冰川对气候变暖反应敏感,绝大部分冰川持续后退。20世纪80年代以来,后退速度加剧,但后退幅度和规模因地而异。