Recent variability of the climate and glaciers in China's monsoon region

摘要

Climatic data, ice core records, the tree-ring index and recorded glacier variations have been compared, and used to reconstruct a history of climatic and glacial changes in the monsoonal temperate-glacier region of southwestern China during the last 400 years. The results indicate that the region's temperature has increased in a fluctuating manner during the 20th century, after the two cold stages of the Little Ice Age of the 17th- 19th centuries, with a corresponding retreat of most of the glaciers during the 20th century, against a background of global wanning. Rates of retreat accelerated after the 1980s. The few advancing glaciers that did exist have started to retreat in recent years. 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 in precipitation, the converse of the trend in temperature. However, in the Hengduan Mountains and other areas of the eastern part of the region, a rising trend in rainfall has accompanied increasing temperatures, a result of the variable atmospheric circulations from different sources. The data indicate that the Southwest 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 originating in the Bay of Bengal, passing over Bengal and Burma. This is the major source of precipitation in the Hengduan Mountains and other areas in the eastern part of the region. In addition, the eastern part is influenced by the Southeast Monsoon arriving from the western Pacific, whilst the western part is affected in winter by the southern branch of the westerly circulation. This complex atmospheric situation results in differing patterns of precipitation in the western and eastern zones. Although it is clear that both temperature and precipitation affect the glaciers, further work is needed to confirm which is the major factor influencing present glacier change.