The retreat of glaciers in response to recent climate warming in western China

Glaciers in China are primarily located in the Tibetan Plateau (TP) and surrounding high mountains. The Chinese Glacier Inventory indicates that there are 46 377 glaciers in western China. Meteorological records indicate that air temperature in western China has risen by 0.28C per decade since 1951, and 1998 was the warmest year; precipitation in the region increased by 5–10% per decade from 1953 to 1997. Using remote-sensing and Geographic Information System methods, we have monitored the changes in >5000 glaciers over the past 50 years. We conclude that >80% of glaciers in western China have retreated, losing 4.5% of their combined areal coverage, although some glaciers have advanced. In addition, regional differences characterize glacier changes over the past few decades. For example, glaciers in the central and northwestern TP were relatively stable, while glaciers in the mountains surrounding the TP experienced extensive wastage. Mass-balance variations for some glaciers show accelerated ice shrinkage in the last two decades. 1. GLACIERS IN CHINA Western China is characterized by numerous mountain ranges and high, broad plateaus; 14 mountain ranges run in parallel from north to south, including the Altai, Tien Shan, Pamirs, Karakoram, Kunlun and Himalaya, with the latter four ranges surrounding the Tibetan Plateau (henceforth TP). These four mountain ranges and plateau are the highest in the world (e.g. the average elevation of the TP is 4500ma.s.l.). The cold environment resulting from these high elevations provides excellent conditions for alpine glaciers to develop. It is estimated the total glacierized area in China and other mountainous parts of central Asia is 114 800 km (Dyurgerov and others, 2002). In the mountain ranges of central Asia, 46 377 glaciers are situated within China; they have a total area of 59 425 km (Fig. 1) (Shi and others, 2005), according to the Chinese Glacier Inventory (CGI), based on aerial photographs taken from the late 1950s to the early 1980s and large-scale topographic maps. Our analysis based on observed physical properties (e.g. ice temperature, surface velocity, general climatic characteristics) indicates that these glaciers can be categorized into three types, extremely continental, subcontinental and monsoonal maritime (Shi and Liu, 2000), each with its own distinct physical properties (e.g. ice temperature, precipitation, air temperature). Continental glaciers are mainly located in the central and western Kunlun Shan, the Qiangtang plateau, the east Pamirs, the west Tanggula mountains and the west Qilian Shan. Subcontinental glaciers are distributed over the Tien Shan, the northern slopes of the central and western Himalaya and the north slope of the Karakoram mountains. Small glaciers (area <1.0 km) comprise 77% of glaciers in western China, but only 20% of the total glacierized area. Large glaciers (area >10 km) are relatively scarce, but account for 37.6% of the glacierized area; 33 of these are >100 km in area and constitute 10.4% and 26.3% of the total area and total ice volume, respectively, of glaciers in China (Shi and others, 2005). Glaciers are an economically important fresh-water resource in China and other parts of central Asia (Yang and Zeng, 2001), where many large river systems have their sources in glacierized regions (e.g. Huanghe, Changjiang, Yarlung Zangbo (Brahmaputra), Tarim, Mekong, Nujiang (Salween) and the Ganges). Therefore, glacier changes are likely to have a major impact on human activities and the preservation of the environment, especially in those river systems that depend on meltwater from glaciers to provide an adequate supply of water. Until recently, there has not been general agreement about glacier changes in the region, and in particular the impact on water resources of recent glacier retreat taking place under present-day warming. In this paper, we present an integrated assessment of glacier changes in China during the past several decades. 2. CLIMATE CHANGE DURING RECENT DECADES Global climate change is well described in Folland and others (2001). The Intergovernmental Panel on Climate Change report showed that global climate warming since the end of the 19th century has increased the Earth’s temperature by 0.6 0.28C, and the warming is more pronounced on land surface areas at midand high latitudes in the Northern Hemisphere. Such rapid warming was largely attributed to enhanced anthropogenic emission due to fossil energy consumption. It was shown that the airtemperature increase during the 20th century is likely to have been the largest in any century during the past 1000 years, and the 1990s are likely to have been the warmest decade of the millennium (Folland and others, 2001). An intensification of the global hydrological cycle was also observed; measurements of land surface precipitation showed an increase of 0.5–1% per decade throughout the midand high latitudes of the Northern Hemisphere. Over much of the subtropical land areas, rainfall decreased during the 20th century (by –0.3% per decade) (Folland and others, 2001). Annals of Glaciology 43 2006 97