24 l Glaciers of the Himalayas
be confused with dust- or debris-covered glaciers. Although still inconclusive, some location-specific studies suggest that debris-covered ice has significantly lower melting rates than clean ice. The focus of this report is on climate change and BC-related glacier melt. The base of scientific evidence underscores the role of BC in glacial melt in the South Asia region, with 69 percent of glacier loss between 1991 and 2011 attributed to the impact of human-related activities such as industrial and vehicular emissions, biomass burning, and forest fires. According to a study by Nair et al. (2013), the increasing presence of BC particles in the atmosphere has potential implications for the regional climate and hydrologic cycle over South Asia. The BC concentration in the atmosphere has been found to be highest during the premonsoon season over the Himalayas, especially in Nepal and the Eastern Himalayas. The direct and surface albedo radiative forcing caused by BC deposition leads to significant warming over the Himalayas during the premonsoon period and thus accelerates glacial melting. Another study by Nair et al. (2013) estimates that BC causes 50 to 90 percent of Himalayan glacier melting. A recent study by the International Centre for Integrated Mountain Development and Thakuri finds that glaciers smaller than 1 square kilometer are disappearing faster and have experienced a 43 percent decrease in surface area since the 1960s (Thakuri et al. 2013). These debris-covered sections of glaciers have increased by about 17 percent since the 1960s. The edges of the glaciers have also retreated by an average of 400 meters since 1962 (Thakuri et al. 2013). A comprehensive study in India covering 146 glaciers in the Chandra basin in the western Himalayas finds that glaciers as a whole lost 19 percent of the total basin volume during the period from 1984 to 2012, with the loss of volume for small and low-altitude glaciers being as high as 67 percent (Pandey et al. 2016). Although some studies document significant interannual variability of mass balances and relatively slower melt rates on debris-covered glacier tongues over interannual time scale, the overall effects of surface debris cover are uncertain, as many satellite observations suggest similar ice losses relative to clean-ice glaciers over s imilar or longer periods. Because of the complex monsoon climate in the Himalayas, the albedo effect, due to deposition of anthropogenic BC on snow and ice, and precipitation changes have always been suggested as important drivers.
References Azad, S., and M. Rajeevan. 2016. “Possible Shift in the ENSO-Indian Monsoon Rainfall Relationship under Future Global Warming.” Scientific Reports 6: 20145. doi:10.1038/srep20145. Bollasina, M. A., Y. Ming, and V. Ramaswamy. 2011. “Anthropogenic Aerosols and the Weakening of the South Asian Summer Monsoon.” Science 334 (6055): 502–05. doi:10.1126 /science.1204994.
