Contrasting patterns of early twenty-first-century glacier mass change in the Himalayas

Abstract

Glaciers are among the best indicators of terrestrial climate variability, contribute importantly to water resources in many mountainous regions^1,2 and are a major contributor to global sea level rise^3,4. In the Hindu Kush–Karakoram–Himalaya region (HKKH), a paucity of appropriate glacier data has prevented a comprehensive assessment of current regional mass balance⁵. There is, however, indirect evidence of a complex pattern of glacial responses^5,6,7,8 in reaction to heterogeneous climate change signals⁹. Here we use satellite laser altimetry and a global elevation model to show widespread glacier wastage in the eastern, central and south-western parts of the HKKH during 2003–08. Maximal regional thinning rates were 0.66 ± 0.09 metres per year in the Jammu–Kashmir region. Conversely, in the Karakoram, glaciers thinned only slightly by a few centimetres per year. Contrary to expectations, regionally averaged thinning rates under debris-mantled ice were similar to those of clean ice despite insulation by debris covers. The 2003–08 specific mass balance for our entire HKKH study region was −0.21 ± 0.05 m yr⁻¹ water equivalent, significantly less negative than the estimated global average for glaciers and ice caps^4,10. This difference is mainly an effect of the balanced glacier mass budget in the Karakoram. The HKKH sea level contribution amounts to one per cent of the present-day sea level rise¹¹. Our 2003–08 mass budget of −12.8 ± 3.5 gigatonnes (Gt) per year is more negative than recent satellite-gravimetry-based estimates of −5 ± 3 Gt yr⁻¹ over 2003–10 (ref. 12). For the mountain catchments of the Indus and Ganges basins¹³, the glacier imbalance contributed about 3.5% and about 2.0%, respectively, to the annual average river discharge¹³, and up to 10% for the Upper Indus basin¹⁴.