Journal Article

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

Nuth, Christopher, Arnaud, Yves, Kääb, Andreas, Berthier, Etienne, Gardelle, Julie

2012

Overview

Data for the Hindu Kush–Karakoram–Himalaya region from satellite laser altimetry and a global elevation model shows that glacier thinning varied by an order of magnitude across the region, with surface debris not seeming to provide effective insulation, and that the melting ice added several per cent to the annual discharge of the mountain rivers. Recalculating glacier mass loss in the Himalayas Glacier changes over the high mountains of Asia can have knock-on effects on water resources and sea levels, but it has been difficult to accurately monitor ice-mass changes. A recent gravimetric survey of mass loss in ice-covered areas around the globe — published in Nature — suggested that the high mountains of Asia were approximately in balance during the early twenty-first century. Now, Andreas Kaab and colleagues present a more detailed analysis using satellite altimetry and show a small but statistically distinguishable mass loss from the Hindu Kush–Karakoram–Himalaya region. A larger mass loss in much of the Hindu Kush–Himalaya was partly offset by a scarcely distinguishable mass loss in the Karakoram. 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 balance 5 . There is, however, indirect evidence of a complex pattern of glacial responses 5 , 6 , 7 , 8 in reaction to heterogeneous climate change signals 9 . 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 rise 11 . 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 basins 13 , the glacier imbalance contributed about 3.5% and about 2.0%, respectively, to the annual average river discharge 13 , and up to 10% for the Upper Indus basin 14 .

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 704/106/694 / 704/2151/213 / Altimetry / Altitude / Analysis / Asia, Western / Bhutan / Budgets / Climate change / Climate variability / Earth, ocean, space / Environmental aspects / Exact sciences and technology / External geophysics / Footprints / Forecasts and trends / Glacial drift / Glaciers / Global temperature changes / Gravimetry / Groundwater - analysis / History, 21st Century / Humanities and Social Sciences / Ice / Ice caps / Ice Cover / Insulation / letter / Mountain regions / multidisciplinary / Natural history / Nepal / River discharge / River flow / Rivers / Science / Sea level rise / Snow. Ice. Glaciers / Thinning / Water resources / Water Supply - analysis / Water Supply - history / Year 2000