Thinning out

Geophys. Res. Lett. 35, L22503 (2008)

Credit: ISTOCKPHOTO.COM / DAVID CIEMNY

High elevation glaciers in the Himalayas release meltwater into the Indus, Ganges and Brahmaputra Rivers, contributing up to half of their total river flow. A new study suggests that these glaciers may be thinning, endangering water resources in one of the most populous regions of the world.

Natalie Kehrwald of the Ohio State University and colleagues collected ice cores from the summit of Naimona'nyi Glacier in Tibet. The team measured the level of beta radioactivity and the concentration of two radioactive isotopes, chlorine-36 and hydrogen-3, in the ice. These isotopes are common signatures of nuclear weapons testing in the 1950s and 60s. The notable absence of any radioactive signal in the cores, together with negligible concentrations of radioactive isotopes, indicates that the glacier contains no ice deposited since the 1950s; lead dating confirmed this finding. The authors suggest that increased ice melt resulting from recent warming may be responsible.

Current estimates of the impact of Himalayan glacial retreat on water resources have failed to account for high elevation glacial thinning. If Naimona'nyi is characteristic of other glaciers in the region, meltwater supply is likely to shrink much faster than currently predicted, with considerable negative consequences for up to half a billion people.

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Armstrong, A. Thinning out. Nature Clim Change 1, 2 (2009). https://doi.org/10.1038/climate.2008.136

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