Slight glacier mass loss in the Karakoram region during the 1970s to 2000 revealed by KH-9 images and SRTM DEM

An anomalously slight glacier mass gain during 2000 to the 2010s has recently been reported in the Karakoram region. However, to date, no investigations of the region-wide glacier mass balance in the Karakoram prior to 2000 have been reported, leaving a knowledge gap for assessing glacier responses to climate change. We calculated elevation and mass change using DEMs generated from KH-9 images acquired during 1973-1980 and the 1 arc-second SRTM DEM. We find a slight mass loss of -0.09 +/- 0.03 m w.e. a(-1) (12 366 km(2)) for 1973-2000, which is less negative than the global average rate for 19712009 (-0.31 +/- 0.19 m w.e. a(-1)). Within the Karakoram, the glacier change patterns are spatially and temporally heterogeneous. In particular, a nearly stable state in the central Karakoram (-0.04 +/- 0.05 m w.e. a(-1) during the period 1974-2000) implies that the Karakoram anomaly dates back to the 1970s. Combined with the previous studies, we conclude that the Karakoram glaciers as a whole were in a nearly balanced state during the 1970s to the 2010s.