A new satellite-based estimate of glacier mass change for High Mountain Asia (HMA), the world’s third largest glacier conglomeration after Antarctica and Greenland, reveals a relatively modest retreat rate for the first 17 years of the 21st century.
The results from Brun et al. (2017) indicate that HMA glaciers are nearly in balance for 2000-2016, contributing the equivalent of just 0.046 millimeters per year to sea level rise during this period. This is a glacier-melt contribution rate of less than half a centimeter per century, which is “much smaller” and “in marked disagreement” with other recent estimations.
Previous model-based estimates have generated HMA glacier melt and sea level equivalent values nearly 4 times greater (-46 Gt yr-1, +0.13 mm yr-1). The new study’s authors attribute the discrepancy to the historical “sparse spatial sampling” and “lack of direct measurements”, or extrapolating data from limited coverage areas to represent much larger areas.
In this study, for example, glaciers in the Kunlun and Karakoram regions of HMA have been observed to be in balance or even gaining mass. The model-based studies indicate significant mass losses are occurring in these regions.
The high estimates of HMA glacier melt and sea level rise contribution are preferred (and thus “widely used in the literature”) by those advancing the position that modern glacier melt rates are unusual or unprecedented. This study makes a strong case that past and present high glacier-melt values in this region are unsupported by comprehensive analyses from satellite observations.