Analyzing the Geodetic Mass Balance Uncertainty Budget on North American Benchmark Glaciers

The USGS Glaciers and Climate Project calculates geodetically derived glacier mass balance for select North American benchmark glaciers across decadal intervals. To ensure that these results are robust and complete, we quantify uncertainty associated with computing glacier volume change and assigning material density in the volume to mass conversion. Analysis of this uncertainty budget reveals key knowledge gaps that can steer future research. We find that the proportion of the uncertainty budget attributable to elevation errors often decreases as glacier volume change increases. Therefore, elevation errors tend to contribute less to the overall uncertainty budget on longer time steps. Yet errors associated with converting volume to mass, namely the material density assignment, scale with the magnitude of glacier thickening/thinning. Hence our results suggest that tamping down uncertainty on geodetic mass balance requires enhanced insight into physical processes that control material density, namely firn densification.