Reanalysis of the U.S. Geological Survey Benchmark Glaciers: Long-term insight into climate forcing of glacier mass balance

Mountain glaciers integrate climate processes to provide an unmatched signal of regional climate forcing. However, extracting the climate signal via intercomparison of regional glacier mass balance records can be problematic when methods for extrapolating and calibrating direct glaciological measurements are mixed or inconsistent. To address this problem, we reanalyzed and compared long-term mass balance records from the U.S. Geological Survey Benchmark Glaciers. These five glaciers span maritime and continental climate regimes of the western United States and Alaska. Each glacier exhibits cumulative mass loss since the mid-20th century, with average rates ranging from –0.58 to –0.30 m water equivalent (w.e.) a-1. We produced a set of solutions using different extrapolation and calibration methods to inform uncertainty estimates, which range from 0.22–0.44 m w.e. a-1. Mass losses are primarily driven by increasing summer warming. Continentality exerts a stronger control on mass loss than latitude. Similar to elevation, topographic shading, snow redistribution, and glacier surface features often exert first-order control on mass balance. The reanalysis underscores the value of geodetic calibration to resolve mass balance magnitude, as well as the irreplaceable value of direct measurements in contributing to process-based understanding of glacier mass balance.