A continuous history and projection of the mass balance of western North America's alpine glaciers: 1900-2100

While ice sheets and and ice caps will dominate sea level rise in coming centuries, alpine glaciers are currently the largest cryospheric contributor to sea level rise. The varying response times of alpine glaciers confound efforts to quantify volume change when approached from a snap-shot, or short-term transient point of view. To quantify the contribution of alpine glaciers this study approaches the problem as a continuum from the year 1900 (shortly after the so-called Little Ice Age) through 2100 (approximately when larger ice masses will begin to dominate eustatic sea level rise). The retrospective portion of this study combines GCM simulations of western North American climate available from the IPCC-AR4 simulations; a hybrid Climate Research Unit TS2.1 and North American Regional Reanalysis (NARR) temperature reconstruction; and a contemporary baseline period covering the 1979-present NARR data span. Future projections are based on the same GCM simulations as the retrospective. These simulations are carried out on a 200 m grid covering roughly 912,000 km2 of western USA and southern British Columbia and Alberta, Canada. Results illuminate the changing roles of precipitation and temperature over the distinct climate regimes of the study area and indicate that temperature change will far outpace the potential offset of increasing precipitation in this region.