1Climate, Ocean, and Sea Ice Modeling Group, Computational Physics and Methods, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
2Glaciology and Climate Change Laboratory, Center for Scientific Studies/Centro de Estudios Cientificos (CECs), Chile
3Climate, Ocean, and Sea Ice Modeling Group, Fluid Dynamics and Solid Mechanics, Los Alamos National Laboratory, New Mexico, USA
4Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO 80309, USA
5Institut für Geographie, Universität Innsbruck, Innrain 52, 6020 Innsbruck, Austria
6Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, Canada
7Department of Geography, University of Zurich, Zurich, Switzerland
Abstract. Most glaciers and ice caps (GIC) are out of balance with the current climate. To return to equilibrium, GIC must thin and retreat, losing additional mass and raising sea level. Because glacier observations are sparse and geographically biased, there is an undersampling problem common to all global assessments. Here, we further develop an assessment approach based on accumulation-area ratios (AAR) to estimate committed mass losses and analyze the undersampling problem. We compiled all available AAR observations for 144 GIC from 1971–2010 and found that most glaciers and ice caps are farther from balance than previously believed. Accounting for regional and global undersampling errors, our model suggests that GIC are committed to additional losses of 30 ± 11% of their area and 38 ± 17% of their volume if the future climate resembles the climate of the past decade. These losses imply global mean sea-level rise of 163 ± 73 mm, assuming total glacier volume of 430 mm sea-level equivalent. To reduce the large uncertainties in these projections, more long-term glacier measurements are needed in poorly sampled regions.