Partitioning the Uncertainty of Ensemble Projections of Global Glacier Mass Change

Glacier mass loss is recognized as a significant contributor to current sea-level rise. However, large uncertainties remain in projections of glacier mass loss on global and regional scales. We present an ensemble of 279 global-scale glacier mass and area change projections for the 21st century based on eleven glacier models using up to ten General Circulation Models (GCMs) and four Representative Concentration Pathways (RCPs) as boundary conditions. We partition the total uncertainty into the individual contributions caused by glacier models, GCMs, RCPs, and natural variability. We find that emission scenario uncertainty is growing throughout the 21st century, and is the largest source of uncertainty by 2100. The relative importance of glacier model uncertainty decreases over time, but it is the greatest source of uncertainty until the middle of this century. The projection uncertainty associated with natural variability is small on the global scale but has strong effects on small regional scales. The projected global mass loss by 2100 relative to 2015 (75±64 mm sea-level equivalent (SLE) for RCP2.6, 165±98 mm SLE for RCP8.5) is lower than, but within the uncertainty range of previous projections.