Global glacier volume projections under high-end climate change scenarios

The Paris agreement aims to hold global warming to well below 2 °C and to pursue efforts to limit it to 1.5 °C relative to the pre-industrial period. Recent estimates based on population growth and intended carbon emissions from participant countries, suggest global warming may exceed this ambitious target. Here we present glacier volume projections for the end of this century, under a range of high-end climate change scenarios, defined as exceeding +2 °C global average warming relative to the preindustrial period. Glacier volume is modelled by developing an elevation-dependent mass balance model for the Joint UK Land Environmental Simulator (JULES). To do this, we modify JULES to include glaciated and un-glaciated surfaces that can exist at multiple heights within a single grid-box. Present day mass balance is calibrated by tuning albedo, wind speed, precipitation and temperature lapse rates to obtain the best agreement with observed mass balance profiles. JULES is forced with an ensemble of six Coupled Model Intercomparison Project Phase 5 (CMIP5) models which were downscaled using the high resolution HadGEM3-A atmosphere only global climate model. The ensemble mean volume loss at the end of the century plus/minus one standard deviation is, minus;64 ± 5 % for all glaciers excluding those on the peripheral of the Antarctic ice sheet. The uncertainty in the multi-model mean is rather small and caused by the sensitivity of HadGEM3-A to the boundary conditions supplied by the CMIP5 models. The regions which lose more than 75% of their initial volume by the end of the century are; Alaska, Western Canada and US, Iceland, Scandinavia, Russian Arctic, Central Europe, Caucasus, High Mountain Asia, Low Latitudes, Southern Andes and New Zealand. The ensemble mean ice loss expressed in sea-level equivalent contribution is 215.2 ± 21.3 mm. The largest contributors to sea level rise are Alaska (44.6 ± 1.1 mm), Arctic Canada North and South (34.9 ± 3.0 mm), Russian Arctic (33.3 ± 4.8 mm), Greenland (20.1 ± 4.4), High Mountain Asia (combined Central Asia, South Asia East and West), (18.0 ± 0.8 mm), Southern Andes (14.4 ± 0.1 mm) and Svalbard (17.0 ± 4.6 mm). Including parametric uncertainty in the calibrated mass balance parameters, gives an upper bound global volume loss of 247.3 mm, sea-level equivalent by the end of the century. Such large ice losses will have inevitable consequences for sea-level rise and for water supply in glacier-fed river systems.