Mountain glaciers, perennial ice masses excluding the Greenland and Antarctic ice sheets, are a critical water resource for nearly two billion people and are threatened by global warming. Rounce et al. projected how those glaciers will be affected under global temperature increases of 1.5° to 4°C, finding losses of one quarter to nearly one half of their mass by 2100 (see the Perspective by Aðalgeirsdóttir and James).
Their calculations suggest that glaciers will lose substantially more mass and contribute more to sea level rise than current estimates indicate. —HJS
Glacier mass loss affects sea level rise, water resources, and natural hazards. We present global glacier projections, excluding the ice sheets, for shared socioeconomic pathways calibrated with data for each glacier. Glaciers are projected to lose 26 ± 6% (+1.5°C) to 41 ± 11% (+4°C) of their mass by 2100, relative to 2015, for global temperature change scenarios.
This corresponds to 90 ± 26 to 154 ± 44 millimeters sea level equivalent and will cause 49 ± 9 to 83 ± 7% of glaciers to disappear. Mass loss is linearly related to temperature increase and thus reductions in temperature increase reduce mass loss.
Based on climate pledges from the Conference of the Parties (COP26), global mean temperature is projected to increase by +2.7°C, which would lead to a sea level contribution of 115 ± 40 millimeters and cause widespread deglaciation in most mid-latitude regions by 2100.