Description: The land ice contribution to global mean sea level rise has not yet been predicted1 using ice sheet and glacier models for the latest set of socio-economic scenarios, nor using coordinated exploration of uncertainties arising from the various computer models involved. Two recent international projects generated a large suite of projections using multiple models2,3,4,5,6,7,8, but primarily used previous-generation scenarios9 and climate models10, and could not fully explore known uncertainties. Here we estimate probability distributions for these projections under the new scenarios11,12 using statistical emulation of the ice sheet and glacier models. We find that limiting global warming to 1.5 degrees Celsius would halve the land ice contribution to twenty-first-century sea level rise, relative to current emissions pledges. The median decreases from 25 to 13 centimetres sea level equivalent (SLE) by 2100, with glaciers responsible for half the sea level contribution. The projected Antarctic contribution does not show a clear response to the emissions scenario, owing to uncertainties in the competing processes of increasing ice loss and snowfall accumulation in a warming climate. However, under risk-averse (pessimistic) assumptions, Antarctic ice loss could be five times higher, increasing the median land ice contribution to 42 centimetres SLE under current policies and pledges, with the 95th percentile projection exceeding half a metre even under 1.5 degrees Celsius warming. This would severely limit the possibility of mitigating future coastal flooding. Given this large range (between 13 centimetres SLE using the main projections under 1.5 degrees Celsius warming and 42 centimetres SLE using risk-averse projections under current pledges), adaptation planning for twenty-first-century sea level rise must account for a factor-of-three uncertainty in the land ice contribution until climate policies and the Antarctic response are further constrained.

Description: The land ice contribution to global mean sea level rise has not yet been predicted1 using ice sheet and glacier models for the latest set of socio-economic scenarios, nor using coordinated exploration of uncertainties arising from the various computer models involved. Two recent international projects generated a large suite of projections using multiple models2,3,4,5,6,7,8, but primarily used previous-generation scenarios9 and climate models10, and could not fully explore known uncertainties. Here we estimate probability distributions for these projections under the new scenarios11,12 using statistical emulation of the ice sheet and glacier models. We find that limiting global warming to 1.5 degrees Celsius would halve the land ice contribution to twenty-first-century sea level rise, relative to current emissions pledges. The median decreases from 25 to 13 centimetres sea level equivalent (SLE) by 2100, with glaciers responsible for half the sea level contribution. The projected Antarctic contribution does not show a clear response to the emissions scenario, owing to uncertainties in the competing processes of increasing ice loss and snowfall accumulation in a warming climate. However, under risk-averse (pessimistic) assumptions, Antarctic ice loss could be five times higher, increasing the median land ice contribution to 42 centimetres SLE under current policies and pledges, with the 95th percentile projection exceeding half a metre even under 1.5 degrees Celsius warming. This would severely limit the possibility of mitigating future coastal flooding. Given this large range (between 13 centimetres SLE using the main projections under 1.5 degrees Celsius warming and 42 centimetres SLE using risk-averse projections under current pledges), adaptation planning for twenty-first-century sea level rise must account for a factor-of-three uncertainty in the land ice contribution until climate policies and the Antarctic response are further constrained.

Description: The data file contains projections for area and mass change of glaciers on the global scale, from 11 different glacier models, forced by 10 different climate models, under 4 different scenarios. The values are specified by regions, following the region definition of the Randolph Glacier Inventory (https://www.glims.org/RGI/). Values are given annually for the years 2000 to 2100. The data were produced in the second experiment of the Glacier Model Intercomparison Project, based on standardized boundary and initial conditions (http://www.climate-cryosphere.org/mips/glaciermip/activities-experiments).

Description: This dataset contains estimates of debris emergence elevations for 974 debris-covered glaciers 〉 5 km^2 in High Mountain Asia, calculated for three compositing periods: 1985-1999, 2000 - 2010, and 2013 - 2017. Composites were constructed in Google Earth Engine with Landsat imagery, with relatively cloud-free imagery and pixels that were preferentially selected for high brightness temperatures to remove biases due to cloud or snow cover. The elevation of the transition zone between ice and debris was calculated as the median elevation of pixels that for each debris-covered glacier in the Randolph Glacier Inventory (RGI V5) using Shuttle Radar Topography Mission (SRTM) elevation data and the boundary between ice and debris delineated in the composites. Also included in this dataset are the average date of acquisition and day of year of acquisition for individual glacier composites, individual glacier mass balance trends from 2000 - 2017 (m w.e./yr; Brun et al. 2017), changes in glacier velocity (Dehecq et al. 2019), and modelled estimates of future glacier change (Kraaijenbrink et al., 2017).