Global climate model projections suggest that 21st century climate change will bring significant drying in the midlatitudes. Recent glacier modeling suggests that runoff from glaciers will continue to provide substantial freshwater in many drainage basins, though the supply will generally diminish throughout the century. In the absence of dynamic glacier ice within global climate models (GCMs), a comprehensive picture of future basin-scale water availability for human and ecosystem services has been elusive. Here, we leverage the results of existing GCMs and a global glacier model to compute the effect of glacial runoff on the Standardized Precipitation-Evapotranspiration Index (SPEI), an indicator of basin-scale water availability. We find that glacial runoff tends to increase mean SPEI and reduce interannual variability, even in basins with relatively little glacier cover. However, in many basins we find inter-GCM spread comparable to the amplitude of the ensemble mean glacial effect, which suggests considerable structural uncertainty.

The rate of land ice loss due to iceberg calving is a key source of variability among model projections of 21st century sea-level rise. It is especially challenging to account for mass loss due to iceberg calving in Greenland, where ice drains to the ocean through hundreds of outlet glaciers, many smaller than typical model grid scale. Here, we apply a numerically efficient network flowline model (SERMeQ) forced by surface mass balance to simulate an upper bound on decadal calving retreat of 155 grounded outlet glaciers of the Greenland Ice Sheet—resolving five times as many outlets as was previously possible. We show that the upper bound holds for 91\% of glaciers examined and that simulated changes in terminus position correlate with observed changes. SERMeQ can provide a physically consistent constraint on forward projections of the dynamic mass loss from the Greenland Ice Sheet associated with different climate projections.

Glaciers are major contributors to global sea level change and regional freshwater resources. In light of the worldwide societal importance of glacier change, we see a need for accessible glacier-education materials in many languages. We have developed a set of Jupyter notebooks, available in both Spanish and English, that coaches users through basic simulations with the Open Global Glacier Model (edu.oggm.org). The notebooks are freely available via GitHub (github.com/ehultee/CdeC-glaciologia), with no special software installation requirements for users. Participants in a week-long glaciology workshop at Clubes de Ciencia Peru 2019 used our notebooks to study glacier physics and make future projections for mountain glaciers of their choice. Only one participant had previously used Python, and none had experience with numerical modelling of Earth systems in any language. All were able to run the notebooks and explain their findings. Most participants were also able to modify the notebooks to conduct experiments of interest to them. We consider this a particularly successful case of science outreach, in that workshop participants are now equipped to explore their own important questions independently. The notebooks we have developed can support multilingual glaciology outreach; we hope that sharing our experience can support public geoscience more broadly.

The Greenland Ice Sheet discharges ice to the ocean through hundreds of outlet glaciers. Recent acceleration of Greenland outlet glaciers has been linked to both oceanic and atmospheric drivers. Here, we leverage temporally dense observations, regional climate model output, and newly developed time series analysis tools to assess the most important forcings causing ice flow variability at one of the largest Greenland outlet glaciers, Helheim Glacier, from 2009 to 2017. We find that ice speed correlates most strongly with catchment-integrated runoff at seasonal to interannual scales, while multi-annual flow variability correlates most strongly with multi-annual terminus variability. The multiple relevant time scales and the influence of subglacial topography on Helheim Glacier’s dynamics highlight different regimes that can inform modeling and forecasting of its future. Notably, our results suggest that the recent terminus history observed at Helheim is a response to, rather than the cause of, upstream changes.