A realistic freshwater forcing protocol for ocean-coupled climate models

A high-end scenario of polar ice loss from the Greenland and Antarctic ice sheet is presented with separate projections for different mass-loss sites up to the year 2100. For each large ice sheet three potential sources of freshwater release to the ocean are considered: run-off from surface melt, basal melt through heat exchange with the ocean, and iceberg calving and subsequent mass loss through melt of drifting icebergs. The location and relative magnitude of freshwater forcing due to drifting icebergs is calculated from a separate iceberg drift simulation. We assume fixed annual spatial patterns with magnitudes varying in time. These magnitudes are based on a severe warming scenario based on expert elicitation. The resultant freshwater forcing is applied to a global climate model and the effects on sea-level rise are discussed. The simulations show strong sea level rise on the Antarctic continental shelves. The effect on the Atlantic overturning circulation is very small, however.