01-11-2010: Greenland's contribution to global sea-level rise by the end of the 21st century.

The largest uncertainty in future sea-level rise scenarios stems from the calving, or ice discharge from large ice sheets. Present-day ice sheet models are unable to simulate ice flow dynamics and the recently observed speed-up of outlet glaciers. A simple parameterization of increased flow in outlet glaciers was implemented in a positive degree day model, which decreases the bias in surface height. With this parameterization we have been able to simulate the Greenland ice-sheet evolution of the last 100,000 years. The uncertainty in Greenland's contribution to future sea-level rise was estimated by driving the model with high resolution output of the RAMO-model and adding temperature and precipitation anomalies from an ensemble of model simulations from the CMIP3 archive. We estimate the maximum mass loss in 2100 to be equivalent to 17 cm sea-level rise, higher than the IPCC AR4 estimate, but lower than high-end estimates by the Delta Committee and other expert elicitation. The reason is that ice flow velocities saturate for long-lasting enhanced lubrication (decreased friction) as the surface height gradient in the enhanced outflow regime strongly diminishes, counteracting the decrease in bottom friction. (Grand Graversen, et al)