Effect of initial states on the uncertainty in sea-level rise projections until 2100 and beyond

Projections for Antarctica's contribution to global sea-level rise until 2100 range from a positive contribution due to increased ice loss, caused by an increase in surface melt and in dynamic loss of grounded ice, to a negative contribution due to increased snowfall. The high uncertainties in projections can be attributed to different sources, including emission trajectories, climate forcings from Global Circulation Models (GCMs) and Regional Climate Models (RCMs), as well as inter- and intra-ice-model differences.Here, we present an ensemble of future projections based on simulations with the Parallel Ice Sheet Model (PISM), driven by multiple climate forcings. These are based on several initial states and ice-sheet trajectories over the historical period, consistent with observations.We assess the influence of the initial states on the spread in projected sea-level change and compare these to the uncertainties arising from climatic forcings, to compare the sources of uncertainty in future sea-level projections until 2100 and beyond.