Impact of extreme melt events on the future mass balance of the Greenland Ice Sheet

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Over the past decade, Greenland has experienced several extreme melt events, with unexpectedly strong impacts on the surface mass balance and ice flow, particularly in the years 2010, 2012 and 2015. While some of these melt events were rather localized (like the one in 2015), others covered almost the entire ice-sheet surface (as was the case in 2010).With progressing climate change, extreme melt events can be expected to occur more frequently and become more severe and persistent. So far however, longer-term projections of ice loss from Greenland typically rely on scenarios which only take rather gradual changes in the climate into account, as for instance based on the Representative Concentration Pathways (RCPs) commonly used in the last IPCC report. So far, extreme melt events have generally been underestimated in projections – and their effect on the future climate and sea-level rise remains an open question. In the proposed project, we plan to investigate the impact of extreme melt events on the future evolution of the Greenland Ice Sheet. In particular, we aim at quantifying the possible immediate and long-lasting effects on the surface mass balance and ice dynamics and thus contributions to sea-level rise. These include direct effects from mass loss through surface melting as well as indirect effects, e.g., through submarine melting or basal lubrication that may alter glacier velocities.The main objective of this research project is to assess the potential impacts of extreme melt events on the ice-sheet’s mass balance, and to identify critical thresholds in the frequency, intensity or duration of extreme events which, once transgressed, trigger large-scale dynamic ice loss from the Greenland Ice Sheet.To this end, we will investigate the dynamic response of the Greenland Ice Sheet to a suite of different climate scenarios including extreme melt events with varying onset, duration and magnitude. To evaluate indirect effects via, e.g., enhanced submarine melting, we will couple the well-established Parallel Ice Sheet Model (PISM) with the state-of-the-art Line Plume Model (LPM). The LPM calculates submarine melting by accounting for changes in ocean temperature and subglacial discharge. It is computationally very efficient, such that the coupled PISM-LPM allows for ensemble runs on high resolution. Consequently, a wide range of model parameters and climate input uncertainties can be considered in future projections.With the interactively coupled model PISM-LPM we will give an uncertainty range of Greenland’s contribution to sea level rise by the year 2100 considering regional changes in precipitation, atmosphere and ocean temperatures and, importantly, the impacts of extreme events. As one of our main results, we will create a risk map indicating the most vulnerable regions of Greenland to future extreme melt scenarios.