Control of Ocean Temperature on Jakobshavn Isbræ's Present and Future Mass Loss

Large uncertainties in model parameterizations and input data sets make projections of future sea level rise contributions of outlet glaciers challenging. Here we introduce a novel technique for weighing large ensemble model simulations that uses information of key observables. The approach is robust to input errors and yields calibrated means and error estimates of a glacier's mass balance. We apply the technique to Jakobshavn Isbræ, using a model that includes a dynamic calving law, and closely reproduce the observed behavior from 1985 to 2018 by forcing the model with ocean temperatures only. Our calibrated projection suggests that the glacier will continue to retreat and contribute about 5.1 mm to eustatic sea level rise by 2100 under present‐day climatic forcing. Our analysis shows that the glacier's future evolution will strongly depend on the ambient oceanic setting. Projections of future sea level rise are important planning information for coastal communities and ecosystems. Large uncertainties in model parameterizations and input data sets make the projections of the contributions of outlet glaciers and ice sheets challenging. Jakobshavn Isbræ in West Greenland is the world's fastest glacier, which retreated for more than 20 km and contributed alone more than 0.1 mm per year to sea level rise after its floating ice tongue broke up at the turn of this millennium. We use a novel technique to calibrate model simulations of Jakobshavn Isbræ using a record of observations in order to (a) understand the causes triggering its recent retreat and (b) produce weighted estimates of the glacier's future contribution to sea level rise. Our analysis shows that the glacier behavior is largely controlled by the oceanic thermal forcing and that its future evolution will strongly depend on the sustained intrusion of warm waters in its fjord. We project that the glacier will contribute an average of 5.1 mm to global sea level rise until 2100 under present‐day climatic forcing. We present a novel approach to calibrate projections of outlet glaciers using observationsWe model Jakobshavn Isbræ's observed evolution and retreat driven by oceanic forcing onlyJakobshavn Isbræ will contribute 5.1 mm to eustatic sea level rise by 2100 under present‐day climate