Modeling the Greenland Ice Sheet's Committed Contribution to Sea Level Rise During the 21st Century

Mass loss from the Greenland Ice Sheet (GrIS) can be partitioned between surface (and basal) mass balance, and discharge due to ice dynamics, predominantly through large outlet glaciers. While there is an instantaneous response in outlet glacier velocity to a perturbation at the terminus (e.g. a large calving event), the diffusive response - due to the evolution of ice thickness over time - means that the total effect of a perturbation can take decades to be fully realized. Here we model the committed sea level response of GrIS. That is, overlooking any future climate perturbations or mitigation, we find the sea level contribution from GrIS that is locked in due to the slow dynamic response of the ice to past changes. We use the ice flow model ISSM, along with various input datasets, to find an initial state representing the ice sheet in the early 2000s, from which we run forward simulations, holding the climate constant. We apply perturbations to the outlet glacier termini that represent recent observed changes, and model the ice sheet's committed sea level contribution over the 21^st century. We explore the sensitivity of the ice sheet response to the timing and magnitude of the perturbation, as well as to uncertainty in model parameters associated with the flow of ice.