Prospects for useful sea-level predictions from Earth-system models (Invited)

Earth-system models (ESMs) to date have been unable to provide useful predictions of 21st century sea-level rise, largely because of uncertainties in the dynamic response of the Greenland and Antarctic ice sheets. As a result, planners and policymakers have had to rely on semi-empirical methods and extrapolations of current trends. In order to obtain comprehensive, physically-based sea-level predictions from ESMs, two major innovations are required: (1) Ice sheet models must represent the physical processes responsible for fast ice flow, and (2) these models must be integrated with models of the ocean, land, and atmosphere. There has been much recent progress in developing ice sheet models that include (among other improvements) higher-order stresses, adaptive and unstructured grids, and more realistic treatments of basal sliding and iceberg calving. Progress has been slower, however, in coupling ice sheet models to ESMs. In particular, work is needed to simulate small-scale ice-ocean interactions that could trigger the abrupt retreat of marine ice sheets. The barriers to coupling are cultural and technical as well as scientific. As new ice sheet models are added to ESMs, scientific understanding will grow quickly, but large uncertainties in sea-level predictions will likely remain. New assessment mechanisms are needed to communicate complex results to end users in a useful, timely fashion.