Sea levels will rise significantly in the coming decades as a result of greenhouse gas emissions, but there are large uncertainties about how fast they will rise in different emission futures. In a warming climate, the main causes of sea level rise are thermal expansion of sea water, melting of glaciers and ice sheets, and ice-flow directly into the oceans (dynamic ice loss). Dynamic ice loss from the Greenland and Antarctic Ice Sheets is, by a large margin, the greatest source of uncertainty in predictions of sea level rise, and ranges from 10 cm to over 1 m by 2100 in a high emissions scenario.
The upper and lower limits of this range have very different implications for coastal communities and economies, hampering efforts to plan for the future. Identifying safe limits on carbon emissions and adopting appropriate mitigation strategies require reliable predictions of dynamic ice loss from the ice sheets. Dynamic ice loss is complex because it is controlled by the fracture and detachment of icebergs (calving) and the submarine melt of ice in contact with the ocean. Calving and melting can reduce resistance to ice flow, leading to faster transfer of mass from land to the oceans and potentially to irreversible ice-sheet collapse. Despite their importance, calving and submarine melting are very poorly represented in the models used to predict ice-sheet response to climate change, resulting in high uncertainties in future dynamic ice loss and hence sea-level rise. There is an urgent need to develop reliable calving laws for ice sheet-models, based on a thorough understanding of calving processes and their interactions with ice flow and submarine melt. We aim to solve this problem using a new high-resolution model of fracturing, ice-dynamics and ocean processes (FIDO), to build a solid foundation for the development of the calving laws required for predictive ice-sheet models. FIDO combines state-of-the-art methods of modelling ice-flow and ocean circulation with a revolutionary ice-fracture model. Unlike conventional approaches, the fracture model represents ice as assemblages of particles linked by breakable bonds – much like real ice – allowing calving to be simulated with impressive realism. We will use FIDO to simulate calving, submarine melt and ice flow in a wide range of environmental conditions, and rigorously test the validity of the results using satellite observations of ice margin behaviour in Greenland and Antarctica. From the FIDO model results, we will distil the essential rules of calving and define new, comprehensive calving laws incorporating interactions with submarine melt and ice dynamics. In collaboration with UK and international partners, we will implement our new calving laws in models of the Greenland and Antarctic Ice Sheets, to predict their 21st Century sea-level contributions for a range of greenhouse gas emission scenarios. We anticipate radically improved sea-level rise predictions by 2020, in readiness for the 6th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR6).