The 2007 IPCC 4th Assessment Report did not account for dynamical ice sheet change within its projections of future sea level due to limited understanding of the processes involved and a lack of consensus on their magnitude. Since then, our understanding of ice sheet dynamics has expanded dramatically thanks to significant advances in our ability to measure and model the drivers of ice sheet change. The majority of research has focused on climatic factors controlling ice sheet change but in this talk I will consider an important non-climatic factor: the role of the ice sheet bed.

Basal conditions determine whether an ice sheet slides freely or is frozen to its bed, but for a marine-grounded ice sheet such as Antarctica, the shape of the bed also plays an important role as it determines whether the ice sheet can recover from short-term ice loss or whether it is likely to tip into a state of unstable retreat. Crucially, the current shape of the bed beneath West Antarctica means that it is at risk of runaway ice loss. I will describe various factors that may play a role in destabilizing or stabilizing this ice sheet, including a negative feedback process, related to the isostatic response of the solid Earth to ice sheet change, that has the potential to slow the rate of ice loss. The strength of this feedback depends on the rheology of the upper mantle and I will describe recent efforts to determine the material properties of the solid Earth beneath Antarctica, drawing on both modelling and observational approaches.