Deliverable D4.2 Uncertainty results integrated into UKESM (Milestone MS13)

This milestone links the research performed in Work Packages 4, “Quantification of Antarctic Ice Sheet deep uncertainty and freshwater fluxes under climate forcing” and 6, “Role of Antarctica in the global climate: long-term impacts of short-term decision-making”. WP4 uses ice sheet models (ISMs) to constrain the freshwater fluxes produced during the future retreat of the Antarctic ice sheet (AIS). This was done using a large ensemble of experiments in which climate forcing is prescribed and details of the ice sheet model varied. In this way, a probabilistic prediction was created. In contrast, the projections of WP6 use a fully coupled Earth system model (ESM), which has the advantage of including feedbacks between the ice sheet and the wider climate system that may affect future freshwater release (which are largely absent in WP4’s approach). The disadvantage is that ESMs are computationally demanding, and only very few experiments are possible. In WP6’s ESM experiments, retreat of the AIS is spontaneously triggered by changes in the coastal waters surrounding Antarctica. The aim of the milestone is to use WP4 results to provide a wider context for this retreat. This is done by comparing the time series of freshwater release in the ESM with the range of freshwater-release scenarios produced in WP4.