Advaenced state estimats of the ocean and cryosphere: innovative new tools to better understand, predict, and prepare for sea level changes

Sea level rise (SLR) is one of the most serious adaptation challenges facing humanity today. SLR increases the frequency and severity of storm surges, coastal flooding, and erosion, thereby damaging critical infrastructure, hampering economic activity, and potentially displacing more than 100 million people globally who live in coastal communities. Under "business as usual" conditions, global flood costs could increase to over £10tn per year by 2100, under 86 cm of sea level rise. Despite its importance, projections of SLR over this century are very uncertain. The greatest single source of uncertainty in SLR projections comes from the West Antarctic Ice Sheet (WAIS), which has the potential to eventually raise sea levels by over three metres if it melts entirely. The WAIS is held back from flowing into the ocean and raising sea levels by large floating ice shelves that protrude from the Antarctic coastline, acting like dams. These crucial ice shelves are melting increasingly rapidly; in recent decades, the rate of ice loss from all Antarctic ice shelves has increased by more than a factor of twelve. The ice shelves are very dynamic systems that can respond quickly to changes in ocean circulation, e.g. increased intrusion of warm water under the ice shelves can melt them from underneath. The threat of rapidly rising seas in the near-to-medium term future highlights the need for improved understanding of how ocean currents deliver heat to the vulnerable undersides of Antarctic ice shelves. Thus far, progress in this area has been hampered by the challenges associated with extracting detailed heat budgets, ice shelf melt rates, and sensitivities from a limited set of observations. In this Fellowship, I will use sensitivity analysis techniques (i.e. adjoint modelling) to establish a next-generation framework for ocean and ice shelf modelling that will make a step change in our ability to make robust and useful SLR projections. I will, for the first time, combine observations and realistic physical models in a hierarchical ocean-ice state estimation framework that will allow me to: (1) obtain spatially-varying, observationally-constrained estimates of melt rates and other hard-to-observe parameters at the ocean-ice interface; (2) quantify the sensitivities of heat content and melt rates at the ocean-ice interface to local and remote air-sea interactions and ocean circulation; (3) create spatially and temporally detailed heat budgets to track how heat is delivered from the open ocean to the ice shelves; and (4) optimise future observing campaigns by intelligently targeting key locations for new measurements. This ocean-ice state estimation framework will be applicable to any ocean-ice system on Earth, offering the potential to transform our ability to understand the present and future behavior of these key sea level regulators. As a result, global societies will be better informed and hence better able to respond to sea level rise, reducing risks to low-lying infrastructure, communities, and businesses.