Progress and future directions in constraining uncertainties in sea-level projections using observations

Coastal planning, mitigation and adaptation efforts rely on credible sea-level projections generated by physical models. However, the large uncertainties in these projections pose a challenge for policymakers. Here we provide an overview of the main sources of uncertainty in model projections of sea-level change on multi-decadal to centennial timescales and we offer perspectives on the use of observations to narrow uncertainties. We propose several directions for future research, including improvements in emerging emulation techniques, more systematic quantification of uncertainty structure within both observations and models, lengthening observational records of processes, and expanding collaborations across physical and social sciences. Advancements in these areas are urgently needed, as the next phase of the Intergovernmental Panel on Climate Change assessment cycle gets underway.