Dynamic Earth Impacts on Past, Present, and Future Sea Levels

forthcoming

Nearly 700 million people live along flood-susceptible coastlines and actionable sea-level forecasts are urgently needed to protect these populations and their €4 trillion of critical infrastructure from rising sea levels. Unfortunately, current sea-level projections are of limited use due to deep uncertainties in the ice-sheet model calculations used to produce them. For example, the last Intergovernmental Panel on Climate Change report found end-of-century sea level could reach anywhere from 0.3 to 2 m above present. Most of this uncertainty relates to ice-sheet instabilities that, once triggered, could lead to rapid sea-level rise. It can be substantially reduced by calibrating model parameterisations of these instabilities so that they reproduce past ice volumes, but the reliability of existing calibrations is challenged by the recent discovery that mantle flow generates much faster changes in Earth’s surface elevation than had been recognised. This paradigm shift in geodynamics implies that: i) accepted estimates of past ice volume may be ~25–50% too high, since the ancient shoreline elevations underpinning them have been uplifted by mantle flow; and ii) existing models are missing key physics, leading them to underestimate modern post-glacial bedrock rebound rates by a factor of ~10 and overestimate ice-sheet instability. I will solve these issues by integrating new sea-level marker datasets with innovative mantle flow reconstructions to obtain probabilistic and geodynamically corrected estimates of past ice-sheet volume and sensitivity. By calibrating ice-sheet models that are compatible with this revised understanding of the palaeorecord and correctly incorporate mantle–ice-sheet feedbacks, I will produce the first geodynamically accurate global and regional-scale sea-level projections. These groundbreaking forecasts will enable decisionmakers to improve long-term coastal defence plans and better protect human life.