Abstract:
Sea level rise (SLR) is predicted to be one of the most serious consequences of future climate change. It could displace up to 600 million people worldwide by 2100, a tenth of the global population. Projecting its future behaviour is, however, proving difficult using deterministic modelling approaches. This is partly because it integrates many different Earth System responses: global land hydrology, glacier and ice sheet melting, thermal expansion of the oceans as they warm and vertical land motion (VLM) due to past and present changes in surface loading. The viscous part of the VLM, due to past loading changes, is known as Glacial Isostatic Adjustment (GIA) and is responsible for uplift rates of up to 1.5 cm/yr over parts of North America. GIA is important for determining sea level rise for two reasons: first it is relative SLR that influences flooding, that is the height of land relative to sea level, and second because GIA is a result of mantle redistribution at depth and this affects the global gravity field. The Gravity Recovery And Climate Experiment, GRACE, satellites are used to measures changes in ocean mass and melting ice but this signal is contaminated by GIA and to use it for mass movement we must first remove the GIA signal.
To tackle the challenges of estimating the contribution to SLR from all the sources described above, termed solving “the Sea Level Budget”, we have combined a global database of VLM from GPS stations, with GRACE satellite gravity data, satellite altimetry of sea surface height and estimates of glacier and ice sheet melt in a statistical framework that relates each observation to an underlying physical process. We use a Bayesian Hierarchical Model to combine the observations with physical processes, prior knowledge and fundamental constraints such as conservation of mass and salt. The approach enables us to solve for GIA, mass movement (hydrology and ice melt), and thermal expansion of the ocean simultaneously in a way that is consistent with all the observations and priors. I will illustrate the approach for North America, where we solve for GIA and land hydrology and compare with forward models.
You will find the complete schedule for Njord Seminar Series spring '21 here.
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