Sea-level rise is a major societal concern, with potential impacts on population, infrastructure and coastal environments. Global sea levels rose ~20 cm in the last 120 years, but the rate of rise is faster than for anytime in the last 3,000 years, and continues to accelerate. In recent decades mass loss has accelerated from both the Greenland and Antarctic Ice Sheets at rates not seen in our instrumental records, and knowing how much and how fast sea level could rise due to melt of these ice sheets is key to assessing risk, and improving resilience.
Approx. 50 million people in Europe live within low-elevation coastal zone (<10 m elevation above of present sea level) and recent studies suggest that the cost of coastal flooding could increase 2 to 3 orders of magnitude by 2100. Without mitigation and adaptation, the annual damage from coastal flooding in the EU and UK could increase from 1.4 €billion today to almost 240 €billion by 2100 (Vousdoukas et al., 2018). Current projections suggest a low probability of loss from the polar ice sheets, but they cannot be ruled out. Knowing how much and how fast sea level could rise with melting of the polar ice sheets is crucial information for risk analysis and adaptation, particularly for stakeholders with a low tolerance of risk, or where asset life cycles are long (>100 years), and coastal infrastructure safety is paramount (e.g. nuclear energy). These stakeholders need credible “worst case” scenarios to assess the greatest potential risk and costs associated with the long-term, high-end component of future sea-level rise. However, the large uncertainties in long-term projections can make adaptation and planning activities challenging. ExTaSea should help these stakeholders by providing this credible “worst case” scenario.
The ExTaSea project will address two sources of uncertainty in current projections of future sea-level: (1) our understanding of the system and, (2) the degree to which we can simulate natural variability. ExTaSea will do this by producing well quantified natural bounds on both the rate and magnitude of sea level rise (objective 1) and probability distributions that include specific information on high-end extremes for global mean and regional sea levels (objective 2). These will contribute to our understanding of these sources of uncertainty and will form the basis for policy-relevant extreme sea-level scenarios (objective 3) that account for the dynamic response of the ice sheets to climate forcing. ExTaSea will produce statistical distributions by: (1) collating and quality checking already available geological data from past time intervals of the last 200,000 years that are useful analogues for future change; (2) novel statistical techniques (e.g. modified Bayesian partition modelling) and (3) modelling of solid Earth deformation processes (GIA) that will allow absolute magnitudes of sea levels to be determined. As the geological record integrates all processes, the statistical distributions on the natural bounds of sea-level will include the high-impact (extreme) tail associated with mass loss from the polar ice sheets.
