Adaptation to uncertain sea-level rise; how uncertainty in Antarctic mass-loss impacts the coastal adaptation strategy of the Netherlands

Uncertainties in the rate and magnitude of sea-level rise (SLR) complicate decision making on coastal adaptation. Large uncertainty arises from potential ice mass-loss from Antarctica that could rapidly increase SLR in the second half of this century. To deal with uncertain SLR, the Netherlands has adopted an adaptive pathways strategy. Monitoring of new insights on climatic risks and societal developments is an essential ingredient of this strategy. The implications of SLR may be existential for a low-lying country as the Netherlands, and warrant exploration of high- impact low-likelihood scenarios. Therefore, a study was initiated to analyse the implications of storylines leading to extreme SLR for the current adaptive plan. This paper reports on the process and findings of uncertain high SLR consequences on flood, drought, and coastal management in the Netherlands, and discusses implications for coastal adaptation considering timescales of adaptation including lifetime of decisions and their lead-in time for preparation and implementation. We find that for extreme SLR transformative measures are needed, not only because of the unanticipated sea level values that are inconsistent with current strategy boundary conditions, but also because of high SLR rates that challenge adaptation. Anticipating deeply uncertain high SLR helps to enable timely adaptation and to appreciate the value of emission reduction and monitoring of the Antarctica contribution to SLR