Connecting the Past and the Future to Build Regional Sea-Level Projections

Sea level is rising and increasing the risk of flood, erosion and salt intrusion along the coastlines of the world. We describe the latest sea-level projections designed to help the Netherlands adapt to climate change. To improve on previous projections, we develop here a framework that allows a better connection between observed sea-level changes and projections. First, a sea-level budget provides an attribution of observed sea level to its contributors. This budget is applied to the same region as the projections. Second, the projections start in 1995 allowing a long overlapping period with observations, which allows an evaluation of the projections for total sea level and for each individual contributor. The framework helps identify issues in a former version of process-based sea-level projections and guides decision making to avoid them in this and future updates. In particular, we decide to select plausible climate models for ocean dynamic sea-level change. The resulting sea-level rise median and 5th to 95th percentile ranges in 2100 compared to 1995–2014 are 44 (26–73) cm, 59 (40–95) cm and 82 (59–124) cm for the SSP1-2.5, SSP2-4.5 an SSP5-8.5 emissions scenarios respectively. The framework is extended with a new way to develop low-likelihood high-impact scenarios to explore the deeply uncertain future.