Probabilistic 21st and 22nd century sea-level projections at a global network of tide gauge sites

Sea-level rise due to both climate change and non-climatic factors threatens coastal settlements, infrastructure and ecosystems. Projections of mean global sea level (GSL) rise provide insufficient information to plan adaptive responses; local decisions require local projections that accommodate different risk tolerances and time frames and that can be linked to storm surge projections. Here we present a global set of local sea level (LSL) projections to inform decisions on timescales ranging from the coming decades through the 22nd century. We provide complete probability distributions, informed by a combination of expert community assessment, expert elicitation, and process modeling. Between the years 2000 and 2100, we project a very likely (90% probability) GSL rise of 0.5–1.2 m under Representative Concentration Pathway (RCP) 8.5, 0.4–0.9 m under RCP 4.5, and 0.3–0.8 m under RCP 2.6. Site-to-site differences in LSL projections are due to varying non-climatic background uplift or subsidence, oceanographic effects, and spatially-variable responses of the geoid and the lithosphere to shrinking land ice. The Antarctic ice sheet (AIS) constitutes a growing share of variance in GSL and LSL projections. In the global average and at many locations, it is the dominant source of variance in late 21st century projections, though at some sites oceanographic processes contribute the largest share throughout the century. LSL rise dramatically reshapes flood risk, greatly increasing the expected number of ‘1-in-10’ and ‘1-in-100’ year events. Summary. Local sea-level rise generally differs from global sea-level rise, with differences arising from local uplift or subsidence, ocean dynamics, and the sea-level response to shrinking land ice. Uncertain Antarctic ice sheet mass loss is the largest source of uncertainty in late-century projections globally and at most sites, although ocean dynamics is the major source in some locations. Sea-level rise greatly amplifies flood risk, pointing to the need for including sea-level rise allowances in flood risk assessments.