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

TLDR

Sea‑level rise from climate change and non‑climatic factors threatens coastal settlements, infrastructure, and ecosystems, and global mean projections are insufficient for local adaptive planning. The study aims to provide a global set of local sea‑level projections to guide decisions from the coming decades to the 22nd century. The authors generate complete probability distributions for each tide‑gauge site using expert community assessment, elicitation, and process modeling, accounting for site‑specific uplift, oceanographic effects, and the growing influence of the Antarctic ice sheet. They project a very‑likely 0.5–1.2 m global sea‑level rise under RCP 8.5 (0.4–0.9 m under RCP 4.5, 0.3–0.8 m under RCP 2.6), find the Antarctic ice sheet dominates late‑century variance, and show local sea‑level rise will dramatically increase the frequency of 1‑in‑10 and 1‑in‑100 year flood events.

Abstract

Abstract 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.