Global Patterns of Detection and Emergence in Extreme Sea Levels

Extreme sea level (ESL) events, resulting from the combined effects of tides, storm surge, waves, and mean sea level rise, are a key driver of coastal flooding risk worldwide. While future increases in ESL magnitude and frequency due to anthropogenic climate change are well established, it remains unknown whether such changes, unlikely to be caused by internal variability alone, are already detectable in historical records, and whether their amplitude has emerged beyond the range of natural/internal variability at the global scale. Although a few studies have reported long-term increases in ESLs using historical tide-gauge records, the extent to which such changes are detectable and have emerged remains largely unknown, particularly at the global scale. This knowledge gap persists due to several challenges: (1) the infrequent, short-lived, and highly localized nature of ESL events, requiring high temporal and spatial resolution data; (2) the need for long, consistent time series to robustly characterize internal variability; and (3) the methodological complexity of detecting climate change signals and their emergence in extremes, compared to mean climate variables. Here, we assess the detection and emergence of climate change signals in ESLs along the global ice-free coastline using a 74-year (1950–2023) hydrodynamically modelled dataset with global coverage. Applying a detection and emergence framework tailored for extremes, we identify statistically significant increasing trends in ESL magnitude (global median 2.6 mm yr⁻¹) along approximately half of the global ice-free coastline. At nearly all computational points where a significant trend is detected, the associated ESL signal has already emerged beyond internal variability during the 1970–2023 period. The earliest times of emergence (regional-median ToE = between 1979 and 1982) occur in several IPCC reference regions, including the Equatorial Atlantic Ocean, Central Africa, the Equatorial Indian Ocean, Western Africa, Northeastern South America, Arabian Sea, and Northern South America. Linking times of emergence with national-level socio-economic indicators reveals that socioeconomically vulnerable countries with minimal historical CO₂ emissions have experienced increasing ESL magnitudes for the longest period.