Detection and Emergence of Climate Change Signals in Extreme Sea Levels: A Global-scale Analysis

Climate change driven variations in extreme sea level (ESLs) are projected to increase the frequency and severity of damaging coastal flooding in most of the world’s regions over the 21st century. However, to date, detection and emergence of climate change signals in ESLs have not been studied at the global scale. Addressing this knowledge gap is important for informing climate policy, and coastal flood adaptation strategies. Here, we present the first global-scale analysis of detection and emergence of ESL, using a 74-year long (1950–2023) hydrodynamically modelled ESL dataset. We detect a statistically significant increasing trend at 10,136 computational points, collectively spanning 50.5% of the global ice-free coastline. The median increasing trend in ESL magnitude at these computational points is 2.6 [0.8–6.1] mm/yr (values in square brackets denote the 90% confidence interval). Highest increasing trends (median 6–13 mm/yr) are observed along extratropical coastlines, while tropical coastlines show lower increasing trends (median 1–3 mm/yr). At almost all computational points where a detected trend is present, the ESL signal has already emerged. The IPCC AR6 WGI regions with the earliest time of emergence (ToE) are located in the Equatorial Atlantic Ocean, Central Africa, Equatorial Indian Ocean, Western Africa, Northeastern South America, Arabian Sea, and Northern South America (regional-median ToE = between 1979 and 1982), which are also home to many of the world’s socioeconomically vulnerable nations.