Observed thresholds in sea-level rise driving global tidal wetland loss

Tidal wetlands, such as salt marshes and mangroves, are highly vulnerable to drowning under accelerating relative sea-level rise. Yet its role as a driver of wetland loss has thus far been difficult to establish. Here we integrate multi-source remote sensing data spanning the past two decades and show that wetland area loss accelerates nonlinearly as relative sea-level rise rates increase. We find a critical threshold of 9 mm yr−1, beyond which the probability of loss acceleration exceeds 92% and the loss rate rises eightfold. Although salt marshes and mangroves share a similar threshold for abrupt loss acceleration, their trajectories diverge before reaching it: salt marshes exhibit modest and progressive area reduction, whereas mangroves remain comparatively stable until the threshold is crossed. Globally, lateral wetland change exhibits a marginally higher threshold than direct inundation loss ( ~ 8 mm yr−1), suggesting that lateral dynamics, modulated by tidal range and sediment supply, can partially buffer against rapid loss onset. These findings provide an empirical benchmark for refining projections of coastal wetland vulnerability and guiding management interventions. Using global multi-source observations, this study shows that tidal wetland loss accelerates sharply once relative sea-level rise exceeds ~9 mm yr⁻1, with loss rates increasing nearly tenfold, while lateral dynamics may provide only limited buffering against escalating risk under continued sea-level rise.