Ocean Warming Weaken Sea Land Breeze in Coastal Megacities

Sea-land breeze (SLB), driven by sea-land thermal contrasts, forms a distinct circulation in coastal cities, crucial for regulating urban heat islands, air quality, and livability. However, its response to rising sea surface temperatures (SST) under global warming remains unclear. Here, we advance a regional weather model by incorporating daily and diurnal SST variations, enabling the evolution of SLB across 18 major coastal megacities worldwide under different SST variations. We find that historical SST rise reduced SLB days by 3%-45% in 67% of coastal megacities, with mid-latitude cities experiencing maximum declines (29%-45%) due to >5% diminished diurnal sea-land thermal contrast. 2% greater SST increase lead 4.5-fold amplified SLB reduction in high impact regions and heightened sensitivity in moderate impact regions under higher emission scenarios. SST-driven SLB erosion has been a critical yet overlooked threat to coastal livability. Mitigating ocean warming yields nonlinear, amplified benefits for sustaining SLB activity and resilience.