Ocean Warming Weakens the Sea–Land Breeze in Coastal Megacities
Rising ocean temperatures are quietly weakening the sea breeze that cools coastal megacities — with a small further SST rise causing 4.5x more decline.
More than half the world's urban population lives within 100 km of a coast, and much of what makes those cities livable in summer comes down to a simple daily rhythm: the sea–land breeze (SLB), which pulls cool marine air inland by day and pushes warm land air back out at night. That circulation lowers heat, clears pollutants, and moderates humidity — but its response to rising sea-surface temperatures (SST) has never been systematically modeled.
Xiao et al. (2026) fill that gap, running a high-resolution regional weather model across 18 major coastal megacities worldwide to trace exactly how ocean warming is eroding this circulation, city by city.
Key Findings
Two-thirds of coastal megacities have already lost sea breeze days
Comparing 1970 to 2010, the study finds SLB days declined in 12 of the 18 megacities as SST rose, with 67% of all cities examined showing a drop of 3–45%. The losses aren't evenly spread: mid-latitude cities like London, New York, Shanghai, Tianjin, Lisbon, and Buenos Aires saw declines of 29–45% as local SST rose by an average of 0.73°C (9%) — a far steeper relative warming than the modest 0.25–0.44°C increases seen around tropical megacities like Mumbai, Jakarta, and Dubai, several of which actually gained sea breeze days.
The mechanism is a shrinking temperature gradient, not wind itself
The authors trace the decline to a specific physical chain: rising SST narrows the thermal contrast between sea and land (SLTD), which is the fundamental driver of the breeze in the first place. In the hardest-hit cities — dubbed high-impact regions (HIRs) — this shrinking thermal gradient accounts for more than 50% of the decline in breeze days, reaching 65% or higher in London, Tianjin, and Shenzhen. An average SST rise of just 0.43°C, against a comparatively modest 0.15°C rise in land temperature, was enough to meaningfully weaken sea breeze development.
A small additional temperature rise causes a dramatically larger loss
The most striking number in the paper: a further 0.52°C SST increase beyond historical levels produces a 4.5-fold greater reduction in SLB days in high-impact regions. Under the moderate-emissions SSP245 scenario, HIR megacities lose an average of 6% of their sea breeze days by 2050; under the high-emissions SSP585 scenario — where SST rises just 0.41°C more — that loss jumps to 27%, roughly 4.5 times worse. Moderate-impact cities like Tokyo, Cape Town, and Rio de Janeiro, currently only mildly affected, are projected to shift toward HIR-like sensitivity as warming continues, effectively joining the most vulnerable tier.
A Quiet Threat to Urban Livability
The paper's throughline is that this isn't a marginal meteorological detail — the sea breeze is doing real work for coastal cities that has no easy substitute. It cools the urban heat island, clears vehicle and industrial pollutants, and regulates humidity, all without any infrastructure cost. Unlike urbanization's effects on local circulation, which planners can influence through zoning and building design, SST-driven decline is a global forcing that individual cities can't engineer their way around.
The authors frame this as a case for building sea-breeze preservation directly into urban planning — protecting coastal ventilation corridors and building layouts that channel rather than block onshore airflow — while treating the underlying SST rise as a problem only global emissions policy can actually solve.
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