Assessing present and future coastal moderation of extreme heat in the Eastern United States

Climate models suggest a rapid increase of extremely hot days in coming decades. Cool marine air currently ventilates extreme heat in populous coastal regions, diminishing its impacts, but how well climate models capture this effect is uncertain. Here we conduct a comprehensive observational analysis of coastal extreme-heat ventilation—its length scale, magnitude, and regional patterns—and evaluate two ensembles of downscaled global climate models along the eastern US coast. We find that coastal areas are 2 °C–4 °C cooler than ∼60 km inland, resulting in reductions near 50% in population exposure to temperatures above 35 °C. Large seasonal and inter-regional variations are closely linked with land-sea temperature contrasts. High-resolution models underestimate coastal cooling by 50%–75%, implying that substantial and spatiotemporally varying model bias correction is necessary to create accurate projections of coastal extreme heat, which is expected to rise considerably with anthropogenic forcing. Our results underline the importance of regionally- and observationally-based perspectives for assessing future extreme heat and its impacts, and for positioning effective heat-risk management for communities and jurisdictions that span coast-to-inland areas.