A Global Assessment of Coastal Marine Heatwaves and Their Relation With Coastal Urban Thermal Changes

Ocean temperature significantly influences global and regional weather and climate. Coastal marine heatwaves (MHWs) do not only profoundly impact marine ecosystems but can influence the climate of coastal regions. This study provides the first observational assessment of global coastal MHWs changes, showing a latitudinal-dependent pattern with considerably strengthened severity of MHWs in the past four decades. Coastal MHWs have been found closely linked to remarkable changes in coastal urban thermal environments, showing consistent trends of increase in air temperature and moisture, and mostly reduced wind speed among 38 major coastal cities. These effects collectively exacerbate the thermal discomfort during the warm season. The findings demonstrate the strong coupling of coastal oceans and lands under the influence of global warming and regional interactions of ocean, land, and the atmosphere, and contribute to a global initial understanding of the characteristics and co-variation of thermal extremes over the coastal regions. Plain Language Summary The abnormally warm and prolonged episodes of oceans, known as marine heatwaves (MHWs), have considerable negative impacts on marine ecosystems as well as their economic benefits from marine resources. Coastal regions, as one critical contributor to marine biodiversity, have been largely influenced by the land and offshore oceans. Thus, the spatial and temporal patterns of coastal MHWs can be different but not well-understood. This study shows a growing number of more severe, more frequent, and longer-lasting coastal MHWs in the past four decades. Further, the statistical relationship shows that during the MHWs, the adjacent cities also experience abnormally higher temperature and humidity during the summer months. At a higher latitude region, it is more likely to see summer heatwaves happening at the same time over the coastal cities and their adjacent oceans. The study offers observational evidence of a close relationship between heatwaves over the lands and coastal oceans. Key Points Coastal marine heatwaves show an enhancement of intensity, duration, and occurrence in the past decades Elevated urban air temperature and moisture, and reduced wind speed are found during warm-season marine heatwaves Higher-latitude coastal regions exhibit strengthened co-occurrence of marine and urban heatwaves

Automated summary

Coastal marine heatwaves have intensified in intensity, duration, and occurrence over the past four decades, leading to significant impacts on the thermal environments of coastal urban areas. The study highlights a close relationship between heatwaves in coastal oceans and on lands, emphasizing the interplay of global warming and regional interactions in shaping thermal extremes in coastal regions.