Humid heatwaves have intensified rapidly in recent decades and are projected to worsen, raising the risk of heat-related mortality. Previous research has indicated that even healthy people can succumb to wet bulb temperatures – a measure combining heat and humidity – above 31.5°C, when the body is no longer able to cool itself by sweating. However, the widespread occurrence of humid heatwaves across large regions, like the 2023 heatwave in Asia, has so far remained poorly understood.
“We see a strong link between warming coastal waters and clustered hot, humid extreme events, especially in the tropics, where oceans supply more moisture to the atmosphere, which is then transported to land, amplifying the heat”, says lead author and PIK scientist Fenying Cai. “In regions further from the equator, combined land-ocean warming, linked to large-scale atmospheric wave patterns, also plays an important role.”
Analysing climate data from 1982 to 2023 using a complex network approach, the international research team uncovered strong land-ocean linkages. For example, warming Indian Ocean waters are closely tied to rising humid heat risks in South Asia and the Middle East, while tropical North Atlantic Ocean warming intensifies risks in northern South America. The study also shows that these ocean influences are stronger for large-scale events than for isolated local heatwaves.
“Better understanding these land-ocean interactions can help to improve climate adaptation strategies. Crucially, coastal sea surface temperatures emerge as a potential early warning indicator for widespread humid heat extremes,” says co-author and PIK scientist Jürgen Kurths.
Nature Geoscience
Large-scale aggregation of humid heatwaves exacerbated by coastal oceanic warming.
24-Mar-2026