Warming coastal waters emerge as primary driver of large-scale humid heat waves

Groundbreaking research has identified rising coastal sea surface temperatures as the dominant force behind large-scale humid heat waves, contributing to 50-64% of their increase. This comprehensive study, conducted by researchers from the Potsdam Institute for Climate Impact Research (PIK), Princeton University, and Sun Yat-sen University, reveals that coastal water temperatures could serve as crucial early warning indicators for predicting widespread humid heat extremes. The findings are published in Nature Geoscience.

Humid heat waves have experienced dramatic intensification over recent decades, with climate projections indicating continued worsening that heightens the risk of heat-related fatalities. Scientific research demonstrates that even healthy individuals face life-threatening conditions when exposed to wet bulb temperatures—a combined measure of heat and humidity—exceeding 31.5°C, at which point the human body loses its ability to regulate temperature through perspiration. Despite this understanding, the mechanisms behind widespread humid heat waves spanning vast regions, such as the devastating 2023 Asian heat wave, have remained inadequately explained until now.

"Our analysis reveals a robust correlation between warming coastal waters and clustered hot, humid extreme weather events, particularly in tropical regions where oceans contribute increased atmospheric moisture that subsequently travels inland, intensifying heat conditions," explains lead author and PIK scientist Fenying Cai. "In areas more distant from the equator, the combination of land-ocean warming, associated with large-scale atmospheric circulation patterns, also contributes significantly to these events."

The international research team employed a sophisticated complex network approach to analyze climate data spanning 1982 to 2023, successfully identifying strong interconnections between terrestrial and oceanic systems. Their analysis demonstrates that warming waters in the Indian Ocean correlate directly with elevated humid heat risks across South Asia and the Middle East, while rising temperatures in the tropical North Atlantic Ocean intensify hazards throughout northern South America. Notably, the study confirms that oceanic influences exert greater impact on large-scale events compared to isolated, localized heat waves.

"Enhanced understanding of these land-ocean interactions provides valuable insights for developing more effective climate adaptation strategies. Most significantly, coastal sea surface temperatures present themselves as viable early warning indicators for predicting widespread humid heat extremes," states co-author and PIK scientist Jürgen Kurths.

Publication details

Fenying Cai et al, Large-scale aggregation of humid heatwaves exacerbated by coastal oceanic warming, Nature Geoscience (2026). DOI: 10.1038/s41561-026-01952-z