Ocean Warming Fuels Up to 64% Rise in Global Humid Heatwaves, Says Report

Rising sea surface temperatures in coastal waters are driving 50-64% of increase in land heatwaves globally, according to a study titled ‘Large-scale Aggregation of Humid Heatwaves Exacerbated by Coastal Oceanic Warming’ published in the journal Nature. 

The researchers wrote in the report that they used a complex network approach applied to climate reanalysis data to show that the observed intensification of humid heatwaves was closely associated with coastal oceanic warming over the period 1982-2023.

According to Jürgen Kurths, co-author of the study, the land-ocean linkage will help in employing better adaptation strategies. “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,” Kurths said.

The report further stated that humid heat waves 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 degrees Celsius, when the body is no longer able to cool itself by sweating. However, the widespread occurrence of humid heat waves across large regions, like the 2023 heat wave 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,” said lead author and Potsdam Institute for Climate Impact Research scientist Fenying Cai. 

By using a complex network approach, instead of looking at heatwaves at individual locations or silos, the scientists were able to map connections between land-ocean linkages. Citing the example of warming Indian Ocean waters being closely tied to rising humid heat risks in South Asia and the Middle East, the report stated that 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 heat waves.

Ocean-Heat Link

As the excessive heat and energy warms the ocean, the change in temperature leads to cascading effects, including ice-melting, sea-level rise, marine heatwaves and ocean acidification, according to the United Nations report.

These changes ultimately cause a lasting impact on marine biodiversity, and the lives and livelihoods of coastal communities and beyond - including around 680mn people living in low-lying coastal areas, almost 2bn who live in half of the world’s megacities that are coastal, nearly half of the world’s population (3.3bn) that depends on fish for protein and almost 60mn people who work in fisheries and the aquaculture sector worldwide.