1238. Global warming increases the duration of marine heatwaves

Marine heatwaves are extreme weather events characterized by persistent warm ocean waters that severely impact marine life. These events have become more intense, longer, and more frequent as a result of anthropogenic global warming.

A paper published in the Proceedings of the National Academy of Sciences (PNAS) on April 14 provided a comprehensive, quantitative assessment of the impact of global warming on marine heatwaves. To do so, they constructed a counterfactual version of the world's sea surface temperatures since 1940, corresponding to a stationary climate unaffected by long-term global warming, and used it to calculate the impact of global warming on the intensity and persistence of marine heatwaves.

The results showed that nearly half of these extreme events are due to global warming, and that on global average, the number of days per year in which the ocean experiences extreme surface heat conditions has increased threefold. They also showed that global warming has caused a 1°C increase in the maximum intensity of these events. They also found that extreme marine heatwaves, which occurred only 15 days per year in the 1940s, have now skyrocketed to 50 days, and in some parts of the Indian Ocean, up to 80 days per year.

The research team points out that marine heatwaves occur in addition to rising ocean temperatures, because the ocean absorbs about 90% of the excess heat trapped by greenhouse gases. They recommend that the only solution to prevent further global warming is to reduce greenhouse gas emissions.

The findings highlight the detrimental effects of anthropogenic global warming on marine heatwaves. The study supports the need for mitigation and adaptation strategies to address these threats to marine ecosystems.

(References)
Marta Marcos et al, Global warming drives a threefold increase in persistence and 1 ° C rise in intensity of marine heatwaves, Proceedings of the National Academy of Sciences (2025). https://www.pnas.org/doi/10.1073/pnas.2413505122

Contributor: Miyuki IIYAMA, Information Program