With the arrival of El Niño, prepare for stronger marine heatwaves
Record-high ocean temperatures, combined with a confluence of extreme climate and weather patterns, are pushing the world into uncharted waters. Researchers must help communities to plan how best to reduce the risks.
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These extreme temperatures, fuelled by the climate crisis, have manifested as a series of marine heatwaves — periods of anomalously warm sea temperatures that can last for weeks, months or even years — across the Northern and Southern hemispheres. In some areas around the United Kingdom and Ireland, for example, surface waters in June and July were 4–5 °C warmer than is usually recorded at this time of year. Temperatures are also soaring off the coast of Florida and into the Gulf of Mexico, extending across the tropical Pacific, around Japan, and off the coasts of Ecuador and Peru. Marine heatwaves are more intense, last longer and occur more frequently than they used to. From 1925 to 2016, the number of days classed as experiencing marine heatwaves increased by 54%.
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Marine heatwaves disrupt, threaten and damage ecosystems. They are particularly dangerous for temperature-sensitive organisms that live in cool waters, such as kelps, and immobile warm-water organisms, such as corals. Many species might be susceptible to disease or mortality, with knock-on effects. For example, in 2014–15, a marine heatwave off the west coast of the United States, dubbed the Blob, caused widespread loss of sea stars. This in turn caused a bloom of sea urchins (on which sea stars predate), which in turn damaged kelp forests. Rising water temperatures can also cause some species to migrate to cooler waters.
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Monitor impacts of warmer waters
For the scientific community, warnings months ahead of likely rises in temperatures provide the opportunity for in-depth studies. Hypotheses can be developed and tested, data can be gathered — for example, by using underwater gliders to determine the vertical structure of heatwaves — and samples can be collected and analysed.