Scientists say that record-breaking marine heatwaves in 2023 and 2024 had lethal global impacts, triggering mass coral bleaching, collapsing fisheries, intensifying storms, and disrupted weather patterns—along with tens of billions in damage.
Both years saw nearly 3.5 times the number of marine heatwave days compared to any other year on record, reveals a new study published in the journal Nature Climate Change by an international team of marine biologists and oceanographers.
Fuelled by anthropogenic climate change and super-charged by El Niño, record-high temperatures affected nearly 10% of the global ocean, causing the fourth global coral bleaching event, the study authors said in a release.
‘Radically Changing’ Marine Ecosystems
Regional fisheries in South America were devastated as ocean heat caused species to move northward in search of cooler waters, the study authors said. In Peru, the anchovy fishery lost an estimated US$1.4 billion over the two years of extreme heat. The shellfish industry in northern Spain also suffered, affecting the women who are the traditional harvesters.
The heatwaves caused “mass fish deaths” in the Gulf of Mexico, increased whale and dolphin strandings off New Zealand, and pushed the Mediterranean’s fan mussel to the brink of extinction.
Marine heatwaves have “radically changed our marine ecosystems,” said Alex Sen Gupta, associate professor at the University of New South Wales. “This is clear in the permanent loss of kelp forests along hundreds of kilometres of the Western Australia coastline, and from the severely degraded state of the Great Barrier Reef compared to just a few decades ago.”
Worsening marine heatwaves will continue to modify ecosystems, he added.
Devastating Impacts On Land
Intense marine heat fueled storms in New Zealand, Libya, and North and Central America, triggering severe flooding in Ecuador and record-breaking heat in Japan.
In February 2023, New Zealand’s Cyclone Gabrielle killed 11 people and caused US$8 billion in damages.
Seven months later, Storm Daniel—supercharged with moisture and high winds due to surging ocean temperatures—slammed into Libya. Nearly 6,000 people died when heavy rains from the storm caused the Derna Dam to collapse. The tragedy was the “deadliest single flood event on record in Africa.” Daniel also caused deadly flooding in Greece, Bulgaria, and Turkey.
Marine heatwaves played a role in a near-record number of storms in both the 2023 and 2024 Atlantic hurricane seasons, including Hurricane Beryl, the earliest-ever Category Five hurricane, which tore through parts of the Caribbean and the United States in late June and July 2024.
With advance warning, authorities were able to protect some sea creatures. Some 25% of Tasmania’s endangered red handfish were extracted from their overheating home waters and placed in aquariums until it was safe to return, while “some corals and conches” were moved out into deeper and cooler locales.
Anticipating that they would have to close the anchovy fishery, Peruvian authorities paid benefits to the fishers who would otherwise have been unable to sustain themselves and their families.
Only One ‘Permanent Solution’
But remedial action and emergency action are no replacement for cutting the emissions that are driving marine heatwaves, lead author Kathryn E Smith, marine ecologist at the Marine Biological Association in the United Kingdom, warned in the team’s media release.
“The more regularly our marine ecosystems are being hit by marine heatwaves, the harder it is for them to recover from each event,” Smith said. No amount of scrambling ahead of the storm can replace the “permanent solution” of shifting away from fossil fuel use.
“The solution is clear: we cannot rely on restoring nature after we break it,” said study co-author Thomas Wernberg, a marine botanist at the University of Western Australia. “We must phase out fossil fuels before it’s too late.”
Should humanity fail to rein in global heating, “marine heatwaves could be 20 to 50 times more frequent and 10 times more intense by the end of the century,” the researchers warned.
