Global sea temperatures reached an all-time high in 2024, according to a new study published Friday in the journal Advances in Atmospheric Sciences.
The 54 researchers from seven countries deployed thousands of instruments to collect ocean data both at the surface and up to 2,000 meters below the surface — the latter called ocean heat content — covering all the world’s oceans.
“The broken records in the ocean have become a broken record,” professor Lijing Cheng with the Institute of Atmospheric Physics at the Chinese Academy of Sciences, said in a press release.
The researchers found that all three major metrics they analyzed broke records this year: global sea surface temperature, average global sea surface temperature and the temperature of water up to 2,000 meters below the surface.
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From 2023 to 2024, the researchers recorded an enormous increase of the upper 2,000 meters of ocean heat content of 16 zettajoules. That increase represents about 140 times the world’s total energy production in 2023.
Kevin Trenberth, a co-author and researcher at the University of Auckland, said it’s unusual for all three metrics to break records in a single year.
“The biggest years on record globally are the year following an El Niño event,” Trenberth told EcoWatch in a video interview. “The last major one was 2016. That’s the last time that the global mean surface temperature and the sea temperatures and the ocean heat content were all at record levels.”
2024, like 2016, was a year marked by the tail-end of an El Niño event, which, as lead author Lijing Cheng explained on a video call, leads to higher-than average sea temperatures. “During El Niño,” he said, “global surface temperature is very high. La Niña is cold… so year-to-year fluctuations are dominated by El Niño-La Niña cycles.”
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Cheng explained that although the El Niño phenomenon has an enormous impact on sea surface temperatures, it only has a minor role on ocean heat content — or ocean temperature below sea level — which also broke record highs last year.
Ocean temperatures are a critical indicator of human-caused climate change. The vast majority — about 90% — of the Earth’s excess heat from global warming is stored in the oceans.
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The researchers used multiple instruments to record ocean data, John Abraham, a co-author and researcher at the University of St. Thomas, told EcoWatch in an email. “Most importanly, we use devices called Argo floats which are robotic sensors that move up and down in the oceans 2000 meters and send temperature data to laboratories through satellites.”
Abraham also explained that the researchers used instruments called expendable bathythermographs with long wires going up to the surface that dropped from ships passing the ocean to record data. “Other instruments,” he added, “are buoys that have sensors, and we also attach sensors to animals so they gather data as they swim.”
The authors estimate in the study’s concluding remarks that the recorded 16 zettajoule increase in ocean heat content in the upper 2,000 meters of the oceans led to a sea level rise of 1.0 millimeters, with a total rise of 54 millimeters since 1960. “Sea level rise, in turn, increases the risk of coastal infrastructure and habitats being impacted by saltwater intrusion, coastal erosion and flooding in low-lying regions,” the study says.
Warming oceans also tend to lead to more and more intense storms, Trenberth explained.
“The warmer ocean temperatures, in general, means that there’s capacity for greater evaporation over the ocean, and so that puts more moisture into the atmosphere, which gets gathered up by weather systems, and where it’s raining, then it rains harder,” he said.
This is especially true for hurricanes, which are fueled by warm waters.
Cheng said that even if we were to stay under the Paris Climate Agreement’s goal of 1.5° C of warming, ocean heating will still continue to rise. “Even if we meet the Paris target, the surface warming can be controlled by two degrees Celsius [but] ocean warming will continue, because ocean warming is delayed response.”
“Climate change mitigation and adaptation need to continue even if we meet can meet [the] Paris Agreement,” she said. “It’s a long-time preparation for the future of climate change.”
The team plans to continue keeping track of ocean warming going forward. “They’ve been putting out these reports in January for the last five years, or something like that. Now the group in China seems to be committed to continuing this, and I think they like the publicity they’ve received in the past,” Trenberth said.
“It indicates that their work is important, and for the funding that they get within China to continue. And as you may know, there are some stresses between the U.S. and China,” he said.
“Congress has been prevented from interacting with Chinese scientists for the most part now, which is rather unfortunate. I think they still can, to some extent, in the area of climate, but [for] areas that involve sophisticated technology of certain kinds then there are restrictions as to how much people can interact on the climate. It’s very much a global phenomenon. It’s very important that everyone who has information share that data, and then we can get a more complete picture of what is going on, and so that’s what our paper is about.”
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