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Japan Times
6 days ago
- Science
- Japan Times
‘Unprecedented' ocean heat waves in 2023 suggest climate tipping point
The world's oceans experienced a staggering amount of warming in 2023, as vast marine heat waves affected 96% of their surface, breaking records for intensity, longevity and scale, according to a new study. That could mark a turning point in the way the oceans behave, potentially signaling a tipping point after which average sea temperatures will be reset higher and some ecosystems may not recover, say the authors of the study, which was published Thursday in the journal Science. "The ocean going to a new normal — that controls everything,' said Zhenzhong Zeng, an Earth systems scientist at China's Southern University of Science and Technology, who led the work. "Once we destroy it, then maybe it cannot go back.' Ninety percent of the 2023 oceanic heating anomalies occurred in the North Atlantic, tropical Eastern Pacific, North Pacific and Southwest Pacific. The average length of the heat waves was 120 days — four times the average length between 1980 and 2023, according to Tianyun Dong, lead author on the paper and an Earth systems scientist at China's Eastern Institute of Technology. The North Atlantic marine heat wave, which began in 2022, stretched for 525 days. "The ocean has a long memory,' Dong said. It plays a key role regulating global temperatures by storing and gradually releasing large amounts of heat, but because it is slower to react than the atmosphere, the impact of long-term heat changes can be both delayed and enormous. The researchers used a combination of real-world measurements from the ocean, satellite data and computer modeling to determine the scope and causes of the heating. The highest temperature spike was seen in the Tropical Eastern Pacific, which was 1.63 degrees Celsius hotter than normal. While the onset of the El Nino weather phase likely contributed to that, a key finding of the paper is the extent to which different drivers played a role in marine heat waves in different locations. Other factors include increased solar radiation from reduced cloud cover; weaker winds; and changes in ocean currents — factors which can themselves be caused by global warming. Taken together, they show climate change is having an intensifying impact on the oceans. What the paper doesn't explain is why so many drivers came together in 2023, resulting in so many smashed records, said Zeng. It may be that these changes are beginning to reinforce each other in ways that are not yet understood. Identifying such feedback loops, and figuring out their mechanics, is critical to understanding future heat events, he said. In the near term, a marine heat wave can be devastating for humans who depend on the ocean for their livelihood, like fishing communities. "It can also fuel stronger hurricanes and storms along the coast,' said Yuntian Chen, a researcher in mechanics at China's Eastern Institute of Technology and one of the study's authors. And if ocean heat reaches a tipping point, some species won't recover. There are already concerns this could be the case for some of the world's largest coral reefs. That has other ramifications: The loss of coral and kelp, for example, reduces the ocean's ability to sequester carbon, which leads to more heating. The hottest year on record was 2023 — until 2024, when the Earth's average temperature reached 1.55 C above the pre-industrial average, according to the World Meteorological Organization, and when the average ocean temperatures hit a new high. This year is unlikely to break the annual record again, but is expected to come close. June 2025 was the third-warmest June in 176 years, after 2024 and 2023, according to a recent report by the U.S. National Oceanic and Atmospheric Administration. The WMO tracks global temperatures based on six international datasets, including one run by NOAA, whose NCEI Coastal Water Temperature Guide was decommissioned by the U.S. government in May. Zeng's team relied on NOAA data for its work, some of which is no longer available. The cutbacks are "a disaster,' he said. "We are all living on the same planet. The climate is really changing.'

Business Standard
6 days ago
- Science
- Business Standard
2023's marine heatwaves signal early irreversible coral damage: Study
Marine heatwaves -- prolonged periods of raised ocean temperatures than what are typical for that time of year -- experienced in 2023 were not only unprecedented, but may have also signalled a potential climate tipping point, with irreversible, negative impacts to coral reefs and ecosystems, according to a new study. Researchers from China and the US found that regions in oceans across the globe, including the North Atlantic, and the tropical, south and north Pacific experienced extreme marine heatwaves -- the longest in duration, widest in extent and highest in intensity on record. The findings, published in the journal Science, show that the most intense warming occurred in the North Atlantic, tropical eastern Pacific, north Pacific, and southwest Pacific, which "collectively accounted for 90 per cent of the global ocean warming". Heatwaves in the North Atlantic which began mid-2022 persisted for 525 days with an intensity four times the typical, making it "the longest recorded marine heatwave in the region", the authors said. The southwest Pacific heat event broke records for its expanse and prolonged duration, while unusual temperatures in the tropical eastern Pacific peaked at 1.63 degrees Celsius during the onset of El Nino, they said. 'El Nino' is the warm phase of the 'El Nino-Southern Oscillation' (ENSO) natural climate pattern, which involves changes in temperatures and atmospheric pressures in the Pacific Ocean. El Nino is linked with warmer ocean temperatures. The authors, including those from the US' Scripps Institution of Oceanography at the University of California, said the marine heatwaves of 2023 were "a global event with a 50-year return period, (with a less than two per cent chance of occurrence)". First author Tianyun Dong, a joint postdoctoral researcher at the Eastern Institute of Technology, Ningbo, and Southern University of Science and Technology in China, told PTI in an email, "Global warming, observed over a long-term and primarily driven by greenhouse gas emissions, has raised the ocean's baseline state, making marine heatwaves increasingly frequent and intense." Further, the trends observed also suggest a "possible indication of an approaching climatic tipping point", the study said. A climate tipping point, potentially a 'point of no return', is related with irreversible, disproportionate health and economic consequences for the world's most vulnerable, such as tropical coral reefs, and ice sheets of Greenland and Antarctica. "While a full (ocean-climate) system collapse has not occurred, irreversible impacts -- mass coral bleaching in tropical reefs, collapse of key habitats -- are already emerging," Dong said. Coral bleaching in reefs, or the loss of algae in reefs causing a 'whitening' and vulnerability to disease and death, are showing few signs of recovering, while the functional collapse of key habitats in some of the world's regions undermine biodiversity and the role of ecosystems, Dong explained. "These impacts reflect more than a short-term stress, suggesting a shift towards a permanent ecological change. The 2023 marine heatwaves may, therefore, mark a dangerous step closer to tipping points in the ocean-climate system," the first author said. Arpita Mondal, associate professor at the department of civil engineering and centre for climate studies, IIT Bombay, and not involved with the study, told PTI, "Based on a primary reading of the paper, I'm quite convinced of the scientific robustness." Mondal explained that the ocean and atmosphere "talk to each other through processes -- called the 'teleconnections' -- through which far-away processes can influence local weather". "For example, processes in the southern and equatorial Pacific Ocean can influence the Indian monsoon," she said. "Of course, El Nino is the most significant phenomenon which affects not only monsoons in South Asia, but ENSO-neutral conditions -- where neither El Nino nor La Nina dominate -- have been linked with the heat waves in the pre-monsoon season too," Mondal explained. "Similarly, oscillations and circulation of currents in oceans and atmosphere can impact weather worldwide," she added. The study team analysed satellite observations and temperature data of the world's oceans. Data from the NASA-funded 'ECCO2' project, focussed on producing a high-resolution estimate of the state of the world's oceans and sea ice, was also analysed. First author Dong said that despite a relatively weak El Nino -- studies show its growth rate unexpectedly decelerated in mid-2023 -- the unprecedented nature of 2023's marine heatwaves cannot be explained by natural climate variability alone. "A continued warming of the planet -- especially when combined with El Nino -- could produce even more extreme marine heatwaves, pointing toward a potential new normal of amplified ocean heat extremes and a higher chance of crossing physical and ecological tipping points," the first author said. Mondal, who is not involved in the study, pointed to the concerning lack of reliable, long-term ocean data. "My concern is more about the lack of long-term, reliable ocean data globally. We have only been monitoring oceans in the recent years. We do not have say, 150 to 200 years of ocean surface temperatures recorded. However, satellites developed in the last 50 years or so have definitely helped in complementing the buoys which have been in place for monitoring the ocean," she said.