Study: Recent Unprecedented Marine Heat Waves May Signal a Climate Tipping Point

By Dave Levitan  |  July 25, 2025 | 9:47am
Photo by David Zhang/Wikimedia Commons
Climate Oceans
Study: Recent Unprecedented Marine Heat Waves May Signal a Climate Tipping Point

It is comforting, in one extremely narrow sense, to know I wasn’t crazy. The marine heat waves that began in early 2023 and produced the 2024 chart of ocean temperatures that I wrote about on the very first day I started at Splinter “exhibited record-breaking intensity, duration, and spatial extent,” according to a study published Thursday in Science. When I said the chart looked like a “malign mistake,” well, it kind of was.

 Researchers in China combined satellite observations with ocean reanalysis data to better understand what happened in the sea a couple of years ago. They found that the North Atlantic marine heat wave, or MHW, lasted an absurd 525 days. The Southwest Pacific’s MHW, meanwhile, was bigger in area than any previously recorded. In the Northern Pacific, the anomaly has lasted four years. The specific drivers of these heat waves are varied, including a reduction in cloud cover and other regional variables. And while the oceans have cooled somewhat from those record highs — this year’s line on the aforementioned chart is hovering, ominously, just below the 2023 and 2024 lines and far above every other year — they don’t say anything good about what comes next.

A chart of sea surface temperatures by year

“Crucially, the extraordinary MHWs of 2023 may represent a major shift in oceanic and atmospheric conditions, potentially indicating an early signal of a tipping point in Earth’s climate system,” the authors wrote. In other words, the extreme ocean temperatures can have impacts that simply don’t get undone if temperatures drop — impacts like coral reef collapse, fish and other animal die-offs, and redistribution of ocean wildlife to fundamentally different regimes.

“Other impacts include the destabilization of polar ice sheets and the weakening of the Atlantic Meridional Overturning Circulation,” they went on. “Such changes amplify climate feedback, accelerating global warming and threatening foundational ecosystems such as kelp forests and seagrass meadows.”

The authors noted that increased and improved ocean observation capabilities are still desperately needed in order to improve monitoring and potentially offer early warning signals for the next “unprecedented” event — just as the world’s formerly biggest scientific and observational enterprise is being taken apart, brick by brick. The line on that chart will jump again, at some point, above 2023 and 2024’s absurdities into newer territory still; we won’t, most likely, be ready.

 
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