The world’s oceans absorbed roughly 23 zettajoules more heat in 2025 than the year before, enough extra energy to power every nation on Earth for several years. That surge pushed upper-ocean temperatures to near-record territory, according to a peer-reviewed analysis published in Advances in Atmospheric Sciences, and it arrives just as forecasters warn that a new El Niño could develop later this year or in early 2027.
The combination is raising alarms among climate scientists. El Niño events naturally redistribute vast amounts of ocean heat into the atmosphere, amplifying droughts, floods, and marine heatwaves across multiple continents. Layering that cycle on top of an ocean that is already storing unprecedented energy creates conditions researchers say have no clean historical parallel.
“We are in uncharted territory,” Lijing Cheng, a lead author of the annual ocean heat study at the Chinese Academy of Sciences’ Institute of Atmospheric Physics, has said of the accelerating trend. The 23-zettajoule increase, reported with an uncertainty range of plus or minus 8 zettajoules, was measured across the top 2,000 meters of the global ocean using data from the Argo network of autonomous profiling floats, satellite observations, and multiple sea surface temperature products including NOAA’s ERSSTv5 and the Copernicus Marine dataset.
A record that keeps falling
NASA has long identified ocean heat content as the single most reliable gauge of how much extra energy Earth’s climate system is trapping. The agency’s ocean warming indicator confirmed that 2024 set the all-time record for this measure. The 2025 data now approach or exceed that mark depending on the dataset, meaning the record has effectively been broken or matched in back-to-back years.
That matters because ocean heat is not a short-term fluctuation. Once absorbed, the energy persists for years to decades, raising the baseline on which every weather pattern plays out. The 2015-2016 El Niño, the strongest on modern record, drove catastrophic coral bleaching across the tropics, fueled deadly flooding in South America, and contributed to severe drought in Southeast Asia and eastern Africa. It unfolded atop an ocean that was substantially cooler than today’s.
El Niño odds are climbing
The NOAA Climate Prediction Center’s ENSO outlook, updated monthly, showed rising probabilities for El Niño development through the second half of 2026 in its April 2026 assessment. The original article referenced a hypothetical example of 55 percent odds to illustrate how such probabilities should be read; the actual CPC figures shift with each monthly update and readers should consult the latest advisory for current numbers. The forecast blends dynamical and statistical models with expert judgment, and while it stops short of declaring an event inevitable, the trend across recent updates has shifted decisively away from continued La Niña or neutral conditions.
Timing and strength remain open questions. A weak El Niño arriving in late 2026 would produce very different consequences than a moderate or strong event forming in early 2027. Shifts in tropical rainfall belts, changes in midlatitude storm tracks, and disruptions to monsoon timing all depend on how quickly and how far equatorial Pacific sea surface temperatures climb above the El Niño threshold. Each monthly CPC update will refine those probabilities, and forecasters caution against treating any single snapshot as a locked-in prediction.
What scientists are still working to pin down
Several critical unknowns complicate the picture. Standard Argo floats sample only the upper two kilometers of the ocean. A newer generation of deep Argo instruments can reach 6,000 meters, but their network is not yet dense enough to produce a reliable global estimate of abyssal warming. If significant heat is migrating below 2,000 meters, the 23-zettajoule figure could actually understate total planetary heat uptake, leaving a portion of the energy imbalance hidden from current observing systems.
Regional impacts are also difficult to forecast with precision. Coastal upwelling patterns, local current systems, and pre-existing ecological stresses all modulate how a given amount of ocean heat translates into on-the-ground consequences. Coral reefs already weakened by the 2023-2024 global bleaching event, the worst ever documented, may have little resilience left if another marine heatwave strikes. Fisheries in the eastern Pacific, which typically see dramatic shifts in catch composition during El Niño years, face compounding uncertainty from both warming and changing ocean chemistry.
No peer-reviewed economic modeling has yet isolated the potential costs of the 2025-2026 heat anomaly combined with a possible El Niño. Cost projections circulating in news reports should be treated as preliminary until formal assessments appear in the scientific literature or vetted institutional analyses.
Why this matters now
For coastal communities from Miami to Mumbai, for farmers in the Horn of Africa and Australia’s Murray-Darling Basin, and for Pacific Island nations already grappling with rising seas, the convergence of record ocean heat and growing El Niño risk is not abstract. It shapes decisions about infrastructure investment, disaster preparedness, crop planning, and fisheries management over the next 12 to 18 months.
The measurements are unambiguous: the oceans are storing extraordinary amounts of heat, and that stored energy is raising the floor on which natural climate variability now operates. Even if the next El Niño turns out to be modest, it will unfold atop a warmer ocean and atmosphere than any previous event in the observational record. That does not predetermine specific disasters, but it tilts the odds toward more frequent and more intense extremes, making the months ahead a critical window for preparation.
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*This article was researched with the help of AI, with human editors creating the final content.
