Earth’s Oceans Absorbed a Record Amount of Heat in 2025—About 23 Zettajoules
The world’s oceans reached their hottest heat-content level ever recorded in 2025, with the upper 2,000 metres gaining an estimated 23 ± 8 zettajoules of heat compared with 2024. That is 23 billion trillion joules—an enormous amount of energy, equivalent to roughly 39 times humanity’s annual primary-energy use by one widely used comparison.
Even more striking, 2025 marked the ninth consecutive year of record-high ocean heat content, the longest uninterrupted streak in the modern record. Scientists track this heat using thousands of measurements from instruments including Argo robotic floats, ships and other observing systems. Multiple independent datasets agreed that 2025 was another record year, although they produced different estimates for the exact size of the annual increase.
The ocean absorbs most of the excess heat accumulating in Earth’s climate system, storing it below the surface and redistributing it around the planet. While global sea-surface temperature actually fell slightly from 2024 and 2025 ranked as the third-warmest year for surface temperatures, the deeper ocean continued accumulating heat. That hidden reservoir can contribute to sea-level rise, marine heatwaves and long-term changes in marine ecosystems.
Source: Advances in Atmospheric Sciences, “Ocean Heat Content Sets Another Record in 2025,” Pan et al.