Overview
- The assessment merged independent datasets from the Institute of Atmospheric Physics, Copernicus Marine, and NOAA/NCEI with an ocean reanalysis (CIGAR‑RT) to gauge heat to 2,000 meters.
- Global mean sea-surface temperature in 2025 ranked third warmest at about 0.5°C above the 1981–2010 average, influenced by a transition from El Niño to La Niña.
- Warming was regionally uneven, with roughly 16% of the ocean setting local records and about 33% ranking in their top three, notably in the tropical and South Atlantic, the North Pacific, and the Southern Ocean.
- More than 3,500 Argo floats, along with buoys, ships, satellites and animal-borne sensors, provided the backbone of measurements confirming the sustained heat gain.
- Scientists warn ocean heat content will continue to rise and new records will follow as long as Earth’s energy imbalance endures, unless emissions fall rapidly toward net zero.