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2025 Recorded as One of the Hottest Years for Oceans Despite La Niña Effects
2025 has been marked as one of the three hottest years for ocean temperatures since monitoring began, despite the influence of the climate phenomenon known as La Niña, which typically cools global temperatures, according to estimates released by Mercator Ocean International.
The center, responsible for operating the European Copernicus Marine Service, noted that ocean temperatures remained exceptionally high throughout the year, indicating that 2025 is the hottest year on record for oceans under the influence of La Niña since observations began in 1993.
The estimates were based on operational ocean prediction systems that provide continuous and accurate analyses of the global ocean state. The data revealed that the average global sea surface temperature reached 20.80 degrees Celsius, with a margin of error of ±0.12, making 2025 the third hottest year on record, as approximately 81% of the world’s oceans experienced above-average temperatures.
Additionally, the center classified 2025 as the warmest year recorded during La Niña conditions. In the North Atlantic, the average sea surface temperature reached 22.42 degrees ±0.18, placing 2025 sixth in the ranking of hottest years over the past 33 years, with around 69% of the area recording some of the highest temperatures ever.
In the Mediterranean Sea, the average temperature was recorded at 21.21 degrees ±0.07, marking the second highest level since monitoring began, with over 98% of its area surpassing the normal average, and a quarter of the surface experiencing a rise of more than one degree Celsius.
Analyses indicated a significant extent of marine heatwaves, affecting 89% of the world’s oceans, 97% of the North Atlantic, and 99.6% of the Mediterranean. June 2025 saw 64% of the Mediterranean’s area impacted simultaneously, reaching unprecedented levels for that month.
At the poles, sea ice extent remained below long-term averages, with historical lows recorded in the Arctic in December, while the winter ice extent in the Antarctic was among the lowest ever documented.
