Global sea surface temperatures have reached a record high, according to new data released by the European Union's Copernicus Climate Change Service. On Aug. 22, the daily global average sea surface temperature outside polar regions reached 21.1° Celsius, exceeding the previous record of 21.09° C set in March 2024.
Even small temperature increases represent a large gain in heat energy given the ocean's vast volume, the 2025 European state of the climate report noted. Global ocean heat content reached a new record high in 2025, surpassing the previous record set in 2024.
The warming is having far-reaching consequences for marine systems. Sea surface temperatures contribute to sea-level rise, increase the likelihood and intensity of marine heatwaves, and put critical ecosystems such as coral reefs and seagrass under greater stress, officials said. The number of marine heatwave days globally has more than tripled since the early 1990s.
Warmer oceans threaten fisheries and food security while also increasing the potential for some extreme weather events and putting coastal communities at risk, officials said. Increased ocean temperatures can reduce the ocean's ability to act as a carbon sink. The world's oceans have absorbed more than 90% of the excess heat produced by human activities since the 1980s, with the rate of warming nearly doubling in the past two decades.
A super El Niño currently strengthening in the tropical Pacific Ocean is adding to human-induced warming. Coastal communities face additional risks as warmer oceans damage fish stocks, create conditions for stronger tropical storms, and increase sea level rise as a result of melting glaciers and thermal expansion. Coral reefs, which are particularly sensitive to heat, face potential die-offs that could affect the roughly 25% of all marine life that depends on them as habitat.
