The world’s oceans reached their highest recorded average surface temperature on Saturday, at 21.1C outside the polar regions, according to the latest data from the European Union’s Copernicus Climate Change Service.
The August record is especially striking because global sea temperatures are usually highest in March and April, after summer in the southern hemisphere, which has substantially more ocean area than the north.
What the new data shows
The records extend back to 1979, when satellites began providing the highest-quality data. The measurements exclude the polar regions, while the Arctic remains the fastest-heating region on the planet.
Dr Samantha Burgess of Copernicus described the record as a signal of an ocean under growing stress. She said global marine heatwave days have more than tripled since the early 1990s.
Related coverage: Europe’s 2026 marine heatwaves linked to carbon pollution.
Why ocean heat matters
More than 90% of the heat trapped by carbon dioxide from fossil fuel burning enters the oceans. Warmer water expands, contributing to sea-level rise and greater flooding risks for coastal communities and low-lying island nations.
Hotter seas can also transfer more energy and water vapour to the atmosphere, intensifying rainfall and storms. Marine heatwaves can damage sea life and undermine coastal livelihoods.
El Niño adds to the warming
The ocean heat spike is being intensified by a rapidly developing El Niño event, which is expected to be the hottest in at least a century. El Niño is a natural climate variation that raises global temperatures and changes weather patterns.
More context: Southwest Europe battles extensive wildfires amid record heatwaves and evacuations.
The developing event has already been associated with low monsoon rainfall in India, major wildfires in Indonesia and heightened fire concerns in Australia. The northern hemisphere summer has also brought record heatwaves, drought and wildfires in Europe and North America, alongside intense rain and typhoons in Asia.
The ocean’s changing role
The oceans absorb much of the planet-heating carbon dioxide released by fossil fuel burning and forest destruction. Scientists warn that hotter water is less efficient at absorbing carbon dioxide, potentially weakening an important natural buffer against global heating.
Reducing fossil fuel emissions and protecting marine and coastal ecosystems are identified as key responses. Kelp beds, mangroves and marshes absorb carbon, while coral reefs help protect against storms and provide habitat. More than 190 governments have committed to protect and conserve at least 30% of the planet by 2030.
Also read: New climate risks endanger the UNESCO rice terraces of the Philippines’ Ifugao region.
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