The world's oceans have reached their highest recorded average surface temperature outside the polar regions. On Saturday, the temperature reached 21.1C, according to data from the European Copernicus climate change service. This was slightly higher than the previous record of 21.09C in March 2024. It was also far above the usual temperature for this time of year.
The data came from measurements taken 10 meters below the surface. Scientists combined information from buoys, ships, and satellites to make a global estimate. A small difference does not remove all uncertainty from the record. However, the timing is unusual because ocean temperatures around the world normally reach their yearly peak in March or April.
One reason for the current heat is El Niño, a natural weather phenomenon. It brings unusually warm water to the surface in the central and eastern tropical Pacific Ocean. El Niño is expected to keep growing until around Christmas, and scientists say it could become one of the strongest in centuries. Since it has not reached its expected peak, ocean temperatures could rise even more.
The heat is not limited to the Pacific. Waters around the United Kingdom and Europe are also unusually warm, and the western English Channel has experienced almost continuous marine heatwave conditions for more than three years. In July, its temperature reached almost 7C above normal. Scientists say this widespread warmth shows the growing effect of human-caused climate change.
Oceans absorb more than 90% of the extra heat trapped by greenhouse gas emissions, mainly from burning fossil fuels. Warmer seas can give storms more moisture and energy, raise sea levels, and increase coastal flooding. They can also harm habitats such as coral reefs and put pressure on marine ecosystems and the communities that depend on them. The new record is therefore a warning about the long-term stress faced by the world's oceans.