The world's oceans are hotter than ever recorded, new data suggests, as they suffer from human-caused climate change and the growing El Niño weather phenomenon.
The average surface temperature of the planet's seas outside the polar regions hit 21.1C (70F) on Saturday, according to figures from the European Copernicus climate change service.
That edges past the 21.09C recorded on three separate days in March 2024, and is far above average for the time of year.
Warmer oceans can have wide-reaching consequences, including supercharging extreme weather, raising sea levels and harming marine life.
"This record is another clear signal of an ocean under growing stress," said Dr Samantha Burgess, deputy director of Copernicus.
"El Niño is adding heat to the system, but it is doing so on top of decades of human-driven warming," she added.
The data is based on sea temperatures 10m (32ft 10in) below the surface, using measurements from buoys, ships and satellites, which are combined to produce a global estimate.
While the margin of record is currently very small and any global estimate comes with uncertainties, scientists say its timing is particularly notable.
Average worldwide sea temperatures tend to reach their yearly peak in March or April, which corresponds to the end of summer in the southern hemisphere – and not in August.
The southern hemisphere contains more of the planet's ocean surface than the northern hemisphere and so exerts a bigger influence on average sea temperatures.
What is especially concerning to scientists is that the oceans are already so hot when the natural El Niño weather phenomenon is still some way off its expected peak.
El Niño brings unusually warm waters to the surface of the eastern and central tropical Pacific Ocean. Warmer waters across such a large area means that global average temperatures typically spike too.
El Niño is expected to keep strengthening until Christmas time, with scientists warning that it is on course to be the strongest in centuries.
This could see ocean temperatures climb yet further.
"The fact that we are already breaking records is an early indicator of how strong the El Niño is becoming," said Dr Jeremy Grist, senior research fellow at the National Oceanography Centre in Southampton.
