On June 21, the European Union's Copernicus Climate Change Service recorded an average sea surface temperature of 20.86C, while the Copernicus Marine Service measured 21C.
Both readings exceeded the previous records for that date set in 2023 and 2024.
The two services maintain separate datasets based on local observations combined with satellite measurements, resulting in slight differences between the figures.
Copernicus said the record had been expected after unusually high ocean temperatures were observed in several regions in recent months, with the naturally occurring El Nino climate pattern adding to the warming.
El Nino, which develops every few years in the equatorial Pacific, amplifies the effects of human-induced climate change and is associated with droughts and flooding, particularly in parts of the southern hemisphere. Its direct effects on Europe are comparatively limited.
Copernicus Director Carlo Buontempo said the current conditions could mark the beginning of a new phase that would take the climate into "uncharted territory".
"With ocean temperatures at these levels and El Nino on the horizon, we are likely to see more temperature records fall in the coming months," he said.
Copernicus experts said additional record temperatures could be recorded both in the oceans and in the lower atmosphere.
They noted that the El Nino event had already been weakening when the previous record was set in 2024, whereas this year's event has only recently begun.
Copernicus said warmer oceans have far-reaching consequences, as higher sea temperatures keep the atmosphere warmer for longer and allow more energy to build up, increasing the risk of extreme storms, heavy rainfall and flooding.
13°C