The world’s oceans have reached their highest recorded temperature, according to data from the European Copernicus climate change service. The average surface temperature of the planet’s seas outside polar regions hit 21.1°C (70°F) on Saturday, edging past the 21.09°C recorded on three separate days in March 2024.
The temperature measurements come from buoys, ships, and satellites combined to produce a global estimate, with data taken from 10 meters below the surface. Scientists emphasize that the timing of this record is particularly significant. Global sea temperatures typically reach their yearly peak in March or April, corresponding to the end of summer in the southern hemisphere—not in August. Since the southern hemisphere contains more of the planet’s ocean surface and exerts greater influence on average temperatures, reaching this record in August is unusual.
According to Dr. Samantha Burgess, deputy director of Copernicus, “This record is another clear signal of an ocean under growing stress.” She noted that while El Niño is adding heat to the system, “it is doing so on top of decades of human-driven warming.”
What concerns scientists most is that oceans are already breaking records when El Niño is still some way from its expected peak. El Niño brings unusually warm waters to the surface of the eastern and central tropical Pacific Ocean. Scientists warn that El Niño is on course to be the strongest in centuries and is expected to keep strengthening until Christmas. Dr. Jeremy Grist, senior research fellow at the National Oceanography Centre, stated that “the fact that we are already breaking records is an early indicator of how strong the El Niño is becoming,” predicting ocean temperature records could be broken again in March or April 2027.
Wider ocean warming extends far beyond the Pacific. Waters around the UK and Europe are extremely warm, with the western English Channel experiencing almost continuous marine heatwave conditions for more than three years, peaking at 7°C above normal in July.
Warmer oceans have widespread consequences. They can fuel extreme weather by providing storms with extra moisture and energy, raise sea levels through thermal expansion, and devastate marine habitats like coral reefs. The oceans absorb more than 90% of excess heat trapped by humanity’s greenhouse gas emissions, primarily from burning fossil fuels, making ocean warming a direct indicator of human-caused climate change’s growing impact.
Key facts
- Ocean surface temperatures reached 21.1°C on Saturday, surpassing the previous record of 21.09°C set in March 2024
- Measurements are based on data from buoys, ships, and satellites taken 10 meters below the surface
- El Niño is expected to strengthen until Christmas and may be the strongest in centuries
- The western English Channel has experienced continuous marine heatwave conditions for over three years, peaking 7°C above normal in July
- Oceans absorb over 90% of excess heat from human greenhouse gas emissions