Global ocean surface temperatures reached a record high on Saturday, with the average sea surface temperature rising to 21.1 degrees Celsius, according to the European Union’s Copernicus Climate Change Service. The reading is described as the highest recorded ocean temperature and is especially concerning because global sea surface temperatures usually peak in March and April, not August.

The previous record for the highest daily average temperature was 21.09 degrees Celsius, recorded in March 2024. Scientists say long-term human-caused climate change has been raising ocean temperatures, while a strong El Niño condition in the Pacific Ocean has added to the warming. They caution, however, that El Niño alone cannot explain the record.

Oceans absorb more than 90 percent of Earth’s excess heat, so warming waters place added strain on the climate system. Higher ocean temperatures can raise sea levels and intensify storms and marine heatwaves, while threatening coral, seagrass and fish species. Experts say rapid cuts in fossil-fuel use and carbon emissions are necessary to limit the situation and protect marine ecosystems.