Scientists have recorded the highest temperature ever measured in the world’s oceans, as climate change combines with a powerful El Niño in the tropical Pacific.

The global average sea-surface temperature hit a record 70 degrees on Aug. 22, according to Europe’s Earth observation agency Copernicus, which has been tracking the metric daily since 1979. The previous single-day record was measured in March 2024.

“El Niño is adding heat to the system, but it is doing so on top of decades of human-driven warming,” said Samantha Burgess, strategic lead for climate at Copernicus’ European Center for Medium-Range Weather Forecasts.

“As ocean temperatures continue to rise, the risks to marine ecosystems and coastal communities also increase,” she said.

Higher ocean temperatures contribute to sea level rise and increase the chance of extreme weather events, as warmer water transfers more heat and moisture to the atmosphere, intensifying storms and heat on land. Warmer oceans also have a reduced capacity to absorb carbon dioxide.

Record temperatures have already been measured in isolated areas of the world’s oceans including the western Mediterranean Sea as well as at the Earth’s poles, driven mainly by human-made climate change. Copernicus expects the trend to continue, with ocean temperatures now being supercharged by El Niño.

The August record is particularly worrying because global ocean temperatures are typically highest in March and April, after the Austral summer, Copernicus said.

Millan writes for Bloomberg.