Global sea surface temperature hits record high of 21.1C: EU climate agency

The daily global average sea surface temperature reached its highest level on record, the EU’s Copernicus Climate Change Service said Monday, warning that the world’s oceans are under growing strain.

The average temperature across the extra-polar global ocean, covering the area between 60 degrees south and 60 degrees north, reached 21.1C (69.98F) on Aug. 22, surpassing the previous record of 21.09C set in March 2024.

The finding is based on the ERA5 dataset produced by the European Centre for Medium-Range Weather Forecasts (ECMWF), with reliable satellite-era records dating back to 1979.

Copernicus said the timing was particularly notable because global ocean temperatures typically peak in March and April following the Southern Hemisphere summer.

The latest figure also exceeded the previous highest temperature recorded for August, 20.98C in 2023, and followed a series of record or near-record monthly sea surface temperatures throughout 2026.

The World Meteorological Organization expects El Nino to strengthen in the coming months, while Copernicus’ seasonal forecasting system indicates that it could reach levels not seen for several decades.

“This record is another clear signal of an ocean under growing stress. El Nino is adding heat to the system, but it is doing so on top of decades of human-driven warming,” said Samantha Burgess, ECMWF's strategic lead for climate.

“As ocean temperatures continue to rise, the risks to marine ecosystems and coastal communities also increase,” she said, noting that the number of marine heat wave days globally has more than tripled since the early 1990s.

Copernicus warned that warmer oceans contribute to sea-level rise through thermal expansion and increase the likelihood and intensity of marine heat waves, threatening coral reefs, seagrass meadows, fisheries, and aquaculture.

Higher ocean temperatures can also supply more heat and moisture to the atmosphere, potentially intensifying heavy rainfall and some storm systems.

In addition, warming reduces the ocean’s ability to absorb carbon dioxide from the atmosphere, according to the report.