Global ocean temperatures are typically highest in March and April, after the southern hemisphere summer.
The record follows a series of monthly sea surface temperature records and near-records through 2026, pointing to persistent warmth across much of the global ocean.
A strong El Niño is developing in the tropical Pacific, adding warmth to an ocean that has already been heating over many decades because of human-driven climate change.
“This record is another clear signal of an ocean under growing stress.
She said risks to marine ecosystems and coastal communities rise with ocean temperatures, and that the number of marine heatwave days globally has more than tripled since the early 1990s.
The timing of the record is also notable. Global ocean temperatures are typically highest in March and April, after the southern hemisphere summer. This record was reached in August.
It also exceeded the previous highest August value, recorded in 2023 at 20.98°C. The record follows a series of monthly sea surface temperature records and near-records through 2026, pointing to persistent warmth across much of the global ocean.
A strong El Niño is developing in the tropical Pacific, adding warmth to an ocean that has already been heating over many decades because of human-driven climate change.
According to the World Meteorological Organization, El Niño is expected to strengthen in the coming months, while Copernicus’s seasonal forecasting system suggests the event could reach levels not seen for several decades.
“This record is another clear signal of an ocean under growing stress. 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 the European Centre for Medium-Range Weather Forecasts.
She said risks to marine ecosystems and coastal communities rise with ocean temperatures, and that the number of marine heatwave days globally has more than tripled since the early 1990s.
On August 22, 1979, the same ocean area averaged 20.15°C — nearly a full degree cooler than this year’s reading on the same date, shows the ERA5 dataset.
Warmer oceans contribute to sea-level rise through thermal expansion, increase the likelihood and intensity of marine heatwaves that damage coral reefs and seagrass meadows, and transfer more heat and moisture to the atmosphere, potentially intensifying rainfall and some storms.
As oceans warm, they can also become less efficient at absorbing carbon dioxide, weakening one of the planet’s most important natural buffers against climate change.
