Global average sea surface temperatures reached a record 21.1°C on 22 August, beating the previous daily record, which was set in March 2024, according to the Copernicus Climate Change Service (C3S).
The previous record stood at 21.09°C, while the highest August temperature prior to this year was 20.98°C, recorded in 2023.
‘Growing stress’
“This record is another clear signal of an ocean under growing stress,” commented Samantha Burgess, strategic lead for climate at ECMWF. “El Niño is adding heat to the system, but it is doing so on top of decades of human-driven warming.
“As ocean temperatures continue to rise, the risks to marine ecosystems and coastal communities also increase. The consequences are already visible: the number of marine heatwave days globally has more than tripled since the early 1990s, putting increasing pressure on marine ecosystems and the communities that depend on them”.
According to C3S, the timing of the new record is ‘particularly notable’, given that global ocean temperatures are usually at their highest in March and April.
Sea temperature records
C3S said that the latest daily record follows on from a succession of monthly sea surface temperature records and near-records observed during the year across the extra-polar ocean (60°S to 60°N), with a strong El Niño in the tropical Pacific adding to the global warming effect.
As El Niño strengthens in the coming months, temperatures ‘could reach levels not seen for several decades’, it added.
It noted that a warming ocean contributes to sea-level rise, putting coastal communities and low-lying island nations at risk, while also increasing the likelihood of marine heatwaves, which can damage key ecosystems. In addition, extreme weather events are more likely, as warmer oceans transfer more heat and moisture to the atmosphere.
‘A warmer ocean becomes less efficient at absorbing carbon dioxide from the atmosphere, potentially weakening one of the planet’s most important natural buffers against climate change,’ C3S commented. Read more here.
