Scientific American: Earth’s oceans just hit their hottest temperature ever

The previous high of 21.09 C (69.96 F) occurred in March 2024. From the report:

Average ocean temperatures hit a record 21.10 degrees Celsius (69.98 degrees Fahrenheit) on August 22, according to the European Union’s Copernicus Climate Change Service (C3S).

That’s not as hot as a warm bath, but it is the hottest the world’s oceans have been since C3S started keeping records in 1979.

“As a climate scientist, this is not surprising to me all,” says Zachary Labe, a climate scientist at Climate Central, a climate research nonprofit. “It’s consistent with decades of research showing how our climate is changing as the planet warms. And without reductions in the burning of fossil fuels, this warming will only continue.”

Link.

From Copernicus press release:

The daily global average sea surface temperature (SST) has reached its highest level on record, exceeding the previous record set in March 2024. The Copernicus Climate Change Service (C3S) confirmed the record, with a temperature of 21.1°C on 22 August, exceeding the previous record of 21.09°C. The C3S ERA5 dataset extends back to 1979.

While daily records should always be interpreted within a broader climate context, this milestone is consistent with the continued long-term warming of the global ocean and the emergence of an extreme El Niño event in the tropical Pacific.

The timing of the record is particularly notable. Global ocean temperatures are typically highest in March and April, following the austral summer, yet this record has been reached in August. It also exceeds the previous highest August value, recorded in 2023 at 20.98°C. This latest daily record follows a succession of monthly sea surface temperature records and near-records observed throughout 2026 across the extra-polar ocean (60°S to 60°N), underscoring the persistent warmth seen across much of the global ocean.

A strong El Niño is now developing in the tropical Pacific, adding further warmth to an ocean that has already been warming over many decades as a result of human-driven climate change. According to the World Meteorological Organization (WMO), El Niño is expected to strengthen during the coming months, while the C3S seasonal forecasting system suggests the event could reach levels not seen for several decades.

Samantha Burgess, Strategic Lead for Climate at ECMWF, commented: “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. 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”.

The long-term rise in ocean temperatures has far reaching consequences for both communities and ecosystems. A warmer ocean contributes to sea-level rise through thermal expansion, increasing risks for coastal communities and low-lying island nations. Higher temperatures also increase the likelihood and intensity of marine heatwaves, which can damage key ecosystems, such as coral reefs and seagrass meadows, which in turn disrupt marine food webs and industries such as fisheries and aquaculture.

Higher ocean temperatures also enhance the potential for extreme weather events. A warmer ocean transfers more heat and moisture to the atmosphere, potentially intensifying rainfall and some storm systems. In addition, 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.