The global average sea surface temperature has reached its highest level ever recorded, according to the experts at the Copernicus Climate Change Service who confirmed that the daily global average of 21.1°C surpasses the previous record of 21.09°C set in March 2024.

The research outfit has stressed that sea temperatures have spiked ‘at a time of year when ocean temperatures are not supposed to peak’, suggesting that “something has shifted in the baseline behaviour of the global ocean.”

Global sea surface temperatures typically reach their annual maximum in March and April, following the austral summer in the Southern Hemisphere. The fact that records have been broken in August – and that it exceeds the previous highest August value of 20.98°C set in 2023 – indicates this is not a seasonal anomaly.

A strengthening El Niño event in the tropical Pacific is contributing additional warmth to a system that is already running hot. According to the World Meteorological Organisation, El Niño is expected to intensify in the coming months. Copernicus suggests the event could reach levels not seen for several decades.

Researchers stress that in the case of record-breaking average sea surface temperatures, El Niño is not the culprit, but simply amplifying a trend being driven by ‘something more persistent.’

“This record is another clear signal of an ocean under growing stress,” said Samantha Burgess, Strategic Lead for Climate at the European Centre for Medium-Range Weather Forecasts. “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.

“And the consequences are already visible. The number of marine heatwaves globally has more than tripled since the early 1990s, putting increasing pressure on marine ecosystems and the communities that depend on them.”

Thermal expansion of seawater contributes directly to sea level rise, increasing flood risk for coastal communities and existential risk for low-lying island nations. Higher temperatures intensify marine heatwaves which can devastate coral reefs, collapse seagrass meadows, and disrupt the food webs that fisheries and coastal economies depend on. 

A warmer ocean also transfers more heat and moisture to the atmosphere, with the potential to intensify rainfall and storm systems. A warmer ocean critically becomes less efficient at absorbing carbon dioxide from the atmosphere – weakening one of the planet’s most important natural mechanisms for limiting the pace of climate change.

For the island communities of the Pacific, many of these are already lived realities. Brianna Fruean, Samoan climate activist and Together for the Ocean Ambassador, said: “Our ocean has a fever. When our bodies run a high temperature, it’s a warning sign that something is wrong, and it’s no different for the ocean. Record-breaking sea surface temperatures are one of the starkest warning signs yet of a rapidly heating planet.

“Decades of fossil fuel addiction have turned up the heat. Now we’re watching scorching temperatures devastate coral reefs, disrupt marine ecosystems, and force fisheries to seek cooler waters – threatening the way of life for coastal communities around the world.

“The ocean has protected us all from the worst impacts of the climate crisis by absorbing vast amounts of heat. Its ecosystems are our natural defence system and the heart of so many island communities. But we cannot rely on the ocean to take the heat for us.

“A healthy ocean is more resilient to the extreme conditions we’re living through, and better able to protect us in return. Protecting the ocean means protecting us all.”

Already pushed to their limits by successive bleaching events driven by marine heatwaves, reefs are now facing the prospect of conditions that exceed what even the most resilient coral systems can withstand.

“Breaking yet another sea surface temperature record is deeply alarming,” said Dr Gabby Ahmadia, Vice President for Seascapes and Science at WWF-US. “Ever-hotter oceans are pushing coral reefs to their limits and making it harder for them to survive and recover. Protecting climate-resilient reefs has never been more urgent.

“Leaders across the public and private sectors must act on both fronts: cut the emissions driving ocean warming and protect the reefs with the strongest prospects for resilience. Every fraction of a degree matters. Every year of delay matters.”

More than 190 governments have now committed to protecting and conserving at least 30% of the planet by 2030 under the global 30×30 framework. Copernicus scientists are continuing to monitor whether the exceedance in daily sea surface temperature represents a temporary spike or a persistent new condition.

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