Global ocean temperatures hit a record 21.1°C in August, reaching the highest surface temperature recorded in the latest Copernicus Climate Change Service data. The average temperature across oceans outside the polar regions reached 21.1°C on Saturday, an unusually high point for a time of year when global sea temperatures are normally lower than their annual peak. More than 90% of the heat trapped by carbon dioxide from fossil-fuel burning enters the oceans, making the latest record an important measure of the continuing accumulation of heat in Earth’s climate system.

The new reading comes as a rapidly developing El Niño adds further heat to already warming oceans. Scientists say the combination is increasing pressure on marine ecosystems and raising risks associated with storms, sea-level rise and marine heatwaves.

Why the August Record Matters

Ocean temperatures usually reach their global maximum around March and April, after the southern hemisphere summer. The southern hemisphere contains considerably more ocean than the northern hemisphere, which helps shape the annual cycle.

An August record is therefore particularly notable.

The Copernicus dataset covers ocean areas outside the polar regions, with records extending back to 1979 using satellite observations.

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El Niño Is Adding More Heat

Ocean warming is being intensified by a fast-developing El Niño, a natural climate pattern that warms the tropical Pacific and can alter temperatures and rainfall across the globe.

The current event is expected to be exceptionally strong.

• Its effects are already being associated with disrupted weather patterns, including below-average monsoon rainfall in India, wildfire concerns in Indonesia and increased fire risk in parts of Australia.

El Niño is not responsible for the long-term warming trend by itself.

• Scientists emphasize that it is adding heat on top of decades of human-driven warming.
• Dr Samantha Burgess of the Copernicus Climate Change Service described the record as another sign of increasing stress on the world’s oceans.

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Warmer Seas Mean Greater Climate Risks

Higher ocean temperatures have consequences far beyond marine ecosystems. As seawater warms, it expands, contributing to sea-level rise. This increases the risk of flooding for coastal communities and low-lying island nations.

Warmer seas can also provide additional energy and moisture to the atmosphere, potentially making storms and extreme rainfall more intense. The record comes after a northern hemisphere summer marked by heatwaves, drought and wildfires across Europe and North America, alongside intense rainfall and typhoons in parts of Asia.

Marine ecosystems face their own risks. Persistent heat can trigger marine heatwaves that damage or kill sensitive organisms, disrupt fisheries and undermine coastal economies.

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Oceans Are Losing Some of Their Protective Capacity

The oceans have absorbed much of the carbon dioxide released through fossil-fuel burning and deforestation, acting as one of Earth’s most important natural buffers against climate change. But warmer seawater is less efficient at absorbing CO₂. Continued warming could therefore weaken one of the planet’s mechanisms for removing carbon from the atmosphere.

Scientists and conservation groups say cutting fossil-fuel emissions remains essential, while protecting ecosystems such as kelp forests, mangroves, marshes and coral reefs can provide additional climate and coastal benefits.

As global ocean temperatures hit a record 21.1°C in August, it is more than a single temperature figure. It reflects the amount of excess heat being stored in the world’s oceans and comes at a time when climate-driven weather extremes are already affecting communities and ecosystems. With El Niño adding another source of heat, scientists will be watching closely to see whether the record signals a broader period of exceptional ocean warming.

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