Global oceans hit record-high temperature of 21.1°C

The average surface temperature of the world’s oceans has reached a new record, with scientists warning that increasingly warm seas could raise the risk of extreme weather and put further pressure on marine ecosystems.

The global average sea surface temperature (SST) reached 21.1°C on Saturday, August 22, according to the EU’s Copernicus Climate Change Service. It is the highest daily average recorded since measurements began in 1979, surpassing the previous record of 21.09°C set in March 2024.

Samantha Burgess, strategic lead for climate at Copernicus, described the new record as another clear indication that the world’s oceans are facing growing pressure. Rising sea temperatures are increasing risks for both marine ecosystems and coastal communities, she said, while the number of days affected by marine heatwaves worldwide has more than tripled since the early 1990s.

Warmer oceans may also contribute to more extreme weather. According to Copernicus, higher sea surface temperatures allow the ocean to release more heat and moisture into the atmosphere, potentially contributing to heavier rainfall and stronger storms.

At the same time, warmer seawater may become less effective at absorbing carbon dioxide from the atmosphere. Scientists warn that this could weaken one of the planet’s major natural mechanisms for slowing the accumulation of greenhouse gases and mitigating climate change.

Unusual timing raises questions

Climate researchers at Copernicus were particularly struck by the timing of the latest record. Global ocean temperatures typically reach their highest levels in March and April, following the Southern Hemisphere summer.

The fact that a new record was instead recorded in August makes the latest development unusual, according to the researchers. The August peak also follows a series of monthly records and near-record temperatures already observed in the world’s oceans this year.

Scientists say the latest measurement adds to growing evidence that ocean warming is continuing to alter marine conditions and increase the potential consequences for ecosystems, coastal areas and global weather patterns.