Global ocean surface temperatures have hit a record high of 21.1°C (70°F) in August, surpassing previous marks as a strengthening El Niño combines with decades of human-driven warming. According to the Copernicus Climate Change Service, the average sea surface temperature across extra-polar oceans reached 21.1°C on August 22.
Global Ocean Surface Temperatures Reach Unprecedented August High
The new figure narrowly surpasses the previous record of 21.09°C set across three different days in March 2024, and sits well above typical averages for this time of year. Copernicus data covers ocean waters between 60 degrees north and 60 degrees south, utilizing measurements taken 10 meters below the sea surface from a network of buoys, ships, and satellites.
Why the Timing Concerns Scientists
The timing of the new temperature spike has drawn particular attention from researchers. Global ocean averages typically reach their peak annual warmth in March or August following the end of the Southern Hemisphere’s summer, making an August record highly unusual.
Scientists are especially concerned because ocean temperatures have climbed to these heights while the natural El Niño phenomenon is still months away from its expected peak. The climate pattern, which causes anomalous warming in the central and eastern tropical Pacific Ocean, is projected to continue strengthening toward Christmas. Researchers have warned that the current El Niño could become the strongest on record by a wide margin.
Samantha Burgess, deputy director at the Copernicus Climate Change Service, noted that while El Niño is injecting heat into the global system, it is building upon decades of continuous warming caused by human activities.
Broader Marine Impacts and Regional Extremes
The extreme warmth extends far beyond the tropical Pacific. Wide swaths of the northern Pacific and Atlantic, alongside much of the Mediterranean Sea, are significantly hotter than the 1991–2020 average.
In the United Kingdom and surrounding European waters, anomalous warmth has also persisted. Tim Smyth, science director at the Plymouth Marine Laboratory, stated that the western English Channel has remained in a continuous marine heatwave state for over three years, peaking in July at temperatures 7°C above normal—a condition described as entirely unprecedented.
Experts emphasize that the wider oceanic heating reflects the growing influence of climate change, with oceans absorbing more than 90% of the excess heat trapped by human greenhouse gas emissions primarily from burning fossil fuels.
Potential Consequences for Weather and Ecosystems
The sustained high temperatures carry profound risks for global weather patterns, sea levels, and marine life. Warmer waters evaporate more moisture into the atmosphere, supplying storms with additional energy and moisture. In coastal zones, elevated sea temperatures can weaken cooling sea breezes and amplify land-based heatwaves.
Furthermore, thermal expansion of warmer seawater pushes sea levels higher, increasing coastal flooding risks. Marine ecosystems face severe threats as well. Frequent marine heatwaves place intense pressure on vulnerable habitats such as coral reefs and disrupt fisheries, including steep historical declines in South American anchovy populations during El Niño cycles.
As scientists monitor the ongoing interaction between high background ocean warmth and the developing El Niño, researchers like Jeremy Grist, a senior researcher at the National Oceanography Centre in Southampton, note that breaking the record early serves as an early indicator of a strengthening El Niño, raising the distinct possibility that global ocean temperature records could be broken again by March or April 2027.
