Global ocean surface temperature hits record 21.1°C amid intensifying El Niño
The daily global average sea surface temperature surged to a record 21.1°C on August 22, surpassing the previous daily record of 21.09°C set in March 2024, according to the Copernicus Climate Change Service, implemented by the European Centre for Medium-Range Weather Forecasts (ECMWF). The reading, unusually late for the time of year, reflects the combined effect of long-term ocean warming and a strengthening El Niño event in the tropical Pacific.
Ocean temperatures typically reach their global peak in March and April following the southern hemisphere summer, but this record was set in August, when temperatures normally decline. The new figure also beats the previous August record of 20.98°C reached in 2023. The record follows a series of monthly sea surface temperature records and near-records observed across the extra-polar ocean throughout 2026, highlighting persistent warmth across much of the global ocean.
The tropical Pacific is now rapidly warming, and a powerful drought-bearing El Niño is taking shape, adding heat to an ocean already warmed by decades of human-driven climate change. The World Meteorological Organization has said El Niño is likely to strengthen in the coming months, with Copernicus seasonal forecasts indicating the event could reach levels not seen for several decades.
Scientists warn of growing ocean stress
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."
Thomas Frölicher, an environmental physicist at the University of Bern, Switzerland, said Europe's seas, from the Atlantic waters off Ireland to the Mediterranean, are experiencing an alarming surge in temperatures. Research shows this surge is driven by climate change, in particular by the continued burning of fossil fuels.
The warmer ocean has wide-reaching consequences: water expands as it heats, contributing to rising sea levels, and a warmer ocean transfers more heat and moisture into the atmosphere, potentially intensifying some rainfall and storm systems. Warmer water is also less efficient at taking up CO2, which could weaken the ocean's role as a carbon sink. Higher sea temperatures increase the likelihood and intensity of marine heatwaves, which can damage coral reefs and seagrass meadows and disrupt marine food webs.
Europe's seas hit by record heat
Recent analysis by the World Weather Attribution group, which uses peer-reviewed methods to assess global warming's role in extreme weather events, found that human-caused climate change was the main driver of recent record-breaking sea temperatures around Europe. The average temperature in the Mediterranean was 27°C in July, the highest for any July on record, while an offshore buoy near Mallorca recorded 33°C in early August.
Human-caused climate change has added about 2°C of warming to the Mediterranean and around 1.4°C to Western European seas, according to the analysis. "This has the potential to completely reshape ecosystems that coastal communities rely on for food and income, and drive damaging extreme weather on land too," said Claire Bergin, a climate scientist at Ireland's Maynooth University and a co-author of the study.
The analysis found that peak sea temperatures recorded this year in the eastern and western Mediterranean and along the Bay of Biscay and Iberian coast would have been "virtually impossible" without human-caused climate change. In the Celtic Sea, off Britain and Ireland, the most extreme temperatures recorded would have been expected only about once a century in a world without human-caused climate change, it found.
Hotter seas increase humidity and overnight temperatures in coastal areas and can help fuel intense storms later in the year. Greenhouse gas emissions, mainly from burning fossil fuels, have raised the planet's average temperature to around 1.4°C above pre-industrial levels, according to the World Meteorological Organization.
Marine biologist John Bruno warned that some species are moving north to seek cooler waters, but not all can adapt: "We are rapidly approaching the absolute biological limits of adaptation for many species." About 90% of the Bay of Biscay and 80% of the western Mediterranean have experienced marine heatwave conditions this year; without global warming that figure would have been closer to 40%.
Scientists are watching to see whether the latest global sea surface temperature record is a short-lived spike or part of a more persistent period of extreme ocean warmth.