21.1 °C: the daily record for ocean surface temperature in the ERA5 series
On August 22, 2026, the average sea surface temperature between 60°S and 60°N reached 21.1 °C according to the Copernicus Climate Change Service. The useful comparison is not with last year, but with the series that starts in 1979 and with the seasonal calendar.
There is only one starting figure, and it comes from an August 24, 2026 statement by the European climate service Copernicus (C3S/ECMWF), built on ERA5 data: on August 22, 2026, the daily average sea surface temperature over the extra-polar ocean, that is, the band between 60°S and 60°N, reached 21.1 °C.
The unit and the range. The figure is a daily average in degrees Celsius over a defined geographic domain: not the temperature of the entire ocean, which also includes polar waters excluded from the calculation, and not an annual average. The previous record for the series was 21.09 °C, recorded in March 2024: the record is decided by hundredths of a degree, and it is worth saying so before any other consideration. The ERA5 series begins in 1979, so “never measured” means “never in forty-seven years of this dataset,” not “never in the planet’s history.”
What it is large relative to. Two comparisons give the scale better than the absolute value. The first is seasonal: the global ocean typically reaches its annual peak between March and April, at the end of the austral summer, and an absolute record reached in August falls outside the usual calendar. The second is monthly: the previous record for a month of August was 20.98 °C, in 2023. Against this backdrop, again according to C3S, over the past three years the extra-polar ocean has remained between 0.35 °C and 0.73 °C above the long-term average — a range, not a single point.
What the source does not state. The statement places the value within a framework, not a single explanation: the record is, according to C3S, “consistent with the continued long-term warming of the global ocean” (transl. from English). The World Meteorological Organization announced on June 2, 2026, the onset of El Niño conditions in the equatorial Pacific, forecasting its strengthening in the following months; how much of that tenth of a degree is background warming and how much is tropical oscillation is not quantified in the document. NOAA’s next ENSO diagnostic discussion is expected on September 10, 2026.
The C3S monthly bulletin for July 2026 points in the same direction: globally, July was tied with 2024 as the second warmest, and sea surface temperature was the highest ever measured for a month of July over the extra-polar ocean.
The same bulletin measures the solid side of the phenomenon with more caution. In July 2026 Arctic sea ice extent was the sixth lowest for that month, with particularly reduced coverage in the northern Barents Sea, around Svalbard and Franz Josef Land; Antarctic sea ice extent was the fifth lowest. Sixth and fifth place are not records: the sea ice series, also starting in 1979, moves more slowly than surface temperature.
The next verifiable data point has a date: the seasonal minimum for Arctic ice is expected in mid-September, at values the National Snow and Ice Data Center describes as typical of the post-2010 era.
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