September 2026 was the second-warmest September on record for the globe, and the average surface temperature of the world’s non-polar oceans set a new high for the month, the Copernicus Climate Change Service (C3S) said in its monthly bulletin dated Oct. 12. A separate analysis by the U.S. National Oceanic and Atmospheric Administration (NOAA), published Oct. 9, reached the same ranking using a different dataset.

According to C3S, which bases its figures on the ERA5 reanalysis, the global average surface air temperature for the month was 16.27°C. That was 0.82°C above the 1991–2020 average and 0.11°C below September 2023, the warmest September in the record. Measured against the 1850–1900 period that C3S uses as an estimate of pre-industrial conditions, September was 1.63°C warmer. C3S said this marks the first time since November 2025 that two consecutive months have been above 1.5°C.

Oceans set the pace

The average sea surface temperature for the oceans between 60°S and 60°N reached 21.05°C, the highest on record for September, surpassing the previous September record of 20.92°C set in 2023. C3S notes that ERA5 sea surface temperatures estimate the ocean temperature at about 10 meters depth, known as the foundation temperature.

In the equatorial Pacific, C3S said the monthly sea surface temperature in the Niño 3.4 region reached an all-time high of 29.70°C, exceeding the peak values of the very strong El Niño events of 1982/1983, 1997/1998 and 2015/2016. NOAA’s Climate Prediction Center (CPC), in its Oct. 8 diagnostic discussion, kept an El Niño Advisory in place and reported a monthly Niño-3.4 anomaly of +2.1°C. CPC said a strong-to-very strong El Niño is likely through January–March 2027, with the chance remaining above 83%.

NOAA’s numbers point the same way. Its September global surface temperature was 1.33°C (2.39°F) above the 20th-century average, second only to 2023 in a record that runs from 1850 to 2026. The global ocean surface averaged 1.10°C (1.98°F) above average, which NOAA said set a record for any month. “For a fourth-consecutive month, the global ocean surface temperature departure set a new record-high,” the agency wrote. Land temperatures were 1.83°C (3.29°F) above average, the third warmest for September.

Europe dries out

For European land, C3S reported an average of 16.26°C, 1.54°C above the 1991–2020 average and the third-warmest September for the continent. Western Europe tied September 2023 for its warmest September on record, at 2.51°C above average. Sea surface temperatures were at record highs for September along Europe’s Atlantic coast and in the western Mediterranean.

Dry conditions spread or intensified across much of western, central and parts of eastern Europe, including Iberia, France, Italy, the western Balkans and Greece. Using data from the European Flood Awareness System, C3S said record-low September river flows occurred in parts of the Rhine, Danube, Vistula and Garonne-Dordogne. Late in the month, rain brought floods to parts of France and Spain.

Sea ice

Around Antarctica, C3S said daily sea ice extent peaked at its third-lowest winter maximum in the satellite record, and the September monthly extent was also third lowest, about 6% below average. In the Arctic, the summer minimum ranked 14th lowest and the monthly extent 16th lowest, about 10% below average. Rankings vary between datasets: NOAA ranked Arctic September extent 13th lowest and Antarctic extent third smallest.

Why it matters

The record ocean temperatures, together with an El Niño that CPC expects to stay strong into early 2027, bear on the rest of the year. NOAA said the January–September period was the second warmest on record behind 2024, and that it is very likely 2026 will rank among the five warmest years, with the highest probabilities favoring second place.

Carlo Buontempo, director of C3S, said September brought exceptionally high temperatures “across parts of Europe after an extreme summer.” He added: “We are in a new run of months above 1.5°C, and with a strong El Niño still intensifying it is likely to last into 2027.” And: “Crossing the Paris Agreement’s long-term limit is only a matter of time.” For Europe, the bulletin’s findings of spreading drought and record-low September river flows in parts of four major basins extend a summer that Buontempo called extreme.

The caveats

C3S and NOAA use different datasets and baselines, the 1991–2020 average and the 20th-century average respectively, so their anomalies are not directly comparable, even though both rank September 2026 second warmest. C3S also cautions that sea surface temperature products measuring at different depths may give different values from ERA5.

What to watch

CPC’s next ENSO diagnostic discussion is scheduled for Nov. 12, 2026.

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