September Was the Second-Warmest on Record, Copernicus Reports

September 2026 was the second-warmest September globally in the ERA5 dataset, the Copernicus Climate Change Service reported in an update published October 12. The global average surface air temperature was 16.27 degrees Celsius, or 0.82 degrees above the 1991–2020 September average. Only September 2023 was warmer, by 0.11 degrees, according to the service’s monthly release.

The report also put September at 1.63 degrees Celsius above the estimated 1850–1900 average. It was the second consecutive month above 1.5 degrees relative to that reference period, following August. Copernicus described this as the first such pair of consecutive months since November 2025, distinguishing a renewed run of monthly warmth from a single isolated reading. Its climate bulletin presents the temperature, moisture and sea-ice indicators together.

Ocean warmth and the Pacific

The average sea surface temperature across oceans between 60 degrees south and 60 degrees north reached 21.05 degrees Celsius, the highest September value in the record used by the service. That exceeded the previous September record of 20.92 degrees, set in 2023. The geographic boundary is important: this measure covers the extra-polar oceans, not every ocean surface including the polar regions.

Copernicus linked the exceptionally warm tropical Pacific to strengthening El Niño conditions. It reported a September temperature of 29.70 degrees Celsius in the Niño 3.4 monitoring region, exceeding the peak values of the previous very strong events it listed. The agency expected further intensification in coming months. That expectation is a forecast, rather than a completed measurement of how the event will ultimately develop or how long the warm spell will last.

The release said the new sequence of months above 1.5 degrees was expected to continue into 2027. In discussing the Paris Agreement, Copernicus director Carlo Buontempo referred separately to its long-term limit. The September figure should therefore be read as a monthly anomaly against a historical reference, not as an announcement that this one month alone establishes a crossing of a long-term temperature threshold.

Europe’s heat came with persistent dryness

European land temperatures averaged 16.26 degrees Celsius, 1.54 degrees above the 1991–2020 September average, making it the continent’s third-warmest September in the service’s record. Western Europe tied September 2023 for its warmest September. Copernicus said unusually warm conditions remained particularly pronounced in western Europe and nearby seas, following the region’s record-warm summer.

The hydrological findings showed widespread dryness across western and central Europe and parts of eastern Europe. Dry conditions intensified or expanded in parts of Iberia, France, Italy, the western Balkans and Greece compared with August. The service reported record-low September river flows in parts of the Rhine, Danube, Vistula and Garonne-Dordogne, with disruption to navigation, water supply and agriculture. Late-month rain provided local relief but also brought flooding in regions of France and Spain.

The polar readings did not follow a single ranking. Arctic daily sea-ice extent reached the 14th-lowest annual summer minimum in the satellite record, while its monthly extent was about 10 percent below average. Antarctic daily extent reached its third-lowest annual winter maximum, with September’s monthly extent about 6 percent below average. Together, the indicators describe widespread warmth with distinct regional conditions, not a claim that every climate measure or location set a new record.