According to the latest Climate Bulletin, published on 10 October 2025 by the Copernicus Climate Change Service (C3S), September 2025 the third warmest September on record worldwide. These findings point to persistently high global air and sea surface temperatures.

C3S, implemented by ECMWF on behalf of the European Commission, provides regular updates on temperatures, hydrological variables and sea ice. The data for this bulletin comes mainly from the ERA5 dataset.

The continuing impact of greenhouse gases

The average global surface air temperature in September 2025 reached 16.11 °CThis ranking is just behind the second warmest September in 2024 (just 0.07°C cooler) and is 0.27°C below the record set in September 2023. The global surface air temperature in September 2025 was 0.66°C above the 1991–2020 average for that month.

More significantly, global air temperatures were 1.47°C above the estimated average of the pre-industrial reference period (1850-1900). As Samantha Burgess, ECMWF’s climate strategy lead, said: Persistently high temperatures on land and at sea reflect the ongoing impact of the accumulation of greenhouse gases in the atmosphereThe average temperature for the 12 months from October 2024 to September 2025 even exceeded the threshold set by the Paris Agreement, being 1.51°C above pre-industrial levels.

Sea surface temperature (SST) in the 60°S–60°N zone was also the third highest for September, averaging 20.72 °C, although it was 0.20°C lower than the record set in September 2023. Marine heat waves with record highs in some areas were recorded in the North Pacific Ocean and contributed to significantly above-average SST temperatures in the Mediterranean Sea and the Northeast Atlantic.

Regional anomalies and extreme precipitation

In Europe, the average temperature over land in September 2025 was the fifth highest for that month, 1.23 °C above the 1991–2020 average. The most significant above-average temperatures were observed in Fennoscandia and Eastern EuropeExceptionally above-average temperatures were also recorded in Canada, where a monthly record was broken, as well as in parts of Greenland and large areas of Antarctica.

September 2025 was also characteristic for occurrence of heavy rainfall and floodsAbove-average rainfall affected much of northwestern and central Europe, with heavy downpours causing flooding in southern Norway and northern Italy. Outside Europe, wetter-than-average conditions were recorded in, for example, the southwestern and central United States and Alaska. Millions of people were displaced by widespread flooding in northern India, Pakistan, eastern China and central Asia.

Sea ice conditions

For sea ice, daily Arctic sea ice extent reached its annual minimum of 5.07 million km², the 14th lowest minimum in the satellite record. Overall, monthly Arctic sea ice extent was the 13th lowest, 12 % below the 1991–2020 average.

In contrast, the ice cover around Antarctica reached its annual maximum on September 13. With an area of 18.28 million km², it was third lowest annual maximum in satellite record, just behind 2024 (second lowest) and 2023 (historically lowest). The monthly Antarctic ice extent ranked fourth lowest, about 5 % below the 1991–2020 average. JRi