1357. Third-warmest September on Record amid Persistently High Ocean Temperature

According to the Copernicus Climate Change Service, September 2025 was the third-warmest September on record globally, with a mean surface temperature of 16.11°C, 0.27°C lower than the hottest September on record in 2023 and only 0.07°C lower than September 2024. September 2025 was 1.47°C higher than the estimated 1850-1900 average temperature used to define pre-industrial levels, and the 12-month average temperature from October 2024 to September 2025 was 1.51°C higher than pre-industrial levels.

The global mean sea surface temperature (SST) for September 2025 was 20.72°C, the third-highest on record for the month and 0.20°C lower than the September 2023 record. Much of the North Pacific continued to experience significantly higher-than-normal SSTs, with some areas experiencing record-high temperatures. Meanwhile, in the central and eastern equatorial Pacific, SSTs were roughly at or below the 1991-2020 average, reflecting a neutral ENSO (El Niño-Antarctic Motion) environment.

Contributor: IIYAMA Miyuki, Information Program