September 2025 was the third warmest September month on record, behind September 2023 (warmest) and slightly behind September 2024 (second warmest), according to the latest update by the Copernicus Climate Change Service (C3S) of the European Union. The warmth comes at a time when the sea surface temperatures in the equatorial Pacific Ocean were closer to La Niña conditions which generally are a cause for cooler than normal global temperatures.
Global average surface air temperature for September 2025 was 16.11°C. This was 1.47°C above the pre-industrial average (1850-1900) and 0.66°C above the 1991-2020 average. The twelve-month global average temperature between October 2024 and September 2025 was 1.51°C above the pre-industrial average and 0.63 above the 1991-2020 average.
Along with the atmosphere, the global oceans were also third warmest on record in September 2025. The global average sea surface temperature (SST) in September 2025 was 20.72°C. This was 0.20°C below the warmest September month in 2023.
The North Pacific Ocean stood out in terms of much warmer than normal SSTs with record temperatures in certain areas, according to C3S. The SSTs in the Norwegian Sea, Mediterranean Sea and Kara Sea were also much higher than the average. In the Mediterranean Sea, the worst affected parts were in the west and centre.
The warm atmosphere and the oceans also led to heavy rainfall in many regions along with floods and related calamities. In Europe, the northwestern and central regions, Finland and Scandinavia, eastern Black Sea coast, parts of Italy, coastal regions of Croatia and eastern Spain were wetter than the others. In some of these regions, the heavy rainfall also caused floods.
The rainfall was higher than the normal in southwestern and central United States, Alaska, northwestern Mexico in North America. In South America, the rains were surplus in some parts of Brazil, Argentina and Chile. In Africa, the northern part of the Horn of Africa region was wetter than normal. In Asia, the rainy regions were in the southern Arabian Peninsula, Pakistan and northwestern India, Central Asia and eastern regions of China.
The streak of much higher-than-average temperatures has continued in 2025 from 2023 and 2024. June to September months in 2025 were all the third warmest on record while March to May were the second warmest on record. February 2025 was the third warmest on record while January 2025 was the warmest on record.
The fact that the streak of higher-than-normal monthly temperatures is still hovering around the third or second or first rank on record after 2023 and 2024 is further evidence that the background warming induced by greenhouse gas emissions is taking a lead in defining global average monthly temperatures instead of natural climatic cycles such as the El Niño Southern Oscillation (ENSO).
The years 2023 and 2024 were characterised by the fifth strongest El Niño event which is the warmer than normal phase of the ENSO. While in late 2024 and early 2025 there was a brief La Niña event, which is the cooler than normal phase of the ENSO, temperatures since then have also been closer to La Niña than an El Niño. The only possible explanation for the record continuing to be set is background warming.