September 2026 was the second-warmest September ever measured worldwide, according to the monthly climate bulletin the European Union’s Copernicus Climate Change Service (C3S) published on 12 October 2026. The month’s global average surface air temperature stood 1.63°C above the 1850–1900 pre-industrial baseline. Ocean surface temperatures outside the polar regions set a new September record. In Europe, river flows in several major basins dropped to record lows after a dry, hot end to summer.
What happened
C3S, which the European Centre for Medium-Range Weather Forecasts runs for the EU, puts September’s global mean surface air temperature at 16.27°C. That is 0.82°C above the 1991–2020 average for the month. Only September 2023 was warmer, by 0.11°C. August was also above the 1.5°C mark, so September makes two months in a row over that threshold. According to C3S, the last time that happened was November 2025.
The ocean data stood out most. Average sea surface temperature between 60°S and 60°N reached 21.05°C, beating the previous September record of 20.92°C set in 2023. In the Niño 3.4 region of the central equatorial Pacific, the standard index area for El Niño, the monthly temperature hit 29.70°C. C3S says that is an all-time high for the region.
Carlo Buontempo, director of C3S, said in the release: “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.”
Europe: heat and record-low rivers
Europe’s average land temperature in September was 16.26°C, or 1.54°C above the 1991–2020 norm, which makes it the continent’s third-warmest September on record. Western Europe tied with 2023 for its warmest September, at 2.51°C above average.
Much of western and central Europe, and parts of eastern Europe, were also drier than normal. C3S reports record-low September river flows on stretches of the Rhine, Danube and Vistula, and in the Garonne–Dordogne basin in France. These rivers carry freight, cool power plants and supply farms. Northern and north-eastern Europe and Türkiye, by contrast, were wetter than average. Heavy rain late in the month caused flooding in parts of France and Spain.
Key facts
- Global air temperature, September 2026: 16.27°C; +0.82°C vs 1991–2020; +1.63°C vs 1850–1900.
- Rank: second-warmest September on record, 0.11°C below September 2023.
- Sea surface temperature (60°S–60°N): 21.05°C, a September record (previous: 20.92°C in 2023).
- Niño 3.4 region: 29.70°C monthly value, the highest recorded there, according to C3S.
- Europe: third-warmest September (+1.54°C); western Europe joint-warmest (+2.51°C).
- Sea ice: Antarctic September extent third-lowest on record, about 6% below average; Arctic monthly extent about 10% below average (16th-lowest).
Background: an El Niño of possibly historic strength
The figures come as the tropical Pacific warms quickly. On 8 October the World Meteorological Organization (WMO) said El Niño was likely to keep strengthening and peak around December 2026. Its consensus of 13 forecasting centres gives almost 100% odds that the event lasts through February 2027. WMO expects the Niño 3.4 anomaly to average about +3.7°C over October–December, which would be the highest since observations began; the previous peak was about +2.6°C in late 2015 and early 2016. WMO Secretary-General Celeste Saulo said El Niño “is firmly established and strengthening rapidly.”
El Niño releases heat from the Pacific into the atmosphere and usually raises global average temperatures. The biggest effect tends to come in the months after the event peaks. This happened after the 2015–16 event, and again after 2023–24, when 2024 became the first calendar year more than 1.5°C above pre-industrial levels.
Analysis: what it means
The Paris Agreement’s 1.5°C limit refers to warming averaged over about 20 years, not a single month or year. September’s 1.63°C figure therefore does not mean the goal has been formally missed. Still, El Niño has not yet peaked and is already lifting monthly temperatures above the threshold. This makes it more likely that 2027, and perhaps late 2026, will set new annual records. Buontempo’s comment that crossing the long-term limit “is only a matter of time” shows how widely scientists now share that view.
In Europe, the low rivers point to a problem that does not depend on El Niño. As in 2018 and 2022, late-summer drought has cut flows on the continent’s main shipping rivers. Low water forces barges to carry lighter loads, which raises transport costs for fuel, grain and chemicals. It also limits how much cooling water some power plants can take. Governments are preparing national adaptation plans, and the C3S data adds to the case for treating water scarcity as a recurring planning risk, not a one-off emergency.
The figures will also feed into the run-up to COP31, the UN climate conference hosted by Türkiye in Antalya. There, countries will be under pressure to show that their new national climate plans match the warming now being recorded.
Sources
- Copernicus Climate Change Service — Second-warmest September; global temperatures stay above 1.5°C
- World Meteorological Organization — Sea-surface temperatures reflect strengthening El Niño
- Down To Earth — September 2026 second hottest on record
- Daily Sabah (Anadolu Agency) — Global temperatures mark 2nd-warmest September on record
