Second-hottest September ever as global temperature rises continue to exceed 1.5C threshold

A bulk carrying cargo vessel navigates a channel on the River Rhine during low water levels.

Last month was the second-hottest September ever recorded globally, and marked the second consecutive month this year when temperatures were 1.5C above the pre-industrial levels.

The latest Copernicus report has found that global temperatures reached 1.63C above the pre-industrial level in September, continuing a run of months above 1.5C that started in August and is set to continue into 2027.

It said this was the first time since November 2025 that two consecutive months have been above that temperature. The average surface air temperature for last month was 16.27C, which was 0.82C above the 1991-2020 average.

Looking at Europe, the average land temperature was 16.26C, 1.54C above the 1991-2020 average for the month, making it the third-hottest September on record.

“Most of Europe experienced warmer-than-average temperatures, with unusually warm conditions continuing to be most pronounced over western Europe and adjacent seas, as they have through much of the summer,” the report said.

It added that last month was the joint-hottest September on record for western Europe, tied with September 2023 at 2.51C above average — this followed the region’s hottest summer on record.

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Looking further into conditions in Europe, much of the central, western, and eastern parts saw “widespread dry conditions” which often coincide with unusually warm weather.

These conditions intensified or expanded across parts of Iberia, France, Italy, the western Balkans, and Greece, bringing in similar conditions as the summer. Exceptionally low river flows also persisted across much of Europe, with record lows found in parts of the Rhine, Danube, Vistula, and Garonne-Dordogne.

The report said the impacts remained widespread, including disruption to navigation, water supply, and agriculture in several countries.

El Niño effects

Meanwhile, El Niño conditions continued to strengthen in the equatorial Pacific, likely resulting in “one of the strongest El Niño events recorded.” 

It said average sea-surface temperatures for the El Niño region reached an “all-time high” of 29.7C. Copernicus said this exceeded the peak values of previous very strong El Niño events of 1982/1983, 1997/1998, and 2015/2016.

It said this “underscores the exceptional intensity of the current El Niño”.

Average temperatures for extra-polar oceans were the highest on record for the month, at 21.05C — surpassing the previous September record of 20.92C set in 2023.

Around Europe, sea-surface temperatures were at record highs along the Atlantic coast and in the western Mediterranean, which the report says contributes “to the unusual warmth over adjacent land”. 

Director of the Copernicus Climate Change Service, Carlo Buontempo, said that with “a new run of months above 1.5C, and with a strong El Niño still intensifying, it is likely to last into 2027”. 

 “Crossing the Paris Agreement’s long-term limit is only a matter of time," he said. "How far we overshoot, and for how long, is still up to us.”