The planet's oceans set a record in September. The air above them did not, quite. That gap, 0.11°C between this September and the warmest one on record, is the most important detail in the Copernicus Climate Change Service's monthly bulletin, released on Oct. 12, because it points to what is likely to happen next.

September 2026 was the second-warmest September globally, with an average surface air temperature of 16.27°C, 0.82°C above the 1991-2020 average, Copernicus reported. September 2023 holds the record at 0.93°C above average.

Ocean Records, Air Second

The sea surface told a different story. The average temperature of the extra-polar ocean, from 60°S to 60°N, was 21.05°C, the highest ever recorded for September and only slightly below the all-time monthly record of 21.07°C set in August. Daily extra-polar sea surface temperature has been the highest on record for each calendar day since June 19.

Two things explain it, according to the bulletin: a rapidly developing El Niño in the equatorial Pacific, and much-above-average temperatures across many other regions, including most of the Indian Ocean, the South Atlantic and the subtropical North Atlantic.

The Record Question, Answered in This Dataset

In an earlier piece, Blogerroom covered the argument over whether this event is already a record, which turns on which index is used: El Niño may hit record strength, depending on the index. Copernicus's reanalysis dataset gives a clear answer for its own measure.

The monthly sea surface temperature in the Niño 3.4 region reached 29.70°C in September, an all-time high that exceeds the peaks of the 1982-83, 1997-98 and 2015-16 events, all of which occurred between November and January. The September anomaly of 2.99°C above the 1991-2020 average beat the previous record of 2.81°C, set in December 1997. The bulletin adds that the current El Niño is already notably stronger than the 2023 event at the same stage of development.

That does not settle NOAA's choice of a relative index, which compares the Pacific with the rest of the tropical ocean and ranks the event differently. It shows how much depends on the ruler.

The 1.5°C Mark, Again

September was 1.63°C above the 1850-1900 pre-industrial average, the second consecutive month above 1.5°C, Copernicus said. Before August, the last month to cross that line was November 2025. The bulletin says the run began in August and is likely to continue into 2027.

The 12-month average, October 2025 to September 2026, was 1.50°C above pre-industrial levels, a return to that level for the first time since October 2025. Carlo Buontempo, the service's director, told reporters that crossing 1.5°C was only a matter of time, as reported by dpa through Bernama. A single month above the line is not a breach of the Paris Agreement goal, which refers to long-term averages, but a sustained run puts that average under pressure.

The year to date is second only to 2024. Copernicus notes that in 2023, global temperature anomalies rose sharply in the final months as El Niño developed. If the last three months of 2026 are as warm as the same months in 2023, the annual average would be close to the 2024 record. With a stronger El Niño and a forecast to intensify, a new record is possible rather than certain.

Heat and Dry Rivers in Europe

Europe's September was hot at the western edge. Western Europe saw its joint-warmest September on record, at 2.51°C above average, tied with 2023, while Europe as a whole ranked third. Anomalies in southern France, Portugal, Spain and parts of Italy reached 4 to 6°C above average, with persistent high pressure and record-warm seas nearby, particularly the western Mediterranean and eastern North Atlantic.

National weather services reported Portugal's warmest September on record and France's second warmest. Météo-France's own review described remarkable heat and historic drought, and Copernicus reported record-low September river flows in parts of the Rhine, Danube, Vistula and Garonne-Dordogne basins, which disrupted navigation, water supply and agriculture, according to dpa.

The Far South

El Niño's reach showed at the other end of the planet. West Antarctica had the largest positive temperature anomalies anywhere in the world, 10 to 15°C above average in September, Copernicus said, consistent with the typical El Niño pattern of high pressure over the Amundsen Sea that channels warm marine air onto the region. The bulletin's sea-ice companion reports that the Antarctic winter maximum was the third lowest in the satellite record.

What to Watch Next

The ocean leads and the air follows, so the interesting numbers come later. Forecasters expect El Niño to peak toward the end of the year and continue into early 2027, and the lag between the Pacific and global air temperature means the largest effects often show up months after the peak. The October bulletin, due in November, will show whether air temperatures start closing the 0.11°C gap.

My view: the habit of treating each month as a separate headline hides the trend. The ocean has been breaking daily records for four months, and the atmosphere is catching up. Blogerroom's report on how warming is breaking a 400-year link between the Indian and Pacific oceans is a reminder that the patterns driving that catch-up are themselves changing.