September 2026 Was the Second-Warmest on Record as Oceans Hit a New Monthly High, Copernicus Reports

BONN — September 2026 was the second-warmest September ever recorded, with a global average surface air temperature of 16.27°C, the European Union's Copernicus Climate Change Service reported on 12 October 2026, marking a second consecutive month in which global temperatures stood more than 1.5°C above pre-industrial levels as a strengthening El Niño pushed ocean heat to a new monthly record.

Illustration: Earth seen from space with glowing heat patterns over the oceans and continents, representing the record warmth recorded in September 2026.

What Happened

The Copernicus Climate Change Service (C3S), implemented by the European Centre for Medium-Range Weather Forecasts (ECMWF), published its monthly bulletin for September 2026 on 12 October, with a newsflash dated 9 October. Its headline finding was stark: September 2026 was the second-warmest September in the ERA5 record, which stretches back to 1940. The month's global average surface air temperature of 16.27°C was 0.82°C above the 1991–2020 September average and 1.63°C above the 1850–1900 pre-industrial reference period.

That made September the second month in a row in 2026 in which the global temperature exceeded 1.5°C above pre-industrial levels, following August. Copernicus director Carlo Buontempo warned, in comments reported by the Emirates News Agency on 12 October, that global temperatures were likely to remain above 1.5°C over pre-industrial levels into 2027, amid intensifying El Niño conditions and exceptional heatwaves. He added that crossing the Paris Agreement's long-term limit of 1.5°C was only a matter of time, while stressing that how far temperatures overshoot the target, and for how long, depends on human action.

The oceans told an even more record-breaking story. The September average sea surface temperature for the band between 60° south and 60° north was the highest on record for the month, at 21.05°C, according to Copernicus. Sea surface temperatures in the Niño-3.4 region of the equatorial Pacific — the key El Niño monitoring zone — hit an all-time September high, signalling an exceptional El Niño event that, according to reporting of the bulletin, could propel global temperatures to a new annual record in 2026, with 2027 potentially exceeding it as ocean heat is released into the atmosphere.

Europe felt the heat directly. September was the joint-warmest on record for western Europe and the third-warmest for Europe as a whole. Prolonged dry conditions led to record-low river flows in parts of the Rhine, Danube, Vistula and Garonne-Dordogne, disrupting navigation, water supply and agriculture in several countries, according to the Emirates News Agency's account of the bulletin. Meanwhile, around Antarctica, sea ice extent reached its third-lowest annual winter maximum, continuing a run of weak winter ice seasons at the southern pole.

Background

Copernicus is one of the world's most closely watched climate monitoring services because it combines satellite observations, weather stations, ocean buoys and other measurements into a single consistent reanalysis, known as ERA5, that allows each month to be compared fairly with every month since 1940. Its monthly bulletins have become a regular drumbeat of the climate story in recent years: 2023, 2024 and 2025 were each, in turn, among the warmest calendar years on record, and Copernicus charts the current year, 2026, against those years in every bulletin.

The 1.5°C figure at the heart of the September bulletin needs careful reading, and scientists themselves have stressed the distinction. The Paris Agreement, adopted by 195 parties in 2015, aims to keep global warming well below 2°C above pre-industrial levels while pursuing efforts to limit it to 1.5°C. That goal refers to the long-term average warming level over decades, not to any single month or even a single year. A month at 1.63°C above pre-industrial levels therefore does not, by itself, mean the Paris limit has been breached — but a run of months above 1.5°C, driven by both long-term warming and a powerful El Niño, shows how close the long-term average is now running to that threshold.

El Niño itself is a natural climate pattern, but it now unfolds on top of decades of human-caused warming. During El Niño, warm water spreads across the central and eastern tropical Pacific, shifting rainfall patterns worldwide and adding extra heat to the global atmosphere. The World Meteorological Organisation has said sea temperatures across the central and eastern tropical Pacific are expected to reach record levels through October to December, with an almost 100 per cent chance that El Niño persists to February 2027, and warned the event could be among the strongest since at least 1950. Japan's weather agency recently described conditions as at their strongest intensity on record, while Copernicus, using an index that accounts for background ocean warming, suggests the current event has not yet surpassed past peaks on that adjusted measure — a reminder that different agencies measure the same event with different yardsticks.

Illustration: A band of warm water spreading across the tropical Pacific along the equator, representing the strengthening El Niño conditions reported in September 2026.

September's bulletin did not arrive in isolation. Just ten days earlier, on 2 October, Copernicus reported that Europe's 2026 summer had been defined by extreme heatwaves and dry conditions, with a record 52 per cent of the continent exposed to "very strong" heat stress by the end of the season, record high surface air temperatures across much of Europe, and record and near-record sea surface temperatures across European seas. And in August, the service confirmed that the daily global average sea surface temperature had reached its highest level on record, at 21.1°C on 22 August, exceeding the previous record set in March 2024. September's monthly ocean record fits that pattern: the seas are not just warm in bursts, but persistently warmer than ever measured.

Why It Matters

Monthly temperature records matter because they are where the abstract curve of global warming becomes concrete: hotter months mean more dangerous heatwaves, more strain on water supplies, lower river levels for shipping and farming, and warmer oceans that fuel stronger storms and bleach coral reefs. The September bulletin connects all of those threads in a single month — record ocean heat, low European rivers, weak Antarctic sea ice and a strengthening El Niño — and it arrives as governments prepare for the next round of United Nations climate talks, COP31, in Turkey in November.

The El Niño dimension raises the stakes further. El Niño years have historically brought floods to parts of South America and East Africa, drought to parts of Australia, Indonesia and southern Africa, and disruption to fisheries and harvests across the Pacific. If this event ranks among the strongest since 1950, as the World Meteorological Organisation has warned it could, its impacts could ripple through food prices, water supplies and disaster-response budgets well into 2027. At the same time, the fact that the background climate is already warmer than during past strong El Niño events means the same natural pattern now starts from a higher baseline — and can therefore push temperatures and extremes further than it did a generation ago.

The Antarctic sea ice finding deserves attention of its own. Sea ice around Antarctica reached only its third-lowest annual winter maximum, meaning that even in the depths of the southern winter, the frozen fringe around the continent failed to grow as far as it used to. Less sea ice means less sunlight reflected back to space, more heat absorbed by dark ocean water, and more exposure for ice shelves that hold back land-based glaciers. Scientists watch Antarctic sea ice closely because changes there can feed back into global sea levels over decades, even if no single winter sets a record.

There is also a communication lesson in the September numbers. Headlines that declare "1.5°C breached" on the basis of one month risk misleading readers, because the Paris goal is a long-term average. But the opposite error — dismissing a hot month as mere weather — is equally misleading. The value of the Copernicus bulletin is precisely that it places one month in a long, consistent record: September 2026 was not an isolated spike but the latest month in a run of exceptional warmth, with ocean heat at record levels and a powerful El Niño still strengthening. That context, rather than any single number, is the real warning.

Illustration: Antarctic sea ice breaking apart at the edge of a frozen coastline, representing the third-lowest annual winter sea ice maximum reported for 2026.

What Happens Next

All eyes now turn to the next monthly bulletins. If, as Copernicus expects, temperatures remain above 1.5°C into 2027 while El Niño persists into February, 2026 could close as a new annual heat record, with 2027 potentially hotter still as stored ocean heat is released into the atmosphere. Forecasters will also watch whether the El Niño peaks and fades on schedule or lingers, and whether Antarctic sea ice recovers during the southern summer melt season or continues its weak run.

For policymakers, the September data lands just weeks before COP31 in Turkey, where countries will be pressed to show how they intend to close the gap between current climate pledges and the emissions cuts scientists say are needed. The bulletin itself makes no policy recommendations, but its figures will feature heavily in those negotiations — particularly the evidence that the world is now running, month after month, above a threshold once treated as a distant guardrail.

For the public, the practical message is simpler: the heat of September 2026 was not a freak event but part of a measurable, ongoing shift, and the months ahead — shaped by a powerful El Niño on top of long-term warming — are likely to stay unusually warm. The next Copernicus bulletin, covering October, will show whether that expectation holds, and by how much.

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FAQ

How warm was September 2026, exactly?

According to Copernicus, the global average surface air temperature was 16.27°C — 0.82°C above the 1991–2020 September average and 1.63°C above the 1850–1900 pre-industrial reference period, making it the second-warmest September on record.

Does two months above 1.5°C mean the Paris Agreement limit has been broken?

No. The Paris Agreement's 1.5°C goal refers to long-term average warming over decades, not individual months. Scientists stress that single months above 1.5°C are a warning sign that the long-term average is approaching the limit, not proof that it has already been crossed.

Why were the oceans so important in September 2026?

The average sea surface temperature between 60° south and 60° north was the highest on record for September, at 21.05°C, and sea surface temperatures in the key El Niño monitoring region hit an all-time September high. Warm oceans store and release enormous amounts of heat, shaping weather worldwide.

What is El Niño, and why does it make things hotter?

El Niño is a natural pattern in which warm water spreads across the central and eastern tropical Pacific, shifting rainfall and adding heat to the global atmosphere. The World Meteorological Organisation says there is an almost 100 per cent chance it persists to February 2027, and it could rank among the strongest since at least 1950.

What happened to Antarctic sea ice in 2026?

Around Antarctica, sea ice reached its third-lowest annual winter maximum. Less winter sea ice means more sunlight absorbed by dark ocean water and greater exposure for ice shelves, with long-term implications for global sea levels.

Sources

• Copernicus Climate Change Service, "Copernicus: Second warmest September as global temperatures stay above 1.5°C," press release, 12 October 2026 (newsflash dated 9 October 2026).
• Copernicus Climate Change Service, press releases index, including "Record heat stress and low river flows marked Europe's 2026 summer," 2 October 2026.
• Emirates News Agency (WAM), "Copernicus warns of El Niño impact after second-warmest September," 12 October 2026.
• World Meteorological Organisation statements on El Niño persistence and strength, as reported in October 2026 coverage of the Copernicus bulletin.
• Copernicus Climate Change Service, "Daily global sea surface temperature breaks 2024 record," 24 August 2026.