Warmest October on Record: 2026 Is Virtually Certain to Pass 1.5°C, and Likely to Finish Second to 2024
October 2026 was the warmest October ever measured. The EU's Copernicus Climate Change Service put the global average surface air temperature at 15.35°C — 0.90°C above the 1991–2020 average and 1.75°C above the pre-industrial level. It was the third consecutive month above 1.5°C, and it leaves 2026 virtually certain — better than 99 percent, in Copernicus's statistical model — to become only the second calendar year ever to end more than 1.5°C above pre-industrial levels. The first was 2024.
The question now is not whether 2026 clears 1.5°C — that is settled for practical purposes — but where it ranks. Copernicus gives the year about an 80 percent chance of finishing as the second-warmest on record, with a 20 percent chance of tying or beating 2024. The year to date is running second, 0.07°C behind the same stretch of 2024 and 0.05°C ahead of 2023. Two months remain, and the El Niño now strengthening in the tropical Pacific is the wild card: I wrote yesterday about that El Niño forming into possibly the strongest on record, and its warming effect on the global mean typically arrives months after the ocean itself peaks.
Not everyone agrees with second place. James Hansen and colleagues at Columbia argued in April, from a physics-based reading of the data, that 2026 will be the warmest year in the instrumental record, beating 2024 by about 0.06°C. Their case is that the budding El Niño looks at least as strong as the one in 2023–24, and that 2026 sea surface temperatures have run about 0.13°C warmer than 2023's. "Of course, 2027 will be still hotter," they add. The UK Met Office's forecast from last December split the difference, with a central estimate of 1.46°C and a range of 1.34–1.58°C — one of the four warmest years, just short of the record.
My read sides with Copernicus, and I put a 70 percent chance on 2026 finishing second to 2024. The year-to-date pace trails 2024, and the statistical model has the October data in hand. Hansen's case needs the El Niño to deliver its full warming in November and December, and ocean heat takes time to reach the global average. But the 20 percent is real: sea surface temperatures just set an October record of their own, the El Niño is still strengthening, and two hot months would close the gap fast. One honest caveat: other datasets — NASA, NOAA, Berkeley Earth — measure the same planet slightly differently, so the verdict here is judged on Copernicus's ERA5 record, as its annual summary in January will state it.
What a year above 1.5°C does and does not mean matters more than the ranking. The Paris Agreement's 1.5°C limit refers to a long-term average, typically twenty years, so a single hot year is not a breach of the treaty. But the four-year average for 2023–2026 is now also expected to exceed 1.5°C, and the last twelve months, November 2025 to October 2026, already averaged 1.51°C above pre-industrial levels. The line was drawn as a guardrail; the planet is now spending multi-year stretches on the wrong side of it. The land, notably, was only joint third-warmest for October, at 10.82°C — the record came from the water, where the extra-polar oceans averaged 20.95°C, the highest October sea surface temperature ever recorded.
What to watch next is straightforward: November's data, due in early December, and Copernicus's annual summary in January, which will settle the ranking. Beyond that, the forecasts point one way. Zeke Hausfather's reading of the ERA5 data puts 2027 at roughly 1.8°C above pre-industrial levels — easily the hottest year on record — and the World Meteorological Organization gives an 86 percent chance that one year between 2026 and 2030 will surpass 2024. The question is no longer whether the 1.5°C years keep coming. It is how many arrive in a row, and what a world that treats them as normal starts to look like.