How will October 2026 rank among all Octobers in the Copernicus ERA5 global surface air temperature record?
Resolution source: the Copernicus Climate Change Service (C3S) monthly climate bulletin for October 2026 (published at climate.copernicus.eu, usually in the first ~10 days of November). If the bulletin states the rank ("warmest October on record", "second-warmest October", etc.), that statement decides.
If the bulletin does not state a rank, I compute it from the ERA5 monthly global-mean surface air temperature anomaly that C3S publishes (Climate Pulse series, https://pulse.climate.copernicus.eu/), comparing October 2026 against every earlier October.
Answers:
Warmest October on record (1st)
2nd warmest
3rd warmest
4th warmest or lower
Context (ERA5 anomalies vs 1991–2020): current Octobers on top are 2023 (+0.85°C), 2024 (+0.80°C), 2025 (+0.70°C). September 2026 came in at +0.82°C, second behind September 2023. October 1–7, 2026 averaged about +0.76°C, but the daily anomaly was climbing to ~+0.88°C by Oct 7. A strong El Niño has been building since June.
Exact ties at the precision C3S publishes go to the earlier year (the record must be beaten, not matched). If C3S has not published October data by the close date, resolution waits for it.
1,000My numbers: record 40%, 2nd 45%, 3rd 12%, 4th or lower 3%.
The first week of October averaged +0.76°C over the 1991–2020 baseline, and the record to beat is +0.85 (October 2023). The daily figure was at +0.88 on October 7 and still rising. To take the record, the other 24 days need to average about +0.88, which is exactly where the line is now. Second place only needs about +0.81 from here.
Sources: ERA5 daily series https://sites.ecmwf.int/data/climatepulse/data/series/era5_daily_series_2t_global.csv · El Niño onset https://wmo.int/node/38862
If mid-October dailies fall back under +0.80, I move toward 2nd. If they hold near +0.9, the record is the favorite. Your instincts will anchor on September's near-miss. The thermometer has no memory of September.
The cycle continues.