Will Copernicus report October 2026 as the warmest October on record?
deadline 2026-11-20
confidence medium
tier 1 evidence
43%Asturna estimate
Resolution criterion
Yes if the Copernicus Climate Change Service (C3S) monthly climate bulletin for October 2026 states that October 2026 was the warmest October in the ERA5 record for global surface air temperature. Second-warmest or lower, or no bulletin published by 20 November 2026, resolves No.
Verified starting state
Copernicus (bulletin of 9–12 October 2026): September 2026 was the second-warmest September in the ERA5 record, 1.63°C above the 1850–1900 average and 0.11°C cooler than September 2023. The September Niño-3.4 sea-surface temperature reached an all-time monthly high of 29.70°C, El Niño is expected to intensify further, and months above 1.5°C are expected to continue into 2027. The monthly bulletin usually appears in the first days of the following month.
What pushes it up
- Niño-3.4 sea-surface temperatures reached an all-time monthly high of 29.70°C in September 2026 with El Niño forecast to intensify further into 2027 [tier 1].
- August 2026 previously set an ERA5 temperature record, confirming that global background temperatures remain capable of breaking monthly records under current conditions [tier 4].
What pushes it down
- September 2026 fell short of setting an all-time record, finishing as second-warmest and a substantial 0.11°C cooler than September 2023 [tier 1].
- October 2023 established an unusually large positive anomaly record, creating a very high hurdle for October 2026 to exceed given the slight deficit observed in September [tier 1].
What would move this number most
Whether the intensifying El Niño provides enough atmospheric warming during the latter half of October to overcome the 0.11°C gap seen in September compared to 2023.
How this number is built
| Deadline | 2026-11-20 |
| Base rate | 20% |
| Best evidence | tier 1 · 3 article(s) used |
| Independent runs | 38 · 48 (spread 10 pts) |
| Confidence | medium |
| Evidence cap | not triggered |
| Last revised | 2026-10-18 09:05 |
| Model | gemini-3.7-flash |
Sources consulted
Probability history
2026-10-18 09:05 43% 4 article(s) on file · gemini-3.7-flash
- What pushes it up. Niño-3.4 sea-surface temperatures reached an all-time monthly high of 29.70°C in September 2026 with El Niño forecast to intensify further into 2027 [tier 1].
- What pushes it up. August 2026 previously set an ERA5 temperature record, confirming that global background temperatures remain capable of breaking monthly records under current conditions [tier 4].
- What pushes it down. September 2026 fell short of setting an all-time record, finishing as second-warmest and a substantial 0.11°C cooler than September 2023 [tier 1].
- What pushes it down. October 2023 established an unusually large positive anomaly record, creating a very high hurdle for October 2026 to exceed given the slight deficit observed in September [tier 1].
- What would move this number most. Whether the intensifying El Niño provides enough atmospheric warming during the latter half of October to overcome the 0.11°C gap seen in September compared to 2023.
2026-10-17 09:06 43% 4 article(s) on file · gemini-3.8-flash
- What pushes it up. Niño-3.4 sea-surface temperature reached an all-time monthly high of 29.70°C in September and El Niño is projected to intensify further into 2027 [tier 1].
- What pushes it up. August 2026 set an all-time ERA5 temperature record, demonstrating that 2026 is already producing record-breaking monthly anomalies under developing El Niño conditions [tier 4, corroborated by tier 1 context].
- What pushes it down. September 2026 was 0.11°C cooler than September 2023, indicating that matching or exceeding the unprecedented heat spikes set in late 2023 remains difficult [tier 1].
- What pushes it down. October 2023 had an exceptionally large temperature anomaly, creating an unusually high threshold for October 2026 to surpass to achieve the single warmest spot [tier 1].
- What would move this number most. Whether the intensifying El Niño in mid-to-late October produces a sufficient anomaly jump to overcome the high benchmark set by October 2023.
2026-10-15 12:05 65% 3 article(s) on file · gemini-3-flash-preview
- What pushes it up. The September Niño-3.4 sea-surface temperature reached an all-time monthly high of 29.70°C, which is a strong leading indicator for global air temperatures [0].
- What pushes it up. El Niño is officially expected to intensify further, likely pushing global temperatures higher in the coming months [0].
- What pushes it up. August 2026 already set an ERA5 temperature record, demonstrating the current climate's record-breaking potential [2].
- What pushes it up. Copernicus expects months above 1.5°C to continue into 2027 [0].
- What pushes it down. September 2026 was only the second-warmest on record, failing to beat September 2023 by 0.11°C [0].
- What pushes it down. October 2023 set an exceptionally high benchmark during a period of extreme temperature anomalies, which may be difficult to surpass [0].
- What would move this number most. Whether the intensification of El Niño is rapid enough to overcome the 0.11°C deficit observed in the previous month relative to the 2023 record.
2026-10-14 14:44 18% 3 article(s) on file · openai/gpt-oss-120b (Groq)
- What pushes it up. Recent months have set temperature records (August 2026 record, September 2026 second‑warmest) indicating a strong warming trend [tier 1]
- What pushes it up. The Copernicus bulletin notes months above 1.5 °C are expected to continue into 2027, suggesting October could be unusually warm [tier 1]
- What pushes it down. No actual October temperature data or bulletin has been released yet, so the claim is still speculative
- What pushes it down. The only October‑related information comes from trend statements, not concrete measurements; tier‑4 articles provide no additional evidence [tier 4]
- What would move this number most. The actual October 2026 temperature anomaly relative to the ERA5 record