Will the NSIDC Sea Ice Index report an average Northern Hemisphere sea ice extent of at least 7.05 million km² for October 2026?
deadline 2026-11-10
confidence medium
tier 1 evidence
44%Asturna estimate
Resolution criterion
Resolves YES if the NSIDC Sea Ice Index v4 monthly file for the Northern Hemisphere (https://noaadata.apps.nsidc.org/NOAA/G02135/north/monthly/data/N_10_extent_v4.0.csv), read for the first time on or after 2026-11-10, shows an extent >= 7.05 million km² for October 2026 (region N). The value read at that moment is final; later revisions do not change the outcome. If the row is not yet published on 2026-11-10, the check is repeated until 2026-11-20, after which the question is voided. Also voided if NSIDC changes the dataset version or the definition of the monthly file. Reference at creation: average daily extent of the first five days of the month = 5.76 million km² (latest daily value 5.96 on 2026-10-06; daily values are an estimation aid only and never decide). Data: NSIDC Sea Ice Index, Version 4 (NOAA@NSIDC, dataset G02135), National Snow and Ice Data Center.
Verified starting state
Computed base rate: 47% of past years (1988 onward, 38 years) saw the NSIDC monthly mean exceed the average of the first five days of the month by at least the margin implied by this threshold (threshold 7.05 million km2, first-five-day mean 5.76). One value per year: small sample. Data: NSIDC Sea Ice Index, Version 4 (NOAA@NSIDC, G02135).
What pushes it up
- The required increase from the first-five-day mean of 5.76 million km² to 7.05 million km² is +1.29 million km², which aligns almost exactly with the historical median gain of +1.29 million km² [tier 1].
- Through October 9, daily extent has steadily increased to 6.02 million km², bringing the 9-day average up to 5.87 million km² as freeze-up progresses [tier 1].
What pushes it down
- Long-term warming trends and elevated sea surface temperatures in recent decades have frequently delayed Arctic freeze-up and suppressed October extents below early-record averages [tier 1].
- Daily extent growth from October 6 (5.96 million km²) to October 9 (6.02 million km²) averaged only ~0.02 million km² per day, indicating a relatively modest rate of expansion in early October [tier 1].
What would move this number most
The rate of freeze-up acceleration across the second half of October, which depends heavily on atmospheric circulation patterns and polar air outbreaks.
How this number is built
| Deadline | 2026-11-10 |
| Base rate | 47% |
| Best evidence | tier 1 · 1 article(s) used |
| Independent runs | 42 · 44 · 58 (spread 16 pts) |
| Confidence | medium |
| Evidence cap | not triggered |
| Last revised | 2026-10-11 09:04 |
| Model | gemini-3.8-flash |
Sources consulted
Probability history
2026-10-11 09:04 44% 6 article(s) on file · gemini-3.8-flash
- What pushes it up. The required increase from the first-five-day mean of 5.76 million km² to 7.05 million km² is +1.29 million km², which aligns almost exactly with the historical median gain of +1.29 million km² [tier 1].
- What pushes it up. Through October 9, daily extent has steadily increased to 6.02 million km², bringing the 9-day average up to 5.87 million km² as freeze-up progresses [tier 1].
- What pushes it down. Long-term warming trends and elevated sea surface temperatures in recent decades have frequently delayed Arctic freeze-up and suppressed October extents below early-record averages [tier 1].
- What pushes it down. Daily extent growth from October 6 (5.96 million km²) to October 9 (6.02 million km²) averaged only ~0.02 million km² per day, indicating a relatively modest rate of expansion in early October [tier 1].
- What would move this number most. The rate of freeze-up acceleration across the second half of October, which depends heavily on atmospheric circulation patterns and polar air outbreaks.
2026-10-09 13:52 49% 6 article(s) on file · gemini-3.7-flash
- What pushes it up. Early daily data through October 7 shows steady refreeze, with extent rising from the 5-day average of 5.76 million km² to 6.01 million km² by October 7 [tier 1].
- What pushes it down. Arctic autumn freeze-up in recent decades has frequently experienced mid-to-late October slowdowns due to elevated sea surface temperatures and atmospheric warmth [tier 1].
- What would move this number most. The pace of Arctic refreeze during the remainder of October, particularly whether storm tracks or warm air intrusions stall ice advance in the peripheral seas.
2026-10-08 19:48 48% 0 article(s) on file · gemini-3.7-flash
- What pushes it up. The required increase from the 5-day baseline (5.76 million km²) to reach 7.05 million km² is 1.29 million km², which aligns with the historical median monthly expansion (+1.29 million km²) [1].
- What pushes it up. Daily extent reached 5.96 million km² on October 6, raising the 6-day average to 5.79 million km² and signaling steady early-month freeze-up momentum [1].
- What pushes it down. Long-term warming trends and elevated sea surface temperatures in recent decades have frequently delayed or dampened the rate of Arctic autumn refreezing [1].
- What pushes it down. Reaching a monthly average of 7.05 million km² requires maintaining a sustained rapid freeze-up pace without mid-month synoptic warm spells or storm disruptions [1].
- What would move this number most. The rate of Arctic sea ice refreeze over the remaining 25 days of October, which depends heavily on atmospheric circulation and oceanic heat loss.