Ongoing record ocean heat, with September 2026 marking the fourth consecutive month of all-time high global sea surface temperatures per NOAA, combined with a strengthening El Niño and the long-term anthropogenic warming trend, underpins the 95% market-implied probability that October 2026 ranks as the hottest on record. Year-to-date global temperatures place 2026 second only to 2024 through September according to Copernicus and NOAA analyses, while U.S. land temperatures hit their warmest September and January–September periods ever. Model consensus and historical analogs during strong El Niño years support continued elevated anomalies into October. A rapid shift to La Niña conditions or major downward revisions in final ERA5 or NOAA datasets remain the primary realistic scenarios that could alter the ranking, though current observations make such outcomes unlikely before month-end.
This market will resolve based on the data for the Global Land-Ocean Temperature Index for October 2026 versus the data points available for all other Octobers on record. Note: If October 2026 is tied for first, second, or third hottest with another year, it will qualify for the bracket it ties with. The primary resolution source for this market will be the figures found in the table titled "GLOBAL Land-Ocean Temperature Index in 0.01 degrees Celsius" under the column for the relevant month (https://data.giss.nasa.gov/gistemp/tabledata_v4/GLB.Ts+dSST.txt). If NASA's "Global Temperature Index" is rendered permanently unavailable, other information from NASA may be used. If no information for October 2026 is provided by NASA by the last day of the following month, 11:59:59 PM ET, a consensus of credible sources will be used to resolve this market.