El Nino and daily heat records, 2026: dataset behind the maccus.fr investigation of November 13, 2026
FR: https://maccus.fr/oceans-records-chaleur-el-nino-2027/
EN: https://maccus.fr/en/ocean-heat-records-el-nino-2027/
Author: Marc Winer, MACCUS (maccus.fr). Built November 13, 2026.

SOURCES (all retrieved November 13, 2026)
- Copernicus Climate Change Service (C3S) / ECMWF, Climate Pulse, ERA5 daily global series:
  air temperature: https://sites.ecmwf.int/data/climatepulse/data/series/era5_daily_series_2t_global.csv
  sea surface temperature, 60S-60N: https://sites.ecmwf.int/data/climatepulse/data/series/era5_daily_series_sst_60S-60N_ocean.csv
  Licence: Copernicus data, CC BY 4.0. Contains modified Copernicus Climate Change Service information 2026.
  Neither the European Commission nor ECMWF is responsible for any use of this information.
- C3S methodology (daily offset to 1850-1900): https://climate.copernicus.eu/climate-bulletin-about-data-and-analysis
- C3S October 2026 bulletin (2026 annual estimate): https://climate.copernicus.eu/surface-air-temperature-october-2026
- NOAA Climate Prediction Center, Relative Oceanic Nino Index (RONI) and ONI:
  https://www.cpc.ncep.noaa.gov/data/indices/RONI.ascii.txt , https://www.cpc.ncep.noaa.gov/data/indices/oni.ascii.txt
  US government work, public domain.

FILES
- era5_sst_2026_records.csv: each 2026 day, sea surface temperature 60S-60N (C), previous record for that calendar date
  (1979-2025) and its year, record_for_date_1979_2026 (1 = warmer than the same date in every earlier year), margin (C),
  ERA5 status (FINAL / PRELIMINARY).
- era5_daily_2026_records.csv: each 2026 day, global air temperature at 2 m (C), anomaly vs 1991-2020, C3S daily offset,
  value above 1850-1900, warmest_for_date_1940_2026 flag, margin over the previous record, previous record year, status.
  Only FINAL days are counted in the article.
- era5_monthly_anomalies.csv: monthly global air anomaly vs 1991-2020 and above 1850-1900, number of final days.
- records_aug1_to_nov10_by_year.csv: for each year, how many days from August 1 to November 10 were records at the time.
- el_nino_events_roni_era5.csv: the strong El Nino events since 1950 (3-month RONI peak 1.5 C or more), peak season, ONI,
  global temperature lag, annual anomaly of the El Nino year and of the next calendar year, and the step between them.
- summary.json, extras.json: every figure quoted in the article (streaks, counts, base rate, implied 2027 range).

METHOD NOTES
- A day is a record when it is warmer than the same calendar date in every earlier year of the series (1940 for air,
  1979 for sea surface). These are records FOR THE DATE, not all-time highs.
- Pre-industrial values use the C3S daily offset to 1850-1900 (0.88 C on average, varying through the year).
- ERA5 is a reanalysis (a weather model constrained by observations), less certain before 1979.
- The 2027 range is arithmetic on a past pattern (C3S 2026 estimate plus past post-El Nino steps), not a climate model.
