HadISST¶

Hadley Centre Sea Ice and Sea Surface Temperature data set, version 1.1

Being replaced

At a glance¶

Note on period: Updated at the start of each month with data typically for the month before last (a delay of about 1–2 months). The whole record from 1870 is provided as a single version, but the inputs (in situ observations, satellites, sea ice charts) change over time, which introduces discontinuities within the series.

Overview¶

The Met Office Hadley Centre's sea ice and sea surface temperature (SST) data set, HadISST1, is a combination of monthly globally complete fields of SST and sea ice concentration on a 1 degree latitude-longitude grid from 1870 to date — one of the standard long-term records. Ship and buoy observations and satellite SSTs are combined by reduced-space optimal interpolation to give complete fields, and sea ice is based on digitised sea ice charts and passive microwave satellite data. It is widely used as the lower boundary condition for AMIP-style atmospheric model experiments and in studies of ENSO and long-term variability.

Available variables¶

Based on the official NetCDF files (HadISST_sst.nc, HadISST_ice.nc); SST and sea ice concentration come as separate files. Units were cross-checked against the metadata of the same files on NOAA ERDDAP.

instantaneous mean accumulated maximum minimum static — instantaneous: value at the time stamp · mean/accumulated/maximum/minimum: over the indicated interval · static: does not change with time

Sea surface temperature (HadISST_sst.nc)¶

Sea ice (HadISST_ice.nc)¶

The full variable list is in the official documentation.

How to get the data¶

• Met Office Hadley Centre download page — Web download (NetCDF .nc.gz / ASCII .txt.gz) No login needed
  • Full-period CF-compliant NetCDF files (HadISST_sst.nc.gz about 240 MB, HadISST_ice.nc.gz about 17 MB) and update files holding only the most recent available month. ASCII files are split by period and by year, with the format described in the read instructions. No account needed.
• NOAA CoastWatch ERDDAP — HadISST SST (erdHadISST) — ERDDAP (subset by region and time, OPeNDAP) No login needed
  • A NOAA mirror of the Met Office files. It may lag behind the original, so check the Met Office page for the latest month.
• NOAA CoastWatch ERDDAP — HadISST sea ice (erdHadISSTIce) — ERDDAP (subset by region and time, OPeNDAP) No login needed

Example code¶

Download HadISST_sst.nc.gz from the download page and decompress it before running.

# pip install xarray netCDF4
import xarray as xr

ds = xr.open_dataset("HadISST_sst.nc")
sst = ds["sst"]
# Handle unphysically low values (e.g. under sea ice) as appropriate for your analysis
sst = sst.where(sst > -2)
nino34 = sst.sel(latitude=slice(5, -5), longitude=slice(-170, -120)).mean(["latitude", "longitude"])
print(nino34.sel(time="2025"))

Practical tips¶

• Sea ice observations before the satellite era are very sparse. In the Antarctic in particular, 1871–1939 and 1947–1962 are filled with climatology, so sea ice variability or trends in those periods should not be read as real signals. For sea ice studies from 1979, compare with a single-algorithm satellite record.
• According to the official service notes, the 2009 switch of satellite sea ice source introduced a discontinuity in Arctic and Antarctic sea ice; satellite SST input moved to METOP from June 2020, and in situ input moved to unadjusted HadSST4 from January 2021. Allow for these input changes when computing recent trends.
• In the ASCII files temperatures are stored as integers in °C × 100, grid boxes fully covered by sea ice are marked -1000 and land -32768. In the NetCDF files, too, check for and mask unphysical values in ice-covered areas first.
• HadISST.2 (HadISST2) provides sea ice concentration only, on a separate page that shows no updates since 2016. Do not mix it with HadISST1, and do not assume it is the HadISST1 successor announced for 2026.

Notices and change history¶

References for your paper¶

Reference papers¶

HadISST reference paper (required citation) — DOI 10.1029/2002JD002670

@article{rayner2003hadisst,
  author  = {Rayner, N. A. and Parker, D. E. and Horton, E. B. and Folland, C. K. and Alexander, L. V. and Rowell, D. P. and Kent, E. C. and Kaplan, A.},
  title   = {Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century},
  journal = {Journal of Geophysical Research: Atmospheres},
  volume  = {108},
  number  = {D14},
  pages   = {4407},
  year    = {2003},
  doi     = {10.1029/2002JD002670}
}

Acknowledgements¶

The terms and conditions require citation of Rayner et al. (2003) plus a credit line: "HadISST data were obtained from https://www.metoffice.gov.uk/hadobs/hadisst/ and are © Crown Copyright, Met Office, [year of first publication], provided under an Open Government Licence, https://www.nationalarchives.gov.uk/doc/open-government-licence/version/2/". Outside the UK, write "© British Crown Copyright, Met Office". Copy the exact wording from the terms and conditions page.

Information on the datasets used in this study was compiled with the help of the Korean Climate Data Navigator (KCDN) (Sim, 2026; https://doi.org/10.5281/zenodo.23300923).

Links¶

• HadISST home page (Met Office Hadley Centre)
• HadISST service notes
• HadISST terms and conditions
• HadISST.2 sea ice concentration page
• NCAR Climate Data Guide — HadISST SST
• NCAR Climate Data Guide — HadISST sea ice concentration