This dataset contains measurements of sea ice content (HadISST1.1). Dataset include monthly mean gridded (1deg grid), global Ice content from 1870 to October 2015. This product replaced the GISST/GICE (Global Sea Surface Temperature/Global sea-Ice content) data sets ended in February 2003.
The sea ice data are taken from a variety of sources including digitized sea ice charts and passive microwave retrievals.

The sea ice fields are made more homogeneous by compensating satellite microwave-based sea ice concentrations for the impact of surface melt effects on retrievals in the Arctic and for algorithm deficiencies in the Antarctic, and by making the historical in situ concentrations consistent with the satellite data. SSTs near sea ice are estimated using statistical relationships between SST and sea ice concentration.
From May 2007 the data set of in situ measurements used in HadISST has changed. The MOHSST data set, which was previously used has been discontinued, and HadSST2 is now being used in its place. The two systems ran in parallel for several months prior to the changeover and no significant differences were seen.

The data were provided by the Hadley centre (Met Office).

Important Notes:
On 13th March 2015: Users have noticed that there is a minor discontinuity at the dateline in HadISST1 SST fields starting in 1982. It appears to only affect gridcells just to the east of the dateline. Please note that this can affect estimates of the mean and variability of SSTs in HadISST1 when analysed across this region.
On 8th March 2011: The switch of satellite source data at the start of 2009 introduced a discontinuity in the fields of sea ice in both the Arctic and Antarctic.
On 3rd December 2010: The SSM/I satellite that is used to provide the data for the sea ice analysis in HadISST suffered a significant degradation in performance through January and February 2009. The problem affected HadISST fields from January 2009 and probably causes an underestimate of ice extent and concentration. It also affected ses surface temperatures in sea ice areas because the SSTs are estimated from the sea ice concentration. As of 3rd December 2010, the Met Office Hadley Centre has reprocessed the data from January 2009 to the present using a difference sea ice data source. This is an improvement on the previous situation but users should still note that the switch of data source at the start of 2009 might introduce a discontinuity into the record.