26/APRIL/2021: We have switched to using unadjusted (for continuity with the HadSST2 data previously used) HadSST4 as the basis for updates to the in situ data in HadISST. HadSST4 data are used for January 2021 onwards.

22/OCTOBER/2020: We have changed the data source used to provide satellite SST retrievals. This was previously supplied by NOAA (as described in the HadISST paper). We now use SST retrievals from METOP which are extracted from the Met Office data base. The first month to use METOP data is June 2020 and every month thereafter. While we have found no obvious discontinuity in the mean or the appearance of the SST fields, a change of data source can introduce unexpected changes. Please be aware of this when using the data. Note that HadISST1 has a cool bias in recent years becase no adjustment is made to account for changing ship biases and the known offset between buoy and ship measurements.

10 March 2016: A detailed analysis of HadISST has identified a number of problems, some of which might limit the utility of the dataset for certain scientific applications, particularly where high resolution SST data or spatial gradients of SST are required. Thanks to Dudley Chelton and Craig Risien for bringing this to our attention and their detailed analysis.

13/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.

08/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.

03/DECEMBER/2010. The SSM/I satellite that was 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 sea surface temperatures in sea ice areas because the SSTs are estimated from the sea ice concentration (see Rayner et al. 2003). As of 3rd December 2010 we have reprocessed the data from January 2009 to the present using a different 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. The reprocessed files are available from the main data page. The older version of the data set is archived here.

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.