Global surface temperature data: HadCRUT4 and CRUTEM4

Extending back to 1850 and frequently updated, HadCRUT4 is the longest data set of its type. HadCRUT4 is a combination of the global land surface temperature data set, CRUTEM4 and the global SST data set, HadSST3. HadCRUT4 is different from the most closely comparable products (e.g. NASA GISTEMP and NOAA MLOST) in that no interpolation is performed. As such, there are many coverage gaps; this may be a limiting factor in regional analyses but hemispheric and global means are very consistent with other data sets. Extensive analysis has been done to characterize uncertainties arising from non-climatic factors, for example changing instrumentation and observing practices, changes in station location, and changes in local land use. The resulting distribution of uncertainty is presented as an ensemble of 100 realizations of the data set. Individual ensemble members may be accessed via the Met Office webpage, though many users will likely focus on the ensemble median fields that are distributed online by CRU, Hadley Centre and other organizations.

In late 2020, the Met Office Hadley Centre released HadCRUT5. HadCRUT5 is offered in two different versions. The first version is similar to HadCRUT4 in that no interpolation has been performed to infill grid cells with no observations. Major updates include using HadSST4 in place of HadSST3, as well as enlarging the ensemble size to model the uncertainty distribution. The second, "analyzed" version is an infilled, globally complete dataset. See the link to HadCRUT5 in the sidebar for more information.