HadCRUT

HadCRUT is the dataset of monthly instrumental temperature records formed by combining the sea surface temperature records compiled by the Hadley Centre of the UK Met Office and the land surface air temperature records compiled by the Climatic Research Unit (CRU) of the University of East Anglia.

The data is provided on a grid of boxes covering the globe, with values provided for only those boxes containing temperature observations in a particular month and year. Interpolation is not applied to infill missing values. The first version of HadCRUT initially spanned the period 1881–1993, and this was later extended to begin in 1850 and to be regularly updated to the current year/month in near real-time.

HadCRUT4 was introduced in March 2012. It "includes the addition of newly digitised measurement data, both over land and sea, new sea-surface temperature bias adjustments and a more comprehensive error model for describing uncertainties in sea-surface temperature measurements". Overall, the net effect of HadCRUT4 versus HadCRUT3 is an increase in the average temperature anomaly, especially around 1950 and 1855, and less significantly around 1925 and 2005.Current HadCRUT4 Graph.

HadCRUT3 is the third major revision of this dataset, combining the CRUTEM3 land surface air temperature dataset with the HadSST2 sea surface temperature dataset. First published in 2006, this initially spanned the period 1850–2005, but has since been regularly updated to 2012. Its spatial grid boxes are 5° of latitude and longitude. A more complete statistical model of uncertainty was introduced with this revision, including estimates of measurements errors, biases due to changing exposure and urbanisation, and uncertainty due to incomplete coverage of the globe by observations of temperature.

HadCRUT2 was the second major version of this dataset, combining the CRUTEM2 land surface air temperature dataset with the HadSST sea surface temperature dataset. First published in 2003, this initially spanned the period 1856–2001, but was subsequently updated to end in 2005. Its spatial grid boxes are 5° of latitude and longitude. An estimate of uncertainty due to incomplete coverage of the globe by observations of temperature was included, as was a version with the variance adjusted to remove artificial changes arising from changing numbers of observations.

...
Wikipedia