CRUTEM4

CRUTEM4 is a gridded dataset of global historical near-surface air temperature anomalies over land. Data are available for each month from January
1850 to present, on a 5 degree grid. The gridded data are based on an archive of monthly mean temperatures provided by more than 5500 weather
stations distributed around the world. Each station temperature is converted to an anomaly from the 1961-90 average temperature for that station, and
each grid-box value is the mean of all the station anomalies within that grid box. As well as the mean anomaly, estimates are made of the
uncertainties arising from thermometer accuracy, homogenisation, sampling grid boxes with a finite number of measurements available, large-scale
biases such as urbanisation and estimation of regional averages with non-complete global measurement coverage.