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January 2010: A number of corrections have been made to the station data that are used to produce CRUTEM3 and HadCRUT3.
CRUTEM3 is a gridded dataset of global historical land surface temperature anomalies. Data are available for each month since January 1850, on a 5 degree grid. The dataset is a collaborative product of the Met Office Hadley Centre and the Climatic Research Unit at the University of East Anglia.
The gridded data are based on an archive of monthly mean temperatures provided by more than 4000 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 caused by poor measurements, uncertainties in the station data, sampling uncertainties caused by the limited number of measurements available, and large-scale biases such as urbanisation. The image below shows near surface temperature anomalies for the most recent available month. A plus sign in any grid box indicates that the temperature anomaly in that grid box this month is the highest since the dataset starts in January 1850. Similarly a minus sign signals the lowest anomaly since 1850.
Various diagnostics are produced from the monthly gridded fields. These include images of monthly anomaly patterns, and global, regional and local time-series.
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