The Global Historical Climatology Network (GHCN) is a data set of temperature, precipitation and pressure records managed by the National Climatic Data Center (NCDC), Arizona State University and the Carbon Dioxide Information Analysis Center.
The aggregate data are collected from many continuously reporting fixed stations at the Earth's surface. In 2012, there were 25,000 stations within 180 countries and territories. Some examples of monitoring variables are the total daily precipitation and maximum and minimum temperature. A caveat to this is 66% of the stations report only the daily precipitation.[1]
The original idea for the application of the GHCN-M data was to provide climatic analysis for data sets that require daily monitoring. Its purpose is to create a global base-line data set that can be compiled from stations worldwide.[2]
This work has often been used as a foundation for reconstructing past global temperatures, and was used in previous versions of two of the best-known reconstructions, that prepared by the NCDC, and that prepared by NASA as its Goddard Institute for Space Studies (GISS) temperature set. The average temperature record is 60 years long with ~1650 records greater than 100 years and ~220 greater than 150 years (based on GHCN v2 in 2006). The earliest data included in the database were collected in 1697.