The Global Historical Climatology Network (GHCN) is a comprehensive global surface baseline climate data set designed for monitoring and detecting climate change. Comprised of surface station observations of temperature, precipitation, and pressure, all GHCN data are on a monthly basis. GHCN is produced jointly by the National Climatic Data Center, Arizona State University, and Carbon Dioxide Information Analysis Center at Oak Ridge National Laboratory.

GHCN version 1 was released in August of 1992 and has data from

The earliest station data is from 1697. The most recent from 1990. It was created from 15 source data sets. Quality Control included visual inspection of graphs of all station time series, tests for precipitation digitized 6 months out of phase, tests for different stations having identical data, and other tests.

The GHCN version 2 temperature data set was released in 1997 while the version 2 precipitation data was made available in July 1999. Version 2 has significant improvements over version 1: more data (e.g., the precipitation data set has data from over 20,000 stations) from more sources (over 30 different sources including the Colonial Era Archive Project contributed to version 2), more elements (mean monthly maximum and minimum temperature data as well as mean temperature), better Quality Control, homogeneity adjustments, and a wider selection of metadata. Version 2 will also be regularly updated and irregularly have data from additional stations added to the data set. Therefore, with the release of GHCN version 2 temperature and precipitation data, we have removed GHCN version 1 temperature and precipitation data from our anonymous ftp site.

There are many unique features in GHCN version 2. For example, we have determined many cases where different sources have provided us with different mean temperature time series for the same station. Because meteorologists calculate daily mean temperature many different ways, there can be many different "correct" mean temperatures. Therefore, for many stations, GHCN provides more than one mean temperature time series. Also, GHCN version 2 has some unique and potentially very useful station metadata such as population and vegetation indicators. To understand GHCN version 2 temperature data and metadata, please read our overview of it. In addition to this overview, we have another document on line that describes GHCN's Quality Control.

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