Global Historical Climatology Network

Project Description
The Global Historical Climatology Network (GHCN) is a comprehensive global
surface baseline climate data set designed to be used to monitor and detect
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 ~6,000 Temperature stations ~7,500 Precipitation stations ~2,000 Pressure
stations 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.

GHCN version 2 is currently being created. A beta release of precipitation
datawas made in April 1998 (the most recent data of which is from 1996) and the
full version 2 temperature data was released in 1997. 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 data, we have removed GHCN version 1 temperature 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


[Summary Adapted from the NOAA/NCDC Home page]