The GHCN data base contains mean monthly temperature data (in tenths of degrees celsius) for 6039 stations throughout the world. The majority (61%) have records for fewer than 50 years, but a significant proportion (10%) have records in excess of 100 years. The longest period of record for any given station is 290 years (1701-1990 for Berlin-Tempelhof, Germany). Most records (90%) end in the 1980s. No data are available for any station after 1990.
The density of stations in central North America and central Europe is extremely high, and moderately high in eastern Europe, central Asia, and eastern Asia. Significant data gaps are evident in northern North America, the Amazon basin, the Sahara desert, the Arabian peninsula, northern Asia, the Tibetan plateau, the East Indies, western Australia, and all of Antarctica. The global distribution of stations with 50 years or more of data is characterized by a lower density of stations in all areas, and the appearance of additional data gaps over South America, Africa, and central Asia. Stations with 100 years or more of data are primarily restricted to eastern North America, central Europe, and scattered pockets in Asia. There are few stations in the Southern Hemisphere with 100 years of data.
In general, the number of stations has increased over the past 300 years, particularly in third-world countries. The rate of increase has accelerated since the late nineteenth century, owing to the widespread introduction of reliable thermometers and the increased habitation of areas that were previously less populated. The sharp increase in the number of stations in 1951 and in 1961 is due to the inclusion of the 1951-1960 and 1961-1970 versions of the WWR data set in the WMSSC. The similar increase in the number of stations in 1981 is due to the inclusion of the Climate Analysis Center global temperature and precipitation data set, which contains a large number of stations that only have data for the period 1981-1990. The decrease in the number of stations in 1971 results from the inclusion of only three of the six volumes of the 1971-1980 WWR publication (i.e., three volumes have yet to be prepared and thus could not be included). The decrease in the number of stations in the late 1980s results from the fact that most of the data sets from which the GHCN was compiled were produced during the late 1980s.
Nearly 77% of all stations are missing less than 10% of their data. Typically, these are the same stations in central North America, Europe, and central Asia with the longest periods of record. In contrast, the data-sparse areas of the Amazon basin and Sahara desert are characterized by higher proportions of missing data.
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