Credit: Created by Robert A. Rohde from data published by the U.S. NOAA Earth System Research Laboratory, Global Monitoring Division
The Global Historical Climatology Network (GHCN) is one of the primary reference compilations of temperature data used for climatology, and is the foundation of the GISTEMP Temperature Record. This map shows the 7,280 fixed temperature stations in the GHCN catalog color coded by the length of the available record. Sites that are actively updated in the database (2,277) are marked as "active" and shown in large symbols, other sites are marked as "historical" and shown in small symbols. In some cases, the "historical" sites are still collecting data but due to reporting and data processing delays (of more than a decade in some cases) they do not contribute to current temperature estimates.
As is evident from this plot, the most densely instrumented portion of the globe is in the United States, while Antarctica is the most sparsely instrumented land area. Parts of the Pacific and other oceans are more isolated from fixed temperature stations, but this is supplemented by volunteer observing ships that record temperature information during their normal travels. This image shows 3,832 records longer than 50 years, 1,656 records longer than 100 years, and 226 records longer than 150 years. The longest record in the collection began in Berlin in 1701 and is still collected in the present day.