Thermometer-Based Temperature Trends (Global and Hemispheric)
The earliest records of temperature measured by thermometers are from western Europe beginning in the late 17th and early 18th centuries. The network of temperature collection stations increased over time and by the early 20th century, records were being collected in almost all regions, except for polar regions where collections began in the 1940s and 1950s.
A set of temperature records from over 7,000 stations around the world has been compiled by the NOAA National Climate Data Center to create
the Global Historical Climatology Network - GHCN
(GHCN Version 2 data set; Peterson and Vose 1997). About 1,000 of these records extend back into the 19th century.
Two widely recognized research programs have used the available instrumental data to reconstruct global surface air temperature trends from the late 1800's through today. Both use the same land-based thermometer measurement records from the GHCN, but the records contain some differences.
These differences are due to different approaches to spatial averaging, the use and treatment of sea surface temperature data
(from ship observations), and the handling of the influence of changes in land-cover (i.e., increases in urbanization). However, both
show the same basic trends over the last 100 years. The units shown are departures from the 1960 - 1990 period. For larger viewing version of these graphed temperature records, please
click here or on the graph. To view animations of mapped CRU-UK global temperatures, click here.
Global surface temperatures are constantly monitored to update and assess temperature trends in real time.
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