The Mauna Loa Observatory began continuous carbon dioxide measurements in 1958. Charles David Keeling of the Scripps Institution of Oceanography started the program in March of that year, creating the record that became known as the Keeling Curve.
Mauna Loa was chosen because its high, remote location in Hawaii is far from major continental pollution sources. The observatory sits above much of the local atmospheric mixing, allowing researchers to sample air that is broadly representative of the free troposphere. Volcanic emissions can occasionally contaminate readings, but those short-lived episodes can be identified and removed.
The first Mauna Loa measurements showed both a long-term rise in CO₂ and a repeating seasonal cycle. Carbon dioxide falls during the Northern Hemisphere’s spring and summer as vegetation absorbs it through photosynthesis, then rises during autumn and winter as plants decay and respiration dominates. The record helped establish modern atmospheric monitoring and remains one of climate science’s most recognizable data series.