Charles David Keeling

The Keeling Curve is a graph showing the continuous measurement of atmospheric carbon dioxide concentrations, initiated by Charles David Keeling in 1958 at the Mauna Loa Observatory in Hawaii. It is the longest-running continuous record of atmospheric CO2 and provided the first clear evidence that global CO2 levels were steadily rising. The curve remains one of the most important datasets in climate science.

Keeling conducted his primary research at the Mauna Loa Observatory, a high-altitude monitoring station on the island of Hawaii operated by the National Oceanic and Atmospheric Administration (NOAA). He was affiliated with the Scripps Institution of Oceanography at the University of California, San Diego, where he maintained his research program. The Mauna Loa site was chosen for its remote location and minimal local pollution.

Keeling's measurements revealed that atmospheric CO2 concentrations were increasing year over year, a finding that had not been definitively established before his continuous monitoring began. His data also showed a seasonal oscillation in CO2 levels caused by plant growth cycles in the Northern Hemisphere. The upward trend he documented has continued to this day and forms a core piece of evidence for human-caused climate change.

Keeling began continuous CO2 measurements at Mauna Loa Observatory in March 1958, during the International Geophysical Year. His initial readings showed concentrations of approximately 315 parts per million. By the time of his death in 2005, levels had risen to around 380 ppm, and they have since surpassed 420 ppm.