Monthly mean atmospheric carbon dioxide at Mauna Loa Observatory, Hawaii The carbon dioxide data, measured as the mole fraction in dry air, on Mauna Loa constitute the longest record of direct measurements of CO2 in the atmosphere. They were started by C. David Keeling of the Scripps Institution of Oceanography in March of 1958 at a facility of the National Oceanic and Atmospheric Administration 1976. NOAA started its own CO2 measurements in May of 1974, and they have run in parallel with those made by Scripps since then 1989. Data are reported as a dry mole fraction defined as the number of molecules of carbon dioxide divided by the number of molecules of dry air multiplied by one million (ppm). Data from 1958 to April 2014.