Presentation of the 20th Century Atmospheric CO2 Record in Smithsonian Spectrographic Plates

The history of 20th century scientific measurement programs does not contain many examples of long-running studies in which an important property of the atmosphere is reliably measured by the same person at the same site with precisions of >1%. One outstanding example is C. D. Keeling’s Mauna Loa record of CO₂ measurements (Keeling et al. 1982). A program that ran for an even longer period of time in the early and mid-20th century is the Smithsonian Solar Constant Program, directed by Charles G. Abbott. Over the past several years, we have been studying whether a portion of the Smithsonian data set can be used to extend the record of atmospheric CO₂ concentrations back to the early 20th century.