An Analysis of the Possible Recent Change in Atmospheric Carbon Dioxide Concentration

Abstract

Criteria minimizing differences in operators, location, and time of observation are established for selecting comparative data on atmospheric CO₂ concentration during the past 100 years. The resulting selection showed in all cases the period 1907–1956 to have a higher mean than 1857–1906. The difference between means was not statistically significant for 5 unweighted comparisons. Weighting by estimates of reliability resulted in a significant difference for yearly and summer non-urban values, but not for the other 3 comparisons. Additional comparisons of all values in the study, of six entire distributions, and of five paired studies with closely comparable data showed increases in a more recent period, with one exception. The magnitude of the increase for weighted yearly non-urban data was 25 ppm (from 294 to 319) for the quarters 1857–1881 to 1932–1956. Several possible explanations for the increase include: 1) an actual atmospheric increase, 2) a coincidence of the influence of micro-atmospheres, 3) improvement (or change) in chemical technique. Need for further sampling is emphasized and suggestions made for considering local influences in this sampling. DOI: 10.1111/j.2153-3490.1959.tb00023.x