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

Criteria minimizing differences in operators, location, and time of observation are established for selecting comparative data on atmospheric CO 2 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