The authors have done an analysis of meteorological data which may add to the growing body of information addressing the cause or causes of recent global warming. If an augmented greenhouse effect, due to increasing atmospheric carbon dioxide concentrations, has been a significant factor producing global warming, then this should be indicated by an increase in the interval of time between the time of maximum insolation, and the time of maximum surface temperature, as well as a decrease in the interval of time between the time of minimum insolation and the time of minimum surface temperature, in the mid latitudes. However, the magnitude of this effect should not be as great during the Northern Hemisphere summer as during the Northern Hemisphere winter because of the reduction in atmospheric carbon dioxide due to increased photosynthesis. The authers have examined surface air temperature data from a mid-latitude, continental area to see if the above expected changes have, in fact, occurred. The results of this study indicate that global warming, during the ca. 50 year study period, is consistent with an increase in the concentration of carbon dioxide in the earth's atmosphere. A comparison of the summer vs winter lag data show that increases in heat retention have occurred mainly during the Northern Hemisphere winter, when annual carbon dioxide concentrations are greatest. The augmentation of the greenhouse effect appears to be mitigated during the Northern Hemisphere summer. The data suggest that factors other than anthropogenic increases in atmospheric carbon dioxide have also significantly influenced the heat budget at the surface of the earth during the period from 1950 to 2003.