On the Amount of Carbon Dioxide in the Atmosphere

Of late years there has been much interest in the effect of human activities on the natural circulation of carbon. This demands a knowledge of the amount of CO2 in atmosphere both now and in the immediate past. Here the average amount obtained by 30 of the most extensive series of observations between 1866 and 1956 is presented, and the reliability of the 19th century measurements discussed. A base value of 290 p.p.m. is proposed for the year 1900. Since then the observations show a rising trend which is similar in amount to the addition from fuel combustion. This result is not in accordance with recent radio carbon data, but the reasons for the discrepancy are obscure, and it is concluded that much further observational data is required to clarify this problem. Some old values, showing a remarkable fall of CO2 in high southern latitudes, are assembled for comparison with the anticipated new measurements, to be taken in this zone during the Geophysical Year.