Variations of the carbon dioxide content of the atmosphere in the northern hemisphere

Abstract

Six years of measurements (1963–1968) of carbon dioxide in the troposphere and the lower stratosphere are presented. The data reveal an average annual increase of the CO₂-content of 0.7 ± 0.1 ppm/year, while during this time the annual industrial output has increased from about 1.9 ppm to 2.3 ppm/year. Thus the increase in the atmosphere is about 1/3 of the total output. Considerations of the possible increase of vegetative assimilation due to the higher CO₂-content of the atmosphere reveals that this is at most 1/4 of the output, probably considerably less. The net transfer to the oceans thus is at least equal to 1/2 of the industrial output. The transfer rate across the sea surface seems effective enough not to represent an appreciable resistance and the decisive factor for determining this transfer therefore is the ocean circulation or turn over rate. The figures quoted indicate that 20–25% of the world oceans must have been available during the time of rapid increase of the industrial output of CO₂ (the last 30–50 years) to explain the rather large amount that has been withdrawn from the atmosphere. Still a continued increase of the fossil fuel combustion as forecast by OECD implies that the CO₂-content of the atmosphere at the end of the century will be between 370 ppm and 395 ppm as compared with 320 ppm, the average value for 1968. The amplitude of the seasonal variation is found to be about 6.5 ppm at 2 km and 3.5 ppm in the uppermost part of the troposphere. The phase shift of the seasonal variation between these two levels is 25–30 days. On the basis of these data a vertical eddy diffusivity K = 2·10⁵ cm² sec^?1 is derived. The amplitude of the seasonal variation in the lower stratosphere, 11–12 km, is less than 1 ppm and the phase is delayed at least 1 1/2 month as compared with the upper troposphere. DOI: 10.1111/j.2153-3490.1970.tb00508.x