Evidence for interannual variability of the carbon cycle from the National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostics Laboratory Global Air Sampling Network

Abstract

The distribution and variations of atmospheric CO 2 from 1981 to 1992 were determined by measuring CO 2 mixing ratios in samples collected weekly at a cooperative global air sampling network. The results constitute the most geographically extensive, carefully calibrated, internally consistent CO 2 data set available. Analysis of the data reveals that the global CO 2 growth rate has declined from a peak of ∼2.5 ppm yr −1 in 1987–1988 to ∼0.6 ppm yr −1 in 1992. In 1992 we find no increase in atmospheric CO 2 from 30° to 90°N. Variations in fossil fuel CO 2 emissions cannot explain this result. The north pole‐south pole CO 2 difference increased from ∼3 ppm during 1981–1987 to ∼4 ppm during 1988–1991. In 1992 the difference was again ∼3 ppm. A two‐dimensional model analysis of the data indicates that the low CO 2 growth rate in 1992 is mainly due to an increase in the northern hemisphere CO 2 sink from 3.9 Gt C yr −1 in 1991 to 5.0 Gt C yr −1 in 1992. The increase in the north pole‐south pole CO 2 difference appears to result from an increase in the southern hemisphere CO 2 sink from ∼0.5 to ∼1.5 Gt C yr −1 .