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


  • Thomas J. Conway,

  • Pieter P. Tans,

  • Lee S. Waterman,

  • Kirk W. Thoning,

  • Duane R. Kitzis,

  • Kenneth A. Masarie,

  • Ni Zhang


The distribution and variations of atmospheric CO2 from 1981 to 1992 were determined by measuring CO2 mixing ratios in samples collected weekly at a cooperative global air sampling network. The results constitute the most geographically extensive, carefully calibrated, internally consistent CO2 data set available. Analysis of the data reveals that the global CO2 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 CO2 from 30° to 90°N. Variations in fossil fuel CO2 emissions cannot explain this result. The north pole-south pole CO2 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 CO2 growth rate in 1992 is mainly due to an increase in the northern hemisphere CO2 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 CO2 difference appears to result from an increase in the southern hemisphere CO2 sink from ∼0.5 to ∼1.5 Gt C yr−1.

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