Detailed analyses of the atmospheric carbon dioxide concentration measurements from Mauna Loa Observatory have produced a model which describes most of the variability in the data. The final model is y (t) =a+deat+Ji=12Aisin <(2&pgr;/Ti)(t+ϕ1)>+Jj=12Fj sin<(2@qL &pgr;/&tgr;j) (t+&THgr;i)>, where a is the preindustrial value, α is the exponential long-term growth rate, i represents the annual cycle and its harmonics, and j represents longer-term periodicities. The exponential growth rate is nearly identical to that calculated for the production of CO2 from fossil fuel burning. A long-period component of about 44 months correlates with the southern oscillation index. Another long-period oscillation-about 142 months-has tentatively been identified with the solar activity cycle and complicates the determination of α because the two sources of curvature interact in the fitting procedure, and the data record is not long enough to specify both of them independently. The generality of the model has been demonstratad by testing it against shorter data sequences from the South Pole and Australia.