Variability of Global Atmospheric CO2 Concentrations over Interannual to Multi-Decadal Timescales: A Linear Approximation

The Keeling curve, which shows the rapidly increasing atmospheric carbon dioxide concentration since 1958, is one of the most important scientific findings of our time - yet a full and detailed understanding of the curve and its variations is still to be achieved. At year-to-year time scales, for instance, the annual growth rate of the Keeling curve have long been linked to variations of the natural climate-carbon system. But questions remain about what (ocean versus land), where (tropics versus mid-high latitudes) and how (e.g., temperature versus precipitation) different drivers affect the observed variability. At longer (multidecadal) timescales, on the other hand, the growths of atmospheric CO2 concentration have almost been constantly proportional (by the so-called "airborne fraction") to the corresponding anthropogenic emissions. This study reviews the literature on these questions and presents a box model to describe carbon exchanges between the atmosphere and the surface reservoirs under the disturbances of anthropogenic emissions as well as global climate changes. The results show that the simple linear model can successfully simulate the observed changes/variations of the atmospheric CO2 concentration and its growth rate across interannual to multi-decadal time scales.