Atmospheric CO2 Projections with Globally Averaged Carbon Cycle Models

The principal objective of this analysis is to attempt to project the level of CO2 in the atmosphere over the next century (to the year 2075). Knowledge of future atmospheric CO2 concentrations is necessary to establish whether there are likely to be significant climatic and biological consequences resulting from continued fossil fuel combustion. To estimate the effects of projected fossil fuel emissions on future atmospheric CO2 levels, it is necessary to know how this anthropogenic source impacts the natural biogeochemical cycle of carbon—a complex and dynamic set of processes linking the atmosphere, the oceans, and the terrestrial environment. Because of the complicated and changing nature of the anthropogenic source terms and the carbon cycle, simulation models that deal with relationships between economic patterns, energy use, and CO2 emissions and with the major components of the global biogeochemical cycle are needed. These models appear to offer the only practical means to integrate the vast array of detailed quantitative data needed to provide projections of future atmospheric change. Such modeling efforts should be internally consistent with the natural carbon fluxes among atmospheric, oceanic, and terrestrial pools; they should accurately reflect the impact of fossil and biospheric releases over past centuries; and, of course, they should satisfactorily account for empirical measurements of recent decades (e.g., 316 ppmv in 1959 rising to 345 ppmv at present).