Limiting future atmospheric carbon dioxide

We estimate anthropogenic carbon emissions required to stabilize future atmospheric CO₂ at various levels ranging from 350 ppm to 750 ppm. Over the next three centuries, uptake by the ocean and terrestrial biosphere would permit emissions to be 3 to 6 times greater than the total atmospheric increase, with each of them contributing approximately equal amounts. Owing to the nonlinear dependence of oceanic and terrestrial biospheric uptake on CO₂ concentration, the uptake by these two sinks decreases substantially at higher atmospheric CO₂ levels. The uptake also decreases with increased atmospheric CO₂ growth rate. All the stabilization scenarios require a substantial future reduction in emissions.