Horizontal displacement of carbon associated with agriculture and its impacts on atmospheric CO 2

The growth of crops represents a sink of atmospheric CO 2 , whereas biomass is consumed by humans and housed animals, yielding respiratory sources of CO 2 . This process induces a lateral displacement of carbon and creates geographic patterns of CO 2 sources and sinks at the surface of the globe. We estimated the global carbon flux harvested in croplands to be 1290 TgC/yr. Most of this carbon is transported into domestic trade, whereas a small fraction (13%) enters into international trade circuits. We then calculated the global patterns of CO 2 fluxes associated with food and feedstuff trade, using country‐based agricultural statistics and activity maps of human and housed animal population densities. The CO 2 flux maps show regional dipoles of sources and sinks in Asia and North America. The effect of these fluxes on atmospheric CO 2 was simulated using a global atmospheric transport model. The mean latitudinal CO 2 gradients induced by the displacement of crop products are fairly small (≈0.2 ppm) compared with observations (4–5 ppm), indicating that this process has a only a small influence in explaining the latitudinal distribution of CO 2 fluxes. On the other hand, the simulated longitudinal mean atmospheric CO 2 gradients at northern midlatitudes (≈ up to 0.5 ppm) are comparable to the ones measured between atmospheric stations, suggesting that CO 2 fluxes from crop products trade are an important component of continental‐ and regional‐scale CO 2 budgets. Thus they should be accounted for as prior information in regional inversions.