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Abstract

[1] The growth of crops represents a sink of atmospheric CO₂, whereas biomass is consumed by humans and housed animals, yielding respiratory sources of CO₂. This process induces a lateral displacement of carbon and creates geographic patterns of CO₂ 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 CO₂ fluxes associated with food and feedstuff trade, using country-based agricultural statistics and activity maps of human and housed animal population densities. The CO₂ flux maps show regional dipoles of sources and sinks in Asia and North America. The effect of these fluxes on atmospheric CO₂ was simulated using a global atmospheric transport model. The mean latitudinal CO₂ gradients induced by the displacement of crop products are fairly small (approximate to 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 CO₂ fluxes. On the other hand, the simulated longitudinal mean atmospheric CO₂ gradients at northern midlatitudes (approximate to up to 0.5 ppm) are comparable to the ones measured between atmospheric stations, suggesting that CO₂ fluxes from crop products trade are an important component of continental- and regional-scale CO₂ budgets. Thus they should be accounted for as prior information in regional inversions. [References: 29]