Horizontal displacement of carbon associated with agriculture and its impacts on atmospheric CO₂

摘要

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