Grain carbon emission transfer and its spatiotemporal shifts based on the increasing supply-demand separation in China over the past three decades

The food system is one of the major sources of anthropogenic greenhouse gas (GHG) emissions. The impact of emission transfer due to the separation between food production and consumption within the context of carbon neutrality remains unclear. In this study, we constructed an emission inventory for three types of grains at the production stage of their life cycle and then analysed the spatiotemporal evolution characteristics of the grain supply and demand. With the use of a spatial equilibrium model, we simulated the spatial distribution flow of the different types of grains from 1990 to 2018 and calculated the resulting GHG emission transfer efficiency. The main results include the following: (1) The imbalance between the grain supply and demand intensified, which was mainly reflected in the distance between the geographic centre of the grain supply and consumption increasing 3.2 times, and thus, the self-sufficiency decreased. (2) The total emission transfer TET of rice and wheat decreased because of the increase in the intra-regional supply, while that of maize gradually increased due to the increase in the inter-regional supply. (3) Overall, grain trade improved the carbon efficiency of grain production in China. The trade efficiency of crops varied, with wheat and maize leading to overall effective carbon reductions, while the carbon transfer efficiency of rice from trade was relatively low. (4) The carbon footprint of grain production in China’s provinces exhibited a downward trend, but due to the intensified separation between the grain supply and demand, certain major grain-producing areas achieved inefficient carbon increases. Therefore, we suggest further optimization of the spatial structure of planting and breeding, strengthening of the grain supply in the region, and enhancement in the optimization of the low-carbon production structure and adjustment of cultivated land use combined with regional governance strategies. The application of these measures could contribute to achieving dual-carbon goals.