Spatially Varying in CO2 Concentrations Regulates Carbon Uptake in the Northern Hemisphere

Against the current climate change background, the mid-high latitudes (>23.7 degrees N) of the Northern Hemisphere have experienced an increase in atmospheric CO2 concentrations, which is higher than the global average. An Beijing Normal University-Earth System Model was used in this study to estimate the carbon uptake in the mid-high latitudes from 2031 to 2060 under the SSP5-8.5 future emissions scenario. Results showed that, in the high latitudes, non-uniform CO2 led to a reduction in net ecosystem productivity (NEP) by -0.1 Pg C yr(-1). This mainly resulted from a 1.5-fold greater increase in heterotrophic respiration than in net primary productivity (NPP). In the mid-latitudes, meanwhile, the decrease in carbon uptake was generally due to a two-fold greater decrease in NPP than heterotrophic respiration. The decrease in precipitation was closely correlated with local carbon uptake, which could explain this decrease in NPP. It was further found that, in East Asia, changes in atmospheric circulation induced by the non-uniform CO2 might have reduced the amount of large-scale precipitation by -9 mm yr(-1). This reduction was the primary contributor (98%) to the decrease in overall precipitation, possibly strengthening the limitation of water on plant growth, which would cause a decline in NEP. In the future, it is suggested that such spatially varying CO2 concentrations should be assessed for possible impacts on local carbon uptake.