Contrasting surface and column-averaged CO₂ responses over terrestrial China under carbon peaking and carbon neutrality emission pathways: anthropogenic, biospheric, and regional transport contributions

Abstract. Understanding how changes in anthropogenic carbon dioxide (CO₂) emissions affect surface CO₂ mole fraction (surface CO₂), column-averaged dry-air CO₂ mole fraction (XCO₂), and the relative contributions of anthropogenic emissions and biospheric fluxes is essential for evaluating the atmospheric effects of emission mitigation. In this study, the Weather Research and Forecasting Model coupled with the Vegetation Photosynthesis and Respiration Model (WRF-VPRM) was used to simulate three emission scenarios: a 2016 baseline, a 2030 carbon peaking scenario, and a 2060 carbon neutrality scenario, under identical meteorological fields constrained by observations. Contribution decomposition, sensitivity experiments, backward trajectory analysis, and potential source contribution function (PSCF) analysis were combined to diagnose the response mechanisms of atmospheric CO₂. Anthropogenic emissions increased by 18.1 % in 2030 relative to 2016, whereas surface CO₂ and XCO₂ increased by only 0.363 and 0.065 ppm, respectively. In 2060, emissions decreased by 90.3 %, reducing surface CO₂ and XCO₂ by 1.914 and 0.359 ppm, respectively. The XCO₂ response was therefore much weaker than the surface CO₂ response. Anthropogenic contributions dominated the differences among scenarios, while biospheric fluxes shaped seasonal variations and became relatively more important under deep emission reductions. The selected high-CO₂ episodes in the Beijing-Tianjin-Hebei (BTH) region were strongly modulated by meteorological conditions. Local accumulation dominated under stagnant conditions, whereas upstream transport dominated under favorable transport conditions. These results indicate that atmospheric CO₂ responses to carbon peaking and carbon neutrality pathways are jointly shaped by anthropogenic mitigation, biospheric fluxes, and regional transport.