| 09 Jul 2026
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.
This manuscript examines how China's surface and column-averaged CO2 respond to different emission pathways under mitigation scenarios by using the WRF-VPRM model. Overall the manuscript is well written, and informative. I recommend it be accepted for publication after minor revision to address the comments.
Major comments:
Minor comments:
1.Line 101-102, ‘online coupled WRF-VPRM model…’
Please provide references here.
2. Line 184 (Figure 1 Caption),
The ‘star’ is very difficult to see. Also it is not clear what the inset plot represented.
3. Line 191: ‘..The 2016 scenario 191 represents…’
Please clarify why 2016 was chosen, given that more recent data are available.
4. Line 240-241: ‘…components: the background component, the biogenic component, and the anthropogenic component’
Please clarify what boundary conditions were applied for the three individual components, respectively.
5. Line 288 (and equation 9): ‘… denote the anthropogenic CO2 contribution in the baseline experiment’
It is not clear for me why the anthropogenic CO₂ contribution in the baseline experiment is used in Eq. 9, rather than the anthropogenic CO₂ contribution from the experiment corresponding to each emission scenario, to calculate the contributions from BTH emissions under different scenario.
6. Line 339-340: Wij was determined according to the number of trajectory endpoints in each grid cell and was defined as follows…’
Please clarify why the weighting factors were chosen as Eq.16.
7. Line 355: ‘…WRF-VPRM reproduced this seasonal phase reasonably well. (Figure 2)’.
During winter months, the model shows a persistent positive bias of ~ 1ppm, which is significant for the mean XCO2 column over the whole terrestrial China. What were the causes ?
8. Figure 5:
Texts in some legends are difficult to read
9. Line 503-504: The vertical profiles in Fig. 7 further explain the difference in response magnitude between surface CO2 and XCO2
It would be interesting to know the vertical profiles at different seasons (e.g., Winter vs Summer)
10. Line 575-576 The combined contribution therefore remained negative,
It is a bit confusing. For me, they are always negative under all three scenarios (Figure 8).
11. Line 969-972, ‘The contribution decomposition result …’,
Is it because that the biospheric fluxes were fixed and only fossil fuel emissions were allowed to vary?