4:30 PM - 4:45 PM
[ACG39-11] Agreement and gaps between the top-down and bottom-up estimates of East Asian carbon sink
Keywords:Land-biospheric carbon sink, Atmospheric CO2 inversion, Fossil Fuel CO2 uncertainty
East Asia is a major hotspot of CO2 emissions and a significant terrestrial carbon sink. Reliable quantification of carbon fluxes in this region is crucial for understanding regional and global carbon budgets. However, substantial discrepancies persist between top-down atmospheric inversions and bottom-up approaches (e.g., Dynamic Global Vegetation Models (DGVMs), inventories). These discrepancies are partly due to large-scale afforestation efforts in China, whose impacts on carbon sinks are not fully captured by current DGVMs. Additionally, uncertainties in prior fossil fuel CO2 (FCO2) emissions are critical for estimating carbon sinks via inversion of observed atmospheric CO2.
Using the MIROC4-ACTM-based inversion system, we find that rapid increases in FCO2 emissions during 2001-2011 artificially inflate global and Chinese land carbon sink estimates. This apparent growth is not supported by DGVM outputs or by an updated process-based model estimate forced by an updated Chinese land cover dataset (Yu et al. 2022), although the mean sink (~0.28 PgC yr-1) remains consistent across approaches and recent RECCAP2 synthesis (Wang et al. 2024). This indicates that while total FCO2 emissions in China may be relatively well constrained, substantial uncertainties persist in their growth rates, primarily due to inconsistent activity data and emission factors during the 2000s. Using the lower bound of FCO2 growth rates in atmospheric inversion improves the consistency between inversion-based and DGVM-based estimates of land carbon sink growth at both regional (China) and global scales. Moreover, biases in China’s FCO2 emissions have broader implications, influencing inversion-based flux estimates beyond national borders. For instance, up to 80% of the apparent increase in Russia’s land-biosphere sink under widely used FCO2 scenarios can be attributed to biases in Chinese emission estimates. Addressing FCO2 emission uncertainties in inversion systems is thus critical for obtaining robust carbon flux estimates, ultimately improving our understanding of the terrestrial carbon sink’s role in supporting nature-based climate solutions.
Using the MIROC4-ACTM-based inversion system, we find that rapid increases in FCO2 emissions during 2001-2011 artificially inflate global and Chinese land carbon sink estimates. This apparent growth is not supported by DGVM outputs or by an updated process-based model estimate forced by an updated Chinese land cover dataset (Yu et al. 2022), although the mean sink (~0.28 PgC yr-1) remains consistent across approaches and recent RECCAP2 synthesis (Wang et al. 2024). This indicates that while total FCO2 emissions in China may be relatively well constrained, substantial uncertainties persist in their growth rates, primarily due to inconsistent activity data and emission factors during the 2000s. Using the lower bound of FCO2 growth rates in atmospheric inversion improves the consistency between inversion-based and DGVM-based estimates of land carbon sink growth at both regional (China) and global scales. Moreover, biases in China’s FCO2 emissions have broader implications, influencing inversion-based flux estimates beyond national borders. For instance, up to 80% of the apparent increase in Russia’s land-biosphere sink under widely used FCO2 scenarios can be attributed to biases in Chinese emission estimates. Addressing FCO2 emission uncertainties in inversion systems is thus critical for obtaining robust carbon flux estimates, ultimately improving our understanding of the terrestrial carbon sink’s role in supporting nature-based climate solutions.