Estimated regional CO₂flux and uncertainty based on an ensemble of atmospheric CO₂inversions

Abstract

Abstract. Global and regional sources and sinks of carbon across the earth's surface have been studied extensively using atmospheric carbon dioxide (CO2) observations and atmospheric chemistry-transport model (ACTM) simulations (top-down/inversion method). However, the uncertainties in the regional flux distributions remain unconstrained due to the lack of high-quality measurements, uncertainties in model simulations, and representation of data and flux errors in the inversion systems. Here, we assess the representation of data and flux errors using a suite of 16 inversion cases derived from a single transport model (MIROC4-ACTM) but different sets of a priori (bottom-up) terrestrial biosphere and oceanic fluxes, as well as prior flux and observational data uncertainties (50 sites) to estimate CO2 fluxes for 84 regions over the period 2000–2020. The inversion ensembles provide a mean flux field that is consistent with the global CO2 growth rate, land and ocean sink partitioning of −2.9 ± 0.3 (± 1σ uncertainty on the ensemble mean) and −1.6 ± 0.2 PgC yr−1, respectively, for the period 2011–2020 (without riverine export correction), offsetting about 22 %–33 % and 16 %–18 % of global fossil fuel CO2 emissions. The rivers carry about 0.6 PgC yr−1 of land sink into the deep ocean, and thus the effective land and ocean partitioning is −2.3 ± 0.3 and −2.2 ± 0.3, respectively. Aggregated fluxes for 15 land regions compare reasonably well with the best estimations for the 2000s (∼ 2000–2009), given by the REgional Carbon Cycle Assessment and Processes (RECCAP), and all regions appeared as a carbon sink over 2011–2020. Interannual variability and seasonal cycle in CO2 fluxes are more consistently derived for two distinct prior fluxes when a greater degree of freedom (increased prior flux uncertainty) is given to the inversion system. We have further evaluated the inversion fluxes using meridional CO2 distributions from independent (not used in the inversions) aircraft and surface measurements, suggesting that the ensemble mean flux (model–observation mean ± 1σ standard deviation = −0.3 ± 3 ppm) is best suited for global and regional CO2 flux budgets than an individual inversion (model–observation 1σ standard deviation = −0.35 ± 3.3 ppm). Using the ensemble mean fluxes and uncertainties for 15 land and 11 ocean regions at 5-year intervals, we show promise in the capability to track flux changes toward supporting the ongoing and future CO2 emission mitigation policies.

Evaluating Northern Hemisphere Growing Season Net Carbon Flux in Climate Models Using Aircraft Observations

“…The Model for Interdisciplinary Research on Climate version 4 atmospheric general circulation model based chemistry transport model (MIROC4‐ACTM) provides posterior 4‐D CO 2 fields and optimized surface fluxes through the HIPPO and ATom periods (Chandra et al., 2022). Atmospheric CO 2 transport in MIROC4‐ACTM was simulated by the Japan Agency for Marine‐Earth Science and Technology's ACTM, a transport model driven by meteorological parameters from the Japanese 55‐year Reanalysis (JRA55, Patra et al., 2018).…”

Meridional Propagation of Carbon Dioxide (CO2) Growth Rate and Flux Anomalies From the Tropics Due to ENSO

“…Inversion cases for prior flux uncertainty (ctl) and model data uncertainty (ux4) are used here (Chandra et al., 2022). Model simulations are sampled at the nearest grid from the measurements location (longitude, latitude and height) and within 30 min from the time of observation from hourly mean model output.…”

“…MIROC4-ACTM simulated two different types simulations using bottom-up a priori (apr) and a posteriori (apos) fluxes produced by top-down inversion. For each simulation types two sets of total CO 2 fluxes are used (following Chandra et al, 2022);…”

“…ACTM experiments at measurements locations are available at https://doi.org/10.5281/zenodo.6683619. A subset of flux files are available in Chandra et al., 2022.…”

Development of a Portable and Sensitive CO2 Measurement Device with NDIR Sensor Clusters and Minimizing Water Vapor Impact

“…With the development of laser spectroscopy technology, a number of continuous measurement CO 2 instruments have been developed for CO 2 monitoring based on highly accurate detection techniques such as cavity ring-down spectroscopy (CRDS) [10], off-axis integrated cavity output spectroscopy [11] and tunable diode laser absorption spectroscopy [12]. The source-sink of CO 2 and climate effects in the environment were revealed by these high-precision analytical devices in CO 2 networks over the world [13][14][15][16]. Due to the cost of the networks, it is difficult to develop them on a large scale with a higher spatial density of observations.…”