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Published February 6, 2025 | Version Published
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Quantification of regional net CO₂ flux errors in the Orbiting Carbon Observatory-2 (OCO-2) v10 model intercomparison project (MIP) ensemble using airborne measurements

Creators

  • 1. ROR icon Jet Propulsion Lab
  • 2. ROR icon California Institute of Technology
  • 3. ROR icon Goddard Space Flight Center
  • 4. ROR icon Morgan State University
  • 5. ROR icon Earth System Research Laboratory
  • 6. ROR icon National Institute for Space Research
  • 7. ROR icon Lawrence Berkeley National Laboratory

Abstract

Inverse model intercomparison projects (MIPs) provide a chance to assess the uncertainties in inversion estimates arising from various sources. However, accurately quantifying ensemble CO2 flux errors remains challenging and often relies on the ensemble spread. This study proposes a method for quantifying the errors in regional net surface–atmosphere CO2 flux estimates from models taken from the Orbiting Carbon Observatory-2 (OCO-2) v10 MIP by using independent airborne CO2 measurements for the period 2015–2017. We first calculate the root mean square error (RMSE) between the ensemble mean of posterior CO2 concentrations and airborne observations and then isolate the CO2 concentration errors caused solely by the ensemble mean of posterior net fluxes by subtracting the observation, representation, and transport errors from seven regions. Our analysis reveals that the flux errors projected onto CO2 space account for 55 %–85 % of the regional average RMSE over the 3 years, ranging from 0.88 to 1.91 ppm. In five regions, the error estimates based on observations exceed those computed from the ensemble spread of posterior fluxes by a factor of 1.33–1.93, implying an underestimation of the actual flux errors, while their magnitudes are comparable in two regions. The adjoint sensitivity analysis identifies that the underestimation of flux errors is prominent where the magnitudes of fossil fuel emissions exceed those of terrestrial-biosphere fluxes by a factor of 3–31 over the 3 years. This suggests the presence of systematic biases in the inversion estimates associated with errors in the prescribed fossil fuel emissions common to all models. Our study emphasizes the value of airborne measurements for quantifying regional errors in ensemble net CO2 flux estimates.

Copyright and License

© Author(s) 2025. This work is distributed under the Creative Commons Attribution 4.0 License.

Published by Copernicus Publications on behalf of the European Geosciences Union.

The author’s copyright for this publication is transferred to the Jet Propulsion Laboratory, California Institute of Technology.

Acknowledgement

We are grateful to NOAA, NASA LaRC, NASA GSFC, INPE, NIES, MRI, the European research infrastructure IAGOS-CARIBIC, the DOE's LBNL, and Harvard University for providing the airborne CO2 observation data. We thank Colm Sweeney, Kenneth Davis, Joshua P. DiGangi, Melissa Y. Martin, John B. Miller, Emanuel Gloor, Wouter Peters, Toshinobu Machida, Hidekazu Matsueda, Yousuke Sawa, Yosuke Niwa, Ed Dlugokencky, Stephan R. Kawa, James B. Abshire, Haris Riris, Florian Obersteiner, Harald Boenisch, Torsten Gehrlein, Andreas Zahn, Christoph Gerbig, Tanja Schuck, Gao Chen, Michael Shook, Giordane A. Martins, Rodrigo A. de Souza, Britton Stephens, Eric Kort, Thomas Ryerson, Jeff Peischl, Ken Aikin, Steve Wofsy, Bruce Daube, and Roisin Commane for contributing airborne CO2 data. We also appreciate all the providers of the datasets used in the GEOS-Chem model simulations. We especially thank all research groups involved in the OCO-2 MIP for their contributions to providing v10 OCO-2 and in situ CO2 datasets, as well as inverse-modeling outputs.

Funding

This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004) and has been supported by the National Aeronautics and Space Administration (grant no. 20-OCOST20-0012). The South American airborne CO2 measurements were supported by the European Research Council through the ASICA project (grant no. 649087). Observations collected at the SGP site were partly supported by the Office of Biological and Environmental Research of the US Department of Energy under contract no. DE-AC02-05CH11231 as part of the Atmospheric Radiation Measurement (ARM) program, the ARM Aerial Facility, and the Environmental System Science (ESS) program.

Data Availability

The inverse-modeling results and airborne CO2 measurement data from the OCO-2 v10 MIP are available on the official website of the NOAA/ESRL Global Monitoring Laboratory at https://www.gml.noaa.gov/ccgg/OCO2_v10mip/download.php (NOAA/ESRL Global Monitoring Laboratory, 2022). The high-resolution global GEOS-Chem simulation results used to calculate the representation errors can be obtained upon request from Brad Weir (brad.weir@nasa.gov) or Lesley Ott (lesley.e.ott@nasa.gov). The forward and adjoint sensitivity simulations for this work were conducted using the publicly available GEOS-Chem adjoint model. This model can be downloaded from http://wiki.seas.harvard.edu/geos-chem/index.php/GEOS-Chem_Adjoint (Henze et al., 2007). ODIAC fossil fuel CO2 emission data are available at https://doi.org/10.17595/20170411.001 (Oda and Maksyutov, 2015). Hourly (or 3-hourly) terrestrial-biosphere carbon flux datasets from CASA-GFED3, CASA-GFED4.1s, SiB4, CARDAMOM, and ORCHIDEE – all OCO-2 v10 MIP prior flux models – are available at https://doi.org/10.5067/VQPRALE26L20 (Ott, 2020), https://doi.org/10.25925/20201008 (Jacobson et al., 2020), https://doi.org/10.3334/ORNLDAAC/1847 (Haynes et al., 2021), https://doi.org/10.5067/1XO0PZEZOR1H (Liu and Bowman, 2024), and on the official website of the CAMS (https://ads.atmosphere.copernicus.eu/datasets/cams-global-greenhouse-gas-inversion?tab=download, Copernicus Atmosphere Monitoring Service, 2020).

Contributions

JY and JL designed this study, and JY performed the analysis. JL, BrB, BW, KM, and BiB reviewed the paper and provided input. BW and LEO provided the high-resolution global GEOS-Chem simulation results. KM, BiB, LVG, and SCB provided the airborne CO2 observations. JY led the writing, with input from all coauthors.

Supplemental Material

The supplement related to this article is available online at: https://doi.org/10.5194/acp-25-1725-2025-supplement.

Ethics

Publisher’s note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors.

Additional Information

This paper was edited by Christoph Gerbig and reviewed by two anonymous referees.

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Additional details

Additional titles

Alternative title
Quantification of regional terrestrial biosphere CO₂ flux errors in v10 OCO-2 MIP models using airborne measurements

Is new version of
Discussion Paper: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-2258/egusphere-2023-2258.pdf (URL)
Is supplemented by
Supplemental Material: 10.5194/acp-25-1725-2025-supplement (DOI)
Dataset: 10.3334/ORNLDAAC/1847 (DOI)
Dataset: 10.5194/acp-7-2413-2007 (DOI)
Dataset: 10.5067/1XO0PZEZOR1H (DOI)
Dataset: https://gml.noaa.gov/ccgg/OCO2_v10mip/download.php (URL)
Dataset: 10.17595/20170411.001 (DOI)
Dataset: 10.5067/VQPRALE26L20 (DOI)

Funding

National Aeronautics and Space Administration
80NM0018D0004
National Aeronautics and Space Administration
20-OCOST20-0012
European Research Council
649087
United States Department of Energy
DE-AC02-05CH11231

Dates

Accepted
2024-11-21

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Published