Improved latitudinal carbon budgets from global airborne surveys

Britton B. Stephens; Yuming Jin; Colm Sweeney; Kathryn McKain; Benjamin Gaubert; David F. Baker; Sourish Basu; Michael Bertolacci; Frédéric Chevallier; Róisín Commane; Sean Crowell; Feng Deng; Matthew S. Johnson; Ralph F. Keeling; Junjie Liu; Zhiqiang Liu; Suman Maity; Eric J. Morgan; Prabir Patra; Sajeev Philip; Steven C. Wofsy; Andrew Zammit-Mangion

doi:10.1073/pnas.2523984123

Improved latitudinal carbon budgets from global airborne surveys

Britton B. Stephens
, Yuming Jin
, Colm Sweeney
, Kathryn McKain
, Benjamin Gaubert
, David F. Baker
, Sourish Basu
, Michael Bertolacci
, Frédéric Chevallier
, Róisín Commane
, Sean Crowell
, Feng Deng
, Matthew S. Johnson
, Ralph F. Keeling
, Junjie Liu
, Zhiqiang Liu
, Suman Maity
, Eric J. Morgan
, Prabir Patra
, Sajeev Philip

Steven C. Wofsy, Andrew Zammit-Mangion

National Oceanic and Atmospheric Administration
Colorado State University
NASA Goddard Space Flight Center
University of Maryland, College Park
University of Western Australia
University of Wollongong
Université Paris-Saclay
Columbia University
University of Rochester
University of Toronto
NASA Ames Research Center
University of California at San Diego
California Institute of Technology
China Meteorological Administration
Japan Agency for Marine-Earth Science and Technology
National Institute for Environmental Studies of Japan
Indian Institute of Technology Delhi
Harvard University
University of New South Wales

Research output: Contribution to journal › Article › peer-review

Abstract

Robust information on the spatial distribution of global carbon fluxes is required to project the future trajectory of carbon-climate feedback effects and atmospheric CO₂ concentrations. Estimates of the latitudinal partitioning of carbon fluxes from top-down atmospheric CO₂ inverse models currently diverge widely, because of methodological limitations or systematic biases in models or observations. We use airborne CO₂ observations from the NASA Atmospheric Tomography Mission to evaluate and refine inverse model estimates from the Orbiting Carbon Observatory version 10 Model Intercomparison Project of total CO₂ exchange for the two-year period of June 2016–May 2018. Applying emergent concentration-flux relationships as constraints reduces zonal total flux uncertainties by 46 to 56% relative to the full v10 MIP ensemble and by 17 to 28% relative to the subset excluding satellite observations over ocean. Subtracting independent estimates of fossil-fuel emissions and air-sea gas exchange results in residual land fluxes with a large northern extratropical sink, a small southern extratropical sink, and a small tropical source. The airborne-derived tropical land source disagrees with a large tropical land sink from process-based terrestrial models combined with estimates of land use emissions and river fluxes, representing an important challenge for our understanding of the global carbon cycle. The large implied northern extratropical sink can be explained either by underestimated land uptake by process models or a combination of process model bias and overestimated fossil fuel emissions.

Original language	English
Article number	e2523984123
Journal	Proceedings of the National Academy of Sciences of the United States of America
Volume	123
Issue number	25
DOIs	https://doi.org/10.1073/pnas.2523984123
State	Published - Jun 23 2026

Funding

We thank the ATom Science Team and the flight crew and support staff of the NASA DC-8 and ATom. For providing additional measurement support, we thank T. Newberger, F. Moore, and G. Diskin for NOAA Picarro CO2 measurements; B. Daube and J. Budney for Quantum Cascade Laser Spectrometer (QCLS) CO2 and N2O measurements; J. Bent for AO2 and Medusa flask sampler CO2 measurements; B. Paplawsky and S. Afshar for Medusa CO2 measurements; F. Moore, S. Montzka, J. Higgs, E. Moglia, S. Wolter, T. Legard, D. Neff, and P. Lang for PFP measurements. For sharing additional ATom measurements, we thank Jim Elkins, Eric Hintsa, and Fred Moore for ATom-1 N2O data; Ilann Bourgeois, Jeff Peischl, Tom Ryerson, and Chelsea Thompson for O3 data; and Glenn Diskin and Joshua DiGangi for H2O data. We thank the OCO-2 Science Team and the OCO-2 Flux Group for conducting the satellite retrievals, bias corrections, and inversions, and sharing the results. For additional OCO-2 v10 Model Intercomparison Project (MIP) output, we thank, Andy Jacobson, Ning Zeng, and Noel Cressie. We acknowledge the Global Carbon Project, which is responsible for the Global Carbon Budget (GCB). We thank the GCB fCO2-mapping groups, Dynamic Global Vegetation Model (DGVM) groups, and Land Use and Land-use Change (LULUC) groups for producing and making available their flux products. In particular, for help with aggregating the GCB flux products to new latitude divisions and months and in their interpretation, we thank Judith Hauck and Peter Landschutzer for the pCO2 products, Mike O'Sullivan for the DGVMs, Clemens Schwingshackl for the LULUC products, Auke van der Woude and Ingrid Luijkx for atmospheric inversions, and Fabrice Lacroix for river fluxes. This study was supported by NASA grants 80NSSC18K1132, NNX15AJ23G, and NNX16AL92A, and by NSF grants AGS-1547626, AGS-1547797, AGS-1623745, and AGS-1623748. Part of the research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the NASA, (80NM0018D0004). J.L. was supported by the NASA Orbiting Carbon Observatory Science Team program. S.M. and P.P. are funded by the Environment Research and Technology Development Fund (JPMEERF20182002 and JPMEERF24S12205) of the Environmental Restoration and Conservation Agency of Japan. This material is based upon work supported by the NSF National Center for Atmospheric Research, which is a major facility sponsored by the U.S. NSF under Cooperative Agreement No. 1852977.

Funders	Funder number
National Science Foundation (NSF)	AGS-1547626
NASA \| Earth Sciences Division (ESD)	80NSSC18K1132

Keywords

airborne observations
atmospheric inverse modeling
global carbon cycle
satellite CO measurements

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10.1073/pnas.2523984123

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Stephens, B. B., Jin, Y., Sweeney, C., McKain, K., Gaubert, B., Baker, D. F., Basu, S., Bertolacci, M., Chevallier, F., Commane, R., Crowell, S., Deng, F., Johnson, M. S., Keeling, R. F., Liu, J., Liu, Z., Maity, S., Morgan, E. J., Patra, P., ... Zammit-Mangion, A. (2026). Improved latitudinal carbon budgets from global airborne surveys. Proceedings of the National Academy of Sciences of the United States of America, 123(25), Article e2523984123. https://doi.org/10.1073/pnas.2523984123

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title = "Improved latitudinal carbon budgets from global airborne surveys",

abstract = "Robust information on the spatial distribution of global carbon fluxes is required to project the future trajectory of carbon-climate feedback effects and atmospheric CO2 concentrations. Estimates of the latitudinal partitioning of carbon fluxes from top-down atmospheric CO2 inverse models currently diverge widely, because of methodological limitations or systematic biases in models or observations. We use airborne CO2 observations from the NASA Atmospheric Tomography Mission to evaluate and refine inverse model estimates from the Orbiting Carbon Observatory version 10 Model Intercomparison Project of total CO2 exchange for the two-year period of June 2016{\textendash}May 2018. Applying emergent concentration-flux relationships as constraints reduces zonal total flux uncertainties by 46 to 56\% relative to the full v10 MIP ensemble and by 17 to 28\% relative to the subset excluding satellite observations over ocean. Subtracting independent estimates of fossil-fuel emissions and air-sea gas exchange results in residual land fluxes with a large northern extratropical sink, a small southern extratropical sink, and a small tropical source. The airborne-derived tropical land source disagrees with a large tropical land sink from process-based terrestrial models combined with estimates of land use emissions and river fluxes, representing an important challenge for our understanding of the global carbon cycle. The large implied northern extratropical sink can be explained either by underestimated land uptake by process models or a combination of process model bias and overestimated fossil fuel emissions.",

keywords = "airborne observations, atmospheric inverse modeling, global carbon cycle, satellite CO measurements",

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note = "Publisher Copyright: Copyright {\textcopyright} 2026 the Author(s).",

year = "2026",

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doi = "10.1073/pnas.2523984123",

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Stephens, BB, Jin, Y, Sweeney, C, McKain, K, Gaubert, B, Baker, DF, Basu, S, Bertolacci, M, Chevallier, F, Commane, R, Crowell, S, Deng, F, Johnson, MS, Keeling, RF, Liu, J, Liu, Z, Maity, S, Morgan, EJ, Patra, P, Philip, S, Wofsy, SC & Zammit-Mangion, A 2026, 'Improved latitudinal carbon budgets from global airborne surveys', Proceedings of the National Academy of Sciences of the United States of America, vol. 123, no. 25, e2523984123. https://doi.org/10.1073/pnas.2523984123

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T1 - Improved latitudinal carbon budgets from global airborne surveys

AU - Stephens, Britton B.

AU - Jin, Yuming

AU - Sweeney, Colm

AU - McKain, Kathryn

AU - Gaubert, Benjamin

AU - Baker, David F.

AU - Basu, Sourish

AU - Bertolacci, Michael

AU - Chevallier, Frédéric

AU - Commane, Róisín

AU - Crowell, Sean

AU - Deng, Feng

AU - Johnson, Matthew S.

AU - Keeling, Ralph F.

AU - Liu, Junjie

AU - Liu, Zhiqiang

AU - Maity, Suman

AU - Morgan, Eric J.

AU - Patra, Prabir

AU - Philip, Sajeev

AU - Wofsy, Steven C.

AU - Zammit-Mangion, Andrew

PY - 2026/6/23

Y1 - 2026/6/23

N2 - Robust information on the spatial distribution of global carbon fluxes is required to project the future trajectory of carbon-climate feedback effects and atmospheric CO2 concentrations. Estimates of the latitudinal partitioning of carbon fluxes from top-down atmospheric CO2 inverse models currently diverge widely, because of methodological limitations or systematic biases in models or observations. We use airborne CO2 observations from the NASA Atmospheric Tomography Mission to evaluate and refine inverse model estimates from the Orbiting Carbon Observatory version 10 Model Intercomparison Project of total CO2 exchange for the two-year period of June 2016–May 2018. Applying emergent concentration-flux relationships as constraints reduces zonal total flux uncertainties by 46 to 56% relative to the full v10 MIP ensemble and by 17 to 28% relative to the subset excluding satellite observations over ocean. Subtracting independent estimates of fossil-fuel emissions and air-sea gas exchange results in residual land fluxes with a large northern extratropical sink, a small southern extratropical sink, and a small tropical source. The airborne-derived tropical land source disagrees with a large tropical land sink from process-based terrestrial models combined with estimates of land use emissions and river fluxes, representing an important challenge for our understanding of the global carbon cycle. The large implied northern extratropical sink can be explained either by underestimated land uptake by process models or a combination of process model bias and overestimated fossil fuel emissions.

AB - Robust information on the spatial distribution of global carbon fluxes is required to project the future trajectory of carbon-climate feedback effects and atmospheric CO2 concentrations. Estimates of the latitudinal partitioning of carbon fluxes from top-down atmospheric CO2 inverse models currently diverge widely, because of methodological limitations or systematic biases in models or observations. We use airborne CO2 observations from the NASA Atmospheric Tomography Mission to evaluate and refine inverse model estimates from the Orbiting Carbon Observatory version 10 Model Intercomparison Project of total CO2 exchange for the two-year period of June 2016–May 2018. Applying emergent concentration-flux relationships as constraints reduces zonal total flux uncertainties by 46 to 56% relative to the full v10 MIP ensemble and by 17 to 28% relative to the subset excluding satellite observations over ocean. Subtracting independent estimates of fossil-fuel emissions and air-sea gas exchange results in residual land fluxes with a large northern extratropical sink, a small southern extratropical sink, and a small tropical source. The airborne-derived tropical land source disagrees with a large tropical land sink from process-based terrestrial models combined with estimates of land use emissions and river fluxes, representing an important challenge for our understanding of the global carbon cycle. The large implied northern extratropical sink can be explained either by underestimated land uptake by process models or a combination of process model bias and overestimated fossil fuel emissions.

KW - airborne observations

KW - atmospheric inverse modeling

KW - global carbon cycle

KW - satellite CO measurements

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DO - 10.1073/pnas.2523984123

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AN - SCOPUS:105042918595

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JO - Proceedings of the National Academy of Sciences of the United States of America

JF - Proceedings of the National Academy of Sciences of the United States of America

IS - 25

M1 - e2523984123

ER -

Improved latitudinal carbon budgets from global airborne surveys

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