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© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 30 Aug 2018

Research article | 30 Aug 2018

Review status
This discussion paper is a preprint. A revision of the manuscript was accepted for the journal Biogeosciences (BG).

Global atmospheric CO2 inverse models converging on neutral tropical land exchange but diverging on fossil fuel and atmospheric growth rate

Benjamin Gaubert1, Britton B. Stephens1, Sourish Basu2, Frédéric Chevallier3, Feng Deng4, Eric A. Kort5, Prabir K. Patra6, Wouter Peters7, Christian Rödenbeck8, Tazu Saeki9, David Schimel10, Ingrid Van der Laan-Luijkx7, Steven Wofsy11, and Yi Yin12 Benjamin Gaubert et al.
  • 1National Center for Atmospheric Research, Boulder, CO, USA
  • 2University of Colorado Boulder and NOAA Earth System Research Laboratory Boulder, CO, USA
  • 3Laboratoire des Sciences du Climat et de l’Environnement, Institut Pierre-Simon Laplace, CEA-CNRS-UVSQ, Gif sur Yvette, 91191 CEDEX, France
  • 4Department of Physics, University of Toronto, Canada
  • 5University of Michigan, Ann Arbor, MI, USA
  • 6RGGC/IACE/ACMPT, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama 236 0001, Japan
  • 7Meteorology and Air Quality, Wageningen University, Wageningen, the Netherlands
  • 8Max Planck Institute for Biogeochemistry, 07745 Jena, Germany
  • 9Center for Global Environmental Research, National Institute for Environmental Studies, Tsukuba, Japan
  • 10Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
  • 11Harvard University, Cambridge, MA, USA
  • 12California Institute of Technology, Pasadena, CA, USA

Abstract. We have compared a suite of recent global CO2 atmospheric inversion results to independent airborne observations and to each other, to assess their dependence on differences in northern extratropical vertical transport and to identify some of the drivers of model spread. We evaluate posterior CO2 concentration profiles against observations from the High-Performance Instrumented Airborne Platform for Environmental Research (HIAPER) Pole-to-Pole Observations (HIPPO) aircraft campaigns over the mid Pacific in 2009–2011. Although the models differ in inverse approaches, assimilated observations, prior fluxes, and transport models, their latitudinal distributions of land fluxes have converged significantly since the Atmospheric Carbon Cycle Inversion Intercomparison (TransCom3) and the REgional Carbon Cycle Assessment and Processes (RECCAP) projects, with model spread reduced by 80% since TransCom3 and 70% since RECCAP. Most modelled CO2 fields agree reasonably well with the HIPPO observations, in particular for annual mean vertical gradients in the northern hemisphere. Northern hemisphere vertical mixing no longer appears to be a dominant driver of northern versus tropical annual flux differences. Our newer suite of models still gives modest northern extratropical land uptake and near neutral tropical land uptake for 2009–2011, thus implying a continued strong uptake in intact tropical forests given estimates of emissions from deforestation. The results from these models for other time periods (2004–2014, 2001–2004, 1992–1996), and re-evaluation of the TransCom3 Level 2 and RECCAP results confirms that tropical land carbon fluxes including deforestation have been near neutral for several decades. However, models still have large disagreements on ocean-land partitioning, and this is influenced by differences in prescribed fossil fuel emissions and is associated with differences in retrieved atmospheric growth rate. The fossil fuel and the atmospheric growth rate terms have been thought to be the best-known terms in the global carbon budget, but we show that they dominate the model spread at the largest scales and currently limit our ability to assess regional scale terrestrial fluxes and ocean-land partitioning from the model ensemble.

Benjamin Gaubert et al.
Interactive discussion
Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Benjamin Gaubert et al.
Data sets

HIPPO Merged 10-Second Meteorology, Atmospheric Chemistry, And Aerosol Data S. Wofsy et al.

Benjamin Gaubert et al.
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Short summary
We have compared global carbon budgets calculated from numerical inverse models and CO2 observations, and evaluated how these systems reproduce vertical gradients in atmospheric CO2 from aircraft measurements. We found that available models have converged on near neutral tropical total and fluxes for several decades, implying consistent sinks in intact tropical forests, and that assumed fossil fuel emissions and predicted atmospheric growth rates are now the dominant drivers of disagreement.
We have compared global carbon budgets calculated from numerical inverse models and CO2...