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Volume 18, issue 15 | Copyright

Special issue: The 10th International Carbon Dioxide Conference (ICDC10)...

Atmos. Chem. Phys., 18, 11097-11124, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 09 Aug 2018

Research article | 09 Aug 2018

A global synthesis inversion analysis of recent variability in CO2 fluxes using GOSAT and in situ observations

James S. Wang1,2, S. Randolph Kawa2, G. James Collatz2, Motoki Sasakawa3, Luciana V. Gatti4, Toshinobu Machida3, Yuping Liu2,5, and Michael E. Manyin2,5 James S. Wang et al.
  • 1Universities Space Research Association, Columbia, MD, USA
  • 2NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • 3National Institute for Environmental Studies, Center for Global Environmental Research, Ibaraki, Tsukuba Onogawa, Japan
  • 4Instituto de Pesquisas Energéticas e Nucleares (IPEN) – Comissão Nacional de Energia Nuclear (CNEN), São Paulo, Brazil
  • 5Science Systems and Applications, Inc., Lanham, MD, USA

Abstract. The precise contribution of the two major sinks for anthropogenic CO2 emissions, terrestrial vegetation and the ocean, and their location and year-to-year variability are not well understood. Top-down estimates of the spatiotemporal variations in emissions and uptake of CO2 are expected to benefit from the increasing measurement density brought by recent in situ and remote CO2 observations. We uniquely apply a batch Bayesian synthesis inversion at relatively high resolution to in situ surface observations and bias-corrected GOSAT satellite column CO2 retrievals to deduce the global distributions of natural CO2 fluxes during 2009–2010. The GOSAT inversion is generally better constrained than the in situ inversion, with smaller posterior regional flux uncertainties and correlations, because of greater spatial coverage, except over North America and northern and southern high-latitude oceans. Complementarity of the in situ and GOSAT data enhances uncertainty reductions in a joint inversion; however, remaining coverage gaps, including those associated with spatial and temporal sampling biases in the passive satellite measurements, still limit the ability to accurately resolve fluxes down to the sub-continental or sub-ocean basin scale. The GOSAT inversion produces a shift in the global CO2 sink from the tropics to the north and south relative to the prior, and an increased source in the tropics of  ∼ 2PgCyr−1 relative to the in situ inversion, similar to what is seen in studies using other inversion approaches. This result may be driven by sampling and residual retrieval biases in the GOSAT data, as suggested by significant discrepancies between posterior CO2 distributions and surface in situ and HIPPO mission aircraft data. While the shift in the global sink appears to be a robust feature of the inversions, the partitioning of the sink between land and ocean in the inversions using either in situ or GOSAT data is found to be sensitive to prior uncertainties because of negative correlations in the flux errors. The GOSAT inversion indicates significantly less CO2 uptake in the summer of 2010 than in 2009 across northern regions, consistent with the impact of observed severe heat waves and drought. However, observations from an in situ network in Siberia imply that the GOSAT inversion exaggerates the 2010–2009 difference in uptake in that region, while the prior CASA-GFED model of net ecosystem production and fire emissions reasonably estimates that quantity. The prior, in situ posterior, and GOSAT posterior all indicate greater uptake over North America in spring to early summer of 2010 than in 2009, consistent with wetter conditions. The GOSAT inversion does not show the expected impact on fluxes of a 2010 drought in the Amazon; evaluation of posterior mole fractions against local aircraft profiles suggests that time-varying GOSAT coverage can bias the estimation of interannual flux variability in this region.

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We used measurements of CO2 in the atmosphere from the GOSAT satellite and from surface sites around the world, together with a transport model and a unique estimation technique, to quantify CO2 sources and removals over a recent period. We find that climate variations can strongly influence uptake by vegetation and release in decay and fires. However, regional gaps in observations and inaccuracies to which current satellite technology is susceptible result in important estimation biases.
We used measurements of CO2 in the atmosphere from the GOSAT satellite and from surface sites...