Global atmospheric CO<sub>2</sub> inverse models converging on neutral tropical land exchange, but disagreeing on fossil fuel and atmospheric growth rate
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Published:2019-01-16
Issue:1
Volume:16
Page:117-134
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ISSN:1726-4189
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Container-title:Biogeosciences
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language:en
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Short-container-title:Biogeosciences
Author:
Gaubert BenjaminORCID, Stephens Britton B.ORCID, Basu SourishORCID, Chevallier FrédéricORCID, Deng FengORCID, Kort Eric A., Patra Prabir K.ORCID, Peters Wouter, Rödenbeck ChristianORCID, Saeki TazuORCID, Schimel DavidORCID, Van der Laan-Luijkx IngridORCID, Wofsy Steven, Yin YiORCID
Abstract
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 (NET) 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 broad
latitudinal separation of land fluxes has converged significantly since the
Atmospheric Carbon Cycle Inversion Intercomparison (TransCom 3) and the
REgional Carbon Cycle Assessment and Processes (RECCAP) projects, with model
spread reduced by 80 % since TransCom 3 and 70 % since RECCAP. Most modeled
CO2 fields agree reasonably well with the HIPPO observations,
specifically for the annual mean vertical gradients in the Northern
Hemisphere. Northern Hemisphere vertical mixing no longer appears to be a
dominant driver of northern versus tropical (T) annual flux differences. Our
newer suite of models still gives northern extratropical land uptake that is
modest relative to previous estimates (Gurney et al., 2002; Peylin et al., 2013) and
near-neutral tropical land uptake for 2009–2011. Given estimates of emissions
from deforestation, this implies a continued uptake in intact tropical
forests that is strong relative to historical estimates (Gurney et al., 2002; Peylin et al., 2013). The results from these models for other time periods (2004–2014,
2001–2004, 1992–1996) and re-evaluation of the TransCom 3 Level 2 and RECCAP
results confirm that tropical land carbon fluxes including deforestation
have been near neutral for several decades. However, models still have large
disagreements on ocean–land partitioning. The fossil fuel (FF) 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 currently limit our ability to assess
regional-scale terrestrial fluxes and ocean–land partitioning from the model
ensemble.
Funder
National Aeronautics and Space Administration
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
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