Influence of Fossil Fuel Emissions on CO2 Flux Estimation by Atmospheric Inversions

Abstract:

Top-down approaches (or atmospheric inversions) using atmospheric transport models with CO₂ observations are an effective way to estimate carbon fluxes at global and regional scales. CO₂ flux estimation by Bayesian inversions require a priori knowledge of terrestrial biosphere and oceanic fluxes and fossil fuel (FF) CO₂ emissions. In most inversion frameworks, FF CO₂ is assumed to be a known quantity because FF CO₂ based on world statistics are thought to be more reliable than natural CO₂ fluxes. However different databases of FF CO₂ emissions may have different temporal and spatial variations especially at locations where statistics are not so accurate. In this study, we use 3 datasets of fossil fuel emissions in inversion estimations and evaluate the sensitivity of the optimized CO₂ fluxes to FF emissions with two different inverse models, JAMSTEC’s ACTM and CarbonTracker Europe (CTE).

Interannually varying a priori FF CO₂ emissions were based on 1) CDIAC database, 2) EDGARv4.2 database, and 3) IEA database, with some modifications. Biosphere and oceanic fluxes were optimized. Except for FF emissions, other conditions were kept the same in our inverse experiments. The three a priori FF emissions showed ~5% (~0.3GtC/yr) differences in their global total emissions in the early 2000’s and the differences reached ~9% (~0.9 GtC/yr) in 2010. This resulted in 0.5–1 GtC/yr (2001–2011) and 0.3–0.6 GtC/yr (2007-2011) differences in the estimated global total emissions for the ACTM and CTE inversions, respectively. Regional differences in the FF emissions were relatively large in East Asia (~0.5 GtC/yr for ACTM and ~0.3 GtC/yr for CTE) and Europe (~0.3 GtC/yr for ACTM). These a priori flux differences caused differences in the estimated biosphere fluxes for ACTM in East Asia and Europe and also their neighboring regions such as West Asia, Boreal Eurasia, and North Africa. The main differences in the biosphere fluxes for CTE were found in Asia and the Americas.