Assessing the magnitude of CO₂ flux uncertainty in atmospheric CO₂ records using products from NASA's Carbon Monitoring Flux Pilot Project

Abstract

NASA's Carbon Monitoring System Flux Pilot Project (FPP) was designed to better understand contemporary carbon fluxes by bringing together state-of-the art models with remote sensing data sets. Here we report on simulations using NASA's Goddard Earth Observing System Model, version 5 (GEOS-5) which was used to evaluate the consistency of two different sets of observationally informed land and ocean fluxes with atmospheric CO 2 records. Despite the observation inputs, the average difference in annual terrestrial biosphere flux between the two land (NASA Ames Carnegie-Ames-Stanford-Approach (CASA) and CASA-Global Fire Emissions Database version 3 (GFED)) models is 1.7 Pg C for 2009-2010. Ocean models (NASA's Ocean Biogeochemical Model (NOBM) and Estimating the Circulation and Climate of the Ocean Phase II (ECCO2)-Darwin) differ by 35% in their global estimates of carbon flux with particularly strong disagreement in high latitudes. Based upon combinations of terrestrial and ocean fluxes, GEOS-5 reasonably simulated the seasonal cycle observed at Northern Hemisphere surface sites and by the Greenhouse gases Observing SATellite (GOSAT) while the model struggled to simulate the seasonal cycle at Southern Hemisphere surface locations. Though GEOS-5 was able to reasonably reproduce the patterns of XCO 2 observed by GOSAT, it struggled to reproduce these aspects of Atmospheric Infrared Sounder observations. Despite large differences between land and ocean flux estimates, resulting differences in atmospheric mixing ratio were small, typically less than 5 ppm at the surface and 3 ppm in the XCO 2 column. A statistical analysis based on the variability of observations shows that flux differences of these magnitudes are difficult to distinguish from inherent measurement variability, regardless of the measurement platform.

Coupling the Canadian Terrestrial Ecosystem Model (CTEM v. 2.0) to Environment and Climate Change Canada's greenhouse gas forecast model

“…Thus, despite the imperfect TEM spin-up procedure used for CTEM-GEM and the change in meteorological forcing, the simulation driven by retrieved fluxes (CT2013B) is similar to that achieved with CLASS-CTEM prior fluxes. This result is consistent with the finding of (Ott et al, 2015) that large differences in prior flux estimates result in only small differences in CO 2 concentrations.…”

Impact of planetary boundary layer turbulence on model climate and tracer transport

“…Prescribed land and ocean CO 2 fluxes were computed as part of NASA's Carbon Monitoring System project and are described in detail in Ott et al (2015). Three hourly net ecosystem production of CO 2 is computed by the Carnegie-Ames-Stanford Approach Global Fire Emissions Database, version 3 (CASA-GFED3) biogeochemical model (Potter et al, 1993;Randerson et al, 1996).…”

Sensitivity of tropical tropospheric composition to lightning NOx production as determined by replay simulations with GEOS‐5

“…For this study, the GEOS-5 model is run in replay mode, utilizing reanalysis data from the Modern-Era Retrospective Analysis for Research and Applications (MERRA) [Rienecker et al, 2011] to constrain model dynamics, as in Buchard et al [2014] and Ott et al [2015]. One of the major benefits of this approach is the facility to focus on a particular time period without allowing dynamical uncertainties and nonlinearities to develop in the model.…”