A stochastic Lagrangian atmospheric transport model to determine global CO2 sources and sinks—a preliminary discussion

A stochastic Lagrangian model describing the global tropospheric distribution of CO₂ is developed. Available source and sink terms are incorporated in the model. Advection terms are derived from the European Centre for Medium Range Weather Forecasting (ECMWF) analysed grids. Statistics for the variation in the advective terms are derived and incorporated in the model from the ECMWF data base. Model output is compared with CO₂ observations obtained from the National Oceanic and Atmospheric Administration (NOAA) Geophysical Monitoring for Climatic Change (GMCC) program. Model estimates of the yearly averaged latitudinal gradient of CO₂ concentration match the observed CO₂ concentrations except over the southern oceans. A biospheric growing season net flux (GSNF) of 6.5 Gt C was found, from model simulations, to explain the observed seasonal cycle in CO₂ concentrations. This value of the GSNF lies within the bounds of previous estimates. The intensity of the biospheric fluxes above 60° N, oceanic fluxes below 45° S and model vertical transport warrant further investigation.