Recent Carbon Cycle Anomalies as Seen From Atmospheric Top-down Information

During the past 10 years, the atmospheric CO2 growth rate underwent large variations still poorly understood, with a striking positive anomaly in the northern hemisphere during the years 2002-2003, not associated to a strong El-Nino event. Whether these perturbations directly reflect anomalous sources from natural fires (suggested by satellite observations) and/or partly reflect impacts of climate on the ecosystems functioning, like the extreme 2003 summer drought in Europe are critical challenges to predict the future of the carbon cycle. From measurements of atmospheric CO2 concentrations at observing sites, the likely geographic origins of anomalous CO2 sources have been estimated for the period 1996-2004, using two independent atmospheric inversion systems. These estimates rely on new techniques where we solve for the fluxes at the grid resolution of the transport model (either TM3 or LMDz) and where we also combine information from process driven model simulations (land and ocean) and fire sources estimates (satellite observations) in one case. We use atmospheric measurements from GLOBALVIEW database, the TCOS project, and Siberian aircraft profiles (NIES-Japan institute). Based on these flux estimates in comparison with climate data and independent information, we discuss the roles of tropical El Nino responses, biomass burning intensity, rising fossil fuel emissions, or drought responses in mid-latitudes, such as the European heat/drought wave in 2003.The comparison of the two independent `top-down' estimates is used to discuss their uncertainties.