Three years of quasi-continuous atmospheric ¹⁴CO₂ observations in Heidelberg (Germany) have been used together with continuous CO measurements to determine the CO/fossil fuel CO₂ ratio in a regional polluted area. Comparison with bottom-up information on fossil fuel CO₂ and CO emissions for the respective catchment area shows that large discrepancies (up to 60%) between inventory data and observations exist. Therefore both, a lot of care and reliable emissions inventory data are necessary if CO shall be used as a quantitative surrogate for fossil fuel CO₂.

Simulations with a regional transport model are evaluated in order to determine to which extend the indirect fossil fuel combustion tracer CO or the purely anthropogenic tracer SF₆ can be used to retrieve the contribution of fossil fuel emissions in the atmospheric CO₂ signal.

The WLEF TV tower in northern Wisconsin is instrumented to take continuous measurements of CO₂ mixing ratio at 6 levels from 11 to 396m. During the spring and summer of 2004 additional CO₂ measurements were deployed on five 76 m communication towers forming a ring around the WLEF tower with a 100-150 km radius.

Atmospheric CO₂ concentrations have been obtained from the Atmospheric Infrared Sounder (AIRS) radiance data within the European Centre for Medium-Range Weather Forecasts (ECMWF) data assimilation system. In a first explorative configuration, a subset of channels from the AIRS instrument has been assimilated providing estimates of tropospheric column-averaged CO₂ mixing ratios representative of a layer between the tropopause and about 700 hPa at observation locations only. Results show considerable geographical and temporal variability with values ranging between 370 and 382 ppmv. The 5-day mean estimated random error is about 1%, which is confirmed by comparisons with flask observations on board flights of Japanese airliners in the west-Pacific region. This study demonstrates the feasibility of global CO₂ estimation using high spectral resolution infrared satellite data in a numerical weather prediction data assimilation system. Currently, the system is being improved to treat CO₂ as a full three-dimensional atmospheric variable included in the forecast model. This allows more flexibility in the constraints on the CO₂ estimation as well as the possibility of assimilating other data sources (e.g., near-infrared satellite data and flasks). The CO₂ fields provided by the data assimilation system have great potential to assist the surface flask network in constraining current top-down carbon flux estimates.

The global biogeochemical cycle of oxygen is closely linked to that of carbon dioxide, because key biological processes, as well as fossil fuel burning, occur with specific stochiometric ratios. In the ocean, however, several processes – carbonate chemistry (buffer effect), physical transport (dilution), and warming/cooling (solubility changes) – decouple O₂ and CO₂ exchanges. Based on a decade of atmospheric O₂/N₂ and CO₂ data, we estimated spatial and temporal patterns of oceanic APO fluxes, using an inversion of atmospheric transport. Seasonal and interannual variations are interpreted in the light of climate variables.

The coupled feedback processes of energy and carbon cycles are an essential mechanism for understanding global environmental change. We developed a simplified one-dimensional carbon and energy cycle coupled model to quantify the feedback processes between energy and carbon cycles. The model was calibrated to reproduce the historical variations in temperature and atmospheric CO₂ concentration. The model results of vertical ocean temperature profiles, and latitudinal NPP and NEP distributions were in good agreement with the observation data and terrestrial biosphere model results. The regional difference of terrestrial ecosystem response by climate feedback appeared in the middle and high latitudes. The north-south distribution is important to investigate the terrestrial ecosystem because the opposite response appeared in the middle and high latitude. The future change of carbon cycle and climate was also simulated up to the year 2100 based on the IPCC scenario. The atmospheric CO₂ concentration reaches 735 ppmv in 2100 and global average temperature increases 1.9 K for 2000-2100.

The measurement results of CO₂ average concentration obtained in the atmospheric column at the Issyk-Kul station (IK) (42.6⁰N, 77.0⁰E, 1650 m a.s.l.) in 1980-2004. A comparison was made with the MBL data (for the IK latitude) presenting mean zonal CO₂ concentrations reduced to the sea level and with the measurement results of CO₂ concentrations obtained at KZD (44.45⁰N, 77.57⁰E, 412 m a.s.l) and KZM (43.25⁰N, 77.88⁰E, 2519 m) sites. The IK station is about 100 km distant from KZM and 220 km distant from KZD.

The decadal variability of air-sea CO₂ fluxes is poorly known in the southern hemisphere. To evaluate the changes or stability of these fluxes over several years, we compare seasonal observations obtained in 1991 and 2000 the Southern Indian Ocean. For summer and winter, we observed a significant increase of ocean fugacity (fCO₂) in subtropical waters (20°-35°S), about the same rate as in the atmosphere. In polar waters south of 40°S where meso-scale biological activity is high in summer, the rising of oceanic fCO₂ is only well detected when comparing austral winter data. The decadal evolution of fCO₂ observed in the cold waters certainly results from anthropogenic CO₂ emissions, but is also probably modulated by variations of primary production.