During the last two centuries, the large population increase and associated agriculture and industrial developments (use of fossil energy, soil use...) led to a large modification of the global biogeochemical cycles.

Atmospheric concentrations of components impacting the greenhouse effect (CO2, CH4, N2O, O3, aerosols...) have increased significantly, which a direct impact on our climate. Such changes also affect marine and terrestrial ecosystems: indeed, climatic changes may deeply affect the geochemistry and the dynamics of the main reservoirs such as the atmosphere, the ocean, and the biosphere..). Atmospheric chemistry and a changing climate also have a direct effect on the vegetation, for example on plant growth and the ability of plants to sequester carbon.

Studies of the present time changes of the bio-geochemical cycles require knowledge of how the different reservoirs (atmosphere, ocean, and biosphere..) evolved over time, and also a better understanding of the impact of climatic changes on these reseroirs.

Our scientific objective is to understand and model interactions between biogeochemical cycles and climate. On the international stage, policies for a moderation of the anthropogenic emissions of greenhouse gases are under development to limit the expected climate change. This requires the development of numerical models able to predict climate evolution for various scenarios of anthropogenic emissions.

With this perspective, we develop and apply a serie of Earth system models, in continuity with present and previous studies.  The main objectives are to:

-  Study and model the processes driving the global carbon cycle and the tropospheric concentrations of CH4, O3 , and aerosols.
- Couple different biogeochemical models, and couple them to Earth system models. 

These studies allow the identification of the most relevant processes, and the areas that are the most vulnerable to anthropogenic climate change.

Models are compared to various types of observations , such as atmospheric measurements and remote sensing data. To better understand differences between model results and data, and to improve our understanding of the global cycles, we have developed a strong expertise in inverse modeling. Because such models cannot be used without a continuous comparison to observations, we operate and develop networks of ground stations for greenhouse gases measurements, and we contribute to the international efforts to create an integrated database.

We also participate in large measurement campaigns for atmospheric chemistry studies, in particular regarding Ozone precursors and transformation of tropospheric arerosols near the sources.  We develop new algorithms for producing global remote sensing data to monitor atmospheric composition and land use change.

The evolution of atmospheric composition since the onset of the industrial revolution is modeled using a set of biogeochemical models coupled to a climate ocean-atmosphere model.