The increase in atmospheric CO2 concentration is the main cause of the global warming observed over the last fifty years. However, the quantities of fossil carbon extracted from the subsoil and injected into the atmosphere are small compared with the natural exchanges between the major reservoirs – the atmosphere, soil and vegetation – and the ocean. Increased atmospheric concentration disrupts the natural carbon cycle. Today, due to the increase in atmospheric concentration, carbon exchanges between these reservoirs lead to a net flow towards the oceans and vegetation, thus limiting the share in the atmosphere.
So nature is helping us to limit the increase in atmospheric CO2 and hence climate change. How long will this help last? We are already seeing an increase in the frequency of major fires around the world, which inject significant quantities of CO2 into the atmosphere. Similarly, in France, climate change is leading to a certain amount of forest dieback, reducing the absorption of carbon by ecosystems on our territory. It is therefore to be feared that climate change will eventually lead to an additional source of carbon in the atmosphere, accelerating global warming. These processes are still highly uncertain and difficult to model, and are therefore a major source of uncertainty as to the speed of climate change.
Several components of the carbon cycle can be observed by satellite. In particular, we can measure the distribution of vegetation, its evolution and inter-annual anomalies linked to climatic disturbances. Orbiting instruments can also measure the concentration of CO2 and methane in the atmosphere to deduce emissions from the main emitting sites, as well as exchanges with vegetation. This is the aim of the MicroCarb mission, developed by CNES and due for launch in 2025.
