Abstract
The increase in atmospheric CO2 concentrations is the primary cause of the global warming observed over the past fifty years. However, the amounts of fossil carbon extracted from the ground and released into the atmosphere are small compared to the natural exchanges between the major carbon reservoirs—the atmosphere, soil and vegetation, and the ocean. The rise in atmospheric concentration disrupts the natural carbon cycle. Today, due to this rise, carbon exchanges between these reservoirs result in a net flow toward the oceans and vegetation, thereby limiting the amount of CO2 in the atmosphere.
Nature is therefore helping us limit the rise in atmospheric CO₂ and, consequently, climate change. How long will this help last? We are already seeing an increase worldwide in the frequency of major wildfires, which release significant amounts of CO₂ into the atmosphere. Similarly, climate change is leading to some forest dieback in France, thereby reducing carbon absorption by ecosystems within our country. There is therefore reason to fear that climate change will eventually result in an additional source of carbon in the atmosphere and thus accelerate global warming. These processes are still highly uncertain and difficult to model, and therefore constitute a major source of uncertainty regarding the rate of climate change.
Several components of the carbon cycle can be observed by satellite. In particular, it is possible to measure vegetation distribution, its changes over time, and interannual anomalies linked to climatic disturbances. Orbiting instruments also measure atmospheric concentrations of CO₂ and methane to estimate emissions from major sources, as well as exchanges with vegetation. This is the objective of the MicroCarb mission, developed by CNES, which is scheduled for launch in 2025.
