Mitigating the effects of climate change

This research theme is concerned with climate change mitigation and aims to understand how land use and agronomic or silvicultural management practices can play a role in limiting ongoing climate change and reducing its impacts. Continental surfaces interact with the atmosphere through exchanges of heat, mass, kinetic energy and radiation, which must be taken into account when mitigating the effects of climate change.

The management of croplands and grasslands has an impact on soil carbon balance and greenhouse gas emissions. Cultivated soils are generally depleted of carbon and could therefore replenish significant amounts of organic matter. Agriculture can improve its greenhouse gas balance by reducing N2O and CH4 emissions, storing more carbon in soils and producing renewable energy (e.g. biogas from methanisation of livestock effluent or crop residues) with a substitution effect on fossil fuels. However, the environmental benefits of these different levers need to be analysed in the light of competing uses of biomass (e.g. return to soil versus methanisation) and taking into account the induced effects, sometimes over long distances (indirect land-use change).

Forestry plays a key role in carbon sequestration. This can occur within the ecosystem, in the biomass and soil compartments, or ex situ, in the harvested products. Substitution of fossil-based products with bio-based forestry or agricultural products also offers mitigation potential.

The challenge for research is to anticipate the behaviour of forest and agricultural systems under different climate scenarios and management pathways. This projection into the future is difficult. First, because of the complexity of crop, grassland and forest ecosystems as biogeochemical and thermodynamic systems. Secondly, because of the uncertainty associated with the rapid evolution of the physical environment (biotope) as a result of climate change, pollution, changes in the hydrological cycle and changes in agricultural or forestry practices. Finally, because of the multiple interactions between these ecosystems and other elements of the landscape (infrastructure, transport networks, urban fabric, etc.).

1. It requires us to think "far ahead". Forests, in particular, have life cycles of more than a century, which means that we need to analyse long-term scenarios (100 years and more) covering all possible futures for the Earth system at a sufficient resolution (10 km). This long-term vision must also be able to take into account extreme events, which are by definition rare, and their major impact on the dynamics of these ecosystems.

2. This means taking into account the complexity of ecosystems, their energy exchanges, the cycles of various key elements (carbon, nitrogen, phosphorus, water, etc.), their complex structure, their food webs and their interactions with the physical environment.

3. It must take into account the full range of ecosystem functions and their impact on the production of marketable goods, the protection of soils, water resources, coastal features and climate, habitat diversity, biodiversity and related recreational and cultural activities.

4. It requires the integration of human activities at different levels: managers and operators, other users of rural or forest areas, processing industries, markets and trade in the materials produced. In cooperation with the stakeholders concerned, we propose approaches to optimise practices that integrate mitigation services (Forêts-21, Biosylve, e-Sylve, OTAF, Grifon projects).

The ISPA unit contributes to this theme by carrying out various research activities and projects, by participating in collective expert assessments and by developing observation networks and resources, ranging from local (ICOS infrastructure network) to global (Copernicus programme) or experimental (ANAEE infrastructure, Xylosylve platform). An important avenue of research is the use of biophysical and biogeochemical models to represent micrometeorology (MUSICA model) and the dynamics of forest or agricultural systems forced by climatic and cropping scenarios (GO+, ORCHIDEE-FM, GOANIM, Roth-C models). It is used for local (e-Sylve project), regional (Grifon, Impacts, Biosylve projects), national and European (CLINORG project) applications and for the analysis of major industrial projects (photovoltaic infrastructure, Champ Captant de Bordeaux Métropole, etc.).