Effets d'amplification du changement d'usage des terres sur le taux de CO2 atmosphériqueAmplification effect of changes in land use and concentration of atmospheric CO2

A model is presented here, which attempts to determine interactions between change in land use and concentration of atmospheric CO₂ over the 1700–2100 period. The main impact of the conversion of forests to agricultural areas is the increase of atmospheric CO₂ because of the losses of biomass and soil carbon in favour of the atmosphere. This raise will probably increase in the next years, correlated with the proportion of cultivated areas. We show here that this first-order effect is amplified by the correlative decrease of terrestrial sinks of CO₂; in fact, as forests are replaced by cultivated parcels, carbon residence time in biosphere decreases, as well as sequestration ability of these ecosystems. This amplification effect leads to an additional increase in atmospheric CO₂, which could reach 100 ppm in 2100. The uncertainties on the range of such an increase are important since they cumulate both uncertainties on the behaviour (sink or source) of terrestrial ecosystems in the future and inherent uncertainties of the modeling of carbon fluxes linked to changing land uses… Such an additional increase in CO₂ is partially limited by the ocean reservoir and by the existing CO₂ sinks in primary non-anthropologically disturbed ecosystems. The results imply that conservation of primary forests, for which primary productivity and carbon time of residence are high, is an efficient strategy for greenhouse-effect mitigation. To cite this article: V. Gitz, P. Ciais, C. R. Geoscience 335 (2003).