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GLOBAL BIOGEOCHEMICAL CYCLES, VOL. 17, NO. 1, 1024, doi:10.1029/2002GB001963, 2003

Amplifying effects of land-use change on future atmospheric CO2 levels

Vincent Gitz

Centre International de Recherche sur l'Environment et le Développement-CNRS/EHESS, Nogent sur Marne, France


Philippe Ciais

Institut Pierre-Simon Laplace/Laboratoire des Sciences du Climat et de l'Environnement-CEA, Gif sur Yvette, France


Abstract

We constructed a model to analyze the interactions between land-use change and atmospheric CO2 during the recent past and for the future. The primary impact of the conversion of forested lands to cultivated lands is to increase atmospheric CO2, via losses of biomass and soil carbon to the atmosphere. This increase is likely to continue in the next decades, but its magnitude can vary according to each land-use scenario. We show that this first-order effect is further amplified by the correlated diminution of terrestrial sinks, because when croplands replace forests, the turnover time of excess carbon in the biosphere decreases, and hence the sink capacity of terrestrial ecosystems decreases. This effect acts to further increase by up to 100 ppm the CO2 level reached by 2100, and it is of the same order of magnitude, although smaller, than climate-carbon feedbacks. Uncertainties on the magnitude of this land-use induced effect are large, because of uncertainties in the sink role of terrestrial ecosystems in the future and because of uncertainties inherent to the modeling of land-use induced carbon emissions. Such an extra rise in atmospheric CO2 is however partially offset by the ocean reservoir and by sinks operating over undisturbed, pristine ecosystems, suggesting that conserving pristine forests with long turnover times might be efficient in mitigating the greenhouse effect.

Published 12 March 2003.

Index Terms: 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 1615 Global Change: Biogeochemical processes (4805); 0322 Atmospheric Composition and Structure: Constituent sources and sinks.

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Citation: Gitz, V., and P. Ciais (2003), Amplifying effects of land-use change on future atmospheric CO2 levels, Global Biogeochem. Cycles, 17(1), 1024, doi:10.1029/2002GB001963.