How uncertainties in future climate change predictions translate into future terrestrial carbon fluxes

Authors

  • Marie Berthelot,

    1. Institut Pierre-Simon Laplace, Laboratoire des Sciences du Climat et de l'Environnement, Commissariat à l'Energie Atomique, l'Orme des Merisiers, 91191 Gif sur Yvette, France,
    Search for more papers by this author
    • 1Present address: CLIMPACT, 12 Rue de Belzunce, 75010, Paris, France.

  • Pierre Friedlingstein,

    1. Institut Pierre-Simon Laplace, Laboratoire des Sciences du Climat et de l'Environnement, Commissariat à l'Energie Atomique, l'Orme des Merisiers, 91191 Gif sur Yvette, France,
    Search for more papers by this author
  • Philippe Ciais,

    1. Institut Pierre-Simon Laplace, Laboratoire des Sciences du Climat et de l'Environnement, Commissariat à l'Energie Atomique, l'Orme des Merisiers, 91191 Gif sur Yvette, France,
    Search for more papers by this author
  • Jean-Louis Dufresne,

    1. Institut Pierre-Simon Laplace, Laboratoire de Météorologie Dynamique, Université Paris 6, 4 place Jussieu, 75252 Paris, France,
    Search for more papers by this author
  • Patrick Monfray

    1. Laboratoire d'Etudes en Géophysique et Océanographie Spatiale, 18 avenue Edouard Belin, 31401 Toulouse Cedex 4, France
    Search for more papers by this author

Marie Berthelot, tel +33 1 55 07 85 75, fax +33 1 55 07 85 79, e-mail: mb@climpact.com

Abstract

We forced a global terrestrial carbon cycle model by climate fields of 14 ocean and atmosphere general circulation models (OAGCMs) to simulate the response of terrestrial carbon pools and fluxes to climate change over the next century. These models participated in the second phase of the Coupled Model Intercomparison Project (CMIP2), where a 1% per year increase of atmospheric CO2 was prescribed. We obtain a reduction in net land uptake because of climate change ranging between 1.4 and 5.7 Gt C yr−1 at the time of atmospheric CO2 doubling. Such a reduction in terrestrial carbon sinks is largely dominated by the response of tropical ecosystems, where soil water stress occurs. The uncertainty in the simulated land carbon cycle response is the consequence of discrepancies in land temperature and precipitation changes simulated by the OAGCMs. We use a statistical approach to assess the coherence of the land carbon fluxes response to climate change. The biospheric carbon fluxes and pools changes have a coherent response in the tropics, in the Mediterranean region and in high latitudes of the Northern Hemisphere. This is because of a good coherence of soil water content change in the first two regions and of temperature change in the high latitudes of the Northern Hemisphere.

Then we evaluate the carbon uptake uncertainties to the assumptions on plant productivity sensitivity to atmospheric CO2 and on decomposition rate sensitivity to temperature. We show that these uncertainties are on the same order of magnitude than the uncertainty because of climate change. Finally, we find that the OAGCMs having the largest climate sensitivities to CO2 are the ones with the largest soil drying in the tropics, and therefore with the largest reduction of carbon uptake.

Ancillary