Pierre Friedlingstein
LSCE Unite mixte CEA-CNRS
CE-Saclay, Bat 701
91191 Gif sur Yvette
France
Tel: 33 1 69 08 87 30
Fax: 33 1 69 08 77 16
email: pierre@lsce.saclay.cea.fr
The biospheric carbon cycle is directly linked to the climate system. CO2 exchanges between the atmosphere and the biosphere are controlled by atmospheric CO2 concentration and surface climate conditions. Elevated atmospheric CO2 increases plant photosynthesis through the so-called fertilization effect. Climate change, through changes in surface temperature, atmospheric humidity, soil temperature and moisture, etc also affects the biospheric carbon storage through imbalance between photosynthesis and organic matter decomposition. On the other hand, future atmospheric CO2 is controlled by anthropogenic emissions but also by surface (land and ocean) CO2 fluxes. It is therefore extremely important to estimate in the context of future climate what is the carbon cycle response to CO2 increase and climatic change. This subproject focus only on the biospheric compound of the carbon cycle, but a similar subproject, in coordination with the OCMIP activity could also be developed.
We will use CASA/SLAVE, a global model of the biospheric carbon cycle to estimate the biospheric response to the climate forcing. CASA/SLAVE has been developed by the investigator, in collaboration with Chris Field (Carnegie, Stanford, California) and Inez Fung (Berkeley, California) over the past 5 years (Friedlingstein, et al, 1995a, 1999). The model estimates, on a monthly time step, the geographical distribution of net primary productivity, carbon allocation in the plant system, leaf fall, litter and soil decomposition, and net CO2 flux between the atmosphere and the biosphere. It has been used for several studies, such as present-day global carbon budget (Friedlingstein, et al, 1995a), paleo studies (Friedlingstein, et al, 1995b) interannual atmospheric CO2 variability (Friedlingstein, et al, 1997) or plant allocation under current and doubled CO2 (Friedlingstein, et al, 1999).
The model will be forced by atmospheric CO2 and monthly means of surface temperature and precipitation field, available from the CMIP2 runs. The model needs to be initialized to steady state using constant climate, then it will be run over the CMIP2 period.
A preliminary study has been performed using the CMIP2 outputs from the LMD GCM. The biospheric response to the atmospheric CO2 increase is an important biospheric carbon uptake, but the climate induced response, because of drying of the surface is a net release. The CO2 induced response being larger than the climate one, the combined effect on the biosphere is a biospheric sink.
Using several CMIP2 GCM results will test the robustness of this preliminary result.
The following monthly mean fields are required from both the control and perturbed integrations: