There are several WCRP and IGBP model inter-comparison projects that are useful for establishing component sensitivities. It is strongly encouraged that groups participate in these component model intercomparison projects before full coupling of the carbon cycle and climate in the Flying Leap. WCRP-WGCM: CMIP - coupled GCM, 1%/y CO2 IGBP-GAIM: TransCom - atmospheric transport models: SF6, C inversions IGBP-GAIM: OCMIP - ocean carbon-circulation models: CFC, C uptake IGBP-GAIM: EMDI - terrestrial Net Primary Productivity IGBP-GAIM: CCMLP/Grand Slam - interannual variations in terrestrial and oceanic C fluxes; DGVM - prognostic vegetation with interactive C