A geographical information system, together with a climate—driven, global, regionalized, carbon—budget model, was used to investigate climatic limitations of grassland and coniferous forest vegetation units. The climatic limitations of the fluxes net primary productivity and litter decay were considered for present climatic conditions and for scenario conditions assuming a 3.5°C temperature rise or a 10% precipitation increase, respectively. The two fluxes behave differently in respect to climatic limitations. Global grassland and coniferous forest areas are quite similar in size, but grasslands have the higher productivity while coniferous forests dominate in phytomass. Therefore, grasslands are more important for the seasonal carbon cycle. Coniferous forests have the stronger potential to influence the long—term carbon balance. The assumed climate change will strongly affect the climatic limitations of both vegetation types.