Strategies are developed to analyze and represent spatially resolved biosphere models for carbon sequestration in response to changes in atmospheric CO2 and climate by reduced-form, substitute models. We explore the High-Resolution Terrestrial Biosphere Model as implemented in the Community Terrestrial Biosphere Model (HRBM/CTBM), the Frankfurt Biosphere Model (FBM), and the box-type biosphere of the Bern model. Storage by CO2 fertilization is described by combining analytical representations of (1) net primary productivity (NPP) as a function of atmospheric CO2 and (2) a decay impulse response function to characterize the timescales of biospheric carbon turnover. Storage in response to global warming is investigated for the HRBM/CTBM. The relation between the evolution of radiative forcing and climate change is expressed by a combination of impulse response functions and empirical orthogonal functions extracted from results of the European Center/Hamburg (ECHAM3) coupled atmosphere-ocean general circulation model. A box-type, differential-analogue substitute model is developed to represent global carbon storage of the HRBM/CTBM in response to regional changes in Temperature, Precepitation and cloud cover. The substitute models represent the spatially resolved models accurately and cost-efficiently for carbon sequestration in response to changes in CO2 or in CO2 and climate and for simulations of the global isotopic signals. Deviations in carbon uptake simulated by the spatially resolved models and their substitutes are less than a few percent. ¿ 1999 American Geophysical Union