A coupled atmosphere-biosphere simulator, CCM3-IBIS, is used to understand the complex interactions between the earth’s surface and the climate system. A better understanding is needed so that the impact of future land use change on the climate can be ascertained. A detailed grid cell energy budget analysis is used to quantify the influence that different vegetation types have on the local, regional, and global climate. The influence of vegetation on the climate system is determined by removing specific vegetation types and examining how and why the climate responds to changes in the surface properties through feedbacks. Although it is generally agreed that the biosphere plays an important role in influencing the climate system, little is understood about what mechanisms are important for a given biome and how the energy budget is partitioned.

CCM3-IBIS consists of a biosphere model, IBIS (Foley et al., 1996; Kucharik et al., 2000), and the NCAR CCM3 Community Climate Model. IBIS is a land surface process model that represents the physical, physiological, and ecological processes at work in vegetation and soil. Seven simulations (and a control run of natural vegetation cover) were run for ten years at a spatial resolution of T31 (~3.75° x 3.75°). In each of the seven simulations a specific vegetation type was completely removed representing a theoretical maximum signal of the vegetation’s influence on the climate. The vegetation types removed include tropical forest, temperate forest, boreal forest, savanna, grassland/steppe, shrubland/tundra, and desert. All of the simulations were performed with fixed vegetation, a fixed atmospheric CO₂ concentration, and fixed sea-surface temperatures. A detailed energy budget was calculated for all grid cells in the model with individual terms representing the latent heat flux, the convergence of radiative heat, and the convergence of the internal, geopotential, and latent energy advective fluxes. By examining each of these terms for the different vegetation removal scenarios the mechanisms and relative importance of the different biomes on forcing the climate system can be determined.

Preliminary results indicate that the individual components of the energy budget are of different relative importance seasonally within the same biome and for the same time period in different biomes. For instance, there is a strong latitudinal distinction between how the energy is partitioned in the tropical versus the temperate and boreal biomes. Differences in the energy budget partitioning between the same or different biomes help explain how different vegetation types force the climate and how changes to the surface parameters might extend to regions removed from the local forcing.