Modeling vegetation and land use in models of the Earth System

Land surfacemodelingwas invented to represent the atmosphere's lower boundary over continental areas in climate models. Mass, momentum, and energy cross this boundary via biogeochemical and biogeophysical processes often involving plants. Scientific research with models and in the field strives to refine how the changing face of the land interacts with climate change. Discussed here are methods by which we simulate the vegetation and land use in global models and ways by which vegetation and land use affect climate. Model simulations suggest that global land cover changes due to land use play a greater role in affecting 20thand 21st-century climate than changes in unmanaged vegetation. Among the biogeochemical and biogeophysical effects of land use, biogeochemical ones seem to dominate and enhance 20th- and 21st- century warming. Among the effects of natural vegetation, the positive biogeophysical snow-vegetation-albedo feedback of the high latitudes is expected to increasingly influence global climate in response to increasing vegetation density. Still, human or natural disturbances and other not well-understood processes may alter expected outcomes. Interactive nitrogen is one of the newer additions to our models. Nitrogen is found to buffer the terrestrial biosphere's response to forcings, such as changing CO₂ or climate. We still have much to learn about nitrogen's role in the Earth System. Yet, if land use dominates the effects of land cover change on climate, then human behavior will be our greatest uncertainty, which includes management choices that are not easy to predict, such as urbanization, deforestation and afforestation, crop expansion or abandonment, as well as crop rotation, irrigation, and fertilization.