ABSTRACT

The structure and function of the terrestrial biosphere are closely coupled to the atmosphere through multiple interactions involving physical changes to the land surface (biogeophysical feedback) and changes in the radiatively active gas composition of the atmosphere (biogeochemical feedback). Human activities are forcing large and pervasive changes in these interactions, making it more important than ever to understand the “natural” regulation of the atmosphere-terrestrial, biosphere-ocean system as it acted in the past as well as the consequences of human perturbations for the state and stability of the system in the future. Earth System Models are being developed for these purposes, although no model includes the full range of interactions that are known to occur. Study of paleoenvironmental records has yielded insights and information that can be used as a test of Earth System Models and as a stimulus to their improvement. For example, biogeophysical (vegetation-atmosphere) interactions as well as ocean-atmosphere interactions seem to be necessary for the correct simulation of major changes in vegetation and climate in response to orbital forcing during the Holocene. There is also considerable scope, as yet unexplored, to use paleorecords to test models with coupled climatic and biogeochemical components. The Last Glacial Maximum, in particular, poses fundamental challenges concerning the causation and radiative effects of low CO2 and high eolian dust concentrations, and the biological effects and consequent feedbacks engendered by low CO2. Fully prognostic models of the terrestrial biosphere (dynamical global vegetation models, or DGVMs) have been developed, partly in response to these challenges posed by paleorecords.