Multiple lines of evidence suggest that tropical forests may respond dramatically to climate change and – because these systems exchange more carbon dioxide with the atmosphere than any other class of terrestrial ecosystem – understanding the consequences for associated carbon cycling feedbacks is critical to climate predictions at the global-scale. Indeed, poor model representation of tropical forest carbon cycling and response to change (due in part to a paucity of data) is the most significant source of terrestrial uncertainty in projections of Earth’s future climate. Here we provide an ecological perspective on aspects of tropical forest structure and function that will present distinctive challenges to the Earth System Modeling community. Specifically, we will discuss: (1) high diversity of species, climate, soil types, and land use history within and among tropical forests and how this diversity influences forest responses to perturbation; (2) nutrient regulation of tropical carbon cycling responses to global change, including limitation by phosphorus; and (3) a lack of physiological data specific for tropical plant and microbial communities (e.g., photosynthetic optima, soil microbial carbon use efficiencies). With the goal of determining which processes and/or measurements should be better constrained in order to improve the capacity to model the tropics, we will examine a set of relevant Earth System Model parameters in the context of data synthesized from the literature and of new tropical forest physiological measurements we have recently made. The objective of this talk is not to discourage modelers from attempting to model the tropics, but rather to support this important work by offering research directions likely to reduce uncertainty in future predictions of Earth System Models.