Framework for thermodynamic constraints on sustainability

This article explores concepts and methods to characterize long-term limits on the capacity of technology to deliver energy services based on thermodynamics, or more generally, physical laws. Carnot's law, for example, places an upper limit in the ability of a heat engine to deliver useful work. The framework developed starts with characterizing different energy services deemed necessary for a sustainable society: food/water, shelter, mobility and information/ communication. Scenarios can be developed which scope the degree of these services demanded in the future for a given level of lifestyle. The minimum energy inputs required to deliver these energy services can be estimated using physical law limits on the capacity of processes to harness energy and transform into services. The utility of this approach only applies if energy supply is constrained. This is a reasonable assumption if one assumes that risk mitigation limits consideration of energy sources to those currently useable (e.g. no fusion power). The bounding of technological progress requires assumptions of how energy sources are converted and used, denoted here as technology paths. While the limits for different technology paths are not estimated quantitatively in this article, I postulate that reasonably tightly constrained paths for food, shelter and mobility result in non-trivial energy demand even in the thermodynamic limit. More work is needed to explore how different assumption for technology paths and scenarios for human needs constrain future delivery of services.