Others were of the view that it is necessary to show the long-term limits of resource use in an easily understandable manner that allows communication to the broad public. The concepts of factor 4 and factor 10 are simple and visible instruments that can alert the broad public to the need to increase the resource efficiency of our society. There was an agreement that there is a need for differentiation and prioritization between various resources and their use since the impacts linked to some of them are worse than others. The question was raised how much such concepts should be underpinned by more detailed scientific analysis. There seemed to be an agreement that movement of mass alone is not a good parameter for prioritization but that it needs to be supplemented by qualitative parameters.
Important issues are also the contribution to climate change, accumulation of metals in soils etc.
Carrying capacity - ecological footprints Like the concepts of factor 4 and 10, the ecological footprints are an instrument to make complex problems understandable to a broader public. They evaluate competing options for the use of limited land surface to show how much of these resources we are currently using compared to the long-term carrying capacity of the planet which preserves the natural capital and prevents climate change. Again, a key issue is whether the underlying goal is strong or weak sustainability, on which there were different views among the experts. For policy making, the footprints can give broad indications as to where we stand in overall resource use but in detail more factors such as technological change, evolution of human consumption patterns over time etc. need to be taken into account. The contribution of thermodynamics to the discussion on market failures in the context of resource use is not fundamentally different from other concepts but uses the specific parameter of exergy as a yardstick for measuring the impacts of resource use.