Isnt the footprint a bit too simplistic?
For sure, it would be ideal to model the total complexities of the worlds ecological systems, but this would require another planet! Some level of abstraction is not only inevitable but perfectly adequate for many applications. The ecological footprint is certainly one of the simpler models that describe human use of nature but one which serves a well defined purpose. Essentially, the ecological footprint is a planning tool to help people understand and deal more effectively with ecological limits. To be an effective planning tool, it is not necessary to have a sophisticated model of how nature works, but rather one which is easy to grasp. In this respect it acts as a least common denominator model of natures function.
