Mathis Wackernagel: The Ecological Footprint

The developer of the ecological footprint concept, Mathis Wackernagel, is interviewed. He defines the concept by a financial analogy, and thus ecological footprints are our world’s ecological capital. Wackernagel continues with the financial analogies likening our current ecological depletion of 25-30% as going into bankruptcy. How is a person’s or country’s ecological footprint calculated?