Footprinting essentially accounts the use of the planet's renewable resources (its 'interest' rather than its 'capital'). Non-renewable resources are accounted for only by their impact on, or use of, renewable, bioproductive capacity.

The footprint deals only with demands placed on the environment. It does not attempt to include the social or economic dimensions of sustainability.

The footprint is a 'snapshot' estimate of demand usually based on data from a single year. Both available supply (the biocapacity) and the eco-efficiency of the economy can change over time which is why it is not possible to forecast or 'backcast' footprints from current data although it is possible to make assumptions about future consumption and thus create informative, but speculative, scenarios.

The use of bioproductive area as an aggregate unit makes it a powerful and resonant means of measuring and communicating environmental impact and sustainability. In this sense it is comparable to many economic indicators such as the Retail Prices Index (RPI), Gross Value Added (GVA) and Gross Domestic Product (GDP).

To find out more read this short primer (25KB) on the ecological footprint. See also our answers to frequently asked questions about the ecological footprint.

Several critiques of the ecological footprint exist (notably VROM-Council 1999, Van Kooten and Bulte 2000, van den Bergh and Verbruggen 1999, Pearce 2000). These reviews contain a mix of positive and negative comments relating to the application of the methodology as well as suggestions for improving its structure and use. Click here to read these criticisms and some reponses to them.