Formal Comment The Shoe Fits, but the Footprint is Larger than Earth

[1] set out to demonstrate that ‘‘Ecological Footprint measure-ments, as currently constructed, are so misleading as to preclude their use in any serious science or policy context.’ ’ Should the reader be confident in this assessment or are Ecological Footprint methods and results adequate to guide sustainability policy? Their Perspective, ‘‘Does the Shoe Fit?’’, does not question the fundamental purpose of Footprint accounting. The method is designed to estimate human demand for biocapacity, defined as: ‘the aggregate area of land and water ecosystems required by specified human populations to produce the ecosystems goods and services they consume and to assimilate their carbon wastes.’ Footprint accounting is thus based on the premise that the regenerative capacity of the ecosphere is associated with produc-tive ecosystem area. The production of food and fibre; the urbanization of once agricultural or forested lands; and the sequestration of that portion of carbon emissions from fossil fuels that is not already absorbed by oceans or by long-term sequestration strategies in agriculture or forestry, all constitute competing or non-overlapping uses of ecosystems. (Typically, one cannot simultaneously use paved-over land for food production or forest products; today’s cropland and commercial forests are usually carbon sources, not sinks). We estimate and sum these separate areas to estimate study populations ’ total Ecologica