The Shoe Fits, but the Footprint is Larger than Earth

In their Perspective in this issue of PLOS Biology, Blomqvist et al. [1] set out to demonstrate that ‘‘Ecological Footprint measurements, 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 productive 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 Ecological Footprints. Global Footprint Network has developed national Footprint accounts, using consistent United Nations data sets to provide both Footprint and biocapacity assessments of most nations [2–4]. One can therefore readily compare national and global Footprints with domestic and global supplies of biocapacity, respectively. This comparison helps to shed light on core research questions fundamental to human wellbeing and sustainability: How does a population’s consumption-based demand compare to its domestic biocapacity? Is the population dependent on local overuse, netimports, or net-appropriations from the global commons? How do various nations/populations compare and what are the trends over time? At the global scale, is H. sapiens living within the regenerative means of nature? Global Footprint Network’s most recent accounts reveal that Earth’s biocapacity in 2008 was 12 billion hectares (ha) compared to humanity’s Footprint of 18.2 billion ha, and that the average Ecological Footprint had reached 2.7 global hectares (gha) per capita compared to only 1.8 gha of available biocapacity per capita [5]. (A global hectare is a hectare of global average productivity.) This difference means that humanity is in ecological overshoot, currently using at least 50% more of nature’s goods and services than ecosystems regenerate [5–7]. These national Footprint estimates are conservative since data limitations prohibit consistent adjustments to account reliably for the over-exploitation of ecosystems (see below), and carbon dioxide, mainly from fossil fuel and cement production, is the only waste stream considered. They nevertheless constitute the most comprehensive assessments of the ecological status of nations available. Independents tests of the method are, of course, essential. In the past few years over a dozen national and international government agencies have reviewed the National Footprint Accounts for their countries (see www.footprintnetwork.org/reviews). The French Ministry of Sustainable Development, for example, independently recalculated the French Footprint from 1961 to today obtaining results within 1–3 percent of Global Footprint Network’s assessments [8].