ecological indicators 9 (2009) 812–817
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/ecolind
Short communication
Answers to common questions in Ecological Footprint
accounting
Justin Kitzes *, Mathis Wackernagel
Global Footprint Network, 312 Clay Street Suite 300, Oakland, CA 94607, USA
article info
Article history:
Received 21 May 2008
Received in revised form
25 August 2008
Accepted 21 September 2008
Monfreda et al., 2004; WWF, 2006; Galli et al., 2007; Kitzes et al.,
1. Introduction 2007, 2008), and these publications have engendered specific
critiques and commentary (Van Den Bergh and Verbruggen,
The Ecological Footprint measures the amount of biologically 1999; Chambers, 2001; George and Dias, 2005; Schaefer et al.,
productive land and water area required to support the 2005). The resulting discontinuous back-and-forth dialogue
demands of a population or productive activity. Since its has created a great deal of confusion among both the general
creation more than 15 years ago by William Rees and Mathis public and practitioners in the field, and few attempts have
Wackernagel (Wackernagel, 1991a,b; Rees, 1992; Wackernagel been made in recent years to systematically lay out the
and Rees, 1996), Ecological Footprint accounts have been fundamental framework of Ecological Footprint accounting in
created for nations (Wackernagel and Rees, 1996; Bicknell a public forum.
et al., 1998; Van Vuuren and Smeets, 2000; Ferng, 2001; Haberl This article aims to help clarify the discussion surrounding
et al., 2001; Lenzen and Murray, 2001; McDonald and Patterson, Ecological Footprint accounting methodology by providing
2004; von Stokar et al., 2006; WWF, 2006; Moran et al., 2008), brief answers to 16 common questions often asked about
cities and regions (Folke et al., 1997; Wackernagel, 1998; Best Ecological Footprint accounting.
Foot Forward, 2002; Bagliani et al., 2003; EPA Victoria, 2005;
Walsh et al., 2006; Lammers et al., 2008), businesses (Barrett
and Scott, 2001; Lenzen et al., 2003), and individuals (Redefin- 2. Questions and responses
ing Progress, 2002; EPA Victoria, 2008). Across scales, analysts
apply Ecological Footprint accounting methods to understand We compiled these questions from technical support
a population’s or activity’s demand for the planet’s limited queries sent to Global Footprint Network (www.footprint-
capacity to provide a range of ecosystem goods and services. network.org), an international non-governmental organiza-
The basic methodologies behind Ecological Footprint tion dedicated to advancing the science and application of
accounting have been widely published in various forms the Ecological Footprint, from summer 2005 through spring
(Wackernagel et al., 1996; Ferng, 2001; Lenzen et al., 2001; of 2008.
* Corresponding author.
E-mail address: justin@footprintnetwork.org (J. Kitzes).
1470-160X/$ – see front matter # 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ecolind.2008.09.014
, ecological indicators 9 (2009) 812–817 813
Responses are grouped into three categories, covering hectares are hectares with world-average productivity for all
general accounting methods and principles, the relationship productive land and water areas in a given year. The use of a
of the Ecological Footprint to specific environmental concerns, common unit makes Ecological Footprint results globally
and matters of interpretation and application of the Footprint comparable, similar to financial assessments that use one
indicator. All replies are based on an Ecological Footprint currency such as dollars or Euros to compare transactions and
framework and basic concepts of the original Wackernagel financial flows throughout the world.
and Rees (1996). Ecological Footprint book, subsequent
extensions (Monfreda et al., 2004; Kitzes et al., 2007), and How is an Ecological Footprint calculated?
current Ecological Footprint Standards (Global Footprint Net-
work, 2006). Other authors who have employed very different Ecological Footprints can be calculated for individual
methods (e.g., Lenzen et al., 2007) may propose responses people, groups of people (such as a nation), and activities
differing from those below. (such as manufacturing a product).
Interested readers who wish to review more background on The Ecological Footprint of a person is calculated by
Ecological Footprint methodology, or read beyond the brief considering all of the biological materials consumed, and all
responses here, are encouraged to begin by consulting of the biological wastes generated, by that person in a given
Wackernagel and Rees (1996), Ferng (2001), Lenzen and Murray year. These materials and wastes each demand ecologically
(2001), Monfreda et al. (2004), and Kitzes et al. (2007, productive areas, such as cropland to grow potatoes, or forest
forthcoming). to sequester fossil carbon dioxide emissions. All of these
materials and wastes are then individually translated into a
2.1. Methodology required number of global hectares.
To accomplish this, the amount of material consumed by
What is the definition of the Ecological Footprint? that person (tonnes per year) is divided by the yield of the
specific land or sea area (annual tonnes per hectare) from
The Ecological Footprint is a resource accounting tool that which it was harvested, or where its waste material was
measures how much biologically productive land and sea is absorbed. The number of hectares that result from this
used by a given population or activity, and compares this to calculation are then converted to global hectares using yield
how much land and sea is available, using prevailing and equivalence factors (Galli et al., 2007). The sum of the
technology and resource management schemes (Rees, 1992; global hectares needed to support the resource consumption
Wackernagel et al., 1996). Productive land and sea areas and waste generation of the person gives that person’s total
support human demands for food, fibre, timber, energy, and Ecological Footprint.
provides space for infrastructure. These areas also absorb the The Ecological Footprint of a group of people, such as a city
waste products from the human economy. The Ecological or nation, is simply the sum of the Ecological Footprint of all
Footprint measures the sum of these areas, wherever they the residents of that city or nation (e.g., EPA Victoria, 2005). It is
physically occur on the planet. These physical areas are often also possible to construct an Ecological Footprint of Production
weighted according to their relative productivity and for a city or nation, which instead sums the Ecological
expressed in global hectares. Footprint of all resources extracted and wastes generated
within the borders of the city or nation.
What is the specific research question behind Ecological Footprint The Ecological Footprint of an activity, such as producing a
accounting? good (an airplane) or service (providing insurance), is
calculated in a similar manner by summing the Ecological
Ecological Footprint accounts answer a specific research Footprint of all of the material consumed and waste generated
question: how much of the regenerative biological capacity during that activity. When applying Ecological Footprint
of the planet is demanded by a given human activity? analysis to a business or organization, analysts must clearly
Activities here may refer to a population’s consumption of define the individual activities to be included within the
resources, the production of a good, or the provision of a boundaries of that organization. The carbon dioxide emitted
service. directly from fuel combustion in an airplane, for example,
To answer this question, the Ecological Footprint measures could be allocated entirely or partially to the airline business,
the amount of biologically productive land and water area an the company that financed the airplane, the company that
individual, a city, a country, a region, or all of humanity uses to built the airplane, the businesses or individuals using the
produce the resources it consumes and to absorb the waste it airplane, and so forth. Organizational Ecological Footprint
generates under current technology and resource manage- studies should clearly document the boundary assumptions
ment practices. This demand on the biosphere can be associated with each study (Global Footprint Network, 2006).
compared to biocapacity, a measure of the amount of
biologically productive land and water available for human How does the Ecological Footprint address waste flows?
use. Biologically productive land includes areas such as
cropland, forest, and fishing grounds, and excludes deserts, Waste is associated with all human activities, and hence is
glaciers, and the open ocean. an integral part of Ecological Footprint analysis. From an
Studies that are compliant with current Ecological Foot- Ecological Footprint perspective, the term ‘waste’ includes
print Standards (Global Footprint Network, 2006) use global three different categories of materials, and each category is
hectares (Monfreda et al., 2004) as a measurement unit. Global treated differently within Footprint accounts.
