Since its development by Wackernagel and Rees in the 1990s, Ecological Footprint Analysis (EFA) has become one of the most popular means of accounting for human use of Earth's resources (Kitzes et al 2009a). It involves calculating the area of land required to sustain a particular activity or lifestyle through production of raw materials and assimilation of wastes. This land requirement is known as the 'ecological footprint', and can be compared with the actual available area or 'biocapacity'. An ecological footprint greater than biocapacity is possible through importation of resources from elsewhere or through liquidation of natural capital, although at a global level such 'overshoot' is unsustainable. An ecological footprint lower than biocapacity is deemed sustainable, at least in land use terms, with the leftover biocapacity being available for use by other species. EFA thus allows an assessment of the extent to which the Earth can sustain both human consumption and biodiversity (Chambers et al 2000).
At a national or regional level, the most robust method of calculating an ecological footprint is the 'compound' method, in which total consumption (production plus net imports) of different materials is multiplied by the land area required to produce a unit of each resource sustainably. The area required for the absorption of biodegradable wastes is also considered. Where such information is unavailable, footprints may be estimated instead by a 'component-based' method, in which data on major activities, such as the number of passenger kilometres travelled by car, are multiplied by pre-calculated average footprints for each activity (Chambers et al 2000). Input-output tables of production and consumption can be used as a source of data, though there may be uncertainties involved in converting monetary values into land use figures (Beynon & Munday 2008).
Land requirements of six types are considered in EFA: cropland, grazing land, forest land, built-up land, fishing 'land' (productive marine areas) and carbon uptake land (the area of forest required to absorb CO2 emissions). Required land areas of each type are normalised to account for differences in biological productivity and added up to produce a total ecological footprint expressed in global hectares, a unit of land area representing a hectare of world average productivity (Ewing et al 2008b). A standardised method for calculating ecological footprints, used by over 70 organisations, has been developed by the Global Footprint Network and is periodically updated to incorporate improvements in data sources and methodology (Kitzes et al 2009a).
To products and processes
EFA may be used as a decision-making tool to help consumers, businesses and governments evaluate the environmental impact of different product, process, policy and lifestyle options (Stoeglehner & Narodoslawsky 2008). At the consumer level, a recent popular book on sustainable living makes extensive use of ecological footprinting to inform the reader, for example, that the environmental impact of producing a cotton suit is nearly twice that of a linen suit and more than triple that of a hemp suit, and that organic food production has an impact 40% lower than conventional farming (Vale & Vale 2009). EFA can be used to highlight which aspects of product's life cycle have the greatest environmental impact and should therefore be targeted for improvement - showing, for example, that most of the footprint of a Tuscan wine is due to the grape cultivation and packaging processes (Niccolucci et al 2008). However, whilst EFA is useful for products and activities that are highly energy-intensive or land-demanding, it is inadequate for evaluating product categories associated with high levels of mineral extraction or toxic metal waste, since these impacts are beyond the scope of the ecological footprint (Huijbregts et al 2008).
To geographical areas
EFA has been used to evaluate the total environmental impact of different countries, and determine which are living within their own biocapacity and which are in 'ecological deficit' (Ewing et al 2008a). However, some disagree with the use of ecological deficit as an indicator of national or regional sustainability, arguing that such assessments deny the potential benefits of trade in distributing environmental burden to the areas best able to cope with it (Van den Bergh & Verbruggen 1999), and that self-sufficiency and fairness should not be confused with sustainability (Costanza 2000).
A less controversial use of ecological footprint data has been to draw attention to the differences in consumption levels between richer and poorer countries. The Global Footprint Network calculates that high income countries have an average footprint of 6.4 global hectares per person, more than six times that of low income countries, and three times what the Earth could sustain if its entire population lived similarly rich lifestyles (Ewing et al 2008a). Such findings highlight in a dramatic way the need for sustainable development, and the environmental danger inherent in pursuing development in a 'business-as-usual' way.
Local and regional footprinting can also help encourage sustainability initiatives. A 2003 report by the Greater London Authority, for example, concludes that London's footprint is not only far larger than the city's biocapacity (unsurprisingly), but also larger than its citizens' 'fair Earth share', and makes practical suggestions for reducing this footprint (GLA Economics 2003).
A major benefit of EFA over related metrics such as energy use and human appropriation of net primary production is that provides a clear, non-arbitrary threshold of sustainability: the level at which ecological footprint exceeds biocapacity (Haberl et al 2004). Probably the most widely-reported conclusion to emerge from EFA is that, since the 1980s, humanity's total ecological footprint has exceeded the Earth's entire biocapacity (see chart) - seemingly clear evidence that the planet's resources are being used at an unsustainable rate (Ewing et al 2008a). However, this conclusion is sensitive to the way in which carbon emissions are accounted for (see below).
Limitations and criticisms
Despite EFA's apparent comprehensiveness, it does not capture all human impacts on the environment. As a measure of the land required for sustainable living, it cannot account for "inherently unsustainable" activities such as the depletion of non-renewable resources or the accumulation of non-biodegradable wastes, though the immediate land and energy demands of mineral extraction and waste disposal do feature in ecological footprints (Ewing et al 2008a). It is also difficult for EFA to incorporate ecological services such as water catchment which require a certain area of land but do not exclude the land from other uses. Such non-exclusive land use may be counted as a 'shadow footprint' and reported alongside the main footprint (Chambers et al 2000), but the simplicity of a single metric is then lost.
Another generally-accepted shortcoming of EFA is that it is a static measure which fails to capture long-term degradation of land, such as through soil depletion. Indeed, EFA might actually encourage such negative effects by promoting the intensification of land use (Fiala 2008). Land degradation will show up as reduced biocapacity in future footprint analyses, but EFA does not provide a dynamic way of modelling such changes (Kitzes et al 2009a). The failure to capture ongoing changes in land use allows certain countries with high rates of land clearance and natural capital depletion, such as Brazil and Indonesia, to score undeservedly well in national footprint comparisons (Lenzen & Murray 2003). Niccolucci et al (2009) suggest that this shortcoming of EFA might be redressed by introducing the concept of 'footprint depth', a measure of the erosion of natural capital, alongside footprint area.
The lack of an explicit social welfare dimension in EFA has also been commented upon (e.g. Ewing et al 2008a), although EFA does provide a tool for highlighting and exploring inequalities in land and resource use (White 2007).
The treatment of energy consumption and fossil fuel use in EFA has been the subject of controversy. Fossil fuel use is conventionally dealt with by the inclusion of 'carbon uptake land' in the footprint, but this approach has been criticised on the grounds that carbon uptake is not a sustained ecological service - forests sequester little or no CO2 once mature - and that it is unnecessary to assume that all of humanity's CO2 emissions need to be absorbed (e.g. Fiala 2008). Defenders of the existing methodology point out that no accumulation of atmospheric CO2 can be sustained indefinitely; total carbon sequestration is thus a precondition for sustainability (Kitzes et al 2009b). Possible alternative ways of incorporating fossil fuel use into EFA include calculating the land area required to produce an equivalent amount of biofuel, or reducing biocapacity to account for projected losses in productivity due to climate change (Kitzes et al 2009a). The land required to renew fossil fuels through natural carbon deposition may also be calculated, although this method produces extremely high footprint areas (Stöglehner 2003).
Another area of debate is the way in which trade is accounted for in EFA. Currently, exports count towards the footprint of the consuming country or region (with the exception of tourism, a methodological inconsistency that needs to be addressed), though it has been argued that responsibility should be split between producers and consumers, since producers also derive an economic benefit from the activity (Kitzes et al 2009a, Scotti et al 2009).
A somewhat unrealistic assumption of ecological footprinting is that all biological productivity within the footprint area is appropriated for human use. Lenzen and Murray (2003) present a modified form of EFA which takes into account varying degrees of land disturbance, and gives significantly different results from conventional EFA when applied to Australia. This method arguably captures humanity's ecological impact in a more comprehensive way, although it provides no insight into whether the observed degree of impact is within the tolerance of ecosystems.
The ability of ecological footprinting analysis to combine numerous categories of resource use into a single, easily-understood figure, with a clear threshold that should not be exceeded, at least at a global level, makes it a valuable tool for assessing and communicating the demands placed on the environment by human activity. Though EFA does not make dynamic predictions about the future, it does allow straightforward comparison of the sustainability implications of different choices. Whilst EFA's proponents freely acknowledge that it does not capture every human impact on the environment - impacts that cannot be expressed in terms of exclusive, sustainable land requirements cannot easily be incorporated - they argue that it does at least establish a minimum criterion for sustainability (e.g. Fitzes et al 2009b). There is a danger, however, that too narrow a focus on ecological footprinting will lead to an emphasis on quantity of land use over quality, encouraging overuse and degradation of land, and to the neglect of other important dimensions of sustainability. Although EFA has great power as an aggregate metric, it needs to be integrated with other analytical tools in order to provide a complete measure of sustainability.
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This was originally written as an essay for MSc Ecological Economics at the University of Edinburgh