Convergence of ecological footprint and emergy analysis as a sustainability indicator of countries: Peru as case study

Abstract

In the last decade, two scientific tools have been extensively used worldwide to measure the human impact on nature: ecological footprint (EF) and emergy analysis (EA). Papers trying to combine the strong points of EF and EA, and obtain more accurate results have appeared in scientific literature, in which Zhao’s et al. (2005) [61] approach is an important one. Unfortunately, some weak points of the original methods still remain on the new approaches proposed. The aim of this present work is to discuss some weak points found in Zhao’s approach, trying to overcome them through a new approach called emergetic ecological footprint (EEF). The main difference between Zhao’s approach and EEF is that the last one accounted for the internal storage of capital natural in the biocapacity calculation. Besides that, soil loss and water for human consume were considered as additional categories in the footprint calculation. After discussing it through comparisons with other approaches, EEF was used to assess Peru as a case study, resulting in a biocapacity of 51.76 gha capita⁻¹ and a footprint of 12.23 gha capita⁻¹, with 2004 data; that resulted in an ecological surplus of 39.53 gha capita⁻¹. The load capacity factor obtained was 4.23, meaning that Peru can support a population 4.23 times bigger considering the life style of 2004. The main limitations of the EEF are: (i) it is impossible to make comparisons between the biocapacity and footprint for each category; (ii) a need for a handbook with emergy intensity factors with good quality. On the other hand, the main positive points are: (i) its easiness of application in global and national scales; (ii) its final indicators account for all the previous energy (or emergy) used to make something; (iii) internal natural capital storage was accounted for in the biocapacity calculation, which can be a valid step towards the evaluation and assess of services provided by nature.

Introduction

Sustainability indicators for any system are essential subsidies for decision makers, mainly nowadays when the planet is facing environmental and social problems. Several methods are being used aiming to supply sustainability indicators, focusing on specific aspects, for instance emergy analysis [29], ecological footprint [57], material flow accounting [39], embodied energy analysis [46], exergy analysis [47], modified GDP’s, among others. In fact there is not only one indicator able to accomplish that work [43]. Singh et al. [45] comment that indices and rating systems are subjective despite the relative objectivity of the methods employed in assessing the sustainability. Wilson et al. [60] argue that different approaches reach various interpretations about the sustainability of nations, and emphasize the lack of clear direction at the global level in how to approach sustainable development. Ulgiati et al. [50] suggest using different methods with various indicators to assess the sustainability in a proper way, in which each methodology should be used in accordance with its specific rules.

We deal in this paper with two approaches considered as good alternatives to provide sustainability indicators: ecological footprint (EF) and emergy analysis (EA). Detailed description about these two methodologies can be found in Odum [29], Brown and Ulgiati [3], Ulgiati and Brown [51], Wackernagel et al. [57] and Venetoulis and Talberth [55]. Ecological footprint is able to present its results in an easy-to-understand language, while the strong point of emergy analysis is the capacity to account for all the work done by nature and human-economy in the production of resources used by the economy.

Ecological footprint is a widely used tool by ecological and political communities, stimulated by its didactic way of showing the impact of society on nature as the productive surface needed to support their consumption and waste generated. Even so, it has received strong critiques, as it happens with all the tools that try to evaluate such a complex concept as sustainability [53], [1], [25], [31], [36], [54], [55], [59], [20].

Ecological footprint is also known as EF-GAEZ, because it uses several indices from the global agricultural ecological zones (GAEZ) prepared by Food and Agriculture Organization of United Nations Organization (FAO). GAEZ indices are used to calculate the equivalence factors. These factors represent the world’s average potential productivity of a given bioproductive area relative to the world average potential productivity of all bioproductive areas. According to Wackernagel et al. [57], cropland, for example, is more productive than rangeland or pasture, and so, has a larger equivalence factor than pasture. Despite its popularity, EF authors recognize that these factors are considered a weak point of the methodology, since important natural processes are underestimated resulting in the increase of the footprint¹ and reduction of the biocapacity.² Some weak points of the EF method are described in the following lines:

• EF-GAEZ accounts for each type of area only once, even if the area supplies two or more ecosystem services. This does not happen with forest areas that are considered twice, firstly as bioproductive area to supply forest products and secondly as available area to absorb CO₂ emissions [26]. Even so, forest areas supply other ecosystems services that are not accounted in biocapacity, for instance maintenance of hydrologic cycle, top soil conservation, filtration of solid and atmospheric pollutants, and so on. Oceans, croplands and pasture areas also absorb CO₂ from atmosphere and should be accounted for. Some areas with low biomass productivity, such as mountains, deserts, tundra, and iceland are not accounted for in the EF-GAEZ method [55], but should be considered in the biocapacity calculation, because they produce ecosystems services and contribute to the global system functioning.

• EF-GAEZ accounts for fossil fuel through CO₂ emissions (or CO₂ equivalent), even if it is possible to evaluate this footprint by the area demanded to sustain an alternative production of bio-fuel (fuel from biomass). This methodology assumes a carbon sequester ratio of 0.95 tonC ha⁻¹ year⁻¹[57], based on studies of the CO₂ absorbed by forests considering data from 1980 to 1990. It does not consider the CO₂ absorbed by others biomes and assumes that the ratio does not change over time.

• EF-GAEZ does not consider the human-labor and the embodied energy in materials. Some studies about embodied energy have suggested that global current footprint could be approximately 30% larger [22]. That author recognizes the importance of improving the methodology in this sense.

• EF-GAEZ does not include the footprint derived from water use. The use of water for agricultural and industrial productions, urban areas and for human direct consume can be considered a secondary function in some places of the world, but in others where water is scarce, human use competes with primary functions of biomes. Besides that, half of the water supplied by rivers and lakes is used in human processes nowadays [13]. Water use is an important issue around the world and it is being considered in some methodologies that include it as a relevant category, such as material flow accounting [39] and water footprint [15], [10].

• EF-GAEZ does not consider some important aspects of sustainability as top soil loss, production of solid residues, liquid effluents and most gas emissions (it only considers CO₂ emission). Soil erosion and excessive production of waste can damage primary functions of biomes, thus, it is very important to know their impact on the environment. However it is hard to find data about these impacts, making it impossible to be considered in the EF-GAEZ method. This fact probably results in an underestimation of the true impact on the environment.

The other methodology considered in this paper is the emergy analysis, proposed in the eighties by Odum [28] as a new method for integral evaluation to account for the quality of matter, energy and information within systems. Emergy analysis takes into account every contribution from nature and human economy in order to know the relative importance of each resource [28]. Since the real wealth can be measured by the work previously done to produce something, Emergy is considered a scientific measure of real wealth in terms of the energy previously required to make something [29].

Emergy analysis (EA) allows the accounting for additional flows that influence sustainability, such as waste, soil loss, human-labor, water use, among others. Besides that, all previous available energy used to make something is considered in the calculation procedure, presenting the energy memory of the product or process in the final indicators. On the other hand, EA presents some deficiencies, mainly those related to criteria and accuracy. Below, there is a brief description of the deficiencies on the emergy methodology that we consider important for the purpose of the present paper:

• EA does not define which is its sustainability indicator. Possible indicators are renewability (%R, [3]) or emergy sustainability index (ESI, [49]). Some published papers consider ESI as the sustainability indicator, but others consider the %R, or even all emergy indices assessed at the same time.

• Renewability and emergy sustainability index do not have standards. For example, some authors indicate that in a long time perspective systems with high values of renewability emergy index are acceptable [3], but what is the minimum value of renewability to be considered sustainable? For processes and products, the use of ESI index is more enlightening. Brown and Uligiati [3] indicate that for values of ESI below 1, products and processes are not sustainable at a long time period, while they are rather sustainable if ESI equals 1, and clearly sustainable for ESI higher than 5.

• Assuming a country’s emergy assessment, only the biggest natural renewable flow is considered to avoid double accounting [29]. That procedure occurs, because all of the natural emergy flows come from the same emergy baseline. That approach may be a temporary solution, but the methodology does not consider the flows from internal natural capital storages that produce several environmental services and contribute to the health of human-dominated systems. As well as non-renewable internal storages such as soil, minerals, natural gas, coal, and so on are considered in the analysis, we believe that natural capital should be accounted for as a natural renewable resource.

• The lack of available emergy intensity³ factors with good quality is a deficiency of the emergy methodology. We consider that the International Society for the Advancement of Emergy Research (ISAER, http://www.emergysociety.org) could elaborate a handbook with several emergy intensity factors with controlled quality, taking into account different criteria for that purpose as numeraire (energy, exergy or mass), emergy baseline, technology and calculation year.

By far, strong points overcome weakness on both ecological footprint and emergy analysis methods. Knowing their limitations and advantages allows an attempt for their mutual improvement. The objective of this work is to discuss a potential convergent approach between EF-GAEZ and EA, and apply it to a case study.