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Towards a 3D National Ecological Footprint Geography
Ecological Modelling 222 (2011) 2939–2944
Contents lists available at ScienceDirect
Ecological Modelling journal homepage: www.elsevier.com/locate/ecolmodel
Towards a 3D National Ecological Footprint Geography V. Niccolucci a,∗ , A. Galli b , A. Reed b , E. Neri c , M. Wackernagel b , S. Bastianoni c a
Ecodynamics Group, Dept. of Chemistry, University of Siena, via della Diana 2A, 53100 Siena, Italy Global Footprint Network, 312 Clay Street, Suite 300, Oakland, CA 94607, USA c Ecodynamics Group, Dept. of Chemistry, University of Siena, via A. Moro 2, 53100 Siena, Italy b
a r t i c l e
i n f o
Article history: Available online 27 May 2011 Keywords: Ecological Footprint Flow Footprint size Footprint depth Stock
a b s t r a c t In the last decades several indicators have been proposed to guide decision makers and help manage natural capital. Among such indicators is the Ecological Footprint, a resource accounting tool with a biophysical and thermodynamic basis. In our recent paper (Niccolucci et al., 2009), a three dimensional Ecological Footprint (3D EF) model was proposed to better explain the difference between human demand for natural capital stocks and resource flows. Such 3D EF model has two relevant dimensions: the surface area (or Footprint size – EFsize ) and the height (or Footprint depth – EFdepth ). EFsize accounts for the human appropriation of the annual income from natural capital while EFdepth accounts for the depletion of stocks of natural capital and/or the accumulation of stocks of wastes. Building on the 2009 Edition of the National Footprint Accounts (NFA), global trends (from 1961 to 2006) for both EFsize and EFdepth were analyzed. EFsize doubled from 1961 to 1986; after 1986 it reached an asymptotic value equal to the Earth’s biocapacity (BC) and remained constant. Conversely, EFdepth remained constant at the “natural depth” value until 1986, the year in which global EF first exceeded Earth’s BC. A growing trend was observed after that. Trends in each Footprint land type were also analyzed to better appraise the land type under the higher human induced stress. The usefulness of adopting such 3D EF model in the National Footprint Accounts was also discussed. In comparing any nation’s demand for ecological assets with its own biocapacity in a given year, four hypothetical cases were identified which could serve as the basis for a new Footprint geography based on both size and depth concepts. This 3D EF model could help distinguish between the use of natural capital flows and the depletion of natural capital stocks while maintaining the structure and advantages of the classical Ecological Footprint formulation. © 2011 Elsevier B.V. All rights reserved.
1. Introduction About thirty years ago Prof. Enzo Tiezzi, published the first Italian edition of his most famous book Tempi Storici Tempi Biologici (Tiezzi, 1984) then translated in English as The end of time (Tiezzi, 2003). He wrote: “[. . .] It is my firm conviction that we must change route as soon as possible and set about defining a new idea of development. A culture so based will be firmly founded on biology and thermodynamics, and their fundamental relationship to the economy, the society and the means of production. My conviction is based on three points: (a) the equilibrium of nature is extremely delicate and can be irreversibly upset by man: the resources of nature are not infinite; (b) the destruction of the environment and waste of natural resources is never of long term benefit either economically or socially; (c) the false prosperity of the consumer
∗ Corresponding author. Tel.: +39 0577232044; fax: +39 0577232004. E-mail address: [email protected] (V. Niccolucci). 0304-3800/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ecolmodel.2011.04.020
society is based on the exploitation of three classes of people [. . .]. Dominant economic theory, based as it is on mechanistic principles, remains ignorant of the law of entropy and the role of the time variable. The classical dynamic concept of time and its reversibility, has nothing to do with reality and nature. Time is not without its preferred directions (it is not isotropic) as is space. Time has a direction. Thermodynamics introduces “knowledge of the unidirectional flow of time”, traces the limit between past reality and future uncertainty, indicates the orientation of time in natural processes. [. . .] The technological or economic concept of time is exactly the opposite to entropic time. Nature obeys different laws to economics, it works in “entropic time”: the faster we consume natural resources and the energy available in the world, the less time is left for our survival. Technological time is inversely proportional to entropic time, economic time is inversely proportional to biological time. Our limited resources and the limited resistence of our planet and its atmosphere clearly indicate that the more we accelerate the energy and matter flow through our Earth system, the shorter is the life span of our species [. . .].” It is then important to underline “[. . .] the
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asymmetry of the ecological and historical time scales: millions of years for the evolution of life on the Earth with extremely slow ecological changes and historical knowledge of only the last brief period (a few thousand years); in contrast to this, the rapid ecological changes induced by technology in very short historical time. [. . .] Biological and historical tempos follow different rhythms”. Tiezzi’s thought represents the milestone from which a three dimensional Ecological Footprint (3D EF) model (Niccolucci et al., 2009) was developed. Although the ‘classical’ Ecological Footprint (EF) method recognizes the crucial role of natural capital and natural income (Rees, 2006), it is not sufficiently informative regarding the differentiation between biophysical stocks and flows. Already in the early ‘90s, economists belonging to the “thermodynamic school of thought” such as Daly and Georgescu-Roegen (Daly and Farley, 2004), widely highlighted the implications of a stock/flow distinction in dealing with sustainability issues. For instance, three operational rules defining the condition of ecological (thermodynamic) sustainability were identified by Daly (1990): (i) renewable resources such as fish, soil, and groundwater must be used no faster than the rate at which they regenerate; (ii) non-renewable resources such as minerals and fossil fuels must be used no faster than their renewable substitutes can be put in place; (iii) pollution and wastes must be emitted no faster than natural systems can absorb, recycle, or render them harmless. Making the role of time explicit within the EF methodology has therefore represented an important step towards a deeper interpretation of this indicator in the sustainability framework and could help the EF to better appraise Daly’s rules. As such, the ability to track depletion of natural capital stocks and use of natural capital flows plays a central role within this new approach. The aim of this paper is to test whether the 3D EF model recently proposed (Niccolucci et al., 2009) can serve as a useful biophysical measure of the flows and stocks used by a population. To address some of the unanswered questions from the previous paper, global trends for both the size and the depth components of the EF are analyzed here. These trends have been broken down by land type to highlight the areas under critical stress. Finally, the 3D EF model is suggested as proxy to redefining a new world geography based on the differentiation between flow and stock. 2. Ecological Footprint and natural capital accounting Historically the Ecological Footprint has been presented as a spatial indicator for natural capital accounting (Rees, 1992). The EF of a population or an individual is defined as the aggregated area of land and water1 required on a continuous basis to provide the energy and material resource flows used and to assimilate the CO2 emissions generated, given prevailing technologies and resource management practices (Wackernagel and Rees, 1996). From a thermodynamic point of view, the Ecological Footprint can be defined as the area continuously required to generate, via photosynthesis, a quantity of biomass, and thus negentropy, equivalent to the amount used and dissipated by the population’s consumptive activities (Rees, 2006). EF accounts for both direct and indirect land requirements and it is measured in global hectares (gha) (Wackernagel and Rees, 1996; Wackernagel and Kitzes, 2008). The term global refers to a normalized hectare with world average productivity (Galli et al., 2007; GFN, 2009). Land area is a very effective proxy to communicate the finiteness of planet Earth and its ability to generate resources (Wackernagel and Rees, 1997).
To give a measure of the (un)sustainability threshold of human consumption, a benchmark called biocapacity (BC) is also provided (Wackernagel and Rees, 1996; Monfreda et al., 2004), which quantifies how much regenerative capacity exits within a given area, in terms of ecologically productive space. BC is also measured in global hectares (gha) (Galli et al., 2007; GFN, 2009). As EF and BC represent flows of ecological assets (i.e., natural resources and ecological services), they can be directly compared to define an ecological balance in the same way that expenditure and income are compared in economics (Monfreda et al., 2004). The difference between the two terms is proportional to four main factors: (i) population size; (ii) consumption patterns, (iii) ecological productivity and (iv) technology. This ecological balance has significance both at the global and the national level: 䊉 At global level, the 2009 Edition of the Global Footprint Network’s National Footprint Accounts (GFN, 2009) show that the Earth is actually operating in a state of ecological overshoot (EO). Demand for natural resources exceeds the regenerative capacity of existing natural capital by 44% (GFN, 2009; Ewing et al., 2009). Furthermore, the global gap between EF and BC has been continuously increasing since the mid-1980s. From that period up to 2002, an ecological debt of about 2.5 years worth of the Earth’s regenerative capacity has been accumulated as calculated by Kitzes et al. (2008). This debt has likely increased in the last 9 years and it will keep accumulating until humanity reduces its demand below the Earth’s biocapacity. Though the Earth is characterized by a high resilience, sustained ecological deficit is not possible due to insuperable ecological and thermodynamic constraints. It is thus important to bring our consumption levels back within the limits of our ecological budget. 䊉 At national level, when the ecological balance is positive (EF < BC), the country analyzed runs an ecological remainder (ER) or surplus. The human load is within the country’s carrying capacity, though this does not necessarily imply sustainable use of domestic ecological resources. This remainder is often used to provide goods and ecological services exported and consumed in other countries, and thus might not constitute an actual remainder available to the nation. Vice versa, if the balance is negative (EF > BC) then the country is running an ecological deficit (ED), where its natural resource requirements exceed the regenerative capacity of its natural capital. Such an ecological deficit situation also shows the country’s dependence on further goods and ecological services, which are provided through either each of the three different mechanisms or a combination of them (Monfreda et al., 2004; Ewing et al., 2010): (a) the first is called ecological trade deficit which consists of an import of regenerative capacity from other regions of the world (when possible); (b) the second is known as ecological overshoot. It stimulates an overuse of resources leading to local and/or global depletion of stocks of natural capital. (c) the third originates from a greenhouse gases accumulation in the atmosphere due to the emission of carbon dioxide faster than the natural absorption rate. Each of these has distinctly different ramifications in terms of local and global sustainability. 3. Advances in the Ecological Footprint method
1
Six different land use types are considered by the Ecological Footprint methodology: croplands, grazing lands, forests, fishing grounds, carbon uptake lands and built-up areas.
An advance in the Ecological Footprint method has been proposed in our recent paper (Niccolucci et al., 2009), to better explain
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2 0
0 1960
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Fig. 1. The temporal series of absolute EFsize (grey line – left side scale) and EFdepth (black line – right side scale). Source: our elaboration on Global Footprint Network data.
the difference between human demand for stocks and flows via a three dimensional variant of the Ecological Footprint (3D EF). For instance, if the ‘classical’ Ecological Footprint methodology (EFclassic ) can be depicted as a circle, the 3D EF then becomes a cylinder. In other words, the 3D EF is a volume-based indicator with two relevant dimensions: the surface area (or Footprint size) and the height (or Footprint depth). The Footprint size (EFsize ) deals with the human appropriation of the annual income of natural capital provided by the Earth. As suggested by Hicks (1946, p. 171) the term ‘income’ can be considered as the level of consumption which can be sustained in the long run without reducing wealth. In the EF context, the income from natural capital is thus represented by all resource flows and ecological services annually produced by nature and its biogeochemical cycles. In this sense, EFsize deals with the annual appropriation of biocapacity and it can assume all values between zero and the annual biocapacity of the planet: 0 < EFsize = BC
(1)
As EFsize is an area, it is expressed in global hectares (gha) and can be plotted on a (x,y) plane as the basis of the cylinder. The Footprint depth (EFdepth ) represents the demand for extra land required to meet human needs through depletion of stocks of natural capital and/or saturation of carbon sinks. It can be plotted on the z-axis as it is the height of the cylinder. EFdepth can be considered as the number of years necessary to re-generate resources liquidated in one year (and to absorb emitted carbon dioxide) or as the number of planets necessary to support the total consumption of the Earth’s inhabitants. When overshoot (EO) occurs, EFdepth is calculated according to Eq. (2), otherwise its value is simply equal to 1: EFdepth = 1 +
EO BC
(2)
EFdepth is a dimensionless number that can take any value equal or greater than 1. EFdepth ≥ 1
(3)
where 1 is a reference value termed natural depth. The natural depth corresponds to the intrinsic time (1 year) needed by the planet Earth to restore the previous year’s situation by means of its natural flows. When more resources are consumed than are available, an ‘additional depth’ is required to accommodate this excess demand. From a sustainability point of view, Footprint
depth should be as close as possible to 1 to reduce depletion of stocks. It should be noted that the classical and the three dimensional Ecological Footprint approaches are numerically equivalent and thus the respective final values should be identical. The 3D EF is just a different way of representing classical Footprint values and it is given by the product of the two components: size and depth.
EFclassic = 3D EF 3D
EF = EFsize × EFdepth
(4) (5)
4. Results and discussion Global EF and BC data drawn from the 2009 Edition of the National Footprint Accounts (GFN, 2009) were elaborated for the period 1961–2006. Results are reported in Fig. 1. Absolute EFsize doubles from 1961 to 1986. After 1986, it reaches an asymptotic value equal to the Earth’s BC and remains constant until 2006. Conversely, EFdepth stays constant at the natural depth value until 1986, the year in which world average EF exceeded Earth’s BC for the first time. Since then a growing trend is observed. In 2006 EFdepth was equal to 1.44 meaning that an extra time of 0.44 years (about 5 months) would have been necessary to regenerate what humanity consumed in that year. However, this graph could provide misleading information if read in isolation, as it offers a conservative estimation of the real situation. This is due to the fact that when the total Ecological Footprint is calculated by adding up the demand for different land types, an eventual ecological remainder in any given land type is allowed to compensate for ecological deficits in other land types. For example, the deficit of carbon uptake land could partially be compensated by surpluses in grazing land. In other words, the world values for Footprint size and depth (in particular) could be probably higher than those reported in Fig. 1. For this reason trends in EFsize and EFdepth were analyzed for each land type. Results were plotted in Fig. 2. Fig. 2 shows the presence of a depth component just for forest land. This means that forests are the areas under the highest human induced pressure and that the emission of carbon dioxide is the major driver of global overshoot. A further disaggregation between forest and carbon uptake lands is desirable. Unfortunately, due to data limitations, Global Footprint Network’s National Footprint Accounts are not able to distinguish between the areas of
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Fig. 2. The temporal series of EFsize (grey line – left side scale) and EFdepth (black line – right side scale) for each land type. Forest is given by the sum of forest land and carbon uptake land. Source: our elaboration on Global Footprint Network data.
forest dedicated to forest products and those permanently set aside for carbon uptake services (Ewing et al., 2010). The presence of overshoot in forests begins in the mid-1970s, nearly ten years before global overshoot, when both the capacity to produce timber and to uptake CO2 is considered. An imperceptible depth seems to appear also for cropland. Data are not sufficient to assess whether this is a rounding error or the origin of real depth. All other land types report a growing trend in EFsize without reaching a plateau (i.e., biocapacity), while the depth component is fixed on the natural depth value. If the Footprint methodology were to not allow a remainder in a given land type to compensate for deficit in the others, the global EFdepth would rise from 1.44 to 2.23. The 3D EF approach also enables comparisons between the behavior of different populations, adding more information than classical EF and BC parameters. The comparison among national EFsize components can be used as a proxy for the (in)equality in the appropriation of resources and ecological services between current generations of different countries. On the other hand, comparisons of EFdepth values can be used as proxies for the relationships between current and future generations. This new way of representing the Footprint model can be the starting point to create a new Footprint geography based on both size and depth information. Together with the implementation of
a multilateral trade framework in the National Footprint Accounts, the 3D EF model could help us to better track where biocapacity is coming from and where pressures on flows and stocks are taking place. However, when analyzing sub-global systems (i.e., nations), modifications on Eq. (3) are needed. As nations are open systems able to exchange materials and energy with the surrounding environments, both the two Footprint components can be considered as the sum of a local and a global term as reported in Eq. (6): 3D EF nation
= EFsize × EFdepth
GLOB GLOB = EFLOC × EFLOC size + EFsize depth + EFdepth
(6)
where: 3D EF nation is the total Footprint of consumption of a nation; GLOB EFLOC size and EFsize are the local and global components of the Footprint size of consumption; they refer to the appropriation of annual flows of resources generated inside and outside the given nation, respectively. GLOB EFLOC depth and EFdepth are the local and global components of the Footprint depth of consumption; they refer to the depletion of stocks located inside and outside the given nation, respectively. Please note that the term global refers to all the world other than the single country analyzed. In principle it could be possible to disaggregate this term into small components for each trading partner. In practice this can only be done after the implementation of a
V. Niccolucci et al. / Ecological Modelling 222 (2011) 2939–2944
BC N
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natural depth=1
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B
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Fig. 3. Footprint depth vs Footprint size. It is considered a generic nation N with its own Biocapacity (BCN ). Four different cases (named A, B, C, D) can be detected. Case A is characterized by all points laying on the EFsize axis from zero to BCN . Case B includes all points on the EFsize axis higher than BCN . Both case A and B have a depth value equal to 1 (i.e., natural depth). Case C comprises a set of points where the size component is lower than BCN but the depth component is higher than 1. Case D reports a set of points where the size component is higher than BCN and the depth component is higher than 1.
multilateral trade framework into the National Footprint Accounts. Such improvement is expected to be included in the 2012 Edition of the Global Footprint Network’s National Footprint Accounts. The implications of this stock/flow distinction could constitute a quantifiable and scientifically sound basis for policy makers to then derive more effective and informed decisions to manage demand on and availability of natural capital, both locally and globally. Interesting information on ecological sustainability of nations can be extrapolated when results are plotted on a EFsize vs EFdepth plane. Four different hypothetical situations (A, B, C and D) can be identified when comparing a generic nation’s demand for ecological assets (i.e., natural resources and ecological services) with its own biocapacity (BCN ), with respect to Eq. (6) (see Fig. 3). Case A: nations included in this category consume less ecological assets than those locally available (EFsize < BCN ) and do not deplete stocks (EFdepth = natural depth = 1), thus having a long-term replicable pathway. A surplus of resource flow for other populations could be potentially available. Although local demand and supply are discussed, this should not lead to the misconception that selfsufficiency is a necessary or desirable criterion for sustainability. There is no physical law or social principle requiring all countries to live within their own biocapacity as countries can access biocapacity from elsewhere. The only constraint is that while in the short term it is possible for all countries combined to run an ecological deficit, this is not possible in the long term as this leads to overshoot and gradual depletion of ecological assets. Theoretically, countries belong to this case if they: (i) have very high biocapacity, which more than compensates the human demand. This is likely the case of European Nordic countries such as Finland and Sweden; and/or (ii) have very low Ecological Footprint with respect to Biocapacity. This is the case of Latin American countries such as Brazil, Peru, and Colombia.
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Even if all points on the horizontal line from zero to BCN represent favorable conditions from an ecological point of view, this does not ensure that wealth and well being are also met. Additional indicators should be coupled with the Ecological Footprint to consider these aspects and draw a more comprehensive picture of the system from a sustainability standpoint. Case B: any country falling into this case consumes more flows than those locally available in a specific year and thus requires additional flows (an “extra size”) from elsewhere (EFsize > BCN ); stocks do not appear to be liquidated (EFdepth = 1). When a Footprint size is imported from outside without a corresponding use of Footprint depth, raw materials and/or products refined by means of renewable resources are likely to be imported; it remains to be seen how such products are produced in the exporting nation. All points on the horizontal line from BCN represent long lasting or durable conditions, as long as exporting countries continue to sustainably support the importing nation. However, in an increasingly resource constrained world, dependency on trade and thus the necessity to compete internationally for natural resources (biocapacity) increases the risk of geopolitical, economic and social instability (Moore et al., 2010). The faster a nation shrinks its ecological surplus or shifts from a surplus to deficit condition, the sooner that entity must make decisions about managing biocapacity demand, energy efficiency and related quality of life. In a resource constrained world, running an ecological deficit might in some cases become a risk for a nation’s economy as it takes financial resources (purchasing power) to net import natural resources from elsewhere. It therefore becomes important for each nation to monitor and understand the size of its ecological deficit as in some cases it can provide an indication of the nation’s exposure to ecological risks (Moore et al., 2010). Footprint time series assessment can also enable key decision makers (strategists) to make informed decisions designed to avoid internal instability. Nations belonging to this case are, for example, Morocco and Jordan. Case C: for countries in this situation, Footprint size is lower than BCN (EFsize < BCN ), even if a Footprint depth appears (EFdepth > 1). This means that local resources could be used more effectively without compromising local and/or global stocks. The presence of the Footprint depth term is synonymous with the use of highly refined and energy intensive materials (locally extracted and/or imported). By using stocks, any nation in this category not only appropriates resources from future generations but also contributes to the depletion of our finite natural capital thus affecting the Earth’s ability to provide for humanity in the long term. Most countries in this category have a high population density and/or a high level of industrialization but generally have a high per capita BC value even if not enough to compensate the Footprint value. Countries in this situation are rich and economically competitive countries, which choose to safeguard their local natural capital and rather use (and/or overuse) global stocks because of their import of energy intensive commodities and high emission of carbon dioxide; USA is the typical country belonging to this group. Case D: countries in this situation are characterized by an Ecological Footprint size higher than BCN and a Footprint depth higher than 1. This is due to both overconsumption of local stocks and import of both flows and stocks (e.g. carbon uptake land). From a resource perspective this is the most risky of the four cases. In this situation, local resources are exhausted and a big portion of EF is compensated by importing size and liquidating local and/or global stocks (adding depth). As such all three ways to compensate ecological deficit, as reported above, are used. As for case C, nations in this category not only appropriate resources from actual and future generations but, by demanding stock of natural resources, they draw down the natural capital that allows our planet to sustain human life. This is a characteristic condition of industrialized and densely populated countries, where the lack of ecological space is a limiting
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factor. Nations belonging to this case are, for example, most of the European countries such as Italy, United Kingdom, Germany, Spain, etc. 5. Open questions and research agenda Even if important steps towards the comprehension of the stock and flow relationship were achieved, some questions still remain to be addressed. (i) How are resource overconsumption and stock depletion relevant for the economic resilience of countries? (ii) Can stock depletion substitute for the shortage in resource flows? (iii) What are the long term implications for a nation of using stocks rather than flows? (iv) How much stock can be depleted until ecosystem collapse, for each ecosystem type? (v) What are the consequences of stock depletion on the productivity of ecosystems and well being perceived by the population? (vi) Should the utilization of local resource flows be encouraged to optimize the use of the Earth’s supply and to reduce the risk of ecological and social instability due to a country’s reliance on external resources? (vii) Can a new global trade system be put in place to favor the management of resource flows and the safeguard of the stocks? 6. Conclusion This paper showed the potential implications of recent developments in Ecological Footprint research. A conceptual method to represent the Footprint was introduced through a three dimensional Ecological Footprint (3D EF) model, which allows flow and stock to be accounted for separately. The distinction between depletion of natural capital stocks and the use of natural capital flows proves to be of particular interest, especially in dealing with open systems such as nations. We believe that the 3D EF model explored in this paper could be more suitable in considering the many aspects of sustainability while maintaining the structure and advantages of the classical Footprint format. Even if the 3D EF model offers interesting and informative responses, several questions remain unanswered and additional research would be needed to develop a comprehensive framework for assessing the ecological sustainability of nations. Furthermore a more comprehensive assessment, including both Footprint of Consumption and Footprint of Production, would be needed to complement the analysis performed here and arrive at a better description of the above mentioned four cases. The next step should be the definition of a new world geography where this overuse is represented.
Acknowledgements The authors would like to thank Nicoletta Patrizi for her precious work and fruitful discussions. Acknowledgements are also due to Gemma Cranston for her help in finalizing the paper. This paper is dedicated to the memory of Prof. Enzo Tiezzi, who passed away on June the 25th, 2010. N.V., G.A., N.E. and B.S. are proud to have been Enzo’s students in the Ecodynamics group at the University of Siena. References Daly, H., 1990. Towards some operational principle of sustainable development. Ecological Economics 2, 1–6. Ewing, B., Goldfinger, S., Oursler, A., Reed, A., Moore, D., Wackernagel, M., 2009. The Ecological Footprint Atlas 2009. Global Footprint Network, Oakland (CA–USA) (p. 109). Ewing, B., Reed, A., Galli, A., Kitzes, J., Wackernagel, M., 2010. Calculation Methodology for the National Footprint Accounts, 2009 Edition. Global Footprint Network, Oakland. Daly, H., Farley, J., 2004. Ecological Economics. Principle and Applications. Island Press, Washingtion, USA. Galli, A., Kitzes, J., Wermer, P., Wackernagel, M., Niccolucci, V., Tiezzi, E., 2007. An exploration of the mathematics behind the Ecological Footprint. International Journal of Ecodynamics 2 (4), 250–257. GFN, Global Footprint Network, 2009. Ecological Footprint Standards 2009. Oakland: Global Footprint Network. Available at www.footprintstandards.org (accessed 20.01.11). Hicks, J.R., 1946. Value and Capital: An Inquiry into Some Fundamental Principles of Economic Theory. Oxford, Oxford University Press, UK. Kitzes, J., Wackernagel, M., Loh, J., Peller, A., Goldfinger, S., Cheng, D., Tea, K., 2008. Shrink and share: humanity’s present and future Ecological Footprint. Philosophical Transactions of the Royal Society of London Series B 363 (1491), 467–475. Monfreda, C., Wackernagel, M., Deumling, D., 2004. Establishing national natural capital accounts based on detailed Ecological Footprint and biological capacity assessments. Land Use Policy 21 (3), 231–246. Moore S D., Brooks S N., Cranston S G., Galli S A., 2010. In: Galli, A. (Ed.), The Future of the Mediterranean: Tracking Ecological Footprint Trends. Global Footprint Network, Oakland, CA, USA, Available at: http://www.footprintnetwork.org/images/uploads/MAVA report 5.pdf (accessed 6.04.11). Niccolucci, V., Bastianoni, S., Tiezzi, E.B.P., Wackernagel, M., Marchettini, N., 2009. How deep is the footprint? A 3D representation. Ecological Modelling 220 (20), 2819–2823. Rees, W.E., 1992. Ecological Footprints and appropriated carrying capacity: what urban economics leaves out. Environment and Urbanization 4, 121– 130. Rees, W.E., 2006. Ecological Footprints and bio-capacity: essential elements in sustainability assessment. In: Dewulf, J., Van Langenhove, H. (Eds.), RenewablesBased Technology: Sustainability Assessment. John Wiley and Sons, Chichester UK, pp. 143–158 (chapter 9). Tiezzi, E., 1984. Tempi storici tempi biologici. Garzanti, Milan, Italy (in Italian). Tiezzi, E., 2003. The End of Time. Wit Press, Southampton, UK. Wackernagel, M., Rees, W.E., 1996. Our Ecological Footprint: Reducing Human Impact on the Earth. New Society Publishers, Gabriola Island, British Columbia, Canada (160 pp.). Wackernagel, M., Rees, W.E., 1997. Perceptual and structural barriers to investing in natural capital: economics from an Ecological Footprint perspective. Ecological Economics 20, 3–24. Wackernagel, M., Kitzes, J.F., 2008. Ecological Footprint. In: Jorgensen, S.E., Fath, B.D. (Eds.), In: Encyclopedia of Ecology, 3. Elsevier B.V., Amsterdam, The Netherland, pp. 1031–1037.
Contents lists available at ScienceDirect
Ecological Modelling journal homepage: www.elsevier.com/locate/ecolmodel
Towards a 3D National Ecological Footprint Geography V. Niccolucci a,∗ , A. Galli b , A. Reed b , E. Neri c , M. Wackernagel b , S. Bastianoni c a
Ecodynamics Group, Dept. of Chemistry, University of Siena, via della Diana 2A, 53100 Siena, Italy Global Footprint Network, 312 Clay Street, Suite 300, Oakland, CA 94607, USA c Ecodynamics Group, Dept. of Chemistry, University of Siena, via A. Moro 2, 53100 Siena, Italy b
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Article history: Available online 27 May 2011 Keywords: Ecological Footprint Flow Footprint size Footprint depth Stock
a b s t r a c t In the last decades several indicators have been proposed to guide decision makers and help manage natural capital. Among such indicators is the Ecological Footprint, a resource accounting tool with a biophysical and thermodynamic basis. In our recent paper (Niccolucci et al., 2009), a three dimensional Ecological Footprint (3D EF) model was proposed to better explain the difference between human demand for natural capital stocks and resource flows. Such 3D EF model has two relevant dimensions: the surface area (or Footprint size – EFsize ) and the height (or Footprint depth – EFdepth ). EFsize accounts for the human appropriation of the annual income from natural capital while EFdepth accounts for the depletion of stocks of natural capital and/or the accumulation of stocks of wastes. Building on the 2009 Edition of the National Footprint Accounts (NFA), global trends (from 1961 to 2006) for both EFsize and EFdepth were analyzed. EFsize doubled from 1961 to 1986; after 1986 it reached an asymptotic value equal to the Earth’s biocapacity (BC) and remained constant. Conversely, EFdepth remained constant at the “natural depth” value until 1986, the year in which global EF first exceeded Earth’s BC. A growing trend was observed after that. Trends in each Footprint land type were also analyzed to better appraise the land type under the higher human induced stress. The usefulness of adopting such 3D EF model in the National Footprint Accounts was also discussed. In comparing any nation’s demand for ecological assets with its own biocapacity in a given year, four hypothetical cases were identified which could serve as the basis for a new Footprint geography based on both size and depth concepts. This 3D EF model could help distinguish between the use of natural capital flows and the depletion of natural capital stocks while maintaining the structure and advantages of the classical Ecological Footprint formulation. © 2011 Elsevier B.V. All rights reserved.
1. Introduction About thirty years ago Prof. Enzo Tiezzi, published the first Italian edition of his most famous book Tempi Storici Tempi Biologici (Tiezzi, 1984) then translated in English as The end of time (Tiezzi, 2003). He wrote: “[. . .] It is my firm conviction that we must change route as soon as possible and set about defining a new idea of development. A culture so based will be firmly founded on biology and thermodynamics, and their fundamental relationship to the economy, the society and the means of production. My conviction is based on three points: (a) the equilibrium of nature is extremely delicate and can be irreversibly upset by man: the resources of nature are not infinite; (b) the destruction of the environment and waste of natural resources is never of long term benefit either economically or socially; (c) the false prosperity of the consumer
∗ Corresponding author. Tel.: +39 0577232044; fax: +39 0577232004. E-mail address: [email protected] (V. Niccolucci). 0304-3800/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ecolmodel.2011.04.020
society is based on the exploitation of three classes of people [. . .]. Dominant economic theory, based as it is on mechanistic principles, remains ignorant of the law of entropy and the role of the time variable. The classical dynamic concept of time and its reversibility, has nothing to do with reality and nature. Time is not without its preferred directions (it is not isotropic) as is space. Time has a direction. Thermodynamics introduces “knowledge of the unidirectional flow of time”, traces the limit between past reality and future uncertainty, indicates the orientation of time in natural processes. [. . .] The technological or economic concept of time is exactly the opposite to entropic time. Nature obeys different laws to economics, it works in “entropic time”: the faster we consume natural resources and the energy available in the world, the less time is left for our survival. Technological time is inversely proportional to entropic time, economic time is inversely proportional to biological time. Our limited resources and the limited resistence of our planet and its atmosphere clearly indicate that the more we accelerate the energy and matter flow through our Earth system, the shorter is the life span of our species [. . .].” It is then important to underline “[. . .] the
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asymmetry of the ecological and historical time scales: millions of years for the evolution of life on the Earth with extremely slow ecological changes and historical knowledge of only the last brief period (a few thousand years); in contrast to this, the rapid ecological changes induced by technology in very short historical time. [. . .] Biological and historical tempos follow different rhythms”. Tiezzi’s thought represents the milestone from which a three dimensional Ecological Footprint (3D EF) model (Niccolucci et al., 2009) was developed. Although the ‘classical’ Ecological Footprint (EF) method recognizes the crucial role of natural capital and natural income (Rees, 2006), it is not sufficiently informative regarding the differentiation between biophysical stocks and flows. Already in the early ‘90s, economists belonging to the “thermodynamic school of thought” such as Daly and Georgescu-Roegen (Daly and Farley, 2004), widely highlighted the implications of a stock/flow distinction in dealing with sustainability issues. For instance, three operational rules defining the condition of ecological (thermodynamic) sustainability were identified by Daly (1990): (i) renewable resources such as fish, soil, and groundwater must be used no faster than the rate at which they regenerate; (ii) non-renewable resources such as minerals and fossil fuels must be used no faster than their renewable substitutes can be put in place; (iii) pollution and wastes must be emitted no faster than natural systems can absorb, recycle, or render them harmless. Making the role of time explicit within the EF methodology has therefore represented an important step towards a deeper interpretation of this indicator in the sustainability framework and could help the EF to better appraise Daly’s rules. As such, the ability to track depletion of natural capital stocks and use of natural capital flows plays a central role within this new approach. The aim of this paper is to test whether the 3D EF model recently proposed (Niccolucci et al., 2009) can serve as a useful biophysical measure of the flows and stocks used by a population. To address some of the unanswered questions from the previous paper, global trends for both the size and the depth components of the EF are analyzed here. These trends have been broken down by land type to highlight the areas under critical stress. Finally, the 3D EF model is suggested as proxy to redefining a new world geography based on the differentiation between flow and stock. 2. Ecological Footprint and natural capital accounting Historically the Ecological Footprint has been presented as a spatial indicator for natural capital accounting (Rees, 1992). The EF of a population or an individual is defined as the aggregated area of land and water1 required on a continuous basis to provide the energy and material resource flows used and to assimilate the CO2 emissions generated, given prevailing technologies and resource management practices (Wackernagel and Rees, 1996). From a thermodynamic point of view, the Ecological Footprint can be defined as the area continuously required to generate, via photosynthesis, a quantity of biomass, and thus negentropy, equivalent to the amount used and dissipated by the population’s consumptive activities (Rees, 2006). EF accounts for both direct and indirect land requirements and it is measured in global hectares (gha) (Wackernagel and Rees, 1996; Wackernagel and Kitzes, 2008). The term global refers to a normalized hectare with world average productivity (Galli et al., 2007; GFN, 2009). Land area is a very effective proxy to communicate the finiteness of planet Earth and its ability to generate resources (Wackernagel and Rees, 1997).
To give a measure of the (un)sustainability threshold of human consumption, a benchmark called biocapacity (BC) is also provided (Wackernagel and Rees, 1996; Monfreda et al., 2004), which quantifies how much regenerative capacity exits within a given area, in terms of ecologically productive space. BC is also measured in global hectares (gha) (Galli et al., 2007; GFN, 2009). As EF and BC represent flows of ecological assets (i.e., natural resources and ecological services), they can be directly compared to define an ecological balance in the same way that expenditure and income are compared in economics (Monfreda et al., 2004). The difference between the two terms is proportional to four main factors: (i) population size; (ii) consumption patterns, (iii) ecological productivity and (iv) technology. This ecological balance has significance both at the global and the national level: 䊉 At global level, the 2009 Edition of the Global Footprint Network’s National Footprint Accounts (GFN, 2009) show that the Earth is actually operating in a state of ecological overshoot (EO). Demand for natural resources exceeds the regenerative capacity of existing natural capital by 44% (GFN, 2009; Ewing et al., 2009). Furthermore, the global gap between EF and BC has been continuously increasing since the mid-1980s. From that period up to 2002, an ecological debt of about 2.5 years worth of the Earth’s regenerative capacity has been accumulated as calculated by Kitzes et al. (2008). This debt has likely increased in the last 9 years and it will keep accumulating until humanity reduces its demand below the Earth’s biocapacity. Though the Earth is characterized by a high resilience, sustained ecological deficit is not possible due to insuperable ecological and thermodynamic constraints. It is thus important to bring our consumption levels back within the limits of our ecological budget. 䊉 At national level, when the ecological balance is positive (EF < BC), the country analyzed runs an ecological remainder (ER) or surplus. The human load is within the country’s carrying capacity, though this does not necessarily imply sustainable use of domestic ecological resources. This remainder is often used to provide goods and ecological services exported and consumed in other countries, and thus might not constitute an actual remainder available to the nation. Vice versa, if the balance is negative (EF > BC) then the country is running an ecological deficit (ED), where its natural resource requirements exceed the regenerative capacity of its natural capital. Such an ecological deficit situation also shows the country’s dependence on further goods and ecological services, which are provided through either each of the three different mechanisms or a combination of them (Monfreda et al., 2004; Ewing et al., 2010): (a) the first is called ecological trade deficit which consists of an import of regenerative capacity from other regions of the world (when possible); (b) the second is known as ecological overshoot. It stimulates an overuse of resources leading to local and/or global depletion of stocks of natural capital. (c) the third originates from a greenhouse gases accumulation in the atmosphere due to the emission of carbon dioxide faster than the natural absorption rate. Each of these has distinctly different ramifications in terms of local and global sustainability. 3. Advances in the Ecological Footprint method
1
Six different land use types are considered by the Ecological Footprint methodology: croplands, grazing lands, forests, fishing grounds, carbon uptake lands and built-up areas.
An advance in the Ecological Footprint method has been proposed in our recent paper (Niccolucci et al., 2009), to better explain
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Fig. 1. The temporal series of absolute EFsize (grey line – left side scale) and EFdepth (black line – right side scale). Source: our elaboration on Global Footprint Network data.
the difference between human demand for stocks and flows via a three dimensional variant of the Ecological Footprint (3D EF). For instance, if the ‘classical’ Ecological Footprint methodology (EFclassic ) can be depicted as a circle, the 3D EF then becomes a cylinder. In other words, the 3D EF is a volume-based indicator with two relevant dimensions: the surface area (or Footprint size) and the height (or Footprint depth). The Footprint size (EFsize ) deals with the human appropriation of the annual income of natural capital provided by the Earth. As suggested by Hicks (1946, p. 171) the term ‘income’ can be considered as the level of consumption which can be sustained in the long run without reducing wealth. In the EF context, the income from natural capital is thus represented by all resource flows and ecological services annually produced by nature and its biogeochemical cycles. In this sense, EFsize deals with the annual appropriation of biocapacity and it can assume all values between zero and the annual biocapacity of the planet: 0 < EFsize = BC
(1)
As EFsize is an area, it is expressed in global hectares (gha) and can be plotted on a (x,y) plane as the basis of the cylinder. The Footprint depth (EFdepth ) represents the demand for extra land required to meet human needs through depletion of stocks of natural capital and/or saturation of carbon sinks. It can be plotted on the z-axis as it is the height of the cylinder. EFdepth can be considered as the number of years necessary to re-generate resources liquidated in one year (and to absorb emitted carbon dioxide) or as the number of planets necessary to support the total consumption of the Earth’s inhabitants. When overshoot (EO) occurs, EFdepth is calculated according to Eq. (2), otherwise its value is simply equal to 1: EFdepth = 1 +
EO BC
(2)
EFdepth is a dimensionless number that can take any value equal or greater than 1. EFdepth ≥ 1
(3)
where 1 is a reference value termed natural depth. The natural depth corresponds to the intrinsic time (1 year) needed by the planet Earth to restore the previous year’s situation by means of its natural flows. When more resources are consumed than are available, an ‘additional depth’ is required to accommodate this excess demand. From a sustainability point of view, Footprint
depth should be as close as possible to 1 to reduce depletion of stocks. It should be noted that the classical and the three dimensional Ecological Footprint approaches are numerically equivalent and thus the respective final values should be identical. The 3D EF is just a different way of representing classical Footprint values and it is given by the product of the two components: size and depth.
EFclassic = 3D EF 3D
EF = EFsize × EFdepth
(4) (5)
4. Results and discussion Global EF and BC data drawn from the 2009 Edition of the National Footprint Accounts (GFN, 2009) were elaborated for the period 1961–2006. Results are reported in Fig. 1. Absolute EFsize doubles from 1961 to 1986. After 1986, it reaches an asymptotic value equal to the Earth’s BC and remains constant until 2006. Conversely, EFdepth stays constant at the natural depth value until 1986, the year in which world average EF exceeded Earth’s BC for the first time. Since then a growing trend is observed. In 2006 EFdepth was equal to 1.44 meaning that an extra time of 0.44 years (about 5 months) would have been necessary to regenerate what humanity consumed in that year. However, this graph could provide misleading information if read in isolation, as it offers a conservative estimation of the real situation. This is due to the fact that when the total Ecological Footprint is calculated by adding up the demand for different land types, an eventual ecological remainder in any given land type is allowed to compensate for ecological deficits in other land types. For example, the deficit of carbon uptake land could partially be compensated by surpluses in grazing land. In other words, the world values for Footprint size and depth (in particular) could be probably higher than those reported in Fig. 1. For this reason trends in EFsize and EFdepth were analyzed for each land type. Results were plotted in Fig. 2. Fig. 2 shows the presence of a depth component just for forest land. This means that forests are the areas under the highest human induced pressure and that the emission of carbon dioxide is the major driver of global overshoot. A further disaggregation between forest and carbon uptake lands is desirable. Unfortunately, due to data limitations, Global Footprint Network’s National Footprint Accounts are not able to distinguish between the areas of
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Fig. 2. The temporal series of EFsize (grey line – left side scale) and EFdepth (black line – right side scale) for each land type. Forest is given by the sum of forest land and carbon uptake land. Source: our elaboration on Global Footprint Network data.
forest dedicated to forest products and those permanently set aside for carbon uptake services (Ewing et al., 2010). The presence of overshoot in forests begins in the mid-1970s, nearly ten years before global overshoot, when both the capacity to produce timber and to uptake CO2 is considered. An imperceptible depth seems to appear also for cropland. Data are not sufficient to assess whether this is a rounding error or the origin of real depth. All other land types report a growing trend in EFsize without reaching a plateau (i.e., biocapacity), while the depth component is fixed on the natural depth value. If the Footprint methodology were to not allow a remainder in a given land type to compensate for deficit in the others, the global EFdepth would rise from 1.44 to 2.23. The 3D EF approach also enables comparisons between the behavior of different populations, adding more information than classical EF and BC parameters. The comparison among national EFsize components can be used as a proxy for the (in)equality in the appropriation of resources and ecological services between current generations of different countries. On the other hand, comparisons of EFdepth values can be used as proxies for the relationships between current and future generations. This new way of representing the Footprint model can be the starting point to create a new Footprint geography based on both size and depth information. Together with the implementation of
a multilateral trade framework in the National Footprint Accounts, the 3D EF model could help us to better track where biocapacity is coming from and where pressures on flows and stocks are taking place. However, when analyzing sub-global systems (i.e., nations), modifications on Eq. (3) are needed. As nations are open systems able to exchange materials and energy with the surrounding environments, both the two Footprint components can be considered as the sum of a local and a global term as reported in Eq. (6): 3D EF nation
= EFsize × EFdepth
GLOB GLOB = EFLOC × EFLOC size + EFsize depth + EFdepth
(6)
where: 3D EF nation is the total Footprint of consumption of a nation; GLOB EFLOC size and EFsize are the local and global components of the Footprint size of consumption; they refer to the appropriation of annual flows of resources generated inside and outside the given nation, respectively. GLOB EFLOC depth and EFdepth are the local and global components of the Footprint depth of consumption; they refer to the depletion of stocks located inside and outside the given nation, respectively. Please note that the term global refers to all the world other than the single country analyzed. In principle it could be possible to disaggregate this term into small components for each trading partner. In practice this can only be done after the implementation of a
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Fig. 3. Footprint depth vs Footprint size. It is considered a generic nation N with its own Biocapacity (BCN ). Four different cases (named A, B, C, D) can be detected. Case A is characterized by all points laying on the EFsize axis from zero to BCN . Case B includes all points on the EFsize axis higher than BCN . Both case A and B have a depth value equal to 1 (i.e., natural depth). Case C comprises a set of points where the size component is lower than BCN but the depth component is higher than 1. Case D reports a set of points where the size component is higher than BCN and the depth component is higher than 1.
multilateral trade framework into the National Footprint Accounts. Such improvement is expected to be included in the 2012 Edition of the Global Footprint Network’s National Footprint Accounts. The implications of this stock/flow distinction could constitute a quantifiable and scientifically sound basis for policy makers to then derive more effective and informed decisions to manage demand on and availability of natural capital, both locally and globally. Interesting information on ecological sustainability of nations can be extrapolated when results are plotted on a EFsize vs EFdepth plane. Four different hypothetical situations (A, B, C and D) can be identified when comparing a generic nation’s demand for ecological assets (i.e., natural resources and ecological services) with its own biocapacity (BCN ), with respect to Eq. (6) (see Fig. 3). Case A: nations included in this category consume less ecological assets than those locally available (EFsize < BCN ) and do not deplete stocks (EFdepth = natural depth = 1), thus having a long-term replicable pathway. A surplus of resource flow for other populations could be potentially available. Although local demand and supply are discussed, this should not lead to the misconception that selfsufficiency is a necessary or desirable criterion for sustainability. There is no physical law or social principle requiring all countries to live within their own biocapacity as countries can access biocapacity from elsewhere. The only constraint is that while in the short term it is possible for all countries combined to run an ecological deficit, this is not possible in the long term as this leads to overshoot and gradual depletion of ecological assets. Theoretically, countries belong to this case if they: (i) have very high biocapacity, which more than compensates the human demand. This is likely the case of European Nordic countries such as Finland and Sweden; and/or (ii) have very low Ecological Footprint with respect to Biocapacity. This is the case of Latin American countries such as Brazil, Peru, and Colombia.
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Even if all points on the horizontal line from zero to BCN represent favorable conditions from an ecological point of view, this does not ensure that wealth and well being are also met. Additional indicators should be coupled with the Ecological Footprint to consider these aspects and draw a more comprehensive picture of the system from a sustainability standpoint. Case B: any country falling into this case consumes more flows than those locally available in a specific year and thus requires additional flows (an “extra size”) from elsewhere (EFsize > BCN ); stocks do not appear to be liquidated (EFdepth = 1). When a Footprint size is imported from outside without a corresponding use of Footprint depth, raw materials and/or products refined by means of renewable resources are likely to be imported; it remains to be seen how such products are produced in the exporting nation. All points on the horizontal line from BCN represent long lasting or durable conditions, as long as exporting countries continue to sustainably support the importing nation. However, in an increasingly resource constrained world, dependency on trade and thus the necessity to compete internationally for natural resources (biocapacity) increases the risk of geopolitical, economic and social instability (Moore et al., 2010). The faster a nation shrinks its ecological surplus or shifts from a surplus to deficit condition, the sooner that entity must make decisions about managing biocapacity demand, energy efficiency and related quality of life. In a resource constrained world, running an ecological deficit might in some cases become a risk for a nation’s economy as it takes financial resources (purchasing power) to net import natural resources from elsewhere. It therefore becomes important for each nation to monitor and understand the size of its ecological deficit as in some cases it can provide an indication of the nation’s exposure to ecological risks (Moore et al., 2010). Footprint time series assessment can also enable key decision makers (strategists) to make informed decisions designed to avoid internal instability. Nations belonging to this case are, for example, Morocco and Jordan. Case C: for countries in this situation, Footprint size is lower than BCN (EFsize < BCN ), even if a Footprint depth appears (EFdepth > 1). This means that local resources could be used more effectively without compromising local and/or global stocks. The presence of the Footprint depth term is synonymous with the use of highly refined and energy intensive materials (locally extracted and/or imported). By using stocks, any nation in this category not only appropriates resources from future generations but also contributes to the depletion of our finite natural capital thus affecting the Earth’s ability to provide for humanity in the long term. Most countries in this category have a high population density and/or a high level of industrialization but generally have a high per capita BC value even if not enough to compensate the Footprint value. Countries in this situation are rich and economically competitive countries, which choose to safeguard their local natural capital and rather use (and/or overuse) global stocks because of their import of energy intensive commodities and high emission of carbon dioxide; USA is the typical country belonging to this group. Case D: countries in this situation are characterized by an Ecological Footprint size higher than BCN and a Footprint depth higher than 1. This is due to both overconsumption of local stocks and import of both flows and stocks (e.g. carbon uptake land). From a resource perspective this is the most risky of the four cases. In this situation, local resources are exhausted and a big portion of EF is compensated by importing size and liquidating local and/or global stocks (adding depth). As such all three ways to compensate ecological deficit, as reported above, are used. As for case C, nations in this category not only appropriate resources from actual and future generations but, by demanding stock of natural resources, they draw down the natural capital that allows our planet to sustain human life. This is a characteristic condition of industrialized and densely populated countries, where the lack of ecological space is a limiting
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factor. Nations belonging to this case are, for example, most of the European countries such as Italy, United Kingdom, Germany, Spain, etc. 5. Open questions and research agenda Even if important steps towards the comprehension of the stock and flow relationship were achieved, some questions still remain to be addressed. (i) How are resource overconsumption and stock depletion relevant for the economic resilience of countries? (ii) Can stock depletion substitute for the shortage in resource flows? (iii) What are the long term implications for a nation of using stocks rather than flows? (iv) How much stock can be depleted until ecosystem collapse, for each ecosystem type? (v) What are the consequences of stock depletion on the productivity of ecosystems and well being perceived by the population? (vi) Should the utilization of local resource flows be encouraged to optimize the use of the Earth’s supply and to reduce the risk of ecological and social instability due to a country’s reliance on external resources? (vii) Can a new global trade system be put in place to favor the management of resource flows and the safeguard of the stocks? 6. Conclusion This paper showed the potential implications of recent developments in Ecological Footprint research. A conceptual method to represent the Footprint was introduced through a three dimensional Ecological Footprint (3D EF) model, which allows flow and stock to be accounted for separately. The distinction between depletion of natural capital stocks and the use of natural capital flows proves to be of particular interest, especially in dealing with open systems such as nations. We believe that the 3D EF model explored in this paper could be more suitable in considering the many aspects of sustainability while maintaining the structure and advantages of the classical Footprint format. Even if the 3D EF model offers interesting and informative responses, several questions remain unanswered and additional research would be needed to develop a comprehensive framework for assessing the ecological sustainability of nations. Furthermore a more comprehensive assessment, including both Footprint of Consumption and Footprint of Production, would be needed to complement the analysis performed here and arrive at a better description of the above mentioned four cases. The next step should be the definition of a new world geography where this overuse is represented.
Acknowledgements The authors would like to thank Nicoletta Patrizi for her precious work and fruitful discussions. Acknowledgements are also due to Gemma Cranston for her help in finalizing the paper. This paper is dedicated to the memory of Prof. Enzo Tiezzi, who passed away on June the 25th, 2010. N.V., G.A., N.E. and B.S. are proud to have been Enzo’s students in the Ecodynamics group at the University of Siena. References Daly, H., 1990. Towards some operational principle of sustainable development. Ecological Economics 2, 1–6. Ewing, B., Goldfinger, S., Oursler, A., Reed, A., Moore, D., Wackernagel, M., 2009. The Ecological Footprint Atlas 2009. Global Footprint Network, Oakland (CA–USA) (p. 109). Ewing, B., Reed, A., Galli, A., Kitzes, J., Wackernagel, M., 2010. Calculation Methodology for the National Footprint Accounts, 2009 Edition. Global Footprint Network, Oakland. Daly, H., Farley, J., 2004. Ecological Economics. Principle and Applications. Island Press, Washingtion, USA. Galli, A., Kitzes, J., Wermer, P., Wackernagel, M., Niccolucci, V., Tiezzi, E., 2007. An exploration of the mathematics behind the Ecological Footprint. International Journal of Ecodynamics 2 (4), 250–257. GFN, Global Footprint Network, 2009. Ecological Footprint Standards 2009. Oakland: Global Footprint Network. Available at www.footprintstandards.org (accessed 20.01.11). Hicks, J.R., 1946. Value and Capital: An Inquiry into Some Fundamental Principles of Economic Theory. Oxford, Oxford University Press, UK. Kitzes, J., Wackernagel, M., Loh, J., Peller, A., Goldfinger, S., Cheng, D., Tea, K., 2008. Shrink and share: humanity’s present and future Ecological Footprint. Philosophical Transactions of the Royal Society of London Series B 363 (1491), 467–475. Monfreda, C., Wackernagel, M., Deumling, D., 2004. Establishing national natural capital accounts based on detailed Ecological Footprint and biological capacity assessments. Land Use Policy 21 (3), 231–246. Moore S D., Brooks S N., Cranston S G., Galli S A., 2010. In: Galli, A. (Ed.), The Future of the Mediterranean: Tracking Ecological Footprint Trends. Global Footprint Network, Oakland, CA, USA, Available at: http://www.footprintnetwork.org/images/uploads/MAVA report 5.pdf (accessed 6.04.11). Niccolucci, V., Bastianoni, S., Tiezzi, E.B.P., Wackernagel, M., Marchettini, N., 2009. How deep is the footprint? A 3D representation. Ecological Modelling 220 (20), 2819–2823. Rees, W.E., 1992. Ecological Footprints and appropriated carrying capacity: what urban economics leaves out. Environment and Urbanization 4, 121– 130. Rees, W.E., 2006. Ecological Footprints and bio-capacity: essential elements in sustainability assessment. In: Dewulf, J., Van Langenhove, H. (Eds.), RenewablesBased Technology: Sustainability Assessment. John Wiley and Sons, Chichester UK, pp. 143–158 (chapter 9). Tiezzi, E., 1984. Tempi storici tempi biologici. Garzanti, Milan, Italy (in Italian). Tiezzi, E., 2003. The End of Time. Wit Press, Southampton, UK. Wackernagel, M., Rees, W.E., 1996. Our Ecological Footprint: Reducing Human Impact on the Earth. New Society Publishers, Gabriola Island, British Columbia, Canada (160 pp.). Wackernagel, M., Rees, W.E., 1997. Perceptual and structural barriers to investing in natural capital: economics from an Ecological Footprint perspective. Ecological Economics 20, 3–24. Wackernagel, M., Kitzes, J.F., 2008. Ecological Footprint. In: Jorgensen, S.E., Fath, B.D. (Eds.), In: Encyclopedia of Ecology, 3. Elsevier B.V., Amsterdam, The Netherland, pp. 1031–1037.