How to calculate and interpret ecological footprints for long periods of time: the case of Austria

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1 Ecological Economics 38 (2001) METHODS How to calculate and interpret ecological footprints for long periods of time: the case of Austria Helmut Haberl *,1, Karl-Heinz Erb, Fridolin Krausmann Department of Social Ecology, Institute for Interdisciplinary Studies of Austrian Uni ersities, Schottenfeldgasse 29, A-1070 Vienna, Austria Received 11 September 2000; received in revised form 2 January 2001; accepted 3 January 2001 Abstract In this paper we present calculations of the ecological footprint (EF) for Austria , based upon three different methodological approaches. Basically, EF calculations convert the use of selected materials in a country into the area needed to sustain this material flow. Therefore, biological productivity essentially determines the outcome of EF calculations, given a certain pattern of socioeconomic metabolism. In most EF calculations published thus far, material and energy flows are converted to area (hectares) using global yields of the respective year. In contrast, we analyze the effect different assumptions on yields have on the results of EF calculations by assuming: (1) constant global yields as of 1995; (2) variable global yields; and (3) variable local yields for domestic extraction and variable global yields for imported biomass. Fossil-energy footprint is evaluated on the basis of constant carbon sequestration rates published by Wackernagel. According to our results different assumptions on yields can influence the result of EF calculations by a factor of 2, at least. We conclude that further research is necessary with respect to biomass yields assumed in EF calculations. The purpose for which EF calculations are made, and the interpretation of their results, will determine future development of the EF methodology Elsevier Science B.V. All rights reserved. Keywords: Ecological footprint; Socioeconomic metabolism; Biological productivity; Biomass yield; Overshoot; Sustainability indicators 1. Introduction * Corresponding author. Tel.: ; fax: address: helmut.haberl@univie.ac.at (H. Haberl). 1 In recent years the ecological footprint (EF), developed by Mathis Wackernagel and William Rees in the mid-1990s (Wackernagel and Rees, 1996), has gained much attention in Ecological Economics (e.g. Wackernagel and Rees, 1997; van den Bergh and Verbruggen, 1999a,b; Ecological /01/$ - see front matter 2001 Elsevier Science B.V. All rights reserved. PII: S (01)

2 26 H. Haberl et al. / Ecological Economics 38 (2001) EF calculations also regard ocean areas as appropriated through the consumption of fish and other marine organisms. For reasons of scarce resources available for this project, we had to neglect this EF component in our calculations. In the 1990s Austria s ocean Footprint was about 0.65 hectares per capita (Wackernagel, pers. comm., 2000). Economics Vol. 32 (2000), ). Basically, the EF seeks to determine whether and by what order of magnitude human consumption is currently exceeding the biosphere s regenerative capacity (Wackernagel, 1999, 317). The EF is intended to serve as a comprehensive indicator for ecological sustainability which aims at determining to what extent (human) load is within the present regenerative capacity of the biosphere, or in other words, to what extent humanity lives within the interest of the natural capital (Lewan and Wackernagel, 1999, 604). Basically, any EF calculation tries to assess how much biologically productive area is needed to produce the yearly resource flows consumed by the population of a region (a city, a country, or the world), to absorb wastes or emissions (especially CO 2 ), and to host the built infrastructure in this region. The EF includes: (1) actually used land as, for instance, cropland and pastures needed to produce goods and services derived from these kinds of land use and builtup land; (2) the area of forests that would be necessary to produce the amount of wood used in a sustainable manner; and (3) area that would be necessary in order to absorb the carbon released by burning fossil fuels (or, alternatively, the amount of land that could hypothetically produce the same amount of biomass or biofuels). 2 In a second step, the EF of a defined population can be compared with the area of land available on a global or regional level, usually referred to as biocapacity (BC). If the EF is bigger than the available BC, this is often interpreted as overshoot, this being a situation in which human consumption exceeds ecological limits. The reverse situation EF smaller than BC is more difficult to interpret because EF calculations are conservative, for several reasons: some potentially area-demanding activities are usually not covered by the calculations (e.g. due to lacking data), existing farming methods are assumed to be sustainable (which is not always the case), and only a limited number of resources is considered (e.g. land, CO 2 assimilation capacity). Moreover, domestic BC can be used to produce exported goods which are not considered when calculating the national EF (Wackernagel, pers. comm., 2000). Therefore, if the EF is smaller than the BC in a country, we can not be sure to be within the limits. These caveats notwithstanding, the EF concept has gained much attention in past years. It seems that the success of the EF concept was probably to a large part due to the simplicity of the comparison of EF and BC which suggests a clear distinction between sustainability and unsustainability even though it is obviously better at demonstrating an unsustainable state ( =overshoot) than a sustainable one. Since it is beyond question that the biologically productive area that is, the area inhabitable for green plants capable of converting solar energy into chemically stored energy (biomass) is limited on a global scale, the EF is often regarded as an objective indicator to document overshoot that is not dependent on (subjective) value judgements. 3 Of course, matters are more complicated on the national level because it is questionable whether it makes sense to assume that the population of each nation is entitled to use exactly the BC of its own territory. It is also important to note that the EF is a measure of strong sustainability because it assesses the utilization of the environment in physical terms and compares the extent of resource use with the availability of resources. This ability of the footprint approach not only to measure the size of the physical economy of a country, but also to demonstrate overshoot is especially from the perspective of policy-makers, planners, etc. an important advantage of the EF concept over other approaches for accounting frameworks trying to come to grips with the physical economy. Other concepts, for example, the socioeconomic metabolism approach, be it 3 For example, (Wackernagel, 1999, 317) claims that a Footprint size larger than biocapacity indicates ( ) the very real existence of overshoot and repeatedly stresses that the Footprint mirrors ecological realities.

3 H. Haberl et al. / Ecological Economics 38 (2001) material flow accounting (e.g. Ayres and Simonis, 1994; Adriaanse et al., 1997; Fischer-Kowalski, 1997) or energetic metabolism accounting (Haberl, 1997; Haberl, in press), lack this advantage of offering simple conclusions about sustainability or violation of ecological limits. Of course, the EF is intimately related to socioeconomic metabolism: the largest EF components are usually grasslands, croplands and forests providing socioeconomic biomass inputs, and CO 2 absorption land related to fossil-fuel combustion. Therefore, the EF approach could be regarded as a method for assessing the (un)sustainability of socioeconomic metabolism, although it would be unrealistic to expect that the EF could be able to capture all sustainability problems related to societal material or energy flows as others have already observed (e.g. Wackernagel, 1999; Costanza, 2000; Rapport, 2000; Rees, 2000). In this paper we will present calculations of Austria s EF for This period of time covers a large part of Austria s industrialization, including a surge of fossil-fuel use and the industrialization of agriculture after the Second World War. We are not aware of any published calculation of EF time series covering such a long span of time. Wackernagel, Deumling and Schulz have been working on the global EF for and are planning to publish the results (Wackernagel, pers. comm., 2000). Hanley et al. (1999) and van Vuuren and Smeets (2000) have published time series of national footprints; however, their time series cover less than 15 years. Therefore, we hope that our analysis is useful to discuss methodological problems in calculating and interpreting the EF in long time series. 2. Methods A calculation of the EF for a time span of 80 years is not a straightforward application of the commonly used EF methodology (Wackernagel and Rees, 1996; Wackernagel et al., 1999). Moreover, newly proposed methods, such as the calculation of the EF with input output tables (Bicknell et al., 1998), cannot be used since such data are available for Austria only for 3 years (1976, 1983, 1990). The EF of a national economy is calculated by assessing the ecologically productive area necessary to sustain its material and energy flows (both for producing the used resources and for absorbing the arising wastes or byproducts) and the areas used for infrastructure (built-up land). Whereas the amount of area needed to absorb a defined amount of CO 2 (or to substitute biofuels for fossil-fuels) should arguably be based upon global average forest productivity (because atmospheric CO 2 enrichment is a global problem) and can be assumed to be approximately constant over time, 4 both assumptions are questionable with respect to socioeconomic biomass flows: agricultural and forest yields are not constant over time and vary considerably between regions. Thus, in calculating the EF in time series the question arises which yield (productivity per unit area) should be assumed for converting biomass flows into footprint areas. In order to be able to compare the consumption patterns of different countries, the customary EF methodology uses global productivity averages to calculate the EF of any specific resource used. For example, for calculating the EF of the wheat consumption of country A, the apparent consumption (i.e. domestic extraction plus imports minus exports) of wheat [tonnes] in country A is divided by the global average wheat productivity [tonnes/hectare], resulting in the number of hectares necessary to sustain the wheat consumption of country A, assuming global yields. Of course, actual productivity of the cropland in 4 If forest area changes, forest productivity is likely to change too. Deforestation is likely to cause a decline in average forest productivity because usually the most productive lowland forests are cleared to gain agricultural or built-up land. Similarly, average forest productivity should increase with growing forest area (e.g. in Austria ). While we differentiated between fuels in calculating fossil energy land (considering different CO 2 emission factors), we applied a constant CO 2 /land ratio and constant timber harvests for calculating fossil energy EF and the EF of timber imports, for two reasons: for the sake of conceptual simplicity, and due to lacking availability of data on global forest yields. However, we do not believe that including variable global forest yields would change much: (1) Austria was a net wood exporter in the early decades considered; (2) the share of the fossil energy EF was low in the early decades.

4 28 H. Haberl et al. / Ecological Economics 38 (2001) country A can be higher or lower than the global average. To make BC available in country A comparable to A s consumption, a so-called yieldfactor is introduced for each land-use category, defined as the ratio of the specific productivity of the country to global productivity (Wackernagel et al., 1999). Therefore, the BC of a country is not necessarily equal to its biologically productive area, but depends also on the productivity of this area compared to world average productivity. For example, according to calculations by Wackernagel (pers. comm., 2000), the Austrian BC in the early 1990s was about 3.56 hectares per capita, whereas at that time its biologically productive area amounted to 0.94 hectares per capita. In other words, Austria s biologically productive land is, on average, 3.8 times more productive than the global average, due to favorable climate, soil conditions and agricultural intensification. In a time series calculation this spatial and temporal variability of yields poses a problem: which yield should be used for converting consumption [kg] into area [ha]? This question has a significant impact on the results of EF calculations because yields for any given product can vary by factors of up to 10 over space and time. Instead of deciding this question on the basis of ad hoc considerations, we have chosen to calculate the EF in Austria with three different methods, each of which reflects a consistent set of assumptions (see Fig. 1): 2.1. Method 1 Global Yield 1995 (GY 95 ) In this calculation we use global average productivities of The results of this calculation can be directly compared to current EF calculations. Changes in the EF-GY 95 reflect only changes in consumption levels, not changes in agricultural technology or forest management (Ferguson, 1999a). However, since yields grew considerably both locally and globally, this has to be taken into account in calculating the BC, using so-called yield factors as described by Wackernagel et al. (1999). Hence the BC of Austria and the world changes over time as a result of changes in agricultural yields or forest productivity per unit area Method 2 Variable Global Yield (GY ) In this case we use global average yields at the point of time when consumption occurs; e.g. wheat consumption in 1970 is converted to area using the global average wheat yield in Results for 1995 are identical to method GY 95 and are also directly comparable to current EF calculations. Changes in EF-GY v reflect changes in consumption and changes in global average productivity, but not regional deviations from global productivity trends. Global BC equals globally available bioproductive area, but Austria s BC varies, depending on whether Austrian yields changed faster or slower than global yields Method 3 Variable Local Yield (LY ) As a third possibility, we use local (Austrian) yields for calculating the EF of domestic extraction and global average productivities in order to account for the EF of imported goods; both global and local yields refer to the year of consumption. 5 In order to account for exports, the corresponding yield of the gross domestic consumption (i.e. imports plus domestic extraction) of each product is calculated as the weighted average of global and local yields. In this case, the EF depends on the level of consumption as well as on global and local productivity; that is, it takes into account changes in agricultural production technology both on a local and on a global scale (van den Bergh and Verbruggen, 1999a). In this method the BC is equal to the amount of available bioproductive land. As a consequence, global BC and local BC are equal to the amount of bio-productive area available which is more or less 6 constant over time. The per capita EF of two 5 The calculation could be refined by differentiating between different regions or countries from which products are imported and using the respective yields (van Vuuren and Smeets, 2000). This is feasible, but very demanding. It should be noted that this could significantly influence results; for example, the high Austrian grassland Footprint in 1926 is mostly due to imports of living animals which almost certainly came from neighbouring countries with similar yields as Austria; using global averages probably leads to too high results in this case. 6 The amount of bioproductive area can be reduced through heavy soil degradation or increased through irrigation of dry deserts.

5 H. Haberl et al. / Ecological Economics 38 (2001) Fig. 1. Methodological options for calculating the ecological footprint and the biocapacity of countries over a period of time. countries, assessed with LY v, will not only reveal differences in the per capita consumption of resources, but will also depend on yields and yield changes in the two countries. Of course, the methods GY v and LY v are identical if the region analyzed happens to be the whole world.

6 30 H. Haberl et al. / Ecological Economics 38 (2001) Whereas EF calculations based upon the first two methods are directly comparable to previous work by Wackernagel and Rees, method LY v is related to a different research question and, therefore, leads to significantly different results (van Vuuren and Smeets, 2000). Method GY v refers to the question: how much globally average grassland, cropland, forest (and sea space) would be necessary to sustain the societal metabolism of a country, given yields at that time (and including CO 2 absorption area), and how much area does the infrastructure in the country cover? Method LY v refers to the question: how much bioproductive area is: (1) actually used to supply biomassderived products consumed within a country, domestically or abroad, assuming actual, regionally differentiated yields; 7 and (2) how much world average bioproductive area would be necessary either to absorb fossil-fuel derived CO 2 or to produce an equal amount of energy renewably? While the consumption of 1 kg of wheat will be assigned the same footprint in all countries if the EF in method GY v (and GY 95 ), method LY v assigns different footprints to the consumption of 1 kg of wheat, depending on the supply mix (domestic, import) and on the respective yields. The implications will be discussed below. Note that this differentiation between local and global yields also has implications for BC (see Section 4). EF and BC are standardized to the same productivity in methods GY 95 and GY v ; therefore any comparison of EF and BC on whatever regional level compares hectares with the same productivity. In contrast, method LY v uses different productivities to evaluate the amount of land needed to produce certain products or services or to make their procurement sustainable. Therefore, a comparison of the EF-LY v of a country with the potentially available bioproductive area of this country compares availability of and demand for areas of different productivity (Wackernagel, pers. comm., 2000). We will discuss the implications of this below 7 Austrian forestry can be assumed to be sustainable in terms of non-depletion of forest stocks (which are actually growing). Imports are calculated based upon assumed sustainable yields (data of Wackernagel). Speaking more generally, these different methods show a range of possibilities to define and interpret the EF: should the EF monitor the physical amount of area used in order to produce the goods and services consumed in a country and to make its fossil-fuel consumption sustainable (method LY v )? Or should the EF reveal differences in the amount of resources consumed in different countries, or in one country, at different points in time (method GY 95 )? Or should it monitor the amount of area that would be necessary to make the consumption in a country sustainable, based upon global average yields (GY v )? We will return to these questions after presenting our results. Another methodological remark seems appropriate with respect to fossil-energy footprints. We do not agree with van den Bergh and Verbruggen (1999a,b) criticism of the EF that calculating the fossil-energy EF based on carbon sequestration would imply a defined method of solving the carbon problem (planting forests), because any method that reduces CO 2 emissions (e.g. energy conservation) would also result in a reduction of fossil-energy EF and would thus reduce overshoot (van Vuuren and Smeets, 2000). We are, however, sceptical as to the way in which carbon sequestration is treated (Herendeen, 2000), because as has already been noted (Wackernagel and Silverstein, 2000) only young forests fix significant amounts of carbon, and they do so at a rate quite significantly below net primary production (NPP), because a considerable proportion of the yearly productivity in forests is oxydized again each year and does not contribute to an increase in carbon stocks in the ecosystem. Moreover, maturing forests only sequester significant amounts of carbon for some decades, after which their net carbon balance gets close to zero as they approach a climax state. Therefore, fossil-energy land cannot be used again and again each year; instead, as carbon fixation goes down in maturing forests new land would have to be acquired for carbon sequestration (and mature forests would have to be left standing). We therefore feel more comfortable with two other interpretations of the fossil-energy footprint (Wackernagel and Rees, 1996): the biomass approach and the biofuel

7 H. Haberl et al. / Ecological Economics 38 (2001) For the period we used the statistical yearbooks of the Austrian Central Statistical Office (e.g. O STAT, 1991), for 1995 we used the statistical handbook (O STAT, 1996). Additionally, we used material published by the Austrian Chamber of Agriculture ( Präsidentenkonferenz der Landwirtschaftskammer O sterreichs, Zahlen aus O sterreichs Land-und Forstwirtschaft 1986, 1995, 1997 ). 9 Nutrition balances for years prior to 1995 were published in the Statistische Nachrichten 1/1954, pp. 9 13; 1/1962, pp ; 1/1972, pp ; 1/1982, pp ; 2/1988, pp ; 2/1992, pp approach, both calculating the area that would have been capable of producing the same amount of fuel on a biological basis (see Giampietro and Pimentel, 1991; Read, 1994; Giampietro et al., 1997; Ferguson, 1999b). Some of these calculations indicate that CO 2 approach and substitution approach could lead to similar results. Since this interesting question was outside the scope of this paper, however, we decided to use the conversion factor of Wackernagel et al. (1999), without thereby endorsing a specific interpretation of fossil-energy footprints. Our results rely upon the following data sources. Imports and exports were assessed on the basis of Austrian trade statistics. 8 Domestic extraction of biomass, meat production, Austrian land-use data, etc., were taken from previous work at our department (Krausmann, 2000; Krausmann and Haberl, 2000; Krausmann, 2001). A prominent source was nutrition balances (e.g. Wildling, 1997). 9 In calculating the footprint of fossil-energy use we used a factor of 1.42 tons of carbon per hectare and year underlying Wackernagel s most recently published EF calculations (Wackernagel et al., 1999). We were not able to consider embodied energy of imported and exported goods due to the large amount of data this would require. While this omission could lead to some distortions, we do not believe that inclusion of embodied energy would dramatically alter our results. Wackernagel s (pers. comm., 2000) most recent figures indicate that Austria s trade balance in the mid-1990s resulted in a small net export of embodied energy: about 0.23 ha/cap should be subtracted from our results (for comparison: Sweden exports about 0.37 ha/cap as embodied energy). Since trade has been growing considerably throughout this period, the error should be smaller for earlier points in time. For obtaining technical factors we consulted the spreadsheets of Wackernagel et al. s calculations on Sweden, Santiago de Chile (Wackernagel, 1998) and Italy available over the Internet. 10 In calculating BC we generally followed the assumption that 12% of the biologically productive area should be reserved for biodiversity and is, therefore, not part of the BC (see Fig. 1). We did not consider the equivalence factors introduced only recently (Wackernagel et al., 1999) because they are variable in time and we did not have all data available to calculate these figures over the whole time series. 3. Results The results of our calculations are presented in Figs. 2 4, 6 and 7 for all three methods, both as absolute values and as per capita values. In general, please note that the results for the years between 1936 and 1950 should be left out of consideration. These data are interpolations between the last point of time before the Second World War (1936) and the first point of time after the Second World War (1950) for which we were able to derive consistent data sets. Since large deviations from these values can be expected for the time during and shortly after the Second World War, data for this period should not be interpreted. Fig. 2 shows the results of our footprint calculations. In the left column the EF is expressed in absolute values [km 2 ], the right column presents per capita values [ha/cap]. For comparison: Austria s total area is about km 2 (1 ha/cap in 1995); the potential biologically productive area is about km 2 (0.91 ha/cap in 1995 or about 10 We used material from the homepage of Redefining Progress ( Spreadsheets of the calculations for Italy and Santiago de Chile can be found at and iclei.santiago.htm. The calculations for Sweden, including forest productivity estimates, carbon absorption estimates, etc. are available at Footprint.html.

8 32 H. Haberl et al. / Ecological Economics 38 (2001) Fig. 2. The ecological footprint, Austria

9 H. Haberl et al. / Ecological Economics 38 (2001) Fig. 3. Local biocapacity, Austria

10 34 H. Haberl et al. / Ecological Economics 38 (2001) Fig. 4. Comparison of ecological footprint and biocapacity, Austria

11 H. Haberl et al. / Ecological Economics 38 (2001) ha/cap in 1926). The three methods lead to dramatically different results: method GY 95 yields an EF of km 2 in 1926, dropping to km 2 in 1950, nearly doubling afterwards to km 2 in The decline in EF before the Second World War reflects the effects of the economic crisis, leading to a sharp decline in food (above all meat) imports. The increase in footprint area after the Second World War reflects the rising level of biomass and fossil-energy consumption. If we take into account population growth by calculating a per capita footprint, we get an increase from 3.4 to 4.6 ha/cap. In contrast, method GY v leads to an almost identical EF in 1926 and in 1995 ( and km 2, respectively). Since Austria s population grew from 6.6 to 8 million in the same period, the per capita footprint falls from 5.6 to 4.6 ha/cap. As expected, method LY v gives again different results. In absolute figures Austria s EF drops from in 1926 to km 2 in 1950, increasing afterwards by a factor of km 2. The per capita footprint falls from 2.6 to 1.7 and rises to 3.3 ha/cap subsequently. In discussing the differences between the contributions of different land-use categories to the overall EF we can neglect built-up land because it is not very important quantitatively (at present, infrastructure land amounts to about 4% of the bioproductive area in Austria). What is interesting are the differences between the contribution of biomass and fossil-energy consumption to total EF. In method GY 95, the contribution of fossilenergy to total EF grows from 14% in 1926 to 32% in According to method GY v the contribution of fossil-energy is only 8% in 1926 (the value for 1995 is, of course, identical to GY 95 ). The reason is that GY 95 underestimates the amount of area that would have been necessary to supply the biomass demand in 1926 with global yields because global average agricultural yields were lower in 1926 than in Therefore, the identical fossil-energy EF component (0.46 ha/cap in 1926) contributes less to overall EF with method GY v than with GY 95. Method LY v gives different results again: fossil-energy use accounts for 17% of the EF in 1926 and 45% in This is due to the smaller footprint of biomass use resulting from the fact that yields are much higher in Austria than on the global average. Fig. 3 presents the results of our calculation of local BC in Austria in 1926 according to the three methods. Method GY 95 leads to a sharp increase in local BC to be explained by the fact that local yields grew considerably from 1926; therefore, the same area could produce much more biomass in 1995 than in Method GY v gives a different picture. Changes in BC as calculated with this method reflect differences between the increase in Austrian yields and the increase in global average yields, and changes in Austrian land-use patterns (reduction of cropland and grassland, growth of forest areas). Method LY v leaves the overall local BC constant; changes in land use are accounted for, of course, but the sum of bioproductive land available locally stays constant. Fig. 4 compares Austria s footprint with the locally and globally available Biocapacity, both in absolute values and as per capita figures. Concerning the ratio between Austria s EF and the locally available BC, method GY 95 and method GY v should give similar results because both use global yields to convert biomass flows to EF and the difference between constant yields (GY 95 ) and variable yields (GY v ) is approximately compensated in calculating BC. Both methods result in a small difference between Austria s EF and Austria s local BC: the overshoot over locally available BC remains small for the whole period. According to method LY v, however, Austria s EF is 160% larger than the locally available BC in 1926, 80% in 1950, and 305% in Turning to the comparison between Austria s per capita EF and global per capita BC, we get the result that Austria s per capita EF is similar to global per capita BC according to method GY 95 and GY v for the period between 1926 and Afterwards, Austrian overshoot increases quickly and in 1995 per capita EF is about three times higher than global per capita BC. According to method LY v Austria s per capita EF is about one-third smaller than global BC in 1926, but 84% larger than global BC in This difference between GY and LY methods can be explained by the fact that the EF is smaller according to method LY v because local yields are higher than global yields.

12 36 H. Haberl et al. / Ecological Economics 38 (2001) All three methods lead to the conclusion that Austria s EF was larger than locally available BC for practically all points in time. The overshoot over local BC was about constant with methods GY 95 and GY v, while method LY v gives the intuitively more plausible result that Austria s overshoot grew with growing consumption of biomass and fossil-fuels. Judged on the basis of global per capita BC, methods GY 95 and GY v also find Austria to be in a situation of overshoot in the period between 1926 and 1950, but not by a large margin. In contrast, method LY v indicates no overshoot of Austria over global per capita BC before the 1960s. All three methods find a significant overshoot over global per capita BC for current years. 4. Discussion 4.1. Austria s footprint 1995: comparison to Wackernagel s data Table 1 compares our results for 1995 with Mathis Wackernagel s (pers. comm., 2000) most recent footprint calculations for Austria. As previously stated, methods GY 95 and GY v are identical for the year 1995, and are methodologically comparable to Wackernagel s calculations. In order to facilitate a comparison between Wackernagel s and our results we here report his results without equivalence factors (Wackernagel et al., 1999). We added the third column in order to demonstrate the impact of equivalence factors on EF and BC. The fourth column shows the results obtained with method LY v which are not comparable to Wackernagel s results. Our EF result (GY 95 and GY v ) is about 5% higher than Wackernagel s result whereas our estimate of BC is about 17% higher. Our estimate of overshoot (EF minus BC as percentage of BC) is 10% and Wackernagel s is 23%. While this indicates a reasonably good accordance between the two calculations, there are some differences on the more detailed level. The difference in forest EF can be explained by different data sources: the FAO data Wackernagel uses obviously rely on an Austrian statistical source ( Holzeinschlagsnachweis ) that systematically underestimates wood production because it fails to consider most small forestry companies. The data sources we used correct this omission. The differences between Wackernagel s and our estimates of grassland EF and BC are due to the fact that the appraisal of yields, both globally and locally, is most difficult for grasslands due to low data quality and complicated production chains. The difference in built-up area probably results from the fact that Wackernagel considered urban areas whereas we only considered actually sealed soils (buildings, traffic infrastructure). The differences in BC are probably due to different definitions of the respective land-use classes. Because the area of every land-use class is multiplied with a yield factor (reflecting the difference between Austrian and the global yields) in calculating BC, differences in definitions change not only the relative contribution of each land-use category to BC, but also total BC. Land-use classes are notoriously difficult to define. For example, different estimates of Austrian forest area range from 40 to 46% of Austria s total area, mostly due to different definitions and data sources (Haberl et al., 1999). Whereas total BC (fourth column) can be measured accurately with method LY v, because bioproductive area can be assessed rather precisely and changes in land-use classes do not change the total, classification problems can lead to significant errors with methods GY v and GY 95. Considering equivalence factors enlarges Austrian EF-GY and reduces the estimate of locally available BC-GY, leading to an estimate of overshoot of 33%. Since we did not consider equivalence factors in our calculations, Austrian overshoot would have been bigger than suggested by the results reported here if we had taken equivalence factors into account. The fourth column shows that Austria s EF is more than one hectare per capita smaller if method LY v is used, reflecting the difference in local and global yields. A comparison between EF and BC shows that Austria s fossil-energy footprint alone is 86% larger than locally available productive land (while it only accounts for 46% of local BC if BC is evaluated on the basis of local productivity). That is, method LY v makes the EF more sensitive to fossil-energy use in countries with comparably favorable ecological conditions as Austria.

13 Table 1 Comparison of footprint calculations for Austria by Wackernagel (pers. comm., 2000) with those made by the authors [ha/cap] Wackernagel (pers. comm., Method 1, 2 (GY 95,GY v ) Method 1, 2 (GY 95,GY v ) with Method 3 (LY v ) without 2000) without equivalence without equivalence factors equivalence factors equivalence factors factors a Ecological footprint Austria 1995 Fossil-energy 1.44 b Cropland Grassland Forest Built-up Footprint on Land Local biocapacity Austria 1995 (12% of the area reserved for biodiversity) Fossil-energy Cropland Grassland Forest Built-up Local Biocapacity a Equivalence factors were introduced by Wackernagel in 1999 (Wackernagel et al., 1999) in order to reflect how productive a land-use category is compared to global average productivity. Cropland and built-up land are assigned an equivalence factor of 2.8, forests 1.1, grasslands 0.5. CO 2 land is assumed to be forest land (1.1) (Wackernagel et al., 1999). In order to compare our results (column two) with those of Wackernagel we here report Wackernagel s results for Austria without equivalence factors. b Since we have not been able to consider import and export of embodied energy in the time series we here report Wackernagel s estimate of fossil-energy EF excluding embodied energy for sake of comparability. H. Haberl et al. / Ecological Economics 38 (2001)

14 38 H. Haberl et al. / Ecological Economics 38 (2001) Fig. 5. Global and local (Austrian) cropland yields Fossil energy, biomass trade, and o ershoot While all three methods support the general conclusion that Austria currently is in a situation of global as well as local overshoot, closer analysis reveals quite noteable differences. For example, if we calculate Austria s EF based upon method GY 95,wefind a considerable increase in EF from 1926 to 1995, whereas the EF in 1926 and 1995 are nearly equal if assessed on the basis of method GY v. Per capita the EF increases by about one-third if calculated with method GY 95, while it declines somewhat if method GY v is used. The reason for this is that agricultural productivity gains lead to a reduction in biomass-related EF components (above all for human and livestock nutrition). This reduction is large enough to compensate for the growth in fossil-fuel related EF, despite the fact that overall biomass consumption of Austria grew by 53% from 1926 to 1995 (Krausmann and Haberl, 2000). As an example, Fig. 5 shows the increase in crop yields in Austria and worldwide. Global yields of wheat, rye, oats, barley and corn rise by a factor of 2.5, Austrian yields rise by a factor of 4.3 from 1926 to Method LY v again gives different results: plus 52% in absolute EF and plus 25% in per capita EF. Summing up, we conclude that the choice of yields assumed in footprint calculations can alter the result by a factor of 2 as can be seen from the difference between the result of method LY v (2.6 ha/cap) and that of method GY v (5.6 ha/cap) in Of course, these differences are not primarily the result of uncertainties in data, but are related to different definitions of the EF that answer different questions and might serve different purposes. The differences with respect to overshoot which can be obtained with the three methods (Fig. 4) accrue to the different meanings of the notions of overshoot and biocapacity. In order to analyze how plausible it would be to use overshoot as an indicator of (un)sustainability, we start with a discussion of possible reasons for overshoot in EF calculations. On the global level overshoot (EF BC) can happen for the following reasons: 1. Hypothetical land-use (van den Bergh and Verbruggen, 1999a,b); that is, land that would be needed to absorb fossil-fuel related carbon or grow biomass that could be used instead of fossil-fuels By using the word hypothetical here we do not want to argue that CO 2 enrichment in the atmosphere is no problem that needs to be addressed in order to achieve sustainability. We just want to distinguish between land that is actually used to produce goods and services, and land that would have to be available in order for socioeconomic metabolism to be sustainable.

15 H. Haberl et al. / Ecological Economics 38 (2001) Depletion of wood stocks in forests is a possible cause of overshoot that van den Bergh and Verbruggen (1999a) do not mention. Since wood-related EF is calculated based on an estimate of sustainable harvest rates, forest depletion can hypothetically lead to a situation where the global forest EF is bigger than actually available forest areas. Aboveground biomass-stocks (standing crop) in forests are about 30 times larger than yearly increases (net primary production), even if we do not take into account changes in socioeconomic timber storage. 3. EF can be bigger than BC if more than 88% of the bioproductive land is actually used; that is, if the 12% of bioproductive area that is usually reserved for biodiversity 12 is not kept out of use. On the global level, overshoot with respect to grassland or cropland is impossible except for changes in grain or meat storage because it is impossible to harvest more grass or grain than has been growing in the current year. Therefore, on a global level, consumption of these products must be close to production, at least for a 5 or 10-year average. On the national level, however, trade is another possible reason for overshoot over local BC: in many countries the EF of imported products is larger than the EF of exported products (Wackernagel and Rees, 1996). In Austria, forest area (and probably also forest biomass-stocks) has been growing for at least 150 years (Krausmann, 2001); therefore we can rule out local overuse of forests as a reason for overshoot over local BC. The percentage of biologically productive area in Austria which is not at all used for biomass production is probably smaller than 12%, but this does not help much in explaining changes in overshoot over time. The two dominant potential causes of overshoot in Austria that vary over time are clearly biomass-import/export and fossil-energy use. Analyzing the period from 1926 to 1995 we find two main trends: 1. Imports of agricultural biomass, above all grains, meat and living animals, are high in the early decades, but with agricultural yields growing quickly after 1950, Austria becomes a net exporter of agricultural produce in the 1970s. However, when we also consider forest products, Austria is either self-contained or a small net exporter of biomass-energy over the whole period (see Fig. 7 below). 2. Fossil-fuel consumption rises by a factor of about 4 over the whole period. Fig. 6 analyzes the relation between overshoot and the fossil-energy EF. Since we used a constant ratio between CO 2 emissions and fossil-en- 12 Wackernagel uses the assumption of a necessity to set 12% of the area aside for biodiversity conservation only as an example until better data on area needed for biodiversity conservation become available (Wackernagel, pers. comm.). Fig. 6. Overshoot and fossil-energy footprint, Austria

16 40 H. Haberl et al. / Ecological Economics 38 (2001) ergy EF, the trend in fossil-energy EF (secondary y-axis in Fig. 6) is identical to the trend in fossilenergy-related CO 2 emissions, which is the same in all three methods. However, the contribution of fossil-energy use to total EF is different in the three calculations, and local BC is also defined differently. As a consequence, results for overshoot over local BC derived with method GY v (which is almost identical to that of GY 95 ) differ considerably from those derived from method LY v : method GY v fails to find a relation between fossil-energy consumption and Austrian overshoot. Despite a surge in fossil-energy consumption, overshoot remains more or less constant. This result can be explained by biomass imports and exports (see below). In contrast, method LY v finds overshoot and fossil-energy EF to be closely related after 1950, whereas the trend between 1926 and 1950 has to be explained mainly by biomass-imports. Fig. 7 further discusses the relation between biomass-imports and exports expressed in two units: energy content and EF components. The left column accounts for biomass-imports and exports using their gross calorific value. We use energy because the mass of imports and exports could be dominated by materials with high water content. The import of grassland products (e.g. milk, cheese, meat, living animals) is negligible if it is expressed as energy flow: only in the period are these imports relevant at all. The balance of imports and exports is small. In general, Austria is either self-contained or a small exporter of biomass. The significant food imports in the early years are approximately compensated for by wood exports in energetic terms. The right column shows the respective footprint components, calculated with method LY v. The import of grassland EF shows considerably, especially in the years In that period the import of meat and living animals was significant. Although biomass-energy imports and exports are nearly balanced, imported and exported biomass EF differ significantly: imported EF is considerably larger than export EF. This is due to the assumption used in method LY v that imports are calculated at world average yields, whereas exports are calculated using the weighted average of imported and domestically extracted material (see Section 2). If we remember that Austria s bioproductive area is below km 2, the order of magnitude of imported and exported biomass-related EF is quite relevant. For example, in 1995 the biomass-import EF was more than km 2, compared to a fossil-energy EF of about km 2. In the 1980s and 1990s Austria had a notable net import footprint related to biomass flows, although in these years Austria was a net exporter in terms of biomass-energy. The reason is that exports accrue mostly to domestic extraction with a low EF per unit of biomass-exported (because of high Austrian yields), whereas imports are evaluated with low global average yields. If the EF of imports and exports is assessed on the basis of equal yields, Austria is a (small) exporter of biomass EF. It should also be noted that our assumption (dictated by data availability) that imported biomass is produced at world average yields is likely to be quite unrealistic. For example, meat imports in 1926 came almost exclusively from neighbouring countries with similar yields as Austria. Moreover, it could well be that unfertile countries with low yields tend to be no major net exporters of agricultural produce. Therefore, it would be useful to calculate, for each agricultural product, the global average productivity of traded agricultural produce as weighted average of the productivity of domestic extraction of the product in all net exporting countries. This productivity would probably deviate significantly from global average productivity for many products e.g. if only highly productive countries are exporting significant amounts of biomass. An even more demanding method would be to assess for each product and each year the EF components associated with imports based on the detailed yield data of the countries from which products were imported (van Vuuren and Smeets, 2000). This discussion indicates that overshoot over local BC is not easily interpretable in terms of sustainability trends. Methods GY 95 and GY v lead to the phenomenon that an increase of fossilenergy use by a factor of 4 and an increase in biomass use by a factor of 2 is not really reflected

17 H. Haberl et al. / Ecological Economics 38 (2001) Fig. 7. Biomass-imports and exports expressed as ecological footprint (method 3 LY v ) and energy flow.

18 42 H. Haberl et al. / Ecological Economics 38 (2001) Table 2 Average yields of cropland, grassland and forests in Austria 1926 and 1995 and the world 1995 a AUT 1926 AUT 1995 World 1995 (a)yields [energy/area] Cropland products [MJ/m 2 ] Grassland products [MJ/m 2 ] Forest products [MJ/m 2 ] (b) Corresponding footprint per amount of product [area/energy] Cropland products [ha/gj] Pasture products [ha/gj] Forest products [ha/gj] a Sources: see Section 2. in EF (GY v ) or is compensated by a growth of BC (GY 95 ), leading to nearly constant overshoot over the whole period in both cases a result that is intuitively not very plausible if overshoot should be interpreted as a measure of unsustainability. Method LY v gives an intuitively more plausible result; nevertheless, there are still problems with the plausibility of biomass-trade-related EF components. Of course, it remains an open question whether or not it is useful at all to assume that a country is sustainable if its EF equals its domestic BC (van Vuuren and Smeets, 2000) Biomass yields, footprints, and policy The results discussed above have shown the extent to which EF calculations depend on assumptions on biomass yields which are highly variable in space and time. Additionally, yields are highly dependent on the type of land-use (cropland, grassland and forest): yields are highest on cropland, medium in forests and lowest on grassland. This is not only a function of the net primary productivity (NPP) of these land-use classes, but depends also on the following factors: 1. A different percentage of aboveground NPP (ANPP) is usable for society: about 50% of the ANPP of modern crops can be harvested; in forests only about 25% of ANPP can be harvested as timber; on grasslands about 60 75% of grassland ANPP can be harvested as animal fodder (Haberl et al., 1999). 2. Whereas most cropland products and all forest products are considered in EF calculations on the level of primary produce (plant products), grassland is evaluated on the basis of livestock produce: living animals, meat, milk, eggs, etc. Since about 85 90% of biomass-energy is lost in the transformation process, grassland yields as used in EF calculations are much lower than cropland or forest yields. Table 2 shows the yields we used in our EF calculations in Austria in 1926 and 1995, and the global yield in 1995 as biomass-energy per unit area and the corresponding EF component per energy content of biomass products. A comparison of the first two columns shows to what extent the EF per unit of product can be influenced by increases of yields through agricultural intensification. A comparison of the last two columns demonstrates the difference in Austrian and global average yields. The implications on biomass-related EF depend on the calculation method: if method LY is used, local/global differences influence EF; if method GY is used, local/ global differences are reflected in local BC. The dependency of EF and BC on yields has implications for the policy recommendations that can be derived from the footprint concept. Until now, the footprints have mainly been used to suggest changes in consumption (e.g. Wackernagel and Rees, 1996) or as an argument for the unsustainability of current population trends (Ferguson, 1999a,b). However, given the difficulty to pursue policies that aim at reducing per capita consumption or at a reduction of population in