1 科目：專題討論 2-1 指導教授：林俐玲教授；鄭皆達教授；陳鴻烈教授；林德貴教授 報 告 人 ：翁志成 98 年 12 月 4 日 How to calculate and interpret ecological footprints for long periods of time: the case of Austria 1926–1995 Helmut Haberl, Karl-Heinz Erb, Fridolin Krausmann, 2001, ecological Economics 38

2 Outline  Abstract  Introduction  Methods  Results  Discussion  Conclusions

3  In this paper we present calculations of the ecological footprint (EF) for Austria 1926–1995, based upon three different methodological approaches.  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; (3)variable local yields for domestic extraction and variable global yields for imported biomass. Abstract

4  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.

5 Keywords:  Ecological footprint (EF);  Socioeconomic metabolism;  Biological productivity;  Biomass yield;  Overshoot;  Sustainability indicators

6  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 CO2), 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. 1.Introduction

7  ‘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.  In this paper we will present calculations of Austria’s EF for 1926–1995. 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.

8 2.Methods  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.  actual productivity of country A can be higher or lower than the global average.

9  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]?  We have chosen to calculate the EF in Austria 1926–1995 with three different method (Global Yield 1995 、 Variable Global Yield 、 Variable Local Yield), each of which reflects a consistent set of assumptions (see Fig. 1)

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11 3. Results  Fig. 2 shows the results of our footprint calculations.

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13  Fig. 3 presents the results of our calculation of local BC in Austria in 1926 according to the three methods.

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15  Fig. 4 compares Austria’s footprint with the locally and globally available Biocapacity, both in absolute values and as per capita figures.

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17 4. Discussion  Table 1 compares our results for 1995 with Mathis Wackernagel’s (pers. comm., 2000) most recent footprint calculations for Austria.

18 5% 17% EF-BC=10%EF-BC=23%

19  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. 2. Fossil-fuel consumption rises by a factor of about 4 over the whole period(see Fig. 7 below).

以前出口 以木材為主 進口肉 類是明顯的

21  EF calculations depend on assumptions on biomass yields which are highly variable in space and time.  Yield 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:  The land harvested.  Cropland products and all forest products are considered in EF calculations on the level of primary produce (plant products). 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.

22  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.

23 5. Conclusion  We still believe that area-based indicators such as the EF should be among the few selected aggregated ‘headline indicators’ that can be used to describe the ‘physical economy’ on different spatial levels and in time-series analyses. We also feel that area use is an important process with respect to sustainable development that should be monitored.

24  Our study suggests that, although it is feasible to calculate the footprint of nations in a long time-series, it is not straightforward to interpret the results. Currently used methods are useful to demonstrate local availability and appropriation of biocapacity for one point in time. Biocapacity, in these methods, is defined as area of cropland, grassland or forest with global average productivity (plus built-up area). In this approach biocapacity is implicitly defined as the capacity of area to sustainably produce biomass (biomass-related products) and to absorb CO2.  This convention is useful for the comparison of EF and BC of different nations because both BC and EF are expressed as area [hectares] of standardized productivity. While this is a valuable tool to demonstrate and communicate overuse of natural resources.

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