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There has lately been an increased interest in sustainability assessment, and models have been developed to assess the sustainability of a well-defined area, for instance, a landscape, a region, or an island. The model includes not only ecological processes but also socio-economic activities. Our experiences with sustainability assessment projects are still very limited, but from many sides it has been proposed which key variables to include in such an analysis. The use of work energy as a sustainability indicator that includes expressions of natural and socio-economic activities has been proposed and also tested with reasonable success. The efficiency of the use of work energy in general and the amount of work energy needed to maintain the various subsystem and their capacity of work energy were included in this analysis. It is, however, clear that one indicator is insufficient to assess the sustainability of a very complex system. It has, therefore, been proposed to supplement the use of work energy as an indicator with the development of models of the most important element cycles for natural and socio-economic systems, namely the cycles of carbon, nitrogen, and water. Two ecological factors are in focus when it is discussed what is important to include in a sustainability analysis, namely the services offered by the ecosystems and the biodiversity, which is important for the spectrum of resistances to possible impacts on the systems. It is important to include these two ecological factors as direct indicators in the sustainability analysis, although they both to a certain extent are covered by the work energy analysis. Socio-economic indicators are, of course, also needed but it is beyond the scope of this article.
The result of use of models for the assessment of the global sustainability by the use of a ‘limits to growth’ like model is presented. The model has been used to assess the global development in the case of: (1) more support to the developing countries by the industrialized countries, (2) more green tax, (3) more investment in pollution control, and (4) more investment in education and research. It can be shown that these investments lead to a win–win situation.
biodiversity, ecosystem services, element cycling, exergy, sustainability, work energy
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