干旱区生态环境知识资源中心

As the concept of sustainable development is more accepted and incorporated by institutions, it becomes necessary to evaluate the performance of the national economy based on new methods and not only on economic indicators. Despite the importance of sustainability to the preservation of natural ecosystems and services, there is no agreement in the world scientific community concerning a methodology to evaluate that concept. In the last decade, two scientific tools have been extensively used worldwide to measure the human impact on nature: Ecological Footprint and Emergy Synthesis. Papers trying to combine them, and to obtain more accurate results have appeared in scientific literature, of which Zhao's et al. (2005) approach is an important one. Unfortunately, some weak points of the original methods still remain in the new approaches proposed. The objective of this work is to discuss some weak points found in the Ecological Footprint and Emergy Synthesis and to use the positive aspects and potential improvements from both methodologies at a national level. Emergy deals with the notion that all energy that is used directly and indirectly in a process to deliver an output product, flow or service should be accounted for. A new definition for Biocapacity was introduced meaning "the natural area's capacity of receiving renewable energy", rather than "usable biomass" as proposed by the conventional Ecological Footprint methodology. The questions to be answered by the proposed methodology are how much land would be equivalent to consumption, if products were generated solely by the use of natural renewable resources (Emergetic Footprint), and how much land would be available in the system considering world's average capacity of receiving renewable energy (Emergetic Renewable Biocapacity). A new category called "areas not occupied by humans" is included in the Biocapacity. It is composed of open ocean, deserts and frozen land (areas excluded from the conventional Footprint method). Footprint or consumption means the load imposed by humans on the environment and was grouped in categories: cropland, forestry, animal products and energy resources. Ecological Fooptrint using Emergy was used to assess Brazil as a case study, resulting in a Biocapacity of 62.2 gha person(-1) and a Footprint of 41.9 gha person(-1), using data from 2004. The positive aspects of the approach proposed are: (i) its ease of application at global and national scales; (ii) the indicator of consumption (Footprint) accounts for the direct and indirect energy used to generate products and services; (iii) a new category considering areas excluded from the conventional method was included in the Biocapacity calculation, which can be a valid step towards the evaluation and assessment of services provided by nature. On the other hand, the approach has as main limitations: (i) it is not possible to make comparisons between the Biocapacity and Footprint for each category: (ii) there is a need for a handbook with well-explained calculations of emergy intensity factors. (C) 2011 Elsevier Ltd. All rights reserved.