CO_2 emissions and emergy indices: does a correlation exist?

摘要

Carbon dioxide represents only 0.03% of total atmospheric gas composition but it is nevertheless essential for life in the biosphere. Projections of CO_2-induced climate change may remain equivocal, yet a growing scientific consensus supports a predicted 2-4℃ temperature increase in this century, which will likely affect all the processes and cycles within the biosphere. Two human activities, in particular, contribute dramatically to the increase in atmospheric carbon dioxide concentration: the combustion of fossil fuels (with the ex-novo production of greenhouse gases) and the deforestation (which causes a drastic reduction in photosynthesis by reducing the plant biomass). The study of the carbon dioxide cycle should be the cornerstone of any energy policy compatible with managing our environment and supporting sustainable development. During these last years we had developed a multidisciplinary approach based on different (thermodynamic) methodologies in order to assess the sustainability of a territory or a region by the definition of some sustainability indices, especially the emergy-based ones. Emergy was defined by H.T. Odum as the available solar energy used up directly or indirectly to make a service or product. The emergy concept is the basis of a system of indicators able to evaluate the efficiency, the environmental stress and the sustainable use of resources, involved in a single process or in a system at various scale. The total emergy can be divided into the renewable and non renewable inputs, into the local and imported from outside inputs: these distinctions allow the calculation of several indices useful for a deeper insight of the system under study. The aim of this paper is to verify if a correlation exists between these holistic sustainability indices and the net CO_2 equivalent emitted. This correlation could offer new perspectives and directions in order to define new sustainability indices that take into account the resource use and the CO_2 production. As case studies we have selected several territorial systems in Italy, for preliminary results and comments.