Monitoring patterns of sustainability in natural and man-made ecosystems

By means of a systemic analysis of the relationships among components of a systemʹs web, the flows of energy and other resources converging to produce the output (biomass, biodiversity, assets, industrial products) can be evaluated on a common basis, i.e. the content of solar equivalent energy (hereafter, emergy; Odum, H.T., 1996. Environmental Accounting. Emergy and Environmental Decision-Making. Wiley, New York). Indices and ratios based on emergy flows can be calculated and used to evaluate the behavior of the whole system. Their dependence upon the fraction of renewable and nonrenewable inputs as well as locally available versus purchased inputs from outside is stressed. A new index of sustainability is also defined and applied to case studies. The trends of these indices provide useful information about the dynamics of economic systems within the carrying capacity of the environment in which they develop. When a particular sector or production process is focused on, instead of a national economy, emergy based indices provide insights into the thermodynamic efficiency of the process, the quality of its output, and the interaction between the process and its surrounding environment.