Interactions between societal, natural, and infrastructure systems can be beneficial or harmful to society. Society benefits from natural systems by being provided with the basic necessities of life (air, water, and food). However, events such as stratospheric ozone depletion demonstrate that society ultimately can be harmed by societal impacts on natural systems. Domain knowledge is developed from observation of natural, societal, and infrastructure systems. Domain knowledge is contained within scientific knowledge and engineering knowledge. Scientific knowledge is gained through structured observation and rigorous analysis of natural and societal systems. Engineering knowledge is partially developed from scientific knowledge and is used to manipulate natural and societal systems. Technology is the application of engineering knowledge. In the past two centuries scientific and engineering knowledge have produced technologies that affect the interaction between societal and natural systems. Although scientists and engineers are in positions to advise on policies to address problems involving societal/natural system interactions, their contributions are not always fully utilized. This research examines feedback mechanisms that describe societal, natural, and infrastructure system interaction to develop an improved understanding of the dynamic interactions between society, natural systems, infrastructure systems, scientific and engineering knowledge, technology, and public policy. These interactions are investing through and opposing case study analysis performed using computer simulation modeling. The stratospheric ozone depletion study represents a case in which domain experts successfully influenced public policy. The U.S. civilian nuclear power study represents a case in which domain experts were less successful in influencing public policy. The system dynamics methodology is used to construct these two highly integrated models of societal-natural system interaction. Individual model sectors, based on existing theory, describe natural/infrastructure systems, knowledge and technology development, societal risk perception, and public policy. The work reveals that the influence of scientists and engineers in the public policy is due in part to their ability to shift dominance between causal feedback mechanisms that seek to minimize societal risk from natural systems and feedback mechanisms that seek to minimize the economic risk of increased regulations. The ability to alter feedback mechanism dominance is not solely dependent upon scientists and engineers ability to develop knowledge but to a larger extent depends on their ability to interact with policy makers and society when describing issues involving natural and infrastructure systems.

Global civilisation, and therefore population health, is threatened by excessive inequality, weapons of mass destruction, inadequate economic and political theory and adverse global environmental change. The unequal distribution of global foreign exchange adjusted income is both a cause and a reflection of global social characteristics responsible for many aspects of these inter-related crises. ¶ The global distribution of foreign exchange adjusted income for the period 1964-1999 is examined. Using data for more than 99% of the global population, a substantial divergence in its distribution is found. The global Gini co-efficient, adjusted for national income inequality, increased from an already high value of 71% in 1964 to peak at more than 80% in 1995, before falling, very slightly, to 79% in 1999. The global distribution of purchasing parity power income is also examined, for a similar period. Though also found to be extremely unequal, its trend has not been to increased inequality. Implications of the differences between these two trends are discussed. ¶ A weighted time series index of global environmental change (IGEC) for the period 1960-1997 was also calculated. This uses nine categories of global time series environmental data, each scaled so that 100% represents the level of each category in nature prior to anthropogenic change; zero represents decline to a critical point. This index fell from 82% in 1960 to 55% in 1997, and will further decline during this century. ¶ Using evidence from several disciplines, it is argued that the decline in the IGEC correlates with major macro-environmental changes, which, combined with flawed social responses to scarcity and its perception, place at risk the ability of civilisation to function. This could occur because of the interaction of conflict, economically disastrous extreme climatic events, deterioration of other ecosystem services, regional food and water insecurity, and currently unforeseen events. Uncertainty regarding both a safe rate of decline and the tolerable nadir of the IGEC is substantial. ¶ Substantial reduction in the inequality of foreign exchange adjusted income is vital to enhance the development of policies able to reverse the decline in the environmental goods which underpin civilisation, and to promote the co-operation needed to maximise the chance that civilisation will survive.