Architecture, Building and Planning - Theses
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ItemFitness landscapes and the precautionary principle : the geometry of environmental risk( 2000)Current environmental impact assessment methods assume by default that, where there are multiple stressors on an environmental system, that such stressors act independently and additively. There is evidence suggesting this assumption does not hold for all such sets of stressors. Such evidence places this assumption in conflict with the precautionary principle. This thesis proposes a new means of modelling a set of environmental stressors. The model allows estimation of the sensitivity of the cumulative impact of the set to variations in number of stressors and the degree to which they interact. The method developed has, as its default assumption, the potential for non-linear interaction between stressors within sets. This method is in keeping with the objectives of the precautionary principle. The model draws on empirical data from the environmental sciences, and mathematical and computational techniques from complex adaptive systems theory. In doing so, it draws on methods used in a range of disciplines for modelling non-linear interactions between multiple parts of a complex system. These methods share the common mathematical foundation of fitness landscape theory. It is argued that the proposed model allows statements about the sensitivity of the gross effect from a set of stressars to be made when the number of stressors in the set, and/or their degree of interaction, is varied. It is argued that this can be achieved through identification of properties of the set itself, without reference to the specific causal chains determining behaviour in specific instances. While such properties are very general, they offer the potential of parameterising of the effects of sets of stressors where interactions are highly uncertain and empirical data severely limited, i.e., situations which would typically invoke the precautionary principle. The model represents a generalisation and abstraction of the Scheffe {q,m} simplex-lattice method used for modelling laboratory based chemical mixture experiments. The output of the model suggests that the cumulative impact arising from a set of environmental stressors is: a) acutely sensitive to variations in the number of stressors in the set; b) sensitive to variations in the degree of interaction between these stressors, and that this sensitivity increases with the number of stressors in the set; c) acutely sensitive to simultaneous variation in the number of stressors in the set and the degree to which they interact. It is argued that knowledge of the acuteness of these sensitivities provides a valuable additional input into precautious environmental decision making.