disaster insurance), and bearing the loss (see White, 1974; Burton et al., 1978). Because this literature focuses on hazards over which humans have very limited control, it understandably offers a more detailed typology of adjustments than of mitigations.


Robustness is one of a number of related concepts, all of which need more careful conceptualization and analysis in relation to global change issues. Resilience often refers to the property of returning to a previous state after being altered by changes in the environment. Resistance often refers to the property of remaining unchanged in the face of changes in the environment; vulnerability often refers to the opposite—the characteristic of being easily affected by perturbations in the environment—whether or not the system returns to its previous state. We use the term robustness for its connotation of continued health in the face of environmental change. But health, in human systems, can be a subjective term, with some individuals favoring minimum deviations from preexisting states and others desiring permanent changes in particular directions. Thus, whether it is better for human systems to be resistant in the face of environmental change, or vulnerable but resilient, or vulnerable to certain kinds of permanent alteration, is a value-laden question. But it is one that can be informed by analysis of the different ways human systems change when their environments do.


There is considerable controversy in the literature, both with respect to biological and human systems, over the question of whether diversity tends to produce stability or vulnerability in systems. The effect of diversity may well depend on the definition of stability used or on other factors, such as the spatial or temporal scale of analysis being made. The examples used here are not meant to exemplify general conclusions about diversity and stability. For more detailed discussions of the issue in the biological context, see Elton (1958), May (1973), Pimm (1982), and Kikkaw (1986). For extensions to social systems, see Holling ( 1986), Timmerman ( 1986), and Liverman et al. (1988).


It is, of course, possible for humans to replant tree seeds if the climate shifts faster than tree species can naturally migrate. However, because of sensitivities of tree species to soils, photoperiods, and the presence of other species, artificial migrations of this sort may not be sustainable. Survival of tree species depends on a favorable ecosystem, and ecosystems may not migrate well.


The reciprocal of this ratio, gross national product per unit of energy demand, is a measure of the economic productivity of energy.


This formulation is indebted to Robinson (1989).


Our account of this comparison draws heavily on an analysis done by Mortimore (1989) for the committee.


This section draws heavily on the much more detailed discussion of the relations of decision theory to global climatic change by Fischhoff and Furby (1983). Additional provocative ideas for research can be found there.

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