Since the onset of scientific and public concern over global environmental risks in the mid-1980s, attention has focused prominently on the global scale of impact. Indeed, as noted earlier in this volume, systemic global environmental risks – such as ozone depletion and global warming – have commanded the lion's share of assessment work and the early international efforts to respond to environmental threats to the planet. At its core, however, global environmental risk is about variability –in human driving forces, in vulnerability to change, in the types and magnitude of impacts. Although the assessments of the Intergovernmental Panel on Climate Change (IPCC 1996a, b, c, 1997, 2001) surely advance our understanding of the science of climate change and the general state of knowledge concerning potential impacts, it is also clear that the regional and social patterns of impacts remain unknown at any level of precision. Yet it is the rate and pattern of accumulating stresses and their interaction with place-specific vulnerabilities that will drive the realities as to the eventual severity of these effects and the potential effectiveness of mitigation efforts and human adaptation.
The lesson from climate change is a more general one: risks do not register their effects in the abstract; they occur in particular regions and places, to particular peoples, and to specific ecosystems. Global environmental risks will not be the first insult or perturbation in the various regions and locales of the world; rather, they will be the latest in a series of pressure and stresses that will add to (and interact with) what has come