In its 1987 report, the World Commission on Environment and Development cal
led for a global risk-assessment program to buttress and extend the work of
the United Nations Environment Programme. This article reports on an inter
national project centered at Clark University in the United States that has
explored the causes and consequences of growing environmental risk over a
50-70 year period in nine regions distributed throughout the world. The nin
e regions are: Amazonia, the Eastern Sundaland region of southeast Asia, th
e Ukambani region of southeastern Kenya, the Nepal Middle Mountains, the Or
dos Plateau of China, the Aral Sea, the southern High Plains of the United
States, the Mexico City region, and the North Sea. The authors begin by con
sidering the notion of criticality and developing definitions and a classif
ication of environmentally threatened regions. Research teams were assemble
d for all nine regions and studies conducted. In this article, the authors
review the development of concepts and methods used in these studies and th
e major cross-cutting findings that emerged. They argue that a growing disj
uncture exists in the studied regions between the rapid rates of environmen
tal degradation and the slow pace of societal response, threatening environ
mental impoverishment and loss of options for future generations and escala
ting costs of substitution in resource use and risk mitigation efforts.