From the time it appeared in the 1978 regulations implementing the United States' National Environmental Policy Act, agencies have struggled with the concept of cumulative impacts in their environmental analyses. Although the regulations touch on every aspect of environmental impact analysis, they merely define cumulative impacts and then refer to them only in other definitions in the Terminology section. Agencies have become fairly adept at analyzing direct and indirect effects, but cumulative impacts have posed more difficult methodological problems, giving rise to a host of legal challenges. The courts have attempted to sort out what is required for adequate cumulative impact analysis, causing agencies to reactively develop agency-specific, and often complex, methodologies. This article relates the basic concepts of cumulative impact assessment to emerging case law, focusing on US federal land management issues. From this basis, it proposes a novel approach to cumulative effects analysis that (1) uses the doctrine of proximate cause from tort law to ensure that there is a reasonable probability that a proposal will affect a resource of concern before undertaking analysis of other effects on that resource, and (2) uses the No Action Alternative's trajectory of resource conditions (which incorporates the effects of other past, present, and reasonably foreseeable future actions) as the baseline for assessing an action's incremental effects. The proposed six-step process integrates effects analysis by describing the overall effects of the No Action Alternative, altered by an action's direct and indirect (or incremental) effects, as the cumulative effect on a particular resource of concern.
Environmental Practice 10:107–115 (2008)