Principles and Characteristics of a Cumulative Analysis
The spatial and temporal boundaries of the affected environment must be defined for the cumulative analysis. The components of the affected environment considered in a cumulative analysis are the same resources, ecosystems, and human communities that could be affected by the proposal. However, the spatial limits of the cumulative analysis may be broader than the analysis of the proposal because the cumulative analysis must consider all activities that affect those environmental components, even outside the area affected by the proposal. For example, a migratory animal, such as caribou, may only be affected by the proposal within a 10-kilometer radius of the project site; however, during migration, the caribou may be affected by other activities hundred of kilometers away. Therefore, those activities must be considered in the cumulative analysis. Although other activities must be considered, the geographic boundaries must not be extended to the point that the analysis becomes unwieldy and is not useful for decision-making.
The temporal boundaries of the cumulative analysis often extend beyond the period of time considered in the analysis of the proposed action alone. This is because the cumulative analysis must also take into account activities that occurred before the proposed action is initiated as well as after the proposed action is completed, if those activities affect (or could affect) one or more of the same resources affected by the proposed action.
The description of the affected environment should include an environmental baseline. A baseline is the condition of a resource, ecosystem, or community without the effects of the activities considered in the cumulative analysis. The cumulative analysis will measure effects, quantitatively or qualitatively, relative to this baseline. Baselines for some resources and ecosystems in the Arctic may have to be defined with a greater degree of variability than baselines in non-Arctic areas because many resources and ecosystems in the Arctic vary considerably from year-to-year.
Reasonable assumptions must be made about some activities that would contribute to cumulative effects even if there is uncertainty regarding the activities and their potential effects. The degree of specificity of the cumulative analysis should be consistent with the nature, scale, and degree of certainty regarding the proposed activity.
A cumulative analysis should describe the incremental contribution of the proposal to cumulative effects. Thresholds can be identified for some resources, which are levels of impact beyond which the resources cannot be sustained in a stable state. The cumulative analysis should address whether thresholds could be exceeded because of the contribution of the proposed action to other cumulative activities affecting resources. For example, some contaminants accumulate in biological resources (marine mammals, birds, and fish) used by Arctic communities for subsistence purposes. Subsistence resources make up a large part of the diet of some native communities. Therefore, the potential risk to the health of indigenous people who consume these resources should be a significant issue in the analysis for projects that could add to the contaminant levels of subsistence resources. In these cases, the cumulative analysis should identify thresholds for contaminants in selected subsistence resources.
The cumulative analysis should describe additive and synergistic effects. Additive effects are similar in nature to the effects of the proposal but are greater in magnitude. Synergistic effects do not occur from a single activity but are the result of the interaction of two or more activities.