Among environmental policy questions, consideration of environmental justice (EJ), which began to be examined in the United States during the 1980s, is viewed as increasingly important, not only within the US and other industrialized countries, but when considering trade between richer and poorer countries. In the literature, the term environmental injustice is used to indicate that minority groups and/or the poor receive disproportionate harmful environmental effects. At this moment, we are fairly sure that environmental injustice exists in some circumstances, but there is heated debate as to why. A classical debate is on the degree to which EJ is a function of racial inequalities versus income-based market dynamics. It is important to know what role both race and income-class play, especially dynamically.

Environmental disamenities’ siting decisions may be driven by various factors such as discriminatory intention, economic costs, or political costs. Residential decisions may also be made based on various criteria such as residential similarity preference and utility of a lot given price, quality and proximity to jobs. Dynamically, the racial and ethnic composition of residents may change after disamenity-producing firms and facilities are located within a neighborhood because these produce negative effects. Some residents may want to leave such areas, and individuals who are able to leave are more likely to be comparatively affluent. Poor residents, who have fewer resources, may not have such an option. The movement of affluent people out of the area may depress property values, making housing more affordable, which further attracts the poor to move in. This dynamic aggravates environmental risk disparities. Because minority residents are disproportionately poorer than white residents, observed disparities can appear to be caused by racial factors even when they are not. This dynamic nature of multiple sitings of heterogeneous actors is not easy to examine.

Using an agent-based model (ABM), we can dynamically examine the issue of “race” versus “class.” Firm agents are introduced to a landscape based on different possible social processes. The landscape also contains Resident agents that are defined as “majority” or “minority.” The Resident agents are also assigned differential incomes as a resource constraint. We can compare four different scenarios: when mean and standard deviation (sd) of incomes is the same across races, when sd is the same, but mean is lower for minorities, when means are the same and sd is greater for the minority, and when means are the same and sd is greater for the majority. In the experimental structure of the ABM, by focusing on different possible distributions of income between majority and minority residents, we can explore dynamic effects of race versus class and analyze which seems most important and how they interact.

These experiments not only help us understand what social processes are consonant with observed environmental inequities, but may also help us begin to understand how to solve the observed problems of environmental injustice. In an age of scarcity, we need to understand what factors of dynamic social interaction cause unintended consequences that harm vulnerable populations.