Objective. Sound environmental policy is fully dependent upon sound science. However, we have little scientific knowledge of the driving forces behind environmental change. We use the well-known I = PAT formulation (environmental impacts are the multiplicative product of population, affluence, and technology) as a framework to assess the relative impacts of driving forces. Methods. We introduce the concept of plasticity—the potential for each factor to vary, particularly because of purposive human action (e.g., policy)—to fine tune our understanding of how each factor can influence different impacts. We illustrate plasticity by assessing each driving force for a variety of environmental impacts. Results. We demonstrate that population, affluence, and technology have different potentials for mitigating different types of impacts and that no one factor is of greater importance than the others. Conclusions. We conclude that plasticity measures can guide policymakers toward identifying and prioritizing those environmental problems most responsive to policy solution.