I've had success in using curriculum supplements, such as Project Wild, Project Learning Tree, and Project WET/WILD Aquatic.
Many of the activities are set up as Problem-Based Learning Scenarios which include role-playing and integrate environmental science with engineering design, social studies, civics, public policy, mathematics, and literacy.
As an example, one activity frames a debate about whether to construct a dam in a wilderness area as a town-council meeting. Various 'attendees' or roles for students to play include: the lone sheriff for the existing 700 people in the town, a Native-American tribes-person concerned that their heritage site will be flooded, a farmer- looking for relief from annual flooding, a water-sports-enthusiast- escited for the possiblility of lake sports, a lumber-baron, concerned that their timber-land will be flooded, a fly-fisher- worried that their river will no longer exist, and town-council people who will make the decision, based on evidence that each of the former characters presents at the meeting. Social studies integration via historical parallels, civics- workings of a town council, and civil planning, are integrated with environmental science, bio-diversity, and human impact.