Have one person in each community record the number of pieces taken by each community member in each round. After each round, count how many pebbles each community has remaining in the pile, and add an equivalent number of pebbles to the pile. Play three or four rounds, pausing after each round to find out if any community members did not survive. Compare per capita pebble ownership around the room. Propose that all communities are taking pebbles from one com- munal pile.
Some communities are at war with one another, and some are unaware of the others.
Write suggestions on the chalkboard. Now explain that this scenario represents the current state of our common resource, the atmosphere. Automobile and factory carbon dioxide emissions are heating up the atmosphere, causing the greenhouse effect and changing the ecology of the planet. Each pebble taken represents one share of carbon dioxide emissions generated by that person. The pebbles represent a valuable renewable resource.