In this activity, learners are introduced to tree rings by examining a cross section of a tree, also known as a “tree cookie.” They discover how tree age can be determined by studying the rings and how ring thickness can be used to deduce times of optimal growing conditions. Next they investigate simulated tree rings by applying the scientific method to explore how climatic conditions varied during the Little Ice Age. Use this activity to begin discussions on global warming and climate change. This lesson guide includes background information and handouts. Note: cost of materials does not include cost of purchasing "tree cookies."