The evidence collected so far suggests that climatic changes are simply a natural occurrence on Earth. The extent to which human activity affects the way the global climate is changing is now only beginning to be understood.
Trees are some of nature's most telling timekeepers.
Tree growth depends on local conditions, which include the availability of water. Because the amount of water in the environment varies from year to year, scientists use tree-ring patterns to reconstruct regional patterns of drought and climatic change. This field of study is known as dendrochronology. To study tree rings, dendrochronologists often use straw-sized core samples extracted from trees. In this student activity, drinking straws will be used to simulate tree-ring core samples.