How tree rings tell time and climate history

Most of us learned as children that the age of a tree could be found by counting its rings. Rings of trees growing in temperate climates can indeed tell their age through their annual rings and also help determine the age of wood used to construct buildings or wooden objects. The ages of wooden objects can be revealed by cross-dating, the process of matching ring patterns between wood samples of known and unknown ages. Concentric rings of various widths mark the annual growth of trees. Photo by Peter Brown, Rocky Mountain Tree-Ring Research. What do tree rings tell usThe underlying patterns of wide or narrow rings record the year-to-year fluctuations in the growth of trees. The patterns, therefore, often contain a weather history at the location the tree grew, in addition to its age. In dry environments, such as the Middle East or U.S. Southwest, tree rings typically record wet or dry years, and in cooler areas (high latitudes or high elevation), the ring widths are often a proxy for t...