Studying Tree Rings
Tree rings preserve climate data.
Each year that a tree grows is represented by a ring in its cross-section. Years with good conditions (usually warm or wet) will be represented by wider rings than years with poor growth conditions. A tree-ring record can date back as far as a few thousand years.
Scientists select an area of trees whose growth is most sensitive to climatic variations. In an area of study, scientists collect samples from many living trees using a handheld borer. These contemporary specimens are then compared to an older, and long dead, fossilized tree. Such a fossil tree can be dated with radiocarbon techniques. Scientists study their collection of tree samples to determine annual growth conditions such as precipitation, temperature, and hydrology. They can even determine if fires occurred that did not actually kill the tree.