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Tree rings provide snapshots of Earth's past climate
The first thing that hits you is the smell of wood. These slabs, as well as smaller samples from living trees, are studied and analyzed using dendrochronology, the clunky-sounding technique of tree-ring dating. Using trees with Arctic origins, the scientists in the Lab have reconstructed past climatic patterns and environmental change in the region. Beyond providing valuable insight into how the environment reacted to events like fires and climatic shifts in the past, these observations can help predict how the Arctic environment may respond to the inevitable warming of the future. Living in what was then the Territory of Arizona, astronomer A.
Dendrochronology is the formal term for tree-ring dating, the science that uses the growth rings of trees as a detailed record of climatic change in a region, as well as a way to approximate the date of construction for wooden objects of many types. As archaeological dating techniques go, dendrochronology is extremely precise: if the growth rings in a wooden object are preserved and can be tied into an existing chronology, researchers can determine the precise calendar year—and often season—the tree was cut down to make it. Radiocarbon dates which have been calibrated by comparison to dendrochronological records are designated by abbreviations such as cal BP, or calibrated years before the present. Tree-ring dating works because a tree grows larger—not just height but gains girth—in measurable rings each year in its lifetime. The rings are the cambium layer, a ring of cells that lies between the wood and bark and from which new bark and wood cells originate; each year a new cambium is created leaving the previous one in place. How large the cambium's cells grow in each year, measured as the width of each ring, depends on temperature and moisture—how warm or cool, dry or wet each year's seasons were. At its most basic, during dry years the cambium's cells are smaller and thus the layer is thinner than during wet years.
However, that big tree in your backyard has been keeping a detailed climate record for decades. Trees can live for hundreds—and sometimes even thousands—of years. Over this long lifetime, a tree can experience a variety of environmental conditions: wet years, dry years, cold years, hot years, early frosts, forest fires and more. The light-colored rings represent wood that grew in the spring and early summer, while the dark rings represent wood that grew in the late summer and fall.
How scientists use Arctic trees to map climate change
In this activity, students are introduced to tree rings by examining a cross section of a tree, also known as a 'tree cookie. Next, they investigate simulated tree rings applying the scientific method to explore how climatic conditions varied over time. The CLEAN collection is hand-picked and rigorously reviewed for scientific accuracy and classroom effectiveness. Read what our review team had to say about this resource below or learn more about how CLEAN reviews teaching materials. Educators should explain to students how the matching of tree rings between trees of different ages is done by searching for patterns to extend the record past the life of just one tree.