How Can We Learn About Past Climates from the World Around Us?
Trees contain some of nature’s most accurate records of the past. They have alternating layers of light springwood and darker summerwood called annual rings. You can count the number of annual rings to find the age of the tree. It is possible, in some years, that more than one ring is made. These false rings occur due to disease, frost damage, or injury. Under these conditions, ring counts are not always 100%. Tree growth in a specific year depends on a complex set of local growing conditions. The amount of rainfall and water availability is one key variable affecting the growth rate each year.
In temperate regions, seasonal growth in the diameter of a tree usually continues longer in conifer or softwood trees than in deciduous or hardwood tree. Softwood trees continue to produce growth late into the fall. The growth rings in softwood trees are therefore larger than those in hardwood trees. Some hardwood trees have distinct rings. Other hardwoods produce cells (vessels) of similar size through the growth rings, which makes it more difficult to identify the springwood from the summerwood.
Watch Video 1
Record your observations from Video 1 in the table. Were there any signs of abnormal growth, such as rings being different sizes on different sides of the tree sample? Were the tree rings condensed or spread out? What does this tell you about the climate it grew in?
Identify an Experimental Design Flaw
The effects of climate change vary by region. What are the limitations from studying tree rings to determine climate history?
Refine/Expand the Experiment
How could you expand this experiment to determine what factors may be responsible for any differences in the widths of the growth rings or the reason for abnormal growth?
Practice Scientific Reasoning
Compare and contrast the ages of the trees. If the tree round samples are of similar size, how do their ages differ? What does this tell you about the growth rate of different tree species?
Connect to Your World
With the need to preserve our natural resources, scientist do not usually go around cutting trees down to measure their growth and analyze past climate. Instead, they use a boring device known as an increment borer to extract a small core sample from the tree. The hole is then sealed to prevent disease. How can taking samples from National Parks help bring insight into the effect human activity has on climate change?
Learn More by Exploring This Link
The tree rounds used in this activity were obtained from limbs of trees that had already been cut for some purpose. Scrap limbs are usually burned for waste, so these tree limbs are, in effect, being recycled. See if you can obtain tree rounds from your area. What does the information in those tree rounds say about past climate in your region?
Watch Video 2
Video 2 explains the Paris Climate agreement which exists to reduce human impact on climate change.
If you would like to combine this activity with an in-school experience, try the following kit: