Climate Change Science Tools: Tree Rings

Counting tree rings is one method scientists use to gather data on past climate change. To impress people, the science of counting tree rings is called Dendrochronology. Tree rings indicate dry seasons and wet seasons; this fact is used to determine whether the area the trees come from experienced a dry year or a rainy year as well as the age of the tree. Of course, to count tree rings you have to chop it down, or gather a sample from a newly fallen tree.

How are tree rings are made? The time period trees grow is typically in the Spring, after winter snowfall and rainfall.Tree rings are part of this growth, which begins in the boundary between the old wood and the tree bark (called the cambium). This early growth creates earlywood and it is light colored. Small layers of this light-colored earlywood build upon each other expanding the girth and width of the tree. Growth may continue until Fall; at this season growth will start to slow down. This slower growth is characterized by darker growth called latewood, indicating the end of the growth season. The area from one darker growth ring to the next darker growth ring represents one growth year for the tree. (

How are tree rings used for climate change research and understanding? By gathering many tree samples from the same geographical area, scientists can determine whether a particular year in the past was very wet or very dry. Other factors also can determine past climate conditions: rain, temperature, acidity of soil, plant nutrition, glacial activity, or natural disasters such as volcanic events, fires, floods, and earthquakes. These factors can represent themselves in tree rings. By analyzing hundreds and thousands of tree samples with all this data, scientists have mapped out thousands of years of climate data. This is how we know that the earth is warming and that climate change is real. The past decade was the warmest decade for the entire planet since recording for such data began in 1880; 2005 was the warmest year, period followed second by 2009 (NASA, 2010).

Climate science is not new, but it does make use of the most advanced technology available to scientists. Like any other scientists, climatologists use powerful super computers to run simulations on the global climate. Over and over, these models, known as GCM's or global climate models are run. The institutions and hardware are funded by millions of dollars and run by dedicated people not looking to make a profit, but just to do good and valuable work for society. Compare these hard working citizens to amateur bloggers and internet commentators and it's like comparing Tiger Woods and other professional golfers to the weekend novice. Some people have trained all their lives to be good at what they do; they are simply better equipped and better informed. For climate change, this means that climatologists are the professionals because they have the tools and the proper ability to assess and construct climate change models. These global climate models take thousands of points of data, from precipitation levels to carbon emissions, from ambient air temperatures to borehole temperatures, and of course tree rings to provide the best possible predictions regarding current and future climate change.

Photo Credit: Arpingstone