Scientists can determine a lot about past climates by taking core samples from trees that have lived for hundreds or thousands of years.
The study of a tree’s rings is called dendrochronology.
The width of tree rings indicates the climate while the tree was growing. One ring represents one year. Thinner rings represent years when growth was stunted by lack of water.
Source:LiveScience
Source: http://www.livescience.com/49793-how-tree-rings-predict-dire-future-due-to-warming-infographic.html
