Tree Rings as Climate Archive
World historians who study environmental history sometimes sometimes seek out atypical sources to conduct their research. While a traditional historian may visit an archive to examine governmental records or a collection of personal papers, an archive for an environmental historian might be an x-ray of a cross-section of a coral core or a crosscut of a tree showing its rings like the graphic here. Trees can live to be thousands of years old and their rings can show variations in climate over that time span. Wide rings show that the tree grew more in that year and narrow rings show less growth. The rings also show when in the year the growth occurred and both scientists and historians can use this data to better understand how the climate has changed over time. For more on how world historians use the framework of climate and environment to understand the past, read this J.R. McNeill essay on world environmental history.
"Tree rings provide snapshots of Earth's past climate – Climate Change: Vital Signs of the Planet," NASA: Climate Change and Global Warming,