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What can the width of a tree's annual rings show about climate?

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Tall baobab trees with thick, cylindrical trunks and broad canopies line a dirt road in Madagascar, surrounded by green vegetation under a blue sky. — Plant Grandidier's baobas (*Adansonia grandidieri*) in Madagascar.

The width of a tree's annual growth rings is a valuable indicator of past environmental conditions, a field of study known as dendroclimatology. Because radial growth is closely tied to the weather conditions of a specific year, the amount of growth—represented by the ring's width—tends to vary in proportion to the prevailing temperatures or the amount of available precipitation.123

Beyond simple width, researchers analyze the thickness and composition of cell walls and the diameter of the lumen to reconstruct historical climate data. By correlating these measurements across trees of overlapping ages, scientists can extend climate records back thousands of years.13

However, interpreting these rings requires care, as growth can also be influenced by soil quality and the tree's specific biological processes. Additionally, environmental stressors like drought can cause "false rings," which, while challenging to interpret, provide further insight into specific weather patterns over time. Through dendrochronology, these biological records serve as a critical archive for understanding long-term climatic trends.13