Blue rings in Arctic trees expose a 150-year log of climate chaos

POZNAŃ, Poland — In the Arctic’s harsh borderlands, where trees wage a constant battle for survival, an international research team has discovered that extreme cold leaves lasting fingerprints in wood. These “blue rings,” visible only under a microscope, reveal centuries-old stories of climate disasters that once brought summer temperatures plunging to near-freezing.

The study, published in Frontiers in Plant Science, examined pine trees and juniper shrubs in the Arctic. The research team ventured to Mount Iškoras in northern Norway, where these plants battle harsh Arctic conditions. Here, at the northern limit of where trees can survive, they uncovered a natural record of historical cold events preserved in wood.

“Blue rings look like unfinished growth rings, and are associated with cold conditions during the growing season,” explains lead author Dr. Agata Buchwal from Adam Mickiewicz University, in a statement. “In general, we found more blue rings in trees than in shrubs. Shrubs seem to be more adapted to cooling events than trees, which is probably why shrubs are found further north.”

Tree rings are the circular patterns you see inside a tree trunk when it’s cut crosswise. Each ring represents one year of the tree’s life, with the width and color of the rings reflecting the tree’s growth conditions that year. Wider rings often mean the tree grew in good conditions, like a warm, wet year, while narrow rings can indicate tough times, such as drought or extreme cold. Scientists study tree rings to learn about a tree’s age and the environmental history of the area where it grew.

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