The width and color of tree rings provides an extraordinary glimpse into a tree's history. (Dmitr1ch/Shutterstock) How extreme weather leaves a lasting mark on trees and shrubs 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...