Volcanic eruptions and cold summers leave lasting marks in the wood of northern trees, unlocking the secrets of past climate extremes.

Taken from a tree in Norway, this stained tree sample shows a blue ring from 1902. (Credit: Pawel Matulewski and Liliana Siekacz) Human skin isn't the only thing that can change color after facing the ...

Blue rings found in the stems of trees and bushes in Norway point to a historic cold period in the late 1800s, but the exact cause of this climatic event remains unclear, scientists say.