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

It all seemed to hint that perhaps the endlessly calm and dry days of Washington’s blue-sky October were coming to a close, as indeed the month itself began to approach its end. It was the last ...

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.