Living trees act as analog tape recorders of climate
Long-lived conifers in the Rockies and Andes preserve a year-by-year chemical diary of moisture and temperature, revealing ancient megadroughts that lasted for decades.
A single Douglas fir clinging to a rocky slope in the American West holds a high-definition record of the weather from a millennium ago. These trees grow by adding a distinct ring every year, with the width of that ring dictated by the available water. When researchers compare these living trees to the preserved beams of ancient dwellings or logs submerged in cold lakes, they can overlap the patterns like matching barcodes. This technique, known as cross-dating, allows scientists to assign an exact calendar year to a specific ring with near-perfect accuracy over a span of 1,000 years.