Scientists are studying tree rings to learn about changes in climate over hundreds of years. Researchers showed BBC News how the width of the rings can give clues to rainfall, temperature fluctuations and even tsunamis and earthquakes.
In a new lab, Cambridge University is using trees from around the world to create the "longest, continuous tree ring-based diary" detailing big moments in time.
Professor Ulf Buntgen said the technique of studying changes in tree rings recently uncovered evidence of an ice age in 536 AD that followed a cluster of volcanic eruptions, triggering a cold period of around 100 years. A tree ring from that year shows larger cells with frost damage after a dramatic drop in temperature.
Some of the trees come from building sites and medieval churches. But others, preserved underwater, are being taken from the Scottish lochs.
By reconstructing these clues to climate in the past, scientists can analyze historic trends and the impact on local communities, and better understand if recent warming is unusual. Some already predict 2018 will show large tree rings, demonstrating a warm year.