Coastal redwoods at Muir Woods National Monument in California. (Justin Sullivan/Getty Images)
Scientists have been using tree rings to study the past since the early 20th century, a process called dendrochronology. But the history built up inside of old, giant redwood trees has always been locked away — until now.
Dendrochronology involves looking at changes in the width of the rings that trees grow everywhere. But the rings of redwoods tend to be incomplete, encircling only part of the tree. This had made them essentially useless for studying past climate. Or so researchers thought. In a recent paper published in the Journal of Geophysical Research-Biogeosciences, climate analyst Jim Johnstone described a new method that allows researchers to unlock the climate history packed into the redwoods.
“Redwoods are restricted to a very narrow strip along the coastline,” Johnstone said in a news release. “They’re tied to the coastline, and they’re sensitive to marine conditions, so they actually may tell you more about what’s happening over the ocean than they do about what’s happening over land.”
The method involves looking at proportions of oxygen isotopes in the wood over time, which can reveal data about ocean conditions, fog and rain, according to the release.
The study used wood from northern California coastal trees to document climate for the past 50 years. Cross-checking the data with existing weather records proved the method’s accuracy. “This is sort of a proof of concept, a pilot study, just to see if there were legible climate signals in there and if we could interpret them in a way that makes sense,” Johnstone told Weather.com. “It seems to have worked pretty well.”
Every summer on the west coast, upwellings of cold, deep water bring nutrients to the surface and drive the development of fog and rain. In years when the upwellings are the most intense, a result of unusually strong seasonal north-south winds, there’s more fog and humidity and the ocean temperatures drop.
“The trees are sensitive to all these things,” Johnstone said. “[This method] is potentially useful to understand how the whole system has changed on a year-to-year basis for centuries.”
This is the view of a Dragon Blood Tree, native to the Socotra Islands. (Image: Boris Khvostichenko/Wikipedia)