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UW Researcher: Redwoods Reveal Years of Coastal Climate History

Michael Schweppe

Count the rings on a tree trunk to figure out its age.

Or, if you’re University of Washington climatologist Jim Johnstone, study the molecules of a redwood trunk and crack the code for natural weather data that could date back more than a thousand years.

Johnstone has a keen interest in the interplay of our oceans and the atmosphere near them, which often shows up as fog.

“I’m known as Dr. Fog to some people,” he said.

Redwoods aren’t the oldest trees on the coast, but they do have a special connection to fog. These trees suck up the moisture in the air during dry summers.

Johnstone and his colleagues at the University of California, Berkeley, where he wrote his dissertation, began studying the phenomenon. They soon realized that the molecules of the world’s tallest trees hold a wealth of information about coastal conditions.

“Cool ocean temperatures, foggy summers, strong upwelling on the coast and high humidity—the trees respond to all these things,” said Johnstone.

The redwood’s molecular content reflects these climate conditions, said Johnstone. He found that the proportions of oxygen and carbon in the wood correlate with recorded weather data dating back 50 years. And since redwoods live to be thousands of years old, he’s hopeful the same method can be used to unlock even older data.

“These trees have just been sitting there, recording information about the year-to-year climate,” he said. “And it gives us hope that these trees can tell us things about the climate going back maybe a thousand years or more.”

That information could reveal the history of complex systems that’s hard to define otherwise. And understanding weather cycles can help distinguish natural and man-made climate change.

Johnstone co-authored a study published online this month in the Journal of Geophysical Research-Biogeosciences.

Bellamy Pailthorp covers the environment for KNKX with an emphasis on climate justice, human health and food sovereignty. She enjoys reporting about how we will power our future while maintaining healthy cultures and livable cities. Story tips can be sent to