What began as a casual meeting between two UC Berkeley scientists 14 years ago transformed into an extensive study, published Oct. 24, on how redwood trees can be used to peer into climates of the past.

Jim Johnstone, who graduated from UC Berkeley with a doctorate in 2008, developed a way of discerning past climate conditions through analysis of wood from California redwood trees. Johnstone co-authored the study with UC Berkeley integrative biology professor Todd Dawson and Southern Oregon University associate professor of biology John Roden.

Johnstone, during his second year as a UC Berkeley doctoral student, was struck with the idea after he read a paper by Dawson analyzing water from redwood trees.

“I thought, ‘Wow, (Dawson’s paper) is pretty cool — I wonder if it can be applied to tree rings,’ ” said Johnstone, who now researches at the University of Washington. “(Dawson and I) sat down for about an hour, and by the end, we mapped out this plan to do this study.” That was in 1999.

Now — after cutting out individual tree rings, grinding them up and analyzing the oxygen and carbon atoms in the wood — researchers have used the data to determine the levels of fog, rain and temperature in the surrounding area during the year each tree ring corresponds to, Johnstone said.

The data were then compared to historical weather records, and the method was found to be reliable with a high degree of confidence. The researchers extracted information from tree rings up to 50 years back, he said.

“The trees are sitting there absorbing rainwater and fog water and photosynthesizing carbon dioxide into the atmosphere,” Johnstone said. “They’ve been doing this on a continual basis every year for hundreds and thousands of years — sitting there collecting data from the local climate.”

The data recorded by redwood trees can provide valuable information on how climate changes over time, Johnstone said. Furthermore, the trees’ specialized coastal environments enable them to give a unique reflection of oceanic conditions.

According to Dawson, the data not only enable scientists to reconstruct climate conditions from thousands of years ago, but they also allow researchers to predict how redwood trees and forests will respond to future climate change.

“What’s unique about (this study) is that it has never been done with redwoods,” Dawson said. “A coastal redwood can live up to over 2,500 years. We have the opportunity to go way, way back in time with just a single tree.”

Leander Love-Anderegg, a graduate student in the department of biology at the University of Washington, said the research gives scientists in the field a new source of potentially useful reference data that will be critical for understanding future climates.