Tree rings impart climate change data

MEDFORD, Ore. – In a small room tucked away in an obscure corner of Southern Oregon University’s Science Building, Kenneth Olejar positions himself on a pillow atop a 6-foot-wide slab of redwood, peering intently through a microscope at the tree rings underneath him.

The microscope is attached to an electric micrometer, which in turn is hooked up to a computer in the corner of the room. The micrometer allows Olejar to precisely measure the size of each tree ring, telling him how much moisture the tree got that year and during which part of the year the tree got it.

Olejar spends hours at a time down here, meticulously measuring each tree ring and marking promising years for more analysis. He works in short sleeves, as the room is kept warm to prevent the redwood slabs from soaking up moisture and expanding. Some of the younger slabs lying around are only a few hundred years old, while others are more than 1,900, such as the one casually propped up against the cabinet in the outer office.

Olejar is the lab manager for the Late Holocene Climate Change Facility, a big name for a small laboratory housed in a nondescript room in the depths of the Science Building.

Using these tree rings, Olejar is helping John Roden, an SOU biology professor, and Lin Roden, lab manager for SOU’s Stable Isotope Lab and John’s wife, map out the past 1,000 years of climate change history in redwood country.

“The basic idea for this, and the reason it was funded, is because of a thing called climate variability,” said John Roden. “The idea is that we need to know how climates have changed in the past to better understand how climates might change in the future.”

John Roden has been studying climate change in the Pacific Northwest for years, analyzing the stable isotopes of carbon and oxygen in tree rings to determine the type and amount of moisture the tree absorbed that year. The stable isotopes of carbon and oxygen are naturally occurring elements and typically analyzed by climatologists to determine temperature and precipitation over the years.

“The isotopes in the tree ring are telling us about the environment of the tree when it grew,” Roden said. “If climate change features change the environment and the ratio of isotopes in the tree rings, then the tree rings give us a historic record of those climate features.”

Roden was awarded a National Science Foundation grant in 2003 to conduct a 50-year climate change study comparing the results of his tree-ring analysis to the weather records of the Arcata Airport in Arcata, Calif., and other weather stations scattered throughout the Pacific Northwest. His results correlated closely with the weather station records, so the NSF awarded him two more grants, totaling approximately $1.1 million, to continue his research, this time going back 1,000 years.

Roden said that while tree-ring studies have been conducted in the past, none of them have gone this far back, and very few have analyzed the stable isotopes in the rings. He also explained that of all the long-term climate change studies conducted, none of them are as time-specific as studies using tree rings, because each ring represents one year.