What Trees Tell Us

by John Hopkins

Name: Will Driscoll
Hometown: Shreve, Ohio
Major: Geology
I.S. Title: A New Dendroclimatic Tree Ring Network from Lake Clark National Park and Preserve, Alaska
Advisor: Greg Wiles

Ask Will Driscoll about his Independent Study on finding evidence of global warming in the Arctic and the words begin to pour out, almost faster than he can marshal them into narrative structure. He shifts restlessly in his chair, hands constantly in motion, eyes gleaming as he leans forward to make a point. He pauses for breath and grins. “I guess you can tell I get fired up about this,” he says.

In most parts of the world, temperature and precipitation records only go back about a hundred years. To look further back in time for evidence of climate change, scientists must make use of proxy records such as tree rings. By comparing growth patterns with available data on temperature and precipitation, researchers can develop a model to extrapolate climate variations.

Driscoll developed such tree-ring chronologies from white spruce samples taken from four sites in the Lake Clark National Park and Preserve in Alaska. The project began with fieldwork in June 2004. Along with fellow geology major Nick Young ’05 and Greg Wiles, their adviser, Driscoll spent nine days drilling his coring tool into the park’s trees (the process does not harm the tree).

“We’d core as many trees as we could, collapse, then do it again,” he recalls. “The float plane would come back every couple of days with supplies or to move us to another site.”

In all, they cored more than one hundred and forty trees, some dating back to the mid-1700s.

Back on campus, each sample had to be mounted, dried, sanded, and examined under a microscope, each ring measured down to a thousandth of a millimeter. Only then could Driscoll begin to reconstruct temperature patterns using a statistical technique called principle component regression analysis.

While three of the sites showed a strong correlation between increased temperatures and tree growth, the fourth did not. Digging further into the data, Driscoll found that half of the trees at the fourth site were indeed growing rapidly, but the other half were dying off, probably due to “temperature-induced drought stress.” Both responses were consistent with a warming trend.

Ultimately, Driscoll’s analysis suggested that the average growing season temperatures in the park during the 1990s were the highest since 1769. “The rate and magnitude of late twentieth-century warming is unprecedented in both the reconstruction and the individual chronologies,” he wrote.

Piecing together evidence of global warming is like working an enormous jigsaw puzzle, with researchers all over the globe contributing pieces of data. Driscoll’s results will be shared with researchers from the Lamont-Doherty Earth Observatory at Columbia University and the University of Alaska. He has presented his data at the national meeting of the Geological Society of America and plans to publish a paper with Wiles.

“Will’s I.S. work has really invigorated him,” Wiles says, “and he’s gone further with it than any other student who has worked on a similar project. His work has important implications and contributes to the growing body of evidence that global warming will have complex effects on the bio/geosphere.”

Graduate school is in Driscoll’s future, but not just yet. He wants to take a year off from the classroom.

"There are lots of great jobs in hydrogeology right now, or maybe with the U.S. Geological Survey," he says. "Something where I can get out in the field."