Reading Great Lakes future in Pacific Northwest tree rings


Capital News Service

LANSING -- Answers to Great Lakes climate questions may show up in an unlikely place — the rings of trees growing in the Pacific Northwest.

“We use tree rings to tell us how the past climate changed before written history,” said Professor Gregory Wiles, chair of geology at the College of Wooster in Ohio.

Wiles and a graduate student have put together a 265-year reconstruction of Lake Erie water levels based on this method.

Tree rings, which are evidence of new growth in a tree, reveal more than just age. They show cycles of wet weather, drought and temperature changes.

“What it comes down to is weather,” Wiles said. “When it’s really warm, they are going to put on more wood and have stronger growing seasons.”

His laboratory develops the tree ring data into chronologies, which are used to detect a range of climate conditions.

The Department of Environmental Quality says the combined  influence of a variety of factors determine Great Lakes water levels, including precipitation, surface water runoff, evaporation, agricultural irrigation and water level regulation.

“The interplay between human activities, such as dredging, consumptive uses, in- and-out-of basin-diversions, wetland reduction, urbanization and agriculture, and the ecology of the lakes is highly complex,” according to the department.

A longstanding climate relationship between the Great Lakes and the Pacific Northwest explains how weather in the Gulf of Alaska, as illustrated in tree rings, corresponds to Lake Erie water levels, he said.

The reconstruction shows Lake Erie has been higher in the past few decades than it’s ever been.

Lake Michigan waters are also high, according to the U.S. Army Corps of Engineers Detroit office.

Its latest water summary shows the lake is 9 inches higher than last year due to above-average precipitation and could reach its long-term average by October.

When there’s cooler weather in the North Pacific, lake levels tend to be higher, he said.

The opposite is true when it’s warmer up north, Wiles said.

“Looking in the past, the levels today aren’t that unusual — the ups and downs,” he said.

The connection could be key to understanding what’s in store for the Great Lakes region.

The laboratory doesn’t use the research to predict future water levels or climate conditions, but past cycles could be studied for that purpose.

“The data gives us a wider window of opportunity of what it could be,” said Wiles, who also oversees tree ring projects in Alaska. “What happens in one part of the world really does explain, in part, the changes that occur in the Great Lakes region.”


Rachael Gleason writes for Great Lakes Echo.