Geologist Johannes Koch found fresh and intact tree stumps beside retreating glaciers in British Columbia.
To find out how long ago the glaciers killed the trees and buried them under ice, Koch radiocarbon-dated wood from the stumps. The result was a surprising 7000 years.
"It seems like an unprecedented change in a short amount of time," said Koch. "From this work and many other studies looking at forcings
of the climate system, one has to turn away from natural [explanations] alone to explain this dramatic change of the past 150 years."
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