for National Geographic News
A chemical signature of just about every hurricane to roar across southern Georgia during the past 220 years is preserved in the region's longleaf pine trees, according to a new study.
Further detective work should extend the record for the southeastern United States back another 400 years, says Claudia Mora, study co-author and a geochemist at the University of Tennessee in Knoxville.
Such an extension would be welcome to researchers trying to understand how hurricane activity varies over long periods of timeand could help settle the debate about whether human-driven global warming is affecting hurricanes.
"There are a lot of questions right now about what the root causes of changes in hurricane frequency and intensity are," Mora said.
(Related news: "Global Warming Link to Hurricane Intensity Questioned" [July 2006].)
The current instrumental record is reliable for only about 60 years, which is too short to determine, for example, whether the observed increase in hurricane activity since the mid-1990s is part of a natural cycle or due to human activity.
The new technique, which is based on analysis of the oxygen isotope content in tree rings, "will contribute to our understanding of what controls [hurricane] frequency," Mora said.
She and colleagues report their findings today in the early online edition of the journal Proceedings of the National Academy of Sciences.
But the technique can't tell much about hurricane intensity, only frequency, Mora says.
Hurricanes are dynamic, moving systems, so the oxygen isotope signature in the trees, which are stationary, would be an unreliable gauge.
The oxygen isotope content of rain that falls during a hurricane is different than in rain that falls during a normal thunderstorm, Mora says.
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