Current Hurricane Amount at "Normal" Level, Study Says

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This would have caused greater windiness in the atmosphere, which dampens hurricane formation.

Study co-author Terrence Quinn is a geoscientist who studies past climate changes at the University of Texas at Austin. In the past few decades, both the oceans and atmosphere have begun warming appreciably, he said.

This global warming effect likely adds to the natural variability in hurricane activity, he said, so researchers and forecasters will have to take both factors into account from now on.

The reconstructed 270-year hurricane record, Quinn added, should allow scientists to better model future climate change.

Proxy Record

To get such an extensive record, scientists need to examine things such as corals and marine sediments, since other data only goes so far, Quinn pointed out. (Related: "Over 200 Years of Hurricane Data Recorded in Trees, Study Says" [September 18, 2006].)

In the Caribbean major rainfall events wash large amounts of organic rich matter into the ocean, Quinn explained. Corals absorb these organic compounds.

When scientists shine a special light similar to a black light on a cross-section of these corals, banded layers rich in these organic compounds become luminescent.

"You can see them, you can count them, you can look at their thickness," Quinn said.

The researchers compared the bands to the record of known hurricanes over the past several decades and found they match up.

The researchers also looked at the abundance of a certain type of single-celled marine animal found in a sediment core from a region off the coast of Venezuela.

The abundance of the creatures is driven by trade winds. The stronger the trade winds, the more nutrient-rich waters from the bottom of the ocean rise to the surface. This allows animals to flourish but dampens hurricane activity.

This sediment core record also matches the observational record of hurricanes.

The luminescent banding in corals and changes in abundance of certain microfossils in marine sediment cores thus serve as "proxies" for hurricane activity, the scientists point out.

"The beauty of these proxies is that they can extend the record back to before we have instrumental records," Quinn said.

James Elsner is a professor of geography at Florida State University in Tallahassee who studies the connections between hurricanes and climate.

In a commentary in this week's Nature, Elsner said this type of research "is a valuable tool for answering questions on hurricane climatology."

However, the proxy data collected to date only come from a few points and may not capture shifts in hurricane storm tracks or accurately show when storms did and did not occur, he said.

"More records are needed," he wrote, "before localized prehistoric activity can be used to make sense of large-scale patterns of storminess."

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