Clues from hurricane 'fingerprints'
Scientists decode hurricane 'records' left in trees and rocks to try to predict the strength of future storms.
Hard hats and head lamps are not tools one usually associates with hurricane hunters. But for Amy Frappier they are indispensable.Skip to next paragraph
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The Boston College geochemist and her colleagues have been searching for signs of hurricanes in stalagmites that rise like jagged stone fangs from the floors of caves in Latin America. In the formations' tree-ringlike growth layers, she and her colleagues have shown that stalagmites record individual hurricanes by the unique chemical fingerprints the storms leave on the rain they dump. Buoyed by results published last April from a field trip to Belize in 2001, the team this summer has been focusing its hunt on caves on Mexico's Yucatan peninsula.
Meanwhile, a group of scientists at the University of Tennessee has been looking for similar signatures hidden in tree rings. The samples gathered in 2001 from a region of woods near Valdosta, Ga., have yielded a record of hurricane activity reaching back 220 years. Colleagues at the University of South Carolina say they have conducted similar work that pushes the record there back to the 1400s.
These are among the latest efforts at trying to build a record of Atlantic tropical-cyclone activity reaching as far into the past as these "proxies" for written records will take them. The approaches range from teasing out the chemistry of tree rings and stalagmites to pulling long cores of muck from beneath coastal lakes and lagoons.
The results feed more than academic curiosity. Insurance companies want to know how often major storms strike parts of the coast where the firms have sold large numbers of policies. More broadly, tropical-cyclone specialists have been embroiled over the past two years in a debate over whether global warming's fingerprints are appearing in the recent cyclone record for the Atlantic and globally.
The immediate concern focuses on the likelihood that, on average, storms will grow more intense as the climate warms. Scientists also are finding evidence from these "proxy" studies for a link between hurricanes and wildfires in the years following the landfall of a major storm. This raises the prospect that, as hurricane activity increases for whatever reason, the threat of wildfires in the Southeast and Gulf Coast regions could grow as the climate continues to warm, some researchers say. Scientists theorize that trees downed by storms provide fuel for fires.
While the debate on global warming and hurricanes is not over, scientists on both sides agree that historical records and data from aircraft and satellites fail to reach far enough back in time to help resolve the issue. That's where the slowly growing field of paleotempestology comes in. Some techniques already have yielded records for a single location that reach back 5,000 years. Scientists would like to drive that still further into the past and for many more hurricane-prone locations.
'Footprints' in the sand
As if to underscore the rising interest in what paleotempestology has to offer, the Brazil-based Inter-American Institute for Global Change Research (IAI) last year funded a six-year project to apply these proxy approaches to the entire Caribbean basin. The effort involves a dozen scientists from four countries, including the US.
"We have a fairly limited set of records at any one location, especially for the strongest storms," explains James Elsner, a professor at Florida State University specializing in hurricane climatology, distribution, and risk. The biggest concern revolves around recurrence rates for the most powerful tropical cyclones. The first step involves identifying these in the prehistoric record; the next step is to expand the network of observing points. "Once you have those, you can start to see what kind of patterns there were in these prehistoric events," he says.