Tree-rings and shipwrecks offer clues on link between climate change and regional hurricane patterns

A NASA visualization of Hurricane Floyd approaching the Florida coast.
A NASA visualization of Hurricane Floyd approaching the Florida coast.

Study shows lull in tropical storms during cool era

Staff Report

Climate scientists and meteorologists have long been trying to determine how global warming will affect hurricanes, but with so many variables in play, it hasn’t been easy to make definitive conclusions.

A new analysis of tree rings and shipwreck records has now helped created a more detailed look at historic hurricane activity in the time before scientists were able to accurately count the tropical systems. The findings show there was a big drop in hurricanes between 1645 and 1715, during an era of reduced sunspot activity and generally cool temperatures in the northern hemisphere.

Learning that a lull in Caribbean hurricanes corresponded to a time when Earth received less solar energy will help researchers better understand the influence of large changes in radiation, including that from greenhouse gas emissions, on hurricane activity.

Having better predictions about how anthropogenic climate change affects hurricane activity is important because hurricanes are so destructive and have big societal impacts, said said lead author Valerie Trouet, an associate professor in the UA Laboratory of Tree-Ring Research.

“We’re the first to use shipwrecks to study hurricanes in the past,” Trouet said. “By combining shipwreck data and tree-ring data, we are extending the Caribbean hurricane record back in time and that improves our understanding of hurricane variability.”

Some climate models project hurricanes will be more intense as the climate warms, and other studies indicate there could be more hurricanes for Hawaii, Europe, New England and perhaps even South Africa.

But overall, the models aren’t really able to pinpoint those geographical changes. More information about the historical hurricane record could help develop more accurate regional projections, according to Trouet.

Accurate hurricane record-keeping started in about 1850 and researchers have previously used lake sediments to build a record of historical hurricane activity. But the sediment record only provide century-level resolution.

The new study provides an annual record of Caribbean hurricanes going back to the year 1500, when ships started sailing between Spain and the Caribbean on a regular basis. Storms are seen as the main driver of shipwrecks in the Caribbean.

The new study, “Shipwreck Rates Reveal Caribbean Tropical Cyclone Response to Past Radiative Forcing,” is scheduled to be published online by the Proceedings of the National Academy of Sciences the week of March 7, 2016.

Trouet’s co-authors are Grant Harley of the University of Southern Mississippi in Hattiesburg and Marta Domínguez-Delmás of the University of Santiago de Compostela in Lugo, Spain.

The tree-ring records help date hurricanes because the growth of trees is slower in years with hurricanes. The researchers were also able to date the wood from shipwrecks to match the two records. Using historic records of shipwrecks as a control element in the study, they found that hurricane patterns from the shipwreck database closely matched Florida Keys tree-ring chronology of hurricanes from 1707-1825. The scientists also compared Florida Keys tree-ring records to the systematic recordings of hurricanes from 1850-2009.




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