Hurricane Seasons More Active

Examining evidence of hurricanes going back 1,500 years, researchers have identified factors that contribute to more active hurricane seasons 

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A satellite image of an Atlantic hurricane. A recent study published in the journal Nature concludes that in recent decades, hurricane activity in the Atlantic has reached levels not seen in over 1,000 years. Courtesy of National Oceanic and Atmospheric Administration

For many Americans who live on the Atlantic coast, Andrew, Ivan and Katrina are more than just names — they are reminders of the devastating impact of cyclonic activity in the region during hurricane season. If it seems like hurricane seasons have been more active in recent years, you're on to something. According to a paper published in the August 13 issue of Nature, the frequency and strength of these powerful storms has grown in recent decades.

"We are at levels now that are about as high as anything we have seen in the past 1,000 years," said Michael Mann, director of the Earth System Science Center at Pennsylvania State University and the lead author of the paper. Mann and his collaborators, Jeffrey P. Donnelly of the Woods Hole Oceanographic Institution, Jonathan D. Woodruff of the University of Massachusetts and Zhihua Zhang of Pennsylvania State University examined sediment samples from across the North Atlantic coast and statistical models of historic hurricane activities.

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A sediment core sample collected in a laguna along the Florida Panhandle. The light areas are composed primarily of sand from beaches and sand bars on the ocean that was swept up by a very large storm and then deposited in the laguna. These sediment core samples offer a timeline of past hurricane seasons. Courtesy of Jon Woodruff

Their analysis allowed them to measure the severity of hurricane seasons over the past 1,500 years. The sediment samples match up relatively well with the computer models, both of which show a period of high activity around 1,000 AD, followed by a lull in activity. This medieval peak rivals and possibly exceeds the level of activity seen in recent decades.

The study also adds validity to the theory that two factors fuel higher hurricane activity, namely the La Niña effect and high surface temperatures over the ocean. If climate change continues to warm ocean waters, Mann said, it could lead to more active hurricane seasons. This hurricane season, which has yet to see a named storm, is lighter than usual, Mann said, because of the El Niño effect, which is believed to have the opposite effect of La Nina patterns.