Scientists Ground Truth What Influences Hurricanes

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Scientists looked back 10 to 13 thousand years to gain real-world insight into the environmental factors that influence hurricanes near Florida and, by extension, the U.S. Eastern Seaboard.

New USGS-led research shows the large role ocean circulation has played in modifying the variables—such as wind shear and humidity—that control hurricane activity in the North Atlantic.

While the influence of Atlantic Meridional Overturning Circulation (AMOC) on hurricane activity has been previously hypothesized, former research typically relied on short-term records that don’t extend into episodes of extreme AMOC variability in the geologic past.

The new study was published in the journal Geology. Scientists examined the Younger Dryas and early Holocene periods.

“This was a unique interval of geologic time, and gathering data from real events allows us to ground truth and refine models, which can ultimately lead to better forecasting of future hurricane activity,” said Michael Toomey, USGS scientist and lead author of the new report.

“In recent months,” said Toomey, “we’ve seen devastating hurricanes sweep through the North Atlantic and impact low-lying coastal communities. This highlights the urgency of extending historic observations using geologic records to identify the full range of possible storm hazards facing the U.S East Coast.”

2002 Research Cruise to Collect Sediment Cores Offshore Florida
Photograph taken during the 2002 research cruise to collect sediment cores offshore Florida that have been used to study hurricane activity and environmental conditions during the early Holocene and Younger Dryas periods. Photograph Credit: Dr. Thomas Marchitto, Institute of Arctic and Alpine Research, University of Colorado Boulder

Comparing the Younger Dryas and Early Holocene

The Northern Hemisphere experienced abrupt cooling during the Younger Dryas, likely in response to changes in ocean circulation. The early Holocene provides a point of comparison because it was similar to the environmental conditions of today and occurred immediately after the Younger Dryas.

Scientists found that storm activity was likely stronger during the Younger Dryas compared to the early Holocene near modern-day Florida. This is despite the area having slightly cooler sea surface temperatures—which on their own might work to lower potential hurricane intensity—during the Younger Dryas.

Research noted that this is likely due to a dramatic reduction in AMOC, which triggered other favorable environmental conditions for hurricane development near Florida, apparently outweighing local changes in sea surface temperature.

“This concept of using the Younger Dryas as a test for how storm activity might change in response to a sustained AMOC slowdown hadn’t been explored before,” said Toomey. “Few currently published tropical cyclone records extend beyond the past few thousand years.”

Reliable, global observations of tropical cyclones are even shorter, dating to satellite monitoring in the 1970s. Instrumental records of past storms are relatively robust in some regions, such as the North Atlantic, but still only extend back to approximately 1850. 

“Future research would look at whether increased hurricane activity during the Younger Dryas was more extensive along the East Coast or limited to Florida, as well as whether cyclone activity in the North Atlantic increased during other episodes of AMOC reduction,” said Toomey.

Research was conducted by analyzing sediment cores collected offshore Florida in 2002. Early Holocene and Younger Dryas sections of these cores were identified and sediment-size changes were then measured to identify deposits likely derived from intense storm events.

The article, “Increased hurricane frequency near Florida during Younger Dryas Atlantic Meridional Overturning Circulation slowdown,” is authored by the USGS, the Woods Hole Oceanographic Institution, Texas A&M University, and the Bermuda Institute of Ocean Sciences.

2002 Research Cruise to Collect Sediment Cores Offshore Florida
Photograph taken during the 2002 research cruise to collect sediment cores offshore Florida. Photograph Credit: Dr. Thomas Marchitto, Institute of Arctic and Alpine Research, University of Colorado Boulder
2002 Research Cruise to Collect Sediment Cores Offshore Florida
Photograph taken during the 2002 research cruise to collect sediment cores offshore Florida. Photograph Credit: Dr. Thomas Marchitto, Institute of Arctic and Alpine Research, University of Colorado Boulder