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 30 August 2008 15:18 BST

Hurricanes 'developed in cool seas'

Thursday, 24 May 2007 14:40
Hurricanes are not just due to warm sea temperatures

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Scientists have found evidence that over the past 5,000 years El Nino and African monsoon have been responsible for intense hurricanes in the north Atlantic rather than just warm sea surface temperatures (SST).

Warm SSTs in the north Atlantic have been held to be the key ingredient for fuelling intense hurricanes and as such have formed part of the debate about global warming's impact on the world.

But research published in the journal Nature argues that west African monsoon and El Nino – disruption to the ocean/atmosphere system in the tropical Pacific – play an important part in controlling the frequency of intense hurricanes.

Jeffrey Donnelly and Jonathan Woodruff from the Woods Hole Oceanographic Institution in the US charted a record of intense hurricane activity in the north Atlantic.

To do this they measured sediment which had accumulated in a lagoon after hurricanes hit the island of Vieques in Puerto Rico over the past 5,000 years.

They then compared this with records of El Nino events and rainfall in tropical Africa. Striking similarities were uncovered between the hurricane sediment build-up and the weather changes.

"Despite cooler Little Ice Age SSTs in the region, the sediment record… indicates an increase in intense hurricane landfalls since about 1700 AD," the researchers write.

"Furthermore, the sediment record… indicates that an interval of relatively frequent intense hurricane strikes persisted for over a millennium (2,500 to 1,000 years ago) despite cooler-than-modern SSTs."

The researchers therefore conclude that tropical Atlantic SSTs were "probably not the principal driver of intense hurricane activity" during the past few thousand years but admit that further research is needed to confirm this.
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