The poster for An Inconvenient Truth said it all: fuelled by human activity, warming oceans are spawning ever more monstrous hurricanes. But all may not be lost 鈥� it鈥檚 just possible that El Ni帽o will come to the rescue.
To study Atlantic hurricanes, Jeffrey Donnelly and Jonathan Woodruff of the Woods Hole Oceanographic Institute in Massachusetts analysed sediment records going back 5000 years, only to find little correlation with ocean temperatures. What they did discover was that hurricanes were almost non-existent during periods of increased El Ni帽o-related warming in the eastern Pacific, one of which lasted from 3600 to 2500 years ago. Whenever El Ni帽o fell away, the storms kicked up again (Nature, vol 447, p 465).
An explanation may come from modern observations. El Ni帽o causes warm waters to move eastward in the Pacific, which disrupts atmospheric circulation throughout the tropics. This breaks up storm systems before they can strengthen in the Atlantic. Over the past 30 years rising temperatures in the Atlantic appear to have caused stronger and more frequent hurricanes. But Woodruff says this short-term trend could peter out in the long run.
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鈥淐onsider the whole picture: on the centennial and millennial scale, El Ni帽o seems to trump the warming processes in the Atlantic,鈥� he says.
