While global warming naysayers seem content to continue flouting the overwhelming scientific consensus in favor of this anthropogenic phenomenon, they seem to have gotten one point largely right: hurricanes didn't suddenly begin massing over the past century as a result of warming sea temperatures.
Indeed, a new study carried out by geologists Jeff Donnelly and Jonathan Woodruff from the Woods Hole Oceanographic Institution (WHOI) has shown that the frequency of hurricanes in the Atlantic Ocean is closely related to long-term trends in the El NiÃ±o/Southern Oscillation (ENSO) and the West African monsoon and that bursts of intense activity have occurred in cycles over the past 5,000 years. By examining sediment-core samples obtained from Laguna Playa Grande on Vieques, Puerto Rico, an island particularly vulnerable to strong hurricanes, they were able to piece together a 5,000-year chronology of land-falling hurricanes in that area that they then compared with existing paleoclimate data on ENSO, the West African monsoon and other climate influences. They concluded that the number of intense hurricanes (i.e. category 3, 4 and 5) tended to rise when the effect of El NiÃ±o was weak and that of the West African Monsoon strong. "The processes that govern the formation, intensity, and track of Atlantic hurricanes are still poorly understood," said Donnelly, an associate scientist in the WHOI Department of Geology and Geophysics. "Based on this work, we now think that there may be some sort of basin-wide 'on-off switch' for intense hurricanes."
Although the results of their study seems to contradict recent papers that have drawn a link between a region's hurricane activity and anthropogenic global warming, Donnelly and Woodruff deny this implication, arguing instead that their research shows that factors other than ocean temperature likely influenced the genesis of past stormy weather events. The question their study leaves unanswered, however, is whether global warming will affect ENSO cycles either way in the near future.
"Warm sea-surface temperatures are clearly the fuel for intense hurricanes," he said. "What our work says is that without sea temperatures varying a lot, the climate system can flip back and forth between active and inactive regimes."
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