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Atlantic Hurricanes to Become Less Frequent But More Intense

NOAA-Led Study Looks at the Impact of a Warming Ocean

Jan 22, 2010

As Haiti recovers from last week's earthquake and its aftershocks, a group of scientists says the region may be in the path of greater disasters by the end of the coming century.

Warming ocean temperatures in the Atlantic are projected to almost double the number of the strongest hurricanes over the next 80 years, particularly in the waters off Hispaniola, Cuba and Florida, says a study in today's issue of the journal Science.

While the overall number of hurricanes will decrease, Category 4 and 5 storms — those with sustained winds of 131 miles per hour and above — will nearly double in frequency, according to the study's projections. The most intense of these will more than triple.

These findings build upon those of previous studies and use a model that provides the spatial resolution necessary to predict storms of Category 3 or higher, which earlier work had been unable to simulate, lead author Morris Bender, a climate scientist at the U.S. National Oceanic and Atmospheric Administration, tells SolveClimate. He calls the study a follow-up on lower-resolution studies that had not been able to predict these rare but very significant storms.

The decline in the frequency of hurricanes will occur because the areas where hurricanes normally start will have conditions less favorable to hurricane formation. However, the storms that do start will find the warmer waters of a climate change-affected Atlantic more favorable to hurricanes and will easily intensify as they move onwards, Bender explains.

The decline in the frequency of storms, therefore, will be counterbalanced by a rise in the frequency of the most intense storms and thereby lead to a net increase in potential damage of about 30 percent, the scientists say.

Historically, Category 3 storms have accounted for 86 percent of hurricane damage in the United States, though they make up only 24 percent of hurricanes that make landfall in the country.

Hurricane Katrina, the costliest hurricane recorded in the United States, was a Category 3 storm when it made landfall in U.S. Gulf Coast in 2005. Its damage is estimated at about $75 billion and approximately 1,200 deaths.

Hurricane Flora was a Category 4 storm when it hit Haiti in 1963, killing more than 8,000 people, the sixth deadliest hurricane ever. In 2008, four storms hit the impoverished country, resulting in over a billion dollars in damage, devastated cropland, floods and hundreds of deaths and injuries.

The number of Atlantic hurricanes has doubled over the past 25 years. The models used in the Science study duplicated this increase in recent history, and then showed an overall decline in numbers in the coming decades. This accuracy with regards to past storms lends some credibility to the models' projections for the future, Bender said.

"The model does a good job in the present climate and, since it does a good job applied to the past, there's a good chance it works for the future," he explained.

The increase in frequency of past storms — and those in the next decades — is likely due to natural climate variations in the Atlantic region.

"The impact [of climate change] is likely not yet detectable in the present climate," Bender said. "It is currently being overwhelmed by year to year natural variability." If the study's projections are accurate, it will be 60 years before climate change makes a marked impact on hurricane activity.

Need for Improvements in Projections

While this study is a major advancement in modeling, much work remains to be done to achieve the accuracy in forecasts that scientists, as well as policymakers and those who live in the hurricane-prone regions, would like, Bender said.

"Since 1980, when satellites became available, there's definitely been an increase in hurricane action from 1985 to the present time," he said, "but the ability to observe hurricane activity before 1980 was not as great as it is today." In order to increase that ability even further, the main factor that needs to improve are the projections for what the future climatic conditions will be like.

The study used five different climate projections, including one that is the average of 18 different models, which Bender said the authors "feel is the best representation of the future climate." One of these models, the climate projection from the UK's Hadley Center, showed a decrease in projected hurricane intensity.

But Bender says he is most confident in the findings based on the 18-model ensemble numbers.

"We can't conclude, of course, that this is definitely the right model," he cautions. "You can't completely rule out individual climate models."

"We need to reduce that uncertainty with better climate models," he says, explaining that the more clearly we know what the future climate will be the more clearly we will know what weather events to expect.

The new study largely lines up with the projections of previous studies on climate change's effects on hurricane activity, leading to a possible consensus around the idea that rising ocean temperatures and the additional water vapor they produce both retard the formations of new storms and intensify those storms that do form.

A 2008 study, for instance, found that a changing climate will yield increases in hurricane power. But that study also found variability between projections based on different climate models and for different regions. Despite a growing consensus, then, it seems the science is still working its way toward greater certainty.

 

See also:

Insurance CEOs Call on Industry to Get Proactive About Climate Change

Warming Seas Signal Bad News for the Climate: The Feedback Loops are Starting

Record Breaker: Hurricane Season 2008 by the Numbers

Tipping Points: How Arctic Warming Could Chill Western Europe

(Satellite image: NASA)

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