A hurricane is, put simply, a giant heat engine. In the North Atlantic basin, where many storms that impact the U.S. form, it takes a combination of factors to create one: tropical winds blowing off the coast of Africa, warm ocean waters, and a vast swath of warm, moist air to act as a conveyor toward the East and Gulf coasts
When these meet and form a hurricane over the Atlantic, the storm they create sucks up heat from the ocean to power itself. That’s largely why hurricane scientists are confident that the strongest storms will become even stronger by 2100, when Earth’s land and sea temperatures are expected to warm to levels unseen since the Eemian period, more than 120,000 years ago.
Because so many factors influence their development, however – hurricanes are notoriously “fussy creations” that can be torn apart by wind shear and dry air after gathering strength over thousands of miles of ocean, Dr. Jeff Masters of Weather Underground notes – forecasting them with accuracy can be difficult just days in advance, let alone decades.
Among climate scientists, the intensity and frequency of future hurricanes has been hotly debated in recent years. In 2007, a report by the Intergovernmental Panel on Climate Change (IPCC) suggested that the number of hurricanes both in the Atlantic and around the world might fall in a warming world, thanks largely to the higher wind shear and drier air possible on a hotter planet.
But the newest climate models – which will be used in the IPCC’s upcoming report in September – suggest that future hurricanes may instead become even more powerful and occur more frequently.
Using these new models, Dr. Kerry Emanuel, a professor of atmospheric science at MIT and one of the world’s top hurricane scientists, published a paper in July that said the world could see as much as a 40 percent jump in the number of major hurricanes (Category 3 or higher on the Saffir-Simpson scale) over the next century.
“The behavior of these strongest hurricanes is critical, since they do most of the damage we observe,” Masters notes, adding that Category 4 and 5 hurricanes made up only 6 percent of all U.S. landfalls over the past century, but they caused nearly half of all U.S. damage during that time.
‘We can’t stop these powerful storms’ USGS
High storm surge and wave run-up caused widespread dune erosion in Nags Head, N.C., during 2003’s Hurricane Isabel.
Still, there’s a great deal of uncertainty even in the latest reports, Masters adds. What isn’t uncertain at all is the rapidly rising amount of damage hurricanes cause – it doubles every decade in the United States, at a time when climate change isn’t yet considered a factor.
Had the Great Miami Hurricane of 1926, a Category 4 monster, instead hit Miami Beach in 2005, it would have caused some $150 billion in damage, according to the authors of a 2008 report on U.S. hurricane damage between 1900 and 2005. By 2015, that number would be about $300 billion – twice the damage caused by Katrina, in 2013 dollars.
Why is that damage accumulating so quickly? Because people have been migrating to the coast by the millions. Between 1970 and 2010, the population of America’s shoreline counties grew by nearly 40 percent and are now home to more than 123 million people, or nearly 40 percent of the country’s entire population. By 2020, that number is expected to grow by another 10 million.
Perhaps that’s what Dr. Orrin Pilkey, a professor emeritus of geology at Duke University and the author of more than a dozen books on beaches, sea level rise and climate change, had in mind when he penned his Nov. 14, 2012, editorial in The New York Times titled “We Need to Retreat From the Beach.”
The magnitude of Sandy, which had slammed into New York and New Jersey just two weeks earlier, was still fresh in the public’s mind as Pilkey implored the nation to see storms like it for what they really are: a sign of things to come.
“This ‘let’s come back stronger and better’ attitude, though empowering, is the wrong approach to the increasing hazard of living close to the rising sea,” he wrote. “We can’t stop these powerful storms. But we can reduce the deaths and damage they cause.”
Preventing those losses isn’t easy, however, when government policies encourage people to rebuild in areas ravaged by storms that are likely to get hit again.
Building (again and again) in harm’s way USGS
An aerial view of Dauphin Island, which experienced dramatic shoreline erosion after Hurricane Katrina in 2005.
Consider the case of Dauphin Island, Ala., whose 6.2 square miles are home to just over 1,300 people near Mobile. For decades, the island has been raked by hurricane after hurricane and would likely have been long abandoned were it not for the federal government, which has reportedly spent some $80 million rebuilding homes, bridges, roads and sewers here repeatedly since the late 1970s.
What persuades the people of Dauphin Island to stay and rebuild – as well as many other at-risk coastal communities like it around the country – are programs like subsidized federal flood insurance and the Stafford Act, a federal law that covers most of the cost to repair infrastructure destroyed by storms.
“If the federal government is in there, trying to protect this investment property on the oceanfront, then why in the world would these people not rebuild?” asks Young. “We’re creating this moral hazard, where we provide incentives for these towns and individual property owners to make the wrong decision. But from their perspective, it’s a no-brainer.”
State governments have gotten in on the act, too. In 2010, State Farm Florida canceled 125,000 home insurance policies, mostly in hurricane-prone areas. The company cited severe losses from a string of hurricanes in the mid-2000s, which it said made it impossible to provide coverage after failing to win a 47 percent rate increase from state regulators.
Who saved the day for those 125,000 homeowners? The state government of Florida, which set up a risk pool that today has more than a million policies in force, many in areas hit by hurricanes multiple times through the years.
It may only be a matter of time before costs of repairing and rebuilding after increasingly damaging storms force governments and coastal communities to make different choices in how they respond, however.
When is the right time to retreat? USACE
Sand is moved around the shoreline of Delaware’s Rehoboth Beach during a beach re-nourishment project there in 2012.
Globally, sea levels are projected to rise between 1 and 5 feet by 2100, a range that reflects best- and worst-case scenarios for controlling (or failing to control) greenhouse gas emissions over the rest of the century.
The rate of sea level rise locally, however, relies also on factors like the shape of the land where it meets the ocean and whether the ground is rising or falling, a phenomenon called subsidence.
This is happening rapidly in places like the Mississippi River Delta, where some 1,900 square miles of land have vanished into the sea since the 1930s, after decades of building levees and cutting canals for oil and gas pipelines through fragile wetlands.
Coastal cities and towns deploy a range of defenses against rising seas and erosion, from building dunes and seawalls to re-nourishing their beaches with sand dredged up from the ocean floor. But these defenses only work for a while, especially on barrier islands, notes Dr. Dylan McNamara, an assistant professor of oceanography at the University of North Carolina-Wilmington.
When natural erosion and overwash are blocked by man-made structures, big storms can deliver a much more devastating blow, he said. “They don’t let the barrier island do the things that it would like to do, so the time the big one comes, the island is in much worse position than it would have been otherwise.”
Earlier this year, McNamara co-authored a study in the journal Nature Climate Change that asked, what makes homeowners decide it’s time to give up on the coast? The answer, he found, lies in whether they look to the past as their only guide for the future, or take seriously the projections for rising seas in the future.
Economic incentives – such as rising rents and cheap insurance – were a powerful draw to stay for people who owned these properties, he said. But they didn’t make the difference that large hurricane and storm surge events did, when combined with the highest expected rise in sea levels.
“Those would be the shocks to the system that people would start to register, and say, ‘uh-oh, that was so damaging, I don’t want to go through that again,'” he added. “‘As I’m projecting into the future, I don’t want to have to pay those costs again and again – so I’m outta here.'”
A new era of coastal defense? US Army
An aerial view of the devastation wrought by Hurricane Sandy on the New Jersey coastline, taken Oct. 30, 2012.
In the era before the development of America’s coastlines exploded, natural processes controlled their shape and their destiny. That era has passed, McNamara says.
“Human beings are now a fundamental and intrinsic part of the entire [coastal] system,” he adds. “You can’t project what’s going to happen to the system in the future without understanding the kinds of decisions that human beings are going to make.”
The silver lining of storms like Katrina and Sandy, Young says, is the opportunity they offer to “take that step back from the ocean, and reduce the vulnerability to the next event,” by widening the buffer between the ocean and coastal infrastructure.
“That’s the best chance,” he adds. “Because when the coast is built, when we’ve got a completely developed oceanfront, we’re not going to go in there and tear down buildings – that’s never going to happen in America.”
But coastal development is only expected to keep growing sharply, not just in the U.S. but around the world, notes Laurence C. Smith, a climate scientist at UCLA and author of The World in 2050: Four Forces Shaping Civilization’s Northern Future.
If current population growth trends continue, he explains in the book, by the 2070s the number of people exposed to the risk of flooding worldwide is expected to triple, while the dollar amount of economic assets exposed to flooding – like buildings, utilities and transportation infrastructure – is expected to rise by tenfold.
“Clearly, we are about to begin paying great attention to a new kind of defense spending,” Smith writes. “It’s called coastal defense.“
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