Study finds that off-the-charts hurricanes
are possible but not likely
By Washington Post, adapted by Newsela staff
09.17.15
Looters make their way into and out of a grocery store in New Orleans, Louisiana, Aug. 30,
2005, after Hurricane Katrina hit the city. Photo: AP Photo/Dave Martin
The nation recently focused its attention on the 10-year anniversary of Hurricane
Katrina. It was the most destructive hurricane in U.S. history. However, it wasn't the
worst storm that could have possibly hit New Orleans, Louisiana.
That's true of many other places, too. Now, in a new study, Princeton University's Ning
Lin and Massachusetts Institute of Technology's (MIT) Kerry Emanuel demonstrate that
in three global cities there could come a storm that is much worse than anything in
memory. The three cities are Tampa, Florida; Cairns, Australia; and Dubai, United Arab
Emirates.
Predicting The Probability Of A "Gray Swan"
These theoretical storms are also highly unlikely to occur. In some cases, they could
happen once every 10,000 years or even less often. The researchers call these
possible storms "gray swans." The term is a play on the idea of a "black swan" event,
which is an unpredictable disaster. A "gray swan," by contrast, can actually be
predicted, even though it is extremely rare.
The purpose of the study is "to raise awareness of what a very low probability, very high
impact hurricane event might look like," said Emanuel. The storms were generated by a
special computer program. It took into account hurricane patterns and predictions about
global warming. The program allowed the researchers to look at many different possible
storms in the made up, or simulated, world.
Asteroid Could Leave "Hypercane" In Its Wake
"When you do hundreds and hundreds of thousands of events, you're going to see
hurricanes that are unlike anything you've seen in history," said Emanuel. He developed
math equations that show how strong a hurricane can be. He said that a hurricane with
winds approaching 500 mph is possible if an asteroid hits Earth. Hurricanes gather their
energy from water evaporating over warm ocean surfaces, and an asteroid strike could
heat up ocean waters far beyond their normal temperature. Emanuel called this possible
event a "hypercane."
So what did the researchers see in the future? Let's take Tampa Bay. It hasn't been hit
by a major hurricane since 1921. That storm drove a 3- to 3.5-meter storm surge, or a
10- to 11-foot flood, on the coast, and caused dramatic damage. In 1848, another storm
produced a surge of 4.6 meters, or about 15 feet.
West Coast's Shallow Water Endangers Florida City
Why is Tampa Bay in such danger? The water on Florida's east coast is very deep. But
it is more shallow on Florida's west coast. The city of Tampa may be far from the barrier
islands that get battered by the waves from the Gulf of Mexico, but it is more exposed
than it seems.
Surges can be much larger from shallow water, Emanuel said. Surges can also be
bigger when they move into a bay, a body of water bordered on most sides by land that
opens into the sea.
The new computer model allows the researchers to show that a worse storm than these
historical examples is possible. It is especially possible with sea levels rising and global
warming. The researchers looked at 2,100 possible Tampa Bay hurricanes in the
current climate. Then they simulated 3,100 each for three time periods. They used 2006
through 2036, 2037 through 2067, and 2068 through 2098. The researchers assumed
global warming would continue unstopped.
In the current climate, the study found that a 5.9-meter, or 19-foot, storm surge is
possible in a strong hurricane following a similar track to Tampa's 1921 and 1848
storms. Moreover, in a late 21st century climate with bad global warming, the worstcase scenario followed a very different path. The storm would move north along
Florida's Gulf Coast. Then it would turn inland at Tampa. That storm could cause a
surge of nearly 11.1 meters, or nearly 37 feet.
Chances Of A Super Storm Are Very Low
Granted, the study said that these two "gray swans" are exceedingly unlikely. The
chances are less than 1 in 10,000 years for the 19-foot surge in the current climate. Still,
the study also showed that global warming makes the worst possible surges more likely.
The study also shows that for Cairns, Australia, a 5.7-meter, or 18-foot, storm surge is
possible in the current climate. Such flooding would happen less than once in 10,000
years. Perhaps most strikingly, it also suggests that an extremely powerful hurricane
could happen where we've never yet seen hurricanes occur: the Persian Gulf.
The waters in the Persian Gulf are very hot, meaning there is a lot of energy for a
possible hurricane, though the atmosphere is normally too dry for hurricanes, Emanuel
explained. "It's not likely, but it's not impossible," he said.
The study found that with 3,100 simulated events in today's climate, it is theoretically
possible to get a hurricane with winds of more than 250 mph and a storm surge of 24
feet in Dubai. The hurricane would be stronger than anything we've seen on Earth.
So, is all of this just a mathematical exercise? Or is it more important? In the end it's up
to us to decide how much to worry about an extraordinarily rare event, but you could
make the case that a study like this helps us think a lot better about what risk is all
about.