Cities along the Persian Gulf rarely need to worry about the threat of major tropical storms — but a new study says they should start to. Princeton researchers writing in Nature Climate Change say that warming temperatures are increasing the likelihood of extreme tropical storms in certain regions across the globe. Catastrophic weather events are much more likely to strike Tampa, Florida; Cairns, Australia; and the Persian Gulf by the end of the century, the study authors write. And a direct hit, they say, could decimate these areas.

In their study, the authors dub these threats as "grey swan" storms. They are similar in scope to "black swans" — thought to be the worst of the worst when it comes to extreme storms, but so rare that they are considered impossible to predict. "They’re events that no one has talked about, and no one has been able to show is possible," says study author Ning Lin, a professor of civil and environmental engineering at Princeton.

Grey swans are just as bad as black swans, but they can be predicted to some degree thanks to new modeling techniques. By analyzing physical data — like rising temperatures — and the historical record, researchers can catalog the possibility and risk of such high-impact storms happening.

Using this modeling method, the Princeton researchers cataloged the threat of grey swan storms occurring along the three coastlines. They found that the risk of such tropical storms hitting Tampa, Cairns, or Dubai is increasing substantially with each decade. Currently, the likelihood of a grey swan is extremely low: the odds are one in 10,000 years. But in 50 years, that risk jumps to one storm in every 1,100 to 3,100 years. By the end of the century, Tampa should expect a grey swan within 700 to 2,500 years. That means the chances of a city-destroying storm hitting the area will be up to 14 times higher in the next 100 years.

The severity of these storms will be higher than anything these areas have seen before. It's possible that the storm surges from a grey swan could reach up to 23 feet in Dubai and 36 feet in Tampa. This could be devastating for people living in coastal regions that haven’t been built with such storms in mind. "Since most of the damage and loss of life due to tropical cyclones is due to water and not wind, the consequences are particularly worrisome for coastal areas they impact," says Rick Luettich, director of the Institute of Marine Science as the University of North Carolina, who was not involved in the study, but says the findings seem likely.

Cities in Persian Gulf don't often worry about the threat from tropical storms. (NASA/GSFC)

Lin says such a growing threat in the Persian Gulf came as a surprise to the researchers, since the area rarely experiences these kinds of events. The threat in Tampa was also shocking, even though the area has seen such extreme storms before. "But it hasn’t happened for 95 years, and during those years, Tampa Bay has been greatly developed," says Lin. "It’s really to remind people the risk is there, even though we haven’t had extremes for a while."

Ultimately, Lin says climate change is to blame for the increasing risk. Rising temperatures are warming the world's oceans, which provide energy for hurricanes to grow. She hopes that this research can be used as a tool for policy makers to help mitigate storm risks for these areas. But Luettich argues that the focus shouldn't just be on the regions specified in the study.

"My only suggestion is that many coastal areas, in addition to the three listed, are likely to be impacted by such storms in the future," says Luettich. "I suspect that Cairns, Australia; Tampa, Florida; and cities on the Persian Gulf are examples of such areas but by no means the only ones."