One of the scariest aspects of Hurricane Sandy was that it wasn't really a freak event. The storm surges produced in Lower Manhattan actually were predictable based on historical data and climate modeling, so you could argue that maybe we should have been a bit better prepared for this type of storm.
But what about storms that are truly unprecedented?
This week, researchers discussed their work on so-called "black swan" cyclones at the American Geophysical Union meeting in San Francisco. Black swans, said Ning Lin, a professor of civil and environmental engineering at Princeton, are storms that cannot be predicted based on historical data, and they can have dire consequences. Such storms actually have "retrospective predictability," which means that we can only explain why they happened, after they happened.
You might wonder how it's even possible to study such storms. Lin, whose study at AGU this week was co-authored by hurricane research eminence Kerry Emanuel of MIT, said that predicting these anomalous storms just requires a different approach. While the bulk of tropical cyclone risk assessments are based on historical data, she relied on synthetic models instead. "We can generate large numbers of synthetic storms, and physically possible storms for different climate conditions, and then carry out storm surge simulations," she said during a press conference. So far, they have only modeled a few specific locations, largely because the computational requirements for each run are huge.
In the U.S., the team chose to study Tampa, Florida. Lin said the highest recorded storm surge in Tampa was due to a storm in the 19th century, when waters rose 4.6 meters. But that doesn't mean a new storm couldn't go higher. "Ten meters is possible," she said. She added that the record 3.5 meter storm surge Sandy sent to New York was several meters off from what a black swan would produce. "In terms of storm surge, Sandy was not a black swan." Lin's team also analyzed the possibility for black swan storms that could inundate Darwin, Australia, and, amazingly enough, parts of the Persian Gulf like Doha, Qatar (where, incidentally, somewhat punchless climate talks are ongoing this week).
One of the lessons that emerged out of Sandy's receding waters was the idea that this type of storm is likely to happen again as seas rise and weather patterns shift thanks to climate change. In that context, black swans are still a fringe concern: Lin said the 10-meter storm surge in Tampa, or a 5 or 6 meter surge in New York, are probably around a one-in-ten-thousand event. But the fact that Sandy and its spiraling-into-the-billions cost doesn't even qualify for black swan status is terrifying: there are super-rare superstorms out there that could double Sandy's devastation, but Sandy-like storms are probably on their way again before long.
Image via Maryland National Guard