Are We Ready for 'Gray Swan' Storms?

A satellite image shows Hurricane Frances approaching the Caribbean and Florida in 2004. GES DISC [public domain]/NASA

For many years, climate scientists have warned us about the threat of weather influenced by climate change. Powerful hurricanes, unrelenting droughts and massive wildfires are just some examples we've already experienced.

Now comes another heads-up from scientists that a "gray swan" storm — a devastating weather event that has no historical precedent — could be even worse than some hurricanes we've seen in recent years.

The warning isn't that it's coming. It's that we had better be ready for it.

Tampa under water

In a study published in the journal Nature Climate Change, two climate scientists ran thousands of computer simulations on three vulnerable coastal cities that never have been hit by storms of this magnitude — Tampa, Fla., Cairns, Australia and Dubai, United Arab Emirates — and determined that the chances of a big one coming are growing by the day.

Using current knowledge of climate, coupling that with historical data and factoring in the damaging effects of climate change in the future, the scientists concluded that a storm with a surge of 36 feet could hit Tampa by the end of the century. A sea surge of 17 feet today, says one of the authors of the study, would put most of Tampa under water.

"Tampa needs to have a good evacuation plan," Kerry Emanuel, a professor of atmospheric science at the Massachusetts Institute of Technology, says in an MIT release, "and I don't know if they're really that aware of the risks they actually face."

Scientists call "black swan" storms major weather events which have no precedent and no warning. These "gray swan" storms can be just as major, but the difference is that they can be predicted, at least to some degree. And that's what Emanuel and his co-author, Princeton professor of civil and environmental engineering Ning Lin, have done.

"We are considering extreme cases," Lin says in a Princeton release. "These are relevant for policy making and planning, especially for critical infrastructure and nuclear power plants."

Emanuel and Lin are not predicting when these events will happen. They're not even saying that they will happen. But they are, in a very scientific way, calculating the odds. And those — again, based on history, current climate and the change that is being brought about by what is commonly known as "global warming" — are increasing.

Considering the consequences

The Earth in the coming century not only could see more of these extreme weather events, Emanuel is saying. The events also figure to be more devastating than they are today. "Whereas the upper limit of hurricane wind speeds today might be 200 mph, 100 years from now it might be 220 mph," he says. "That means you’re going to start seeing hurricanes that you’ve never seen before."

The study has its detractors. A USA Today article cites an expert who notes that most scientists don't think coming weather events will be nearly as strong as what Emanuel and Lin foresee.

Still, it's important to know that these are not predictions or doomsday prophecies. A "gray swan" is a long shot. Dubai, for example, never has been hit by a hurricane, and its dry air makes it a less likely target than, say, Tampa. A storm surge of 13 feet has only a 1 in 10,000 chance of happening there.

But it's equally important to remember that those chances are increasing. The 1 in 10,000 for Tampa, for example, drops to 1 in 700 in some scenarios toward the end of the century, according to the study's calculations. With that devastating 36-foot surge.

The lesson, Lin says, is simple enough. Scientists run the numbers. They show what could happen.

It's up to rest of us to prepare, she says, "rather than wait for the consequences."