This is the third in a four-part series on tropical cyclones, beginning with Windy Changes, on last year’s Typhoon Haiyan and continuing with Data of Hurricanes Past. Note that “tropical cyclone” is a catchall term that includes tropical storms, hurricanes, and typhoons. I have not repeated reference links from the previous post.
Last week I went over how “are hurricanes getting worse (because of global warming or any other reason)?” is tough to answer. Basically, there are problems in the data. But even if we did have a lot of great data and could compare storms easily and precisely it would still be hard to say whether one storm is “worse” than another because “worse” is hard to define.
Does getting worse mean more Category 4 and 5 storms? Lower air pressure in the eye? Such metrics are the easiest way to compare tropical cyclones, but that’s not really what most people want to know. We want to know if we can expect another Katrina, another Irene, another Sandy. We want to know if there will be more catastrophes, but catastrophe is more complicated than just violent weather.
Hurricane Katrina, for example, was briefly a Category 5 storm, but it weakened before making landfall as a strong Category 3. Now, that’s still an insanely powerful storm, but it’s hardly unprecedented. Katrina became the catastrophe it did, not because of the hurricane’s own characteristics, but because it passed over a major city that had been built more or less under a lake–I remember that morning, watching on the news as all the weather people expressed relief that, miraculously, New Orleans had dodged a bullet and would be basically ok. And then the levee broke.
Hurricane Irene downgraded to a tropical storm the night it made landfall (and passed right over my house). Our area sustained no real damage, but as the tropical storm headed north over New England its associated flooding destroyed critical roads and bridges, temporarily isolating some towns. Because the storm produced so much rain, and possibly because it hit an area that rarely gets hurricanes, Irene was a truly catastrophic storm, even though it wasn’t even a hurricane anymore.
Katrina and Irene were the first and seventh most costly storms in US history respectively, but a scientist looking at how often Cat 4 and 5 storms hit us would miss both of them.
Sandy and Haiyan were both powerful and genuinely unusual storms, but both were catastrophic for not strictly meteorological reasons–both hit densely populated areas that were unusually vulnerable to storm surges for various reasons (Tacloban sits at the back of a bay that funneled and intensified the surge and New York City’s electrical system wasn’t protected against salt water flooding). Of course, the power of those storms was very much part of the problem, too, but what a storm passes over is at least as important t as how it behaves.
So, even if global warming doesn’t make tropical cyclones more powerful or more frequent (which seems unlikely), if they hit vulnerable places more often they’ll seem worse. Conversely, if we make our infrastructure less vulnerable to storms and deal with the racism and poverty that makes so many storms worse, intensification due to global warming might be less noticeable.
If we want to know whether climate change will make tropical cyclones worse, as opposed to simply more powerful in a strictly meteorological sense, we would probably do best to look at storm surge, rain potential, storm track, and storm frequency, not wind speed.
Flooding is the major killer in tropical cyclones, so whether rain and storm surge increase is important (and, of course, storm surges are getting worse because of sea level rise). If typical storm tracks change, them more storms will hit places that aren’t prepared for them. And if we get catastrophic storms by whatever definition more often, it is possible our capacity to respond will be exhausted.
Repairs from Superstorm Sandy continue. Hurricane Irene hit in August of 2011 and destroyed a lot of roads and bridges in New Hampshire and Vermont. While almost all of the initial repairs were completed within three months, that just meant the roads were functional again. Three years later, the repair work continues. Some repair projects from Katrina were still underway as of last year, eight years after the storm. The United States is one of the richest countries on Earth and we’ve been able to absorb these costs, as well as providing disaster relief abroad. But sooner or later we’ll reach our limits.
As ever, getting a useful answer depends on asking the right questions.