Katrina-like hurricanes could become 10 times more likely

Illustration for article titled Katrina-like hurricanes could become 10 times more likely

For the past century, a storm like Katrina could be expected to hit about once every 20 years or so. But as a new computer simulation suggests, our warming climate could result in a dramatic increase in these extreme hurricanes — and the devastating storm surges they bring along with them.


The latest research to correlate the increased severity of storm surge activity with climate change comes from Aslak Grinsted who works at the Centre for Ice and Climate at the Niels Bohr Institute at the University of Copenhagen. In his paper, which has just been published in Proceedings of the National Academy of Science, Grinsted proposes a new combined model to prognosticate hurricane surge threats — one that compares the record of hurricane activity in the Atlantic based on storm surge statistics (extracted from tide gauges) to changes in global temperature patterns.

To cut to the chase, here’s what the new simulation indicates:

  • If the average global temperature increases by 0.4 degrees Celsius, we can expect to see a doubling in the frequency of storm surges like the one following Katrina
  • Should temperatures increase by one degree, these events will occur with three to four times the frequency
  • A two degree increase in global temperature will result in about 10 times as many extreme storm surges

If Grinsted’s two degree prediction comes to pass, we can expect a Katrina-like hurricane once every two years. Worse, with rising sea levels, the destructiveness of the surges could be greatly exacerbated.

To attain these figures, Grinsted and his colleagues looked at the history of storm surges in the Atlantic dating back to 1923. A storm surge is the the abnormal rise in water that gets pushed inland by high winds and the internal pressure of the cyclonic storm. The climate scientists related the surges to the air temperature when they occurred.

Then, Grinsted used computer models to project how storm surges might be influenced by the changing climate. Specifically, Grinsted combined two models, one focused on regional sea temperatures, the other based on differences between the regional sea temperatures and the average temperatures in the tropical oceans (these two approaches were previously seen as being in competition as they often yielded contradictory results).

Illustration for article titled Katrina-like hurricanes could become 10 times more likely

But by combing them to create a single model, Grinsted could account for the individual statistical models and weigh them according to how effective they were at explaining past storm surges (they were particularly focused on past surges seen at six tide gauges along the Atlantic and Gulf coasts).

But not everyone is happy with Grinsted’s "tide gauge" approach. NBC reports:

Judith Curry, an atmospheric scientist at the Georgia Institute of Technology who is actively researching the relationship, told NBC News in an email that the new paper is "very misleading.”

For one, she said their tide gauge dataset is inferior to the standard dataset of landfalling hurricanes maintained by the National Hurricane Center, which makes using the tide gauge to make statistical projections of future storm surges "unconvincing."


That said, other climate scientists, like Greg Holland of the National Center for Atmospheric Research in Boulder, advocate the use of the tide gauge approach, but cautions that surge data can only reveal so much about a particular storm.

Read the entire study at PNAS.

Supplementary sources: NBC, Reuters.

Images: NOAA; Gordon Tarpley; Aslak Grinsted, Niels Bohr Institute.


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That Small Dark Voice

A number of things tend to get lost in the shouting about Katrina.

First, it was Category 3 when it made its second landfall (first was when it crossed Florida). These are already fairly frequent, though the actual frequency has varied over the period that they've been observed—for decades the frequency had depressed, which led to...

The Gulf Coast is much more built up than it used to be. As a result, a hurricane of the same strength can do more damage, because there's more to damage. It didn't help in Katrina's case that...

New Orleans was particularly vulnerable. Still is. Seriously, just look at a map, it's a depressed area between a lake and the Gulf shore—that's not a good place to be in a hurricane, and odds were one would hit eventually. It didn't help any that...

The deficiencies in the levy system were known for decades—I remember reporting about it from the '90s! A problem that never got fixed thanks to...

Bad bureaucracies making things worse. Talk about your perfect storm. The Army Corps of Engineers screwed the pooch on the levies, the local and state authorities botched the run-up and response, and confusion on federal roles certainly didn't help much either.

I should note that the worst part of the storm—the dreaded northeast quadrant—struck well to the east of New Orleans. Indeed, I saw a lot of the damage done in Mississippi and Alabama—where the real brunt hit—and it was worse. Notice that didn't get the apocalyptic coverage...and that folks basically shrugged and rebuilt.

None of this is to say we shouldn't be concerned about the possibility of enhanced storms, but it helps to remember that many of the human factors involved in these disasters have nothing to do with climate. You'd think that would make them easier to deal with, but these are people we're talking about...