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Is Climate Change Contributing To Slower Moving Hurricanes?


Hurricane Dorian reminds us of three factors that measure the destructive force of a hurricane. There's high wind, which is what defines a storm as a hurricane. There's water - the height of the storm surge, the amount of rain. And then there's the storm's speed - the slower it moves, the worse it is because that means the storm lingers, as Dorian did when it stalled over the Bahamas. Scientists have linked slow-moving storms to climate change. So let's talk through the evidence with Jim Cason. He's a climate scientist with NOAA, the National Oceanic and Atmospheric Administration. Good morning, sir.

JIM KOSSIN: Yes, good morning.

INSKEEP: Basic question first - what is it that makes a hurricane move slowly across the ocean?

KOSSIN: Well, the first thing that causes that is just slower winds that it's embedded in. They tend to move somewhat passively in the wind, like a leaf in a stream. So the stream itself is slowing down, and so the hurricanes tend to slow down as well.

INSKEEP: OK, so you're reminding me of the massiveness of the forces at work here - that a hurricane, giant as it is, powerful as it is, is just kind of drifting along in the wind, like a leaf. Is it purely a random question, then, whether it happens to catch a big wind or doesn't catch a big wind?

KOSSIN: Well, it's certainly partly random. But there's also, in the background, what appears to be a sort of a longer time scale signal of a trend, and they seem to be slowing down over time.

INSKEEP: How bad is the slowing? What are we talking about here?

KOSSIN: Oh, well, it's been about 17% over the past 118 years. So that's really substantial. I mean, quick back-of-the-envelope - means that you get about 17% more rain locally than you would have.

INSKEEP: And once in a while, you get a storm like the one that hit the Bahamas, and it lingers there for a day.

KOSSIN: Yeah. Well, that's certainly an extreme example of what we're talking about. Harvey and Florence have both been good examples as well of what happens when a hurricane doesn't move quickly.

INSKEEP: So you have measured slower storms, storms moving at a slower speed, which means they're more destructive. Then the next question is, are you able to link that to human-caused climate change?

KOSSIN: Yeah, I think that it's a fairly compelling inference, if nothing else. Our studies look at past data. So it's not a direct attribution study, per se, but we know that all of the numerical simulations, in our best theoretical understanding, is that winds will generally slow down as the planet warms. So this is entirely consistent, with a human fingerprint, on what we're seeing.

INSKEEP: So you have seen, over the past century, a substantial slowing of hurricanes. But we're still in the middle of climate change. We're not doing enough, necessarily, to reverse course at this point. Should we expect a lot more of this, a lot more destructiveness of far slower hurricanes?

KOSSIN: Well, yes. I mean, the trend that we're experiencing, that we have seen in the past, is projected to continue into the future. So there's no reason to think that, as long as we keep on with business as usual, that this trend is going to change in any way - so yes.

INSKEEP: Does that mean we have to prepare for hurricanes in a different way?

KOSSIN: I think, ultimately, yeah. For long-term planning, like city planning and things like that, then yes, we do absolutely have to take these climate change trends into consideration. From a more immediate point of view of how do we get out, then that kind of time scale is not so important to us.

INSKEEP: OK. Dr. Kossin, thank you so much. Really appreciate it.

KOSSIN: Sure. Thanks for having me.

INSKEEP: Jim Kossin is a climate scientist with NOAA, the National Oceanic and Atmospheric Administration. Transcript provided by NPR, Copyright NPR.