Is climate change really making hurricanes worse?
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Almost 1,000 people have been fired over the past few months at NOAA, the National Oceanic and Atmospheric Administration, and another 1,000-plus have accepted buyouts. NOAA plays a pretty key role in tracking, forecasting, and understanding hurricanes. It even sends people flying directly into hurricanes to figure out how they work.

But according to a leaked memo, the Trump administration is planning to effectively shut down NOAA's climate science program. They're actively firing the scientists who are doing this research, like the people whose job it was to fly into hurricanes. All of this is making it way harder to answer a pretty fundamental question: Is climate change making hurricanes worse? Now, at first blush, that might seem like a question scientists have already figured out.

But Vox's climate correspondent, Umair Irfan, isn't so sure. Oftentimes the discussion around climate change and hurricanes conflates a lot of things. People will be a little bit fast and loose and say things like climate change is leading to more hurricanes or is causing more severe hurricanes. And those are not strictly true. Figuring out exactly how climate change is impacting hurricanes is pretty fundamental work.

Last year's hurricane season killed hundreds of people. It caused billions of dollars in damage. And scientists are predicting that this year's season is going to be more dangerous than normal too. All while this question of climate and hurricanes might be getting even harder to answer. And so I wanted to try to put some numbers on these vibes to basically see, is what we're feeling part of a real phenomenon? And is it connected to the broader phenomenon of climate change?

So, I'm Noam Hassenfeld, and today on Unexplainable... Exactly how does climate change influence hurricanes? How much of what we're seeing is our fault? So, Umair, if we're going to figure out whether climate change is making hurricanes worse, we probably need to talk about the actual mechanics of hurricanes, right? Like, I know they're big storms. I know they happen over water. But to be honest, I don't really know how they work.

The way I've heard it described to me is that a hurricane is basically a giant heat engine. Think about the engine in your car. If you heat up a lot of gasoline inside the cylinder and ignite it, it creates a pressure wave that pushes down a piston that turns the wheels of your car. That's how a car works. A hurricane takes advantage of the temperature difference between the surface of the ocean and the atmosphere. Basically, when water temperatures get really hot,

It's very cool at the top of the atmosphere. And so that energy wants to equilibrate somehow. You know, when you put something hot next to something cold, the hot thing gets cooler, the cool thing gets hotter. That's sort of a similar thing that's going on. So the warm water in the ocean wants to rise because...

The air at the top is cooler and vice versa. So they're trying to mix and that creates sort of motion energy storm. Yeah. And so as that mechanism speeds up for reasons that we're not entirely sure of, like we don't know what the exact ignition or the spark is for hurricanes. If those conditions get right, if you have enough heat at the ocean, if you have the right amount of wind, that starts to spin. And if that speeds up enough, then.

It starts building its own inertia, at which point it can become a hurricane. But what we've seen is that the oceans have gotten so hot in the past couple of years, that gradient is extremely steep and is allowing these storms to build up to massive strength. And when the water gets warmer, does that mean the hurricane gets stronger? In general, yes.

all other things being equal and assuming a lot of things stay constant, then yeah, the more energy you have at the surface of the ocean in terms of having more heat there, the more fuel there is to energize that hurricane. And one place we actually see that happen in a very acute scale is with this phenomenon called rapid intensification. We've seen that recent years where we've seen hurricanes gain wind speed of about 35 miles per hour or more in 24 hours. And we've

One of the mechanisms that scientists believe is at work is that when the storm moves over an abnormally warm patch of water, it's basically like it gets a lot of high-octane fuel all of a sudden, or it gets that nitrous boost in the engine that makes the cargo really fast. That's kind of what's happening to the hurricane. And so if we see storms suddenly passing over those high-energy areas, they can gain a lot of intensity very quickly.

Okay, so it seems pretty reasonable to make a connection between climate change and stronger hurricanes then, right? Like, if I were a detective and trying to assign blame here, would this be kind of case closed? In a sense, yes. Like, the mechanism there is plausible, but again, as a detective, you also have to show that

that that's actually what's happening. Are we actually seeing hurricanes getting stronger or are we just noticing them more because the same old hurricanes are hitting more and more populated areas? And as more people move there, they build more homes, they build more businesses. And so there's a lot more stuff that's in the line of fire. And when a hurricane does make landfall, it becomes more and more costly. Now, there are other traits though, where we do see a more distinct human fingerprint, right?

The most destructive element of the hurricane is the water. That's the flooding. The flooding is caused by two main things. That's the storm surge, which is the winds from the hurricane pushing water from the ocean inland. And then it's also caused by rainfall.

And based on those two things, we've actually seen the amount of water getting dumped on land going up. And that seems to have a much stronger connection to climate change for a couple reasons. Ice that's on land at the poles is starting to melt into the ocean and is increasing the overall volume of water in there.

but also the ocean itself actually undergoes a little bit of thermal expansion. You know, we tend to assume that water doesn't expand or contract very much when it gets hot or cold, but on the scale of an ocean, temperature differences do actually increase or change the volume a little bit. So you're saying both more water and like larger water? Yes. Okay. So those two variables are both happening at the same time. And so

All things being equal, a Category 3 hurricane with a higher sea level is going to push more water inland than a Category 3 with a standard sea level. The other aspect is the rainfall. Warm air holds on to more moisture.

And so the air is a lot juicier. It's a sponge that's been soaking up a lot more water. And so when you squeeze that sponge, a lot more water gets dispatched. And so on those two signals, we see a stronger connection to human-caused climate change. So it's plausible that climate change is making hurricanes stronger, right?

But we can't really be sure yet? Well, here's the other complication with hurricanes is that in general, they're just not very common weather events. We only see about a couple dozen tropical storms in the Atlantic in any given year. In addition, we've only had weather satellites over the Atlantic Ocean since the 1960s and 70s.

And so we don't have a large field of data to establish a very plausible trend in any direction. The other aspect about hurricanes is that hurricanes can go through a cycle of 20 to 40 years where we see high and low levels of activity. And it's not clear that what we're seeing right now is a function of just a normal upswing in hurricane activity versus something that humans are causing.

You know, it's like analyzing a car accident. How much was it caused by the person speeding? How much was it caused by the person being distracted? How much was it caused by just bad luck? Being able to tease out which specific variable is a little bit tricky. And that's kind of what we're trying to do here. The thing with all climate change is that it's fundamentally about statistics. We have to see more than one thing in order to actually establish a signal. And so looking at any one data point doesn't tell the whole story.

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You're complicating this story. You're not saying that this story is wrong. You know, it's plausible, but there's all these reasons we don't know for sure yet. Still, there's a sense in which that feels like a matter of degree for me. And I'm wondering if we go deeper on the issue of hurricanes, are there any more fundamental things that are still unexplainable here? The main thing is that like a lot of people talk about frequency as well, and that's where it's a lot less clear.

The overall number of hurricanes in a given year doesn't appear to be changing all that much. In fact, if you look at the number of cyclones around the planet, it tends to stay within a fairly narrow margin. And we don't know, again, what is it that actually causes these storms to form? Yeah, the ignition. Yes, exactly. And so, like, you can have all the ripe conditions for a massive storm in place and still not get one.

In fact, we saw that happen last year. We saw a period of several months where we had really hot water, we had really stable air, and it seemed like it was perfectly ripe for a hurricane, and we didn't see one for a while. And so people were talking about this odd lull in the hurricane season and whether forecasts were wrong. The forecasts, though, weren't wrong. It's just that we don't fully know exactly what causes that. That's kind of mind-blowing to me because so much of this seems clear. You know, warm water wants to go up, cool air wants to come down, but...

But then warmer water isn't necessarily leading to more hurricanes, which tells me that there's just a large chunk of this that we still don't understand. Yeah, absolutely. The other thing I'll point out is that hurricanes are not the only way...

of using up heat energy in the ocean. Ordinary thunderstorms use heat energy from the ocean and cause rainfall. We saw an example of that last year where we saw these torrential rainfall events in Spain where warm water from the Gulf of Mexico along the Gulf Stream was getting channeled along the Atlantic and towards the west coast of Europe.

And all that warm, wet air all of a sudden just dispatched as this huge, enormous rainstorm. It wasn't even a tropical cyclone. Now, the number of storms may not change, but maybe the intensity of those storms does change. There may be other ways that they're channeling that excess energy that's not showing up just if you look at the numbers.

And also remember that the ocean is a three-dimensional object. When we talk about hurricanes, we're talking about the surface of the ocean. That heat can also move downward rather than upward, right? We can see more and more warmth at greater and greater depth.

potentially that's also where the energy is going. Keep in mind, like, you know, the majority of heat that humans have caused the Earth to trap since we've been observing this is actually in the ocean. The oceans are the shock absorber for climate change. And so how they dissipate that shock, there's a lot of different ways that it can do that, and we don't fully grasp all of them. Yeah, and I guess if we zoom out on what we don't understand here...

Are there any other explanations for what could be making hurricanes worse? You know,

besides climate change? Yes, actually. Okay. One of the things that hurricanes actually need is essentially a clear atmosphere. And actually what we've seen is that as countries on both sides of the Atlantic implemented more air pollution controls, basically limiting the amount of sulfur dioxide, of nitrogen oxides getting produced by factories and car exhausts, as the quantity of that smog basically went down, there was less of that over the ocean. And so,

And that also created more ripe conditions for hurricanes to form. That essentially this pollution was having sort of a masking effect on hurricane activity. Wow. So you're saying that this sort of positive environmental action taken by a lot of the industrialized world is...

actually made hurricanes worse? Like things that we think of as good for the environment led to stronger hurricanes. I would hesitate to draw that strong of a line. Okay. But what I would say is that they helped create the conditions that can fuel more hurricanes. Yeah. So if I were the climate detective here, there's a lot of evidence pointing to the fact that climate change could be making hurricanes worse.

But it's not like we can point to a specific hurricane and say, you know, if the world were one degree cooler, this hurricane would be less bad. To an extent. Like when we're talking about the intensity, I think that's a fair statement. But there is now a group of researchers who are working on what's called attribution, which is essentially trying to do exactly that, finding the sort of causal link. And so there's a group called World Weather Attribution.

And what they did was they tried to calculate how much worse the rainfall was from some of these storms. What they do is they look at, here's what we would expect the storm to dish out in terms of rainfall in a world that hadn't warmed. And then we compare that to what we actually observed. And by looking at that difference between the non-climate changed world and the climate changed world, they can say that that difference was caused by human activity or was influenced by human activity. But even in that case-

How do you factor in the idea that there just can be worse hurricanes regardless of climate change? I mean, I think that's a fair criticism that a lot of people make of these attribution efforts, right? That again, you know, hurricanes, while they're these big bombastic events, are...

relatively rare and we don't have a whole lot of great data on them. And I think some of the scientists that I spoke to make that point that essentially, yes, there is a plausible mechanism, but to put a specific number on it might be a bridge too far. So then how do we get better answers here? How do we get more confidence in

in the way that climate change is impacting hurricanes? Again, you know, climate change is fundamentally a problem of statistics, and you get better resolution on your statistics with more observations. And so the simple fact is we might just need to wait and see and look at more hurricanes over time in order to understand how much of a signal is there.

We also probably need better resolution in our images of hurricanes, like basically being able to get inside them and actually see how these mechanisms work to be able to track at small scales and at large scales how warm temperatures can lead to evaporation, how subtle changes therein can lead to changes in wind speed and direction. Like to try to pinpoint that moment of ignition. Exactly. And that is one of the other key things is trying to just figure out

what is it that causes a hurricane to form or not form? Can you ignite a hurricane and can you snuff one out before it forms, potentially? These are theoretical experiments, but that helps us understand the mechanism behind it. So given the level of uncertainty here, what do you think we should do? I mean, it would absolutely behoove us to reduce greenhouse gas emissions and mitigate climate change. It would also behoove us to reduce air pollution, even if...

it may have a side effect of exacerbating the ingredients of hurricanes. And the third big component is our own exposure, how much people and property are in harm's way. If we wanted to reduce the amount of damage and devastation from hurricanes, we

Perhaps some of the smartest things that we can be doing is starting to retreat from some of the highest risk areas. And for the people that can't move, developing better infrastructure. So seawalls or channels to move water away, things that allow water to dissipate more readily, building buildings to higher code and teaching people exactly what they're supposed to do during a hurricane. Those will all go a long way towards reducing the amount of devastation that we see from these storms.

Umair, thanks so much for coming on the show. My pleasure, Noam. Thanks for having me. This episode was produced by me, Noam Hassenfeld. We had editing from Meredith Hodnot, who runs the show, sound design from Christian Ayala, music from me, and fact-checking from Melissa Hirsch and Anouk Dussault. Jorge Just and Julia Longoria are editorial directors, and Bird Pinkerton went to the pufferfish, the platypuses, the tortoises, and the fish.

They begged her not to go to Aaron Bird, but she knew she couldn't abandon the octopus. She had to go to JFK Airport, and she had to go alone. Thanks as always to Brian Resnick for co-creating the show. And a special thank you to Thomas Liu, who's been such a wonderful presence on our show the last few months. We can't wait to see what you get up to next.

If you have thoughts about the show, send us an email. We're at unexplainable at vox.com. You can also leave us a review or a rating wherever you listen. It really helps us find new listeners. You can also support this show and all of Vox's journalism by joining our membership program. You can go to vox.com slash members to get ad-free podcasts and a whole bunch of other goodies. Unexplainable is part of the Vox Media Podcast Network, and we'll be back on Wednesday.

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