A condominium resident boards up a home located on Indian Rocks Beach in Pinellas County, Florida, to prepare for the potential impact of Hurricane Ian.

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After it made landfall in Cuba early Tuesday, Hurricane Ian is bearing down on Florida, with more than 1.75 million people under mandatory evacuation orders across the state.

Follow the latest developments here.

If the storm, which has been gaining in intensity, strikes Florida as a major hurricane, it’s likely to cause serious damage.

To see why hurricanes are getting more destructive, check out this in-depth interactive from CNN’s climate team.

Hurricanes are getting more expensive. CNN wrote earlier this year about the growing cost of natural disasters – there were 20 disasters in 2021 alone that each cost $1 billion or more. The total for the year was $145 billion, according to a report from the National Oceanic and Atmospheric Administration.

About half of that total came from one disaster: Hurricane Ida, the slow-moving monster that caused damage from the Gulf Coast up to the Northeast. It was among the most expensive US hurricanes since 1980.

While hurricanes are getting more expensive, they’re not necessarily getting more frequent. I talked to Philip Klotzbach, a senior research scientist in the atmospheric science department at Colorado State University, about what we know about the frequency and intensity of hurricanes and why they are getting more expensive. Our conversation, lightly edited for length and flow, is below.

What’s unique about Hurricane Ian?

WHAT MATTERS: What do you find most interesting about this current storm, Ian?

KLOTZBACH: It’s certainly going to be a very impactful storm. It’s very quickly intensifying after its interaction with Cuba, and it looks poised to continue to intensify this afternoon, in the evening – so it’s gonna be a very serious storm for the west coast of Florida, or somewhere between Tampa all the way down to Fort Myers, Naples.

The hard part with this storm is because it’s going to be approaching at an oblique angle, very subtle changes in how the storm is steered are going to make huge differences on who gets the storm surge.

The west coast of Florida is extremely storm surge prone. But because it’s going kind of parallel to the coast, where it decides to actually come ashore makes a huge difference for how bad it is in Tampa Bay versus further south down the coast. You look at it now on satellite, and it looks like a buzzsaw. It is not looking good.

A vintage car passes by debris caused by Hurricane Ian as it passed in Pinar del Rio, Cuba, on September 27.

Why there are fewer hurricanes overall

WHAT MATTERS: Your report from March says that there has actually been an overall decrease in worldwide storms in recent decades. Explain.

KLOTZBACH: We wrote a paper looking at global cyclone data over the last 30 years. The reason we use 30 years is because in the Atlantic you could go back further in time than other basins.

In the Atlantic, we fly planes in hurricanes. There are three in the hurricane right now. But in other basins, it’s all based on satellite data.

And if you go back prior to about 1990, the satellites just weren’t that great. And if you look over the last 30 years, the overall number of storms has actually gone down. And the number of hurricanes has actually gone down significantly – hurricanes being the catchall for hurricanes in the Atlantic and the eastern Pacific, typhoons in the western Pacific. In other places, they are called tropical cyclones or cyclones.

We attributed that decrease primarily to a trend globally toward La Nina conditions. La Nina is colder than normal water in the eastern and central Pacific. And typically what that does is it increases your Atlantic storms, but decreases your Pacific storms. Because the Pacific has a much larger ocean basin, that means overall you end up with fewer storms when you suppress Pacific activity versus Atlantic activity.

It does not feel like there are fewer hurricanes on the East Coast

WHAT MATTERS: So while the Earth is seeing fewer storms, how come to those of us on the East Coast of the United States it feels like there are more?

KLOTZBACH: If you look at landfall specifically, we don’t see any long-term trend in the number of landfalling hurricanes.

Florida, for example – it’s hard to remember this now, but from 2006 to 2015, we had 10 years in a row with not one landfalling hurricane in the state of Florida. Which was impressive given those seasons were actually pretty busy. But Florida just was really, really lucky.

And then obviously 2017 was very impactful for Florida. Obviously 2018 with Michael. The last few years, despite them being very busy, Florida has generally dodged any significant impact, even in 2020 with all the storms that were out there.

Why storms are more destructive

WHAT MATTERS: When storms do hit, they’re more destructive than they used to be, at least in terms of dollar figures. You had some interesting stuff in your report about that. Why are storms more expensive?

KLOTZBACH: It’s mostly due to growth and exposure along the coastline. Basically, more people and more stuff in harm’s way. That’s the primary reason for the increase in the damage.

Now, in the paper we didn’t say that climate change can’t cause storms to be more damaging in the future. Obviously with sea level rise – that in and of itself means the storm surge is going to move farther inland. Warmer atmosphere means more rain. More rain causes more flooding, which causes more damage, and then obviously, potentially, storms getting stronger in the future as well.

We were just saying overall so far most of the increase in damage is growth and exposure along the coastline. … Since the number of storms and the strength of the storms making landfall hasn’t gone up, we wouldn’t necessarily expect to see the damage going up for anything other than demographic changes and shifts which have occurred.

People stand outside a flooded warehouse in Batabano, Cuba, on September 27, during the passage of Hurricane Ian.

Storms are intensifying more quickly

WHAT MATTERS: But we do have a story on CNN that because ocean temperatures have risen, the intensification of storms has risen. How does that compare with what you’ve found?

KLOTZBACH: That was one of the many metrics we looked at in the paper. The garden variety, generic definition of rapid intensification is a storm intensifying by 35 miles per hour or more in 24 hours. If we use that definition, we haven’t seen an increasing trend in those storms.

However, if you use a really rapid intensification definition of 60 miles per hour over 24 hours, we did see an increasing trend in that statistic globally. We attributed some of that is due to climate change. The challenge is when you’re looking at these thresholds, 30 years of data is not a ton.

What you expect with climate change is when you talk about global temperature going up one degree. It’s like, well, who really cares if it’s 84 or 85? But it’s how that changes the extremes.

And that’s what we saw in our study as well. The overall number of storms hasn’t necessarily changed. Hurricanes have actually gone down. But we are finding an increase in the percentage of hurricanes at these high intensities, or the storms that intensify quickly – really, really fast. It’s really high intensity thresholds that are going up, not just the general definition.

What can we anticipate in the future?

WHAT MATTERS: You’re very careful in your report to say you’re not predicting what’s going to happen in the future. So I’d like to do that right now and ask what you are looking for in the future. Given the trends that you’ve seen, and given what we know about climate change, what are you anticipating?

KLOTZBACH: Sea level rise, in and of itself – we’re very confident that is occurring, and it’s likely to continue to occur.

Even if storms don’t change at all in intensity, just the fact that the sea level is higher means that when you have that storm surge, it’s going to penetrate farther inland, which obviously increases damage.

Warmer atmosphere holds more moisture, more rain. That obviously causes increases in damage. There’s a lot of debate about whether storms are moving slower, kind of like we’re seeing with Hurricane Ian. It’s going to be moving slowly with really, really heavy rain.

Will storms get stronger?

WHAT MATTERS: Is there evidence that storms will get stronger?

KLOTZBACH: The general public always asks if storms are going to get stronger. I think that, unfortunately, from a scientific perspective, is a harder one to answer. Hurricane intensity is a function of water temperatures, which we know are going up, but it’s also a function of temperatures higher up in the atmosphere, which climate change will also increase. That tends to stabilize the atmosphere.

When we said overall storms and hurricanes are actually coming down, a lot of that trend was due to overall the environment trending more toward La Nina, which is colder than normal water in the eastern and central tropical Pacific. Normally that bumps up your Atlantic storms, knocks down your Pacific storms. … The million-dollar question that we don’t know: Is that trend toward La Nina going to continue? Because if that continues, we won’t necessarily see more really strong hurricanes, typhoons – just because overall, the number of storms is going to go down.

But if we trend more toward El Nino, the Atlantic may go down while the Pacific’s can go way, way up. And so you’re gonna see a lot more damage there and a lot more really strong storms.

That is, to me, one of the biggest scientific questions we need to address, because most climate models say that we should be trending more toward El Nino, whereas the real world says we’re trending more toward La Nina.

That is a huge scientific question that we need to get a handle on if we’re going to make any good assessments of how hurricane activity is going to change in the future.

Storms will still get more damaging

WHAT MATTERS: If sea levels are higher and the storms are slower moving and they’re dropping more rain, does that suggest that it will get even more expensive in the future?

KLOTZBACH: What we’re finding is that a lot of the damage is from water, whether it be from storm surge or from rainfall.

Not that wind isn’t a problem. If you didn’t have the wind, you wouldn’t have the surge to begin with. Just the background sea level being higher is going to exacerbate the surge, and then the warmer atmosphere is going to increase the rainfall – and then, if the storms do indeed move slower, that’s kind of a double rainfall whammy.

Another factor that has nothing to do with climate change but can also exacerbate flooding is land-use changes. We saw that a lot in Harvey, where people built in bayous, they built in swamps. These areas where normally the water would have runoff are now concrete. You have exacerbated the runoff.

We can modify the built environment to basically increase the damage from storms or decrease if we do things better. That has nothing to do with climate change but also due to a human cause.

There are certainly ways we can mitigate the damage in the future. Building better and building smarter is going to become even more important with climate change potentially amping these things up even more.