Climate change helped Ian gain strength Abnormally hot water in the Gulf of Mexico helped Hurricane Ian gain strength. Rapidly intensifying major hurricanes are more likely as the Earth gets hotter.

Climate change makes storms like Ian more common

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SCOTT SIMON, HOST:

More than a million people were still without power in Florida last night in the wake of Hurricane Ian. The storm is remarkable not only for the damage it caused to cities along the coast, but the flooding it brought to inland communities. And powerful storms like Ian are more likely as the Earth gets hotter because of climate change. Rebecca Hersher from NPR's climate team joins us now.

Rebecca, thanks for being with us.

REBECCA HERSHER, BYLINE: Hi, Scott.

SIMON: How did climate change affect this storm?

HERSHER: Well, it all goes back to the basics of climate change - you know, heat. The planet is about two degrees Fahrenheit hotter than it was in the late 1800s. And that means the ocean water where hurricanes are born is warming up. All that heat is fuel. So what happened here is when Ian was still a baby hurricane, basically, it moved over abnormally hot water. Some of the water on the surface of the Caribbean and the Gulf of Mexico was nearly 90 degrees, which is significantly hotter than normal for this time of year.

And all that heat helped Ian get really big and really strong. And studies actually show that around the world, climate change is making big, strong hurricanes more common. And that's even though the total number of storms is not going up.

SIMON: Ian gained strength quickly before it hit Florida. It went from a tropical storm to a hurricane in less than a day, and then it became a major hurricane. Is all that also fueled by climate change?

HERSHER: Yeah. And this is actually a very active area of climate research because there is evidence that exactly this kind of rapid intensification, as you've talked about - it's getting more common as the Earth heats up. And we've seen it in recent years here in the U.S., for sure. You know, it happened to Hurricane Harvey in Texas, Hurricane Michael in the Florida Panhandle, Laura and Ida in Louisiana, and now Ian. And the very simple idea is that when the water is abnormally hot, it helps storms grow really quickly. But the other thing to remember is that wind conditions also play a big role. And it's less clear how climate change might be affecting that part of the equation.

SIMON: What about all the flooding we're seeing?

HERSHER: Well, there are two ways that climate change can influence flooding. And let's start with storm surge 'cause that was such a big part of Ian. And that's when a storm pushes ocean water inland. And storm surge from Ian caused enormous amounts of damage. You know, entire neighborhoods are just gone. And the more powerful the storm, the more dangerous the storm surge sort of as a rule. There's another way that climate change can affect storm surge, and that's sea level rise. Remember, global warming is causing oceans to rise slowly and steadily. And there are parts of Florida where ocean water is already flooding streets, even on sunny days. So if you imagine that that's the baseline, that makes the flooding worse when a storm like Ian does make landfall.

SIMON: And what about the areas that are far from where Ian made landfall? - because there are parts of central Florida that got more than two feet of rain from Ian.

HERSHER: You know, it all goes back to that extra heat. You know, as a storm like Ian moves across hot water, it sucks up moisture, and hotter air can hold more water vapor. So when Ian hit land, it was holding a tremendous amount of moisture. And all of that moisture - it fell as rain. And studies have shown that recent storms dumped more rain than they would have if climate change wasn't happening. And actually, there's a really preliminary analysis that shows that Ian dumped at least 10% more rain in Florida than it would have without global warming.

Now, there's one other thing that is really, really important here. Rain does not just fall close to where the storm hits land. It can fall hundreds, even thousands of miles away - in places where people thought they were safe, right? And historically, flooding is the single most dangerous hazard from hurricanes. So as the Earth does get hotter, more and more people will need to be prepared for this kind of weather during hurricane season.

SIMON: Rebecca Hersher from NPR's climate team.

Thanks so much.

HERSHER: Thanks.

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