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A record hurricane season is ending. What does climate change have to do with it?

Hurricane Iota made landfall in Central America earlier this week as a Category 4 storm. It's the 30th storm this Hurricane season, surpassing 2005 as the year with the most hurricanes ever. With this record Atlantic Hurricane season officially ending this month, Hari Sreenivasan speaks with Kevin Reed, a professor at Stony Brook University and director of the Climate Extremes Modeling Group about the connection between climate change and hurricanes.

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  • Hari Sreenivasan:

    Tens of thousands of Hondurans have been left homeless after flooding and damage caused by Hurricane Iota.

    The storm struck Honduras earlier this week as a Category 4 hurricane with sustained winds of 155 miles per hour. Rain from the storm flooded neighborhoods and swelled rivers.

    Iota was the second Category 4 hurricane to hit this part of Central America in two weeks.

    Hurricane Eta caused more than 130 deaths and triggered mudslides as it made its way across the region.

    Iota is the 30th named storm of the Atlantic Hurricane season, topping off a record year that resulted in the national hurricane center resorting to the Greek alphabet for letters.

    As this record hurricane season officially comes to a close at the end of this month, we wanted to understand more about what's been discovered about the connection between climate change and extreme weather events like hurricanes.

    I recently spoke with Kevin Reed, an associate professor at Stony Brook University who leads the school's Climate Extremes Modeling Group. I began by asking him how scientists are teasing out the effect of climate change on individual storms.

  • Kevin Reed:

    When storms make landfall, they make an impact. They have hazards. And those hazards come through things like storm surge, high wind speeds and rainfall, right? Because extreme rainfall can cause flooding.

    And so, one of the things we can do is we can use state-of-the-art models that are used for forecasting storms, and we can run these under different conditions that have climate change to-date in the signal, or removed. And so we basically come up with two sets of reality.

  • Hari Sreenivasan:

    So you're taking a forecast like we would see on the Weather Channel and you're saying, what are the impacts that climate change could have on this storm. And then we take a look at kind of two outcomes with the rain and without the rain that's attributable to climate change?

  • Kevin Reed:

    Yes. And so another way to put it is we run a forecast just like we typically would, the difference is then we also run a forecast in which we've removed the climate signal to-date, right?

    So in the North Atlantic, that's approaching over one to two degrees Fahrenheit. The sea surface has increased in temperature over the last 150-plus years due to human-induced climate change. And we can remove that signal and we can rerun the forecasts. And so, we basically have two sets of forecasts. One we call the actual forecast, right? The kind of the real forecast, as well as the one in which we have this counterfactual, which we've removed warming.

  • Hari Sreenivasan:

    When you look at a storm, say, for example, like Hurricane Laura now, what does this type of modeling tell us?

  • Kevin Reed:

    Yes, so this type of modeling tells us that what we call the maximum accumulated rainfall amount, right, which is just the fancy way of saying how much rain fell during the lifetime of the storm. We're seeing increases of 5 to 10 percent. Meaning that if an example of Hurricane Laura, we had about 12 inches of rainfall in some regions. And so, that's an increase of about an inch in some cases of rainfall. So we're attributing how much rainfall in an individual hurricane is due to climate change.

  • Hari Sreenivasan:

    When you are looking out into the future. Are we likely to see more storms or more intense storms or both?

  • Kevin Reed:

    Yeah, so that's to some extent an open question still. And the consensus is that there will be a decrease or the number of hurricanes, for example, globally will remain about the same or decrease.

    What that means for individual basins like the North Atlantic is a little bit harder to understand, in part because there are things like natural variability from year to year, right? But we do know our models do tell us that the storms are becoming more intense, both in terms of the the maximum wind speed, but also in the amount of rainfall.

    We expect about a 5 to 7 percent increase in rainfall within tropical cyclones, within hurricanes for every degree Celsius of warming that we have. And so if you see in the North Atlantic, right, if we were to flash forward 50 years in the North Atlantic is you know two or three degrees warmer than it is now, then you could start to expect upwards of over 10, maybe approaching 20 percent increase in tropical cyclone rainfall.

  • Hari Sreenivasan:

    What are the data sets that you're looking at now that you hope will help refine the way that you model things, the way that people can prepare going forward? I mean, is there a way that we could look at hurricane forecasts when we're watching TV before the storm sets in and realize that this is going to be worse each time because of all of these other factors of sea level rise and ocean temperatures warming?

  • Kevin Reed:

    Yeah, these type of analysis in which we're able to kind of quantify the impact of climate change on things like hurricanes as well as other extreme weather events has definitely increased in sophistication, meaning each time we do these type of things, like most things in life, we're getting better at analyzing the data, we're getting quicker turnaround in terms of running simulations. And I think that in the future we could have a system in which we're doing that real time. Not only are we exploring the impact of climate change on the storm that occurred to date, but also providing some future, a peek into the future.

    What would the storm look like under one or two or three additional degrees of warming? And I think that that would help both inform decision making, right? To see, OK, this storm was was really impactful, how much worse would this storm be in the future? But also, it allows us to communicate that the impacts of climate change are not one hundred years off.

    The impacts of climate change are here now. They are changing the weather around us and they are having a real impact on society through that.

  • Hari Sreenivasan:

    All right. Kevin Reed, associate professor at Stony Brook University, thanks so much for joining us.

  • Kevin Reed:

    Great. Thanks for having me.

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