Short Wave - 'One Mississippi...' How Lightning Shapes The Climate

Episode Date: December 6, 2022

When lightning strikes a giant tree in the tropical rainforest, there's usually no fire, no blackened crater — you might not even notice any damage. But come back months later, as Evan Gora does, and you may find that tree and dozens around it dead. Gora, a forest ecologist who studies lightning in tropical forests, says we are just beginning to understand how lightning actually behaves in these forests, and what its implications are for climate change. On today's episode, Evan Gora tells Aaron Scott about shocking discoveries in lightning research, and why Evan has developed a healthy respect for the hazards it poses – both to individual researchers and to the forests that life on Earth depends on. See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Hey there, shortwavers, Aaron Scott here, and today we're going to start off with a quick lightning round. Literally, we're going to talk about lightning. Yeah, so lightning is just a big static shock. So it's essentially the same process that happens when you reach out to touch a doorknob. But instead of that little bolt traveling a couple millimeters, it travels kilometers. Evan Gore is a forest ecologist who studies lightning. And with the additional distance comes a much greater amount of power.

So a lightning strike is just this static shock surface, and it carries tens of thousands of volts and tens of thousands of amps in a channel that's about the size of your finger. And that whole idea that you can figure out how far away lightning is by counting the seconds between the flash and the thunder clap. Yeah, that's all true. You just got to make sure that you're up on the speed of sound. When a lightning strike happens,

about five seconds to a mile. So you see the flash, start counting. When the boom gets to you, you know how close it was. Stop. I got to stop you right there because I was raised that it's one second per mile. So I've basically been way overestimating how far away lightning is. So I've been in much greater risk than... For sure.

For sure. I expected. If it's under a second, you are very close. So, yeah, it's a funny... I'm not sure where the misconception comes from, but, you know, the speed of sound, you just take a mile and divide by the speed of sound and you'll get about five seconds. Okay, I am going to shift the way I hike in the wilderness at this point.

Evan studies how lightning strikes in tropical forests contribute to the death of the biggest trees. So today on the show, we're heading to the tropics to track lightning with Evan Gora and to learn about the role it might play in climate change, a role we're just beginning to understand. I'm Aaron Scott, and you're listening to Shortwave. the Daily Science Podcast from NPR.

What is it like to be out in one of these tropical forests during a lightning storm? It's terrifying. The more I've done work on lightning and done work on this topic, the more scared of it I've become. And usually it's a flash in the forest. You can't see where it is. It's just a flash, and then there's a boom sometime after. But as that time gets shorter and shorter, instead of a boom, you start to hear a crack. And that's when you know you're just a few hundred.

meters from the lightning flash. And fortunately, this last part, I've only experienced one time, but when it's very, very close, it just goes silent first. And that's, I believe, the concussive blasts hitting you, and I'm sure it's a millisecond, but it feels super, super long, and everything goes silent, and then there's just an unbelievable boom and flash sort of all at the same time. And it's horrifying, but really brings out the power of this phenomenon. So when lightning strikes a tree, especially a big tree in a tropical forest, can you give us like a beat by beat walk through of what happens? Yeah, so when we think about lightning striking trees, typically, we think about that tree blowing up or catching on fire, which are charismatic, big events,

but they aren't really what happens typically. So we've set up a system, me and a bunch of different colleagues, it's a really large collaborative group in central Panama where we track lightning strikes in real time. And when we go to these sites and we see where lightning is enter the forest, we don't see any evidence of fires. We don't see any explosions. What we see instead is evidence of the electric current entering a big canopy tree and then it flows out its branches and it flows down its trunk and jumps to neighbors. It happens to be near that tree in the canopy and then flows down them and jumps to their neighbors. It's the end up with this sort of spider web effect electrocuting a big group of trees in the forest. And what makes it really

fascinating is those trees only have a little bit of damage initially. So it's really hard to find at first, but then over a period of months, they slowly die in a big groups of dead trees. Wow. I mean, I can think of electricity like traveling down wires, but it never occurred to me that trees would electrocute each other, basically, and that it would create this web of electricity through the canopy and down to the ground. Yeah, yeah, exactly. It's not what we anticipated when we showed up to do work there either. So there's been previous work showing that lightning can damage and kill groups of trees, but we, like most people, thought going in that that was a pretty rare occurrence. And instead, what we've found out is that this is what happens every time when lightning

strikes in these tropical forests. And why was that so surprising? Yeah, I guess we were surprised because it wasn't documented. The damage that happens to those trees is generally very subtle at the space between neighboring trees, you essentially have a few leaves that are dying within a few weeks of the strike. And that's about it. So you would have an event that happened only a few milliseconds. You have to see where it happened in the forest, go out and find where it is, and you only have these tiny little hints that lightning ever touched there. And you need to come back to that tree over and over again over the next six to 18 months to actually see the trees die. So you're going to have to be able to tie a millisecond event to something that happens in the next 18 months.

Which is counter to everything we see on TV or in video games or whatnot where a lightning strike leaves this kind of blackened, scorched circle on the ground or something of that sort. Yeah, exactly. So we've tracked around 100 lightning strikes, gone on the forest, quantified everything they do. We've never seen a tree caught on fire. Maybe one exploded. And that's about it. So it's not what we think about happening at all. And we should be clear that we're talking about tropical forests here, right?

that this is not necessarily the way lightning is interacting with like temperate forests here in North America? Well, that's an interesting question. No one's ever done this in temperate forests. So we have no idea how common that is around, you know, eastern forests in the U.S., for example, where lightning frequency is as high or higher than anywhere else in temperate forests in the world. We know that most of the time lightning strikes a tree. It doesn't cause fire. Now, that doesn't mean lightning isn't an important agent of fire. So a lot of the most destructive fires that happen, you know, for example, in the western U.S. are lightning caused fires. They happen in remote places.

It's hard to find what's going on. So, you know, they can be really, really dangerous. But even there, we know most lightning strikes don't cause fires. And it's kind of just ignored what's happening with the rest of them. What do we know then about why lightning is important to forest health and kind of what role it might be playing when it comes to climate change? Yeah. So the reason lightning is important in forests is that it affects the biggest trees in those forests.

So these are trees that might be 10 feet in diameter at their base and 180 feet tall. So they're really, really massive trees, really big trees are struck most often. Well, just so happens that those really big trees are the most important trees to forest function. So, for example, the largest 1% of trees in a typical tropical forest have about half of the carbon. Wow. So of lightning striking these big trees and it's killing these big trees, then it's going to be causing a lot of that carbon to leave the ecosystem. And how this ties back into climate change then

is that we see some evidence that lightning frequency is becoming more frequent. So if it becomes more frequent, and it specifically affects the biggest and the most important trees in a forest, then it's going to have these big impacts on how our forests can store carbon in the future. And if those forests store less carbon, then that's pretty dangerous for us, because tropical forests in particular have been protecting us from climate change for the last century by accumulating carbon that we emit from our facts. factories and in other places.

So we've been talking about lightning is killing trees, which like the knee jerk is to think, well, that's bad. And yet, I mean, here at least in the northwest, the forest I'm used to, you know, it's all part of the process that when a big tree dies and it falls, it then opens up space in the canopy so that light can reach younger plants and other plants start to grow on them and fungi. And, you know, it's all part of the forest process, which, so I'm guessing it would be the same thing in the, inthropy. tropical rainforests, right? That it's part of how these forests have evolved is having lightning striking the biggest trees. Absolutely. So lightning is 100% just part of the natural process in these ecosystems. And it's probably good for some organism. Where we become concerned is if lightning frequency is increasing, for example, really quickly because of actions we've done, increasing in a rate that maybe it didn't previously and forest can't quite acclimate to.

And there's some evidence that might be happening. So if we think about the eastern U.S., for example, there's an expectation that lightning frequency will increase about 50% by the end of this century. It's a huge, huge increase. And there's some evidence that that's actually already been going on in tropical forests for the last few decades. And if that's the case, that might explain part of why we're seeing increasing rates of tree death in these forests, which is something that's really concerning for climate scientists and really for society if these forests are dying more frequently and not able to store carbon like they normally do. And even if we can recognize it, even if we understand what's happening, is there anything we can do about it?

I mean, it's not like we can flip a switch and turn off lightning. No, and I don't think we would want to flip a switch and turn off lightning. It probably does play some important roles. But if we understand what it's doing, then we can actually manage our forests better. So, for example, if we want to plant trees in reef forests an area, which is something that's become really popular, there's a lot of effort to try to do that right now. We want to plant the trees that will turn into the really big trees to provide these really important functions to our ecosystem. And we can only do that if we actually know what kills those big trees. And we know which species can survive the killers of those big trees, things like lightning or wind.

So what we want to do is essentially figure out which trees are capable of surviving those different drivers, not just today, but the ones that will be important in the future. So that when you're doing reforestation or when you're doing logging, you're picking the right trees to plant. or the right trees to take out. So through this research, you have ended up a little more frightened of lightning. Has it changed the way you see and experience lightning storms? It has changed how I think about storms. Really in a positive way, but some of it in somewhat of a morbid way.

Every time I hear lightning hitting, it's seven megagrams of biomass, three and a half tons of carbon right there that's going to be emitted to the atmosphere. It's a huge, huge amount. And if that's becoming more frequent, it's a huge effect every time it happens. So it's definitely changed how I think about those events. So not just the fight or flight in the moment I might get struck by lightning, but you now have the existential dread of climate change laid on top of it. Yes, but I'm an overly positive and optimistic person about sort of everything.

So I like to look on the positive side. You know, that that is happening. But, you know, there are these trees out there that survive lightning in this miraculous capacity. Evan, it's been a joy talking lightning and forest with you. Thank you for coming on our show. Yeah, thank you for having me. This was a lot of fun. This episode was produced by Devin Schwartz and edited by Gabriel Spitzer. Britt Hansen checked the facts. The audio engineer was Gilly Moon. Our senior supervising editor is Giselle Grayson, Beth Donovan is the senior director, and Anya Grunman is the senior vice president of programming. I'm Aaron Scott. Thanks as always.

for listening to Shortwave from NPR.