Episode 5: March of the beaver

The desolate Alaskan tundra—a landscape that has literally been frozen solid for thousands of years—is suddenly caving in on itself. Colonizing beavers are engineering new wetlands that thaw the soil, rapidly releasing greenhouse methane into the atmosphere. Beavers can survive in the arctic because—like people—they change the environment to make homes for themselves, and their carbon footprint can be seen from space.

Photograph by Katie Orlinsky

The desolate Alaskan tundra—a landscape that has literally been frozen solid for thousands of years—is suddenly caving in on itself. Colonizing beavers are engineering new wetlands that thaw the soil, rapidly releasing greenhouse methane into the atmosphere. Beavers can survive in the arctic because—like people—they change the environment to make homes for themselves, and their carbon footprint can be seen from space.


CRAIG WELCH (WRITER): A lot of people when they think “Arctic,” they think: flat, tundra, endless. You could see forever and there's no landscape to speak of.

PETER GWIN (HOST): Craig Welch writes about the environment for National Geographic and he would like to change your mental picture of the Arctic. 

WELCH: You're in basically this amazingly beautiful alpine system and you know, there's like tall shrubs and you know we, there were grizzly bear tracks everywhere. We actually got to see a wolf chase some caribou up the river drainage and then like a half an hour later the wolf came back alone — clearly hadn't caught what he was after. It's a really stunning place and it does not look like what you might imagine the Arctic to look like. But the Arctic encompasses all sorts of landscapes.

GWIN: Craig says another thing about the Arctic is that it’s not as cold as it used to be, which means it’s becoming prime real estate for all sorts of living things. Craig saw this for himself when he took a canoe trip in the Arctic. He was traveling with an ecologist named Ken Tape.

WELCH: He'd been looking at how plants and vegetation in the Arctic are moving north and they're getting bigger and these, this vegetation, as it gets bigger it draws animals with it. And so he'd noticed that moose and snowshoe hares were moving north into the Arctic in places they hadn't been before.

GWIN: But that ecologist with Craig — Ken Tape — he wasn’t just seeing unfamiliar plants and animals as he paddled along an arctic river. To get a broader, bigger picture of the region, Ken was looking at old satellite photos and comparing them to new ones to see if he could spot changes.

WELCH: So what Ken does is he looks at these satellite images and looks for something that looks like an unusual scar in the landscape. 

GWIN: A scar inflicted by one animal in particular. One that builds dams wherever it goes: beavers.

WELCH: So the cool thing about beaver dams is that they are so dramatic that you can actually see them from aerial photographs from planes or, in some cases, from satellite images.

GWIN: Because beavers don’t just create dams, their dams create lakes and Ken thought, ‘Hey, I could probably see those lakes from space.’

WELCH: But the more he looked, the more he realized that they're coming in great droves. They're coming up a bunch of different river drainages all at once and they're moving in very quickly. 

GWIN: A straight-up beaver invasion — but that’s just the beginning. It’s not the beavers that are the problem per se, it’s what they do to the landscape and how that affects climate change. 

WELCH: When lakes appear on tundra that triggers a whole bunch of other changes. It's like a cascade of things that ends up being bad for the planet as a whole.


GWIN: I’m Peter Gwin and you’re listening to Overheard at National Geographic. A show where we eavesdrop on the wild conversations we have here at Nat Geo and follow them to the edges of our big, weird, beautiful world. This week, who knew we had to worry about beavers when it comes to climate change? More after this.


WELCH: Beavers are engineers. They go out and they build stuff. You know, they build their little highways. They build homes. They build lodges. They build little lakes for themselves to play around in. They are completely and utterly changing whatever landscape they're in.

BEN GOLDFARB (JOURNALIST): I think "industrious" is, is the best word to describe them.

GWIN: That’s environmental journalist Ben Goldfarb. On his website, he calls himself a “beaver believer.” But don’t hold that against him. Ben totally geeks out over beavers. Especially their natural scuba gear.

GOLDFARB: A second set of transparent eyelids they can close over their eyes to, to function as goggles. They have a second set of lips that they can close to, to chew and drag branches underwater without getting water down their throats. And of course, they have these, these iconic paddle-like tails.

GWIN: But beavers are most famous for using their teeth to cut down trees and build dams. And those dams create lakes.

GOLDFARB: You know, wolves, bears, cougars, coyotes, all kinds of large sharp-toothed critters love to eat beavers. So the point of dam building is really about expanding these ponds and wetlands in which these, these semi-aquatic animals can be safe from predators.

GWIN: And you know, that’s a lot more possible than it used to be. There was a time when beavers were endangered. Turns out that beaver hats were the must-have headgear way back in the day. And one of the reasons those hats went out of style?

We nearly killed off all the beavers. But they’ve made a comeback.

GOLDFARB: So today in North America, nobody really knows how many beavers we have. But, you know, the best estimates are 15 million or so. So that's, that's, you know, quite a lot of beavers, right? They're not in danger. They're not going to go extinct anytime soon, of course.

GWIN: Definitely not. In fact, they’re moving into brand-new territory and making themselves at home. 

KEN TAPE (ECOLOGIST): They've totally altered tundra regions of Alaska already. 

GWIN: Ken Tape is an ecologist at the University of Alaska Fairbanks. He’s the guy who used satellite photography to figure out that beavers are migrating north into the Arctic.

TAPE: There are parts of tundra regions of Western Alaska, for example, that have hundreds of thousands of beaver dams.

GWIN: And each beaver dam helps create a new lake, meaning thousands of these new beaver lakes, all dotted across his satellite photos.

TAPE: If there was a real human developer who wanted to do what beavers are poised to do - you know, put a few dams on every other stream in the Arctic tundra of Alaska. You know, the permitting for that would be impossible or as one person said, "that would be a lot of paperwork."

GWIN: So you're saying this is all illegal is what you're saying, Ken.

TAPE: I'm saying it's, it's potentially a big deal.

GWIN: If a human developer were to apply for a permit to build in Alaskan tundra, they’d probably have to submit an environmental impact report. But beavers don’t do paperwork and apparently, they’re workaholics. Ken says they’re manipulating their new environment around the clock.

TAPE: I mean, they are brilliant engineers that are working off of, you know, an evolution’s worth of experience doing this. And it remains to be seen how that's going to play out in the tundra because the permafrost changes. It changes everything.

GWIN: Okay, so, permafrost. I’ve heard the term before but if it was a topic on Final Jeopardy, I’d totally get crushed.

KATEY WALTER ANTHONY (ECOLOGIST): When ground stays frozen year-round year after year, It becomes permafrost. 

GWIN: Katey Walter Anthony is one of Ken Tape’s colleagues at the University of Alaska Fairbanks. She’s also a permafrost expert.

WALTER ANTHONY: But permafrost – it’s frozen ground. A rock that's frozen would be permafrost. But a lot of times when we think of permafrost, we think of permafrost soils. And soils have water in them and so when that water freezes, it forms ice. And so if you were to saw into permafrost, you would see soil particles with lenses of ice in between them. And in some places there's massive ice wedges. So just huge ice cubes that go deep into the ground.

GWIN: Katey says when permafrost warms, those huge ice cubes melt, meaning nothing’s holding that soil together, and it creates these arctic sinkholes.

WALTER ANTHONY: If the frozen ground used to support a forest on top and then the ice starts melting, the trees will tip over and we call that "a drunken forest." And that's a sign that permafrost is warming and thawing.

GWIN: This is happening a lot in the Arctic tundra in northern Canada, Russia and Alaska. And sometimes, where the ground sinks, water pools.

WALTER ANTHONY: When you get standing water or pooled or ponded water because of the heat in the water, it accelerates the thaw.

GWIN: More thaw means more water. And more water means more thaw. For beavers — quick-spreading, dam-building, water-loving beavers — this is good news.

WALTER ANTHONY: Beavers can have a really big impact. They’re turning land into water.

GWIN: And here’s the reason this is a really big problem. There’s something in the permafrost that we do not want to get out.

WALTER ANTHONY: So when the ground is frozen — in the soil is carbon. And it's the remains of plants and animals that died in the past. And in some cases, tens of thousands of years ago. So that the remains of these dead plants and animals have been locked away frozen in a freezer for tens of thousands of years. When that ground thaws, it's opening the freezer door and that carbon that's been locked away, it becomes food for microbes that decompose it and digest it.

GWIN: It’s like an all-you-can-eat buffet for microbes. And as those microbes digest the decomposing plants and animals from this buffet, they release gasses. Carbon-rich, greenhouse gasses. Like carbon dioxide and methane. And even though most of us live nowhere near melting permafrost, it affects us.

WALTER ANTHONY: Because when methane escapes out of a lake in the Arctic, it goes into the atmosphere and immediately mixes and it takes about a year for methane to mix around the whole globe. So methane released from the Arctic affects, it goes into causing global warming — warming of the entire globe.

GWIN: So how does methane compare to CO2 as a greenhouse gas? Because that's what we hear all the time. You know, it's coming from our cars, you know, and we need to plant more trees and that'll soak up the CO2. But how does methane compare to, to that?

WALTER ANTHONY: Yeah, it's about 30 times stronger as a greenhouse gas. What that means is that for every one methane molecule, the heat that it absorbs and traps would be equivalent to having 30 carbon dioxide molecules in the atmosphere.

GWIN: Yikes. And melting permafrost releases a lot of methane. And it will happen much faster than climate scientists had projected.

WALTER ANTHONY: The projection for the next 30 to 40 years is that the emissions are going to be so high that it actually will more than double the permafrost carbon feedback.

GWIN: That means these new lakes in the Arctic are doubling the emissions from permafrost thawing. Which brings us back to beavers.

WALTER ANTHONY: What we see is that lakes that recently formed have the highest emissions of any environment in the Arctic and some of those sites are forming in, in conjunction with beaver activity.

GWIN: I mean, so is this the kind of thing that like if we're really concerned about this that we should try to prevent the beavers from doing this?

WALTER ANTHONY: I always hesitate when it comes to management. Beavers were here in the past. They're, they're, they might be rebounding from being hunted out over 100 years ago. So, I don't know. I think I always want to caution on people thinking that they understand how to manage ecosystems well enough without getting into trouble. So beavers are also a natural process.

GWIN: A natural process that beaver-believer Ben Goldfarb says, isn’t all bad.

GOLDFARB: The other really important thing to, to bear in mind is that as beavers move north, they're moving north along with all kinds of other species as well, right? We know that, that moose have, have expanded their range northward. We know that, that salmon are showing up in Arctic rivers that they had never appeared in before. So these are all species that, that do really well with, with beavers around, right? Beavers are creating these ponds and wetlands that benefit those animals.

GWIN: So basically, they’re just setting up the place for all the new inhabitants who are moving north because of a warming climate.

GOLDFARB: I would think about beavers as "agents of assisted Arctic migration" not as "agents of Arctic destruction," right? You know, the way that this story has been represented is as a story of beavers basically ruining the Arctic. So what I would, I would say to that first of course is, is beavers are, are migrating northward because we have changed the climate. Right? We are the agents of Arctic destruction, not the beavers.

GWIN: While beavers are setting the stage for other animals to move into the Arctic, if you think about it, we’ve really set the stage for them. Our one billion cars, trucks and buses contribute way more greenhouse gases than Arctic beaver dams do. Not to mention our air conditioners, our taste for beef, and our devotion to next-day delivery. The Arctic is really warmer because of us. WE are the ultimate beaver.

More after this.


GWIN: When Katey Walter Anthony tests for methane coming out of the permafrost, she sets frozen lakes on fire. Her team captured it on video. You gotta see this, it’s totally crazy.

And permafrost thaw, it’s not just caused by beavers. My colleague Craig Welch reports on what’s making the Arctic sink in a recent Nat Geo feature.

And there are also pictures of grasses that haven’t been seen since the last ice age. Now, here they are. Poking out of thawing soil.

All this and more can be found in our show notes. Look for them in your podcast app.


Overheard at National Geographic is produced by Brian Gutierrez, Jacob Pinter, and Robin Miniter.

Our senior producers are Kristen Clark and Jinae West.

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And I’m your host, Peter Gwin. Thanks for listening and see y’all next week.