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. For more information on this episode, visit nationalgeographic.com/overheard

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Permafrost covers an area more than twice the size of the United States. Read about why it's thawing faster than we expected.

There are drunken trees in forests across Alaska, Canada and northern Eurasia. Check out pictures of some drunken forests.

Ben Goldfarb believes that beavers aren't only not to blame for climate change, they're actually helping fight against it.

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Not only is methane a greenhouse gas, it's also flammable. Watch Katey Walter Anthony set frozen lakes on fire.

Ever wonder why beavers make such great hats? And why they eventually went out of style? Wonder no more.

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