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