Permafrost, an icy expanse of frozen ground covering one-quarter of the Northern Hemisphere, is thawing. As it does, microscopic animals are waking up and feeding on the previously frozen carbon stored in plant and animal remains, releasing heat-trapping gases as a byproduct. These gases warm the atmosphere further, melting more permafrost in a dangerous feedback loop. With permafrost containing twice as much carbon as the atmosphere, its thaw could release 150 billion tons of carbon by the end of the century. Narrated by Richard Gere