Almost 23 million square kilometres in the Northern Hemisphere and roughly half of Canada sit on top of some sort of permafrost. At Woods Hole Research Center in Falmouth, Massachusetts, it's what is trapped inside the permafrost that has scientists most concerned. There are about 1,500 billion tons of carbon locked up in permafrost in the Arctic. If permafrost continues to melt, the potential release of greenhouse gases will have devastating consequences on the Earth's climate.

pt. 1. Permafrost: A Front Row Seat to Climate Change -- pt. 2. A Freezer Full of Carbon: The Consequences of Greenhouse Gases -- pt. 3. Permafrost: Not so Permanent -- pt. 4. Permafrost: Structural and Community Changes -- pt. 5. Tuktoyaktuk: Losing the Land Beneath Our Feet -- pt. 6. The Health Concerns of a Permafrost Thaw.