>> any earth material which is at or below zero degrees celsia for two or more consecutive years. that is permafrost. >> rising temperates aren't the only thing causing permafrost to melt. deforestation, construction - even a bad wildfire season like the summer of 2015 can impact permafrost. to understand why things get lopsided when permafrost melts - you have to understand its structure. and there is no better place to do that than here - almost 50 feet below the ground - in a-one-of-a-kind research facility near fairbanks, alaska. it's a 360 foot tunnel dug out of earth that's been frozen for tens of thousands of years. >> we see 10 to 14 to 15 thousand year old bones in the wall as they began excavating this. >> quentin gehring is a research engineer at the us army corp of engineer's permafrost tunnel. >> they're just everywhere - these bones are giant. >> absolutely. this looks like a pelvic of a mammoth - still right around 14 thousand years carbon dated. >> the tunnel was created in the early 1960s to test excavation techniques in permafrost. after it was built - the corps