Glaciers. They really are the pinup geological formation for climate change. But spare a thought for permafrost. Perma-what? Answer: The gigantic carbon-rich Arctic landmass, that—until recently—has locked away its greenhouse gases in a deep freeze for millennia. That is, until man-made climate change has begun to unlock its CO2 stores, only then to be devoured by methane-spewing organisms. This microbial feast is accelerating climate change. The problem: It's a feedback loop. The hotter it gets, the more the permafrost melts, the more CO2 is emitted. And around and around we go, in a devastating roundabout for Arctic communities and the entire globe. Continuing our "Explained in 90 Seconds" series, here's a primer on permafrost.