Permafrost is ground that stays frozen for at least two years in a row. It i found mai in t Arctic, wh it li beneath ab a qua of a the la in t Northern Hemisphere. In some places, the frozen layer is hundreds of meters deep. Permafrost also contains large amounts of carbon from plants and animals that died long ago but never fully decayed. As the climate warms, some of it is thawing, and microbes begin to break down this material. This releases carbon dioxide and methane, two gases that cause further warming.

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