Permafrost is defined as ground (soil or rock and included ice or organic material) that remains at or below 0°C for at least two consecutive years.

The rise in global temperatures is causing the thawing of the Arctic permafrost, which contains 1700 billion tons of organic material that has been accumulated during thousands of years. The melting of the frozen soil will cause the release of billions of tons of methane (a greenhouse gas that is 22 times more powerful than carbon dioxide) that could cause a feedback loop and make Earth warm itself.